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113. Guayacan (Guaracum angustifolum= Porlieria angustifolia)- Two individual plants of guyacan, a widely distributed shrub of semiarid and arid rangelands. This species is an important, in fact, a very valuable browse plant from the Rio Grande (Tamaulipan) Plains into the Sonoran Desert. The first specimen was from Big Bend Ranch State Park, Presidio County, Texas. Second specimen was from Big Bend National Park, Brewster County, Texas. Both photographed in June.
114. Leader of guyacan with fruit- Characteristic leaves and fruit of guyacan. Leaves are evergreen and palatable to many animal species including some birds. The fruit type is a capsule, a dry dehiscent fruit formed from two or more fused carpels (ovule-bearing parts of flower) which opens by any of several structures like slits orlids (Smith, 1977).
Big Bend Ranch State Park, Presidio County, Texas. June.
115. Fruit of guyacan- Capsule of guyacan, valuable browse plant in Chihuhuan Desert and Rio Grande Plains Savanna. Big Bend Ranch State Park, Presidio County, Texas. June.
116. Thorny member- A plant of whitethorn or mescat acacia (Acacia constricta) growing in association with Torrey yucca or Spanish dagger (Yucca torreyi= Y. treculeana) in a creosotebush-tarbush form of Chihuhuan Desert shrubland in the Big Bend area, a more eastern portion of the Basin and Range physiographic province. There were also some plants of native perennial grass species such Wright's threeawn, plains bristlegrass, tanglehead, sideoats grama, and green sprangletop as well as skeleton-leaf goldeneye (Viguiera stenoloba).
Whitethorn acacia has a biological (species) range that includes both the Chihuhuan Desert and the Sonoran Desert extending westward through much of Arizona and far south into six states of Mexico. Mescat acacia is well- represented throughout the Trans-Pecos portion of the Basin and Range physiographic province. In Texas, whitethorn acacia also extends into the western Edwards Plateau and south to barely reaching the Rio Grande (Tamulipian) Plains. Brief, but good descriptive sources for whitethorn acacia included Vines (1960, ps. 493-494), Shreve and Wiggins (1964, p. 599), Powell (1988, ps. 183-184). Benson and Darrow (1981, ps. 226-228) gave about the best account for mescate acacia.
Big Bend National Park. Early October; late (ripening) fruit phenological stage.
117. Characteristic form- Leaders of whitethorn acacia with maturing legumes (in their characteristic burnished red-brown color and twisted shape) on a plant growing on a creosotebush-tarbush-dominated community of Chihuhuan Desert scrub in Trans-Pecos Texas at the eastern part of the Basin and Range physiographic province. Associated neighbors included skeleton-leaf goldeneye and such perennial grasses as green sprangletop, plains bristlegrass, sideoats grama, and tanglehead.
Benson and Darrow (1981, p. 227) described mescate accia as being of "negligible value" for browse given its spiny leaders of sparse foliage, but noted that it was a major bee plant in some areas. Benson and Darrow (1981, p. 227) also indicated that legumes were eaten by livestock nd wildlife. Perhaps zoochory (plant propagule dispersal by animals) ] is an important factor in distribution of this species which, empherically, seems to increase under disturbance such as overgrazing/overbrowsing.
Big Bend National Park. Early October; late (ripening) fruit phenological stage.
118. Ceniza shrub cover type in Chihuhuan Desert- Kuchler (1964, p. 45; Kuchler in Garrison et al., 1977 including RARE map) mapped and described a potential natural vegetation unit (38) of Ceniza Shrub (Leucophyllum-Larrea-Prosopis) along the lower Rio Grande (east of Big Bend area). Most of this climax range vegetation was converted to cropland so that remnants of the natural vegetation (= relict areas) are "few and far between". Scattered patches or "islands" of Ceniza Shrub (K-38) also occurred at smaller spatial scale in adjoining landscapes and ecoregions such as Rio Grande Plains and Chihuhuan Desert. Shown here and in the two succeeding photographs was an example of such range vegetation (at least of vegetation that fit the species composition and plant community structure of Ceniza Shrub more closely than the typical form of Chihuhuan Desertscrub, the major or most common association of which is Creosotebush-Tarbush).
Creosotebush and honey mesquite were common components of this range plant community as, indeed, these two species are the most consistent and widely distributed dominants or co-dominants of the combined super-region of the Chihuhuan and Sonoran Deserts (the Larrea-Prosopis Formation of Clements [1920,ps. 162-167]. Tarbush, the regional "second place" co-dominant of the Chihuhuan Desertscrub (Larrea-Flourensia Association of Clements [1920, ps. 168-170]), was replaced by ceniza (Leucophyllum spp, esp.L. minus) in this range plant community. A major woody legume in addition to mesquite was whitethorn acacia (Acacia constricta). A specimen of this species was the foremost shrub in the first photograph. Guyacan was well-distributed thoroughout this vegetation (an individual of this species was in left foreground of second photograph). Common, important succulent shrubs included Englemann pricklypear and lechuguilla. Both Big Bend silverleaf and common ceniza or purple sage were common throughout. These Leucophyllum spp. with their shinning gray color were very prominent in the first slide (and in the two immediately succeeding slides). Common lotebush (Ziziyhpus obtusifolia), mariola, and, even, guayule were also major woody species.
Attention was drawn to the pebbly or rocky soil surface known as desert pavement.
Big Bend National Park, Brewster County, Texas. June. Best fit based on species composition: FRES No. 32 (Texas Savanna Shrubland Ecosystem); K-38 (Ceniza Shrub). Best fit based on geographic or ecoregion location: Fres No. 33 (Southwestern Shrubsteppe); K-53 (Trans-Pecos Shrub Savanna). It was explained in the succeeding photo caption that K-38 (and therefore FRES No. 32) was the overall best match. No specific SRM rangeland cover type, but ceniza variant of SRM 508 (Creosotrebush-Tarbush) was somewhat descriptive. No appropriate Brown et al. (1998) Series was appropriate.Chihuhuan Deserts- Low Mountains and Bajadas Ecoregion 24c (Griffith et al., 2004).
119. Ceniza shrub variant or expression of Chihuhuan Desertscrub- Chihuhuan Desert vegetation in which ceniza (Leucophyllum spp.) was a major inidcator genus. Big Bend silverleaf was the common representative but ceniza or purple sage and Boquillas silverleaf were rarely present. Presence of the Leucophyllum element, and at far greater cover and density than ocotillo, tarbush or tasajillos) (common associate or, in case of tarbush and even tasajillo, co-dominants) distinguished this range plant community from other range cover types of the general Chihuhuan Desert.
Creosotebush was the dominant species, but Englemann pricklypear, honey mesquite, mariola, guayule, whitethorn acacia, guyacan, and common lotebush were also important species, especially at local scale. There was no herbaceous understorey, and this range plant community was contiguous with such range types as the creosotebush-ocotillo, creosotebush-tarbush, and creosotebush-grama savana.
The gray or silverish-gray colored shrubs (including some leafless shrubs) were Big Bend silverleaf and, perhaps, a few ceniza or silver sage plants. Tarbush was almost nonexistant.
This range vegetation clearly fit the descripiton of Ceniza Shrub (Leucophyllum-Larrea-Prosopis) given by Kuchler (1964, p. 45) except that Kuchler (1964, p. 45), which corresponded to K-38 (Kuchler in Garrison et al., 1977, including RARE map), description included "a patchy synusia of grass". The first Gramineae genus listed was Bouteloua. This corresponded to the dominant B. ramosa of adjoining plant communities at this location. Otherwise range vegetation shown here was essentially the same as Ceniza Shrub even though this range plant community was outside the map confines of Kuchler (1964, including map) and Kuchler in Garrison (1977). In fact, these two photographs were eerily a near "perfect match" to the photograph provided by Kuchler (1964, p. 45).
Big Bend National Park, Brewster County, Texas. June, early estival aspect. RES No. 32 (Texas Savanna Shrubland Ecosystem). K-38 (Ceniza Shrub). No specific SRM rangeland cover type was descriptive, but ceniza variant of SRM 508 (Creosotebush-Tarbush) was closest. No biotic community (Series) for Ceniza Shrub in Brown et al.(1998). Chihuhuan Deserts- Low Mountains and Bajadas Ecoregion 24c (Griffith et al., 2004).
120. Guayule (Parthenium argentatum)- This woody composite (Heliantheae tribe) is not a major shrub in the Chihuhuan Desert, but it is a unique range shrub that helps define this large arid shrubland and several of the range cover (= dominance) types therein. Guayule is more restricted in its biological (= species) range than most of the major range plants of the greater Chihuhuan Region, being restricted to more southern portions of the Chihuhuan Desert from Texas into Chihuhua but it is not native to the Sonoran Desert.
The most discussed thing about guayule is its natural production of latex. For decades there has been interest in developing an agricultural system by which latex could be produced from guayule on a profitable commercial basis. This potential has yet to be realized. Instead guayule remains a novel range plant being the species that produces the greatest quantity of milky latex and one of several unique species that are a member of the intriguing Chihuhuan Desert.
Big Bend Ranch State Park, Presidio County, Texas. June.
121. Apical portions of guayule- Live shoots including leaves along with flowering stalks and spend inflorescences from the last growing season. Big Bend Ranch State Park, Presidio County, Texas. June.
122. Mariola (Parthenium incanum)- Besides guayule there is mariola, the other woody Parthenium species, in the eastern Chihuhuan Desert (and western Edwards Plateau) Mriola is far more widely distributed than guayule. It also occurs in grasslands adjoining the Chihuhuan Desert as well as westward to the Sonoran Desert. Mariola is larger and has a more upright habit than guayule.
The plant seen here and the two plants seen in the succeeding (immediately following) two slides were blooming profusely in a record-rainfall growing season. Profuse flowering (and from a plant's perspective, hopefully, consequent heavy fruit yields) during times of good growing conditions is an example of the opportunistic nature of plants that make the desert (xeric conditions in general) their home. This opportunistic feature or versatile (plastic) growth response, especially in regards reproduction (sexual or asexual), is an example of natural selection (evolutionary adaptation).
Tthe plants shown in this slide and the one in the immediately following photograph (two genetic individuals; two genotypes) were growing beside creosotebush, the dominant shrub of the Chihuhuan Desert (and the Sonoran and Mojave Deserts as well for that matter).
Big Bend National Park, Brewster County, Texas. Early October; peak-bloom stage of phenology.
123. Blooming in a very wet year- Two more plants (genotypes) of mariola growing in the Big Bend area of the Chihuhuan Desert that served as further examples of this woody composite that can be a local dominant on some local habitats or, even, specific range sites. The first plant (specimen in the first slide) was growing beside creosotebush, dominant shrub of the Chihuhuan, Sonoran, and Mojave Deserts, while the second plant (specimen in second slide) had for its its nearest neighbor the climax perennial grass, tanglehead.
Both of these individual plants were blooming profusely in a record-setting year for rainfall. The opportunistic pattern of growth and reproduction in desert plants was noted in the preceding caption.
Big Bend National Park, Brewster County, Texas. Early October; peak-bloom stage of phenology.
124. Wet-year-deluxe blooms- A cluster of capitula (heads) of mariola in the Big Bend area of the Chihuhuan Desert that had been produced during a rainfall record-setting spring through early autumn growing season. Mariola is a member of the immense compositae tribe, Heliantheae. Mariola and guayule are the two woody plant (shrub) species of Parthenium growing in the Chihuhuan Desert.
Big Bend National Park, Brewster County, Texas. Early October; peak-bloom stage of phenology.
125. Another view of another mariola plant- This specimen of mariola was growing earlier in its annual growing/production cycle than the profusely blooming specimen that introduced this species. Mariola and guayule are the two Parthenium species that are shrubs in the Trans Pecos Texas Region, but there are a total of five Parthenium species in Texas, three of which are herbaceous, forbs (Correll and Johnston, 1979, ps 1625-1627). In New Mexico there are three Parthenium species, one of which is a forb (Allred and Ivey, 2012, p. 161). At least this was the count before the cladists decide to put each of these in its own genus, tribe, or whatever (which, of course, will make no difference in this publication because the author rejected cladistics).
Big Bend Ranch State Park, Presidio County, Texas. June.
126. Shoots of mariola- The apices of these mariola shoots had immature inflorescences. Big Bend Ranch State Park, Presidio County, Texas. June.
Note on references: there are remarkably few summary references for the woody Parthenium species. The supposed compendium or definitive reference for North American shrubs (Francis, 2004) excluded both P. argentatum and P. incanum (as it did so many important North American shrub species). Likewise, the classic Range Plant Handbook (Forest Service, 1940) did not cover either of these Parthenium species. Benson and Darrow (1981, ps. 297-298) gave some coverage to these two species, but overall it was left to the old standby, Vines (1963, ps. 1016-1018), to be the as ever fall-back-to reference.
127. Big Bend Silverleaf or lesser Texas silverleaf (Leucophyllum minus)- This is one of three Leucophyllum species growing on that part of the Chihuhuan Desertscrub in which this genus provides a distinctive floristic element. These species are members of the figwort or snapdragon family, Scrophulariaceae, recognized by (and for) its showy flowers. All three Trans-Pecos Leucophyllum species are valued and frequently planted for their ornamental features, which includes the distinctive leaves as well as jflorescences.
The generic common name for these species-- in both the Rio Grande Plains and Trans-Pecos Basin and Range-- is ceniza. In usage restricted to the species level, ceniza refers to plants known by the English common name of purple sage or Texas silverleaf (L. frutescens). As such the listener or reader has to know the context and specificity (generic or specific) of "ceniza".
This specimen was growing on the example of Creosotebush-Ceniza-Grama Savanna presented in several photographs above. Big Bend National Park, Brewster County, Texas. June.
128. Shoots of Big Bend Silverleaf- The first of these two photographs was of the apical portion of a main leader (woody branch) of Big Bend silverleaf showing the much-branched pattern of this species. The second photograph provided a more detailed view of leaves of Big Bend silverleaf. First photograph was taken in Big Bend Ranch State Park, Presidio County, Texas; second, in Big Bend National Park, Brewster County, Texas. Both taken in June.
129. Ceniza, purple sage, or Texas silverleaf (Leucophyllum frutescens)- Specimens of ceniza grown under cultivation for ornamental purposes. These plants were being used for native plant landscaping (which illustrated value of Leucophyllum species for that purposes) and doubtless had greater plant vigor than most of their wild counterparts. These 'pampered" plants did represent the habit and possible flowering potential of this species.
Erath County, Texas. August.
130. Leaves and flowers of ceniza- Close-up views of characteristic leaf and floral features of ceniza or Texas silverleaf. These were plants grown horticulturally for landscaping with native plants. The figwort or snapdragon flower of the Scrophulariaceae was obvious. Erath County, Texas. August.
131.Obovate-leaf saltbush (Atriplex obovata) - A subshrub (= suffrutescent) found on alkaline or saline soils in the Chihuhuan Desert. This is a dioecious species (as are many of the Atriplex species) and has no known browse value. It provides valuable soil protection and other critical ecosystem functions such as nutrient cycling. Probably furnishes cover for small wildlife species on an otherwise largely bare habitat.
Presidio County, Texas. June.
132. Shoots of obovate-leaf saltbush- One of the less important (at least, least appreciated) Atriplex species with immature inflorescences forming at apices of shoots. Presidio County, Texas. June.
133. Tuberceled saltbush (Atriplex acanthocarpa)- This is another suffrutescent Atriplex species that is also dioecious. It is also a minor species with a rather restricted biological range compared to several other members of this genus that are widespread and valuable browse plants. Obviously any species native to the habitat in which it evolved provides important functions for the plant communities and ecosystems of which it is a part; and plant communities, ecosystems, and landscapes have evolved-- to whatever degree-- to function with the role played by that native species. In other words, just because this minor plant species provides no feed for cows or grain for bread does not mean it is useless. At least, it provides cover on the surface of saline or alkaline soils and thus reduces soil erosion. There is no unimportant species in ecosystem function (this does not mean that every species must be present for the eocsystem to continue to function).
This was a male plant in full-bloom (see next slide).
Presidio County, Texas. June.
134. Sowing wild saltbushes- Shoots of a male tuberceled saltbush plant in full anthesis, and this rascal was putting out the pollen. Presidio County, Texas. June.
135. Tarbush community on Chihuhuan Desert- MacMahon (in Barbour and Billings, 1988, p. 249 and 2000, p. 304) observed that in the Larrea Scrub phase of the Chihuhuan Desertscrub "40-80% of the plant cover can be composed of Larrea or Flourensia cernua or a mixture of the two". Those who tromp the Chihuhuan Desertscrub frequently find local commuities dominated by or composed exclusively of one or the other creosotebush and tarbush. Shown in this and the succeeding photograph was a local consociation of tarbush on a basin generally dominated by creosotebush. Honey mesquite and some fourwing saltbush (the small plants with light-green or gray leaves in center midground) plus lesser cover of spiny allthorn (Koeberlinia spinosa) were also present. An example of mesquite was the tall green shrub at right margin in background. Tobosagrass with some mesa dropseed made up a patchy herbaceous understorey.
Most of the tarbush plants were leafless, presumedly due to on-going severe drought. Some tarbush appeared dead and some were clearly "top-dead" and resprouting from root crowns. Range vegettion was in early stages of recovery from prolongued severe drought.
Dona Ana County, New Mexico. June, early estivval aspect (prior to summer rainy period; tobosagrass still dormant and tarbush in drought-deciduous state). FRES No. 33 (Southwestern Shrubsteppe Shrubland Ecosystem). K-52 (Grama-Tobosa Shrubsteppe). SRM 508 (Creosotebush-Tarbush), "a persistent subclimax of the grama-tobosa shrubsteppe" (Herbel in Shiflet, 1994). Creosotebush-Tarbush Series, 153.21, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41).
136. Tarbush-dominated Chihuhuan Desertscrub community- Tarbush is often a distant co-dominant to creosotebush in the Chihuhuan Desert, especially on creosotebush flats (basins with the Larrea phase of Chihhuhuan Desertscrub). Sometimes, however, tarbush is the dominant range plant or, at least the dominant shrub. Such was the case presented. Live tarbush plants had shed most of their leaves. Some plants had all dead shoots except for resprouts. An example of resprouting tarbush was the shrub in right foreground. This was apparently recovery from prolonged severe to extreme drought. Most shrubs with green leaves were honey mesquite. There were scattred plants of fourwing saltbush and spiny allthorn. Tobosagrass made up the herbaceous understorey except for some mesa dropseed and occasional plants of annual sixweeks grama (Bouteloua barbata). Most of the tobosa plant were "more dead than alive".
The soil was what has typically been referred to as "adobe", referring to high clay content. Tarbush tends to dominate on the higher-moisture retaining clay and silt soils whereas creosotebush dominates on range sites with predominately gravelly soils (Gibbons, in Shiflet, 1994, p. 65).
This range was grazed only by native species including mule deer, pronghorn (Antelocarpa americana), black-tailed jackrabbits (Lepus californicus), and small rodents like kangaroo rats (Didodomys spp.).
Dona Ana County, New Mexico. June, early estival aspect (before onset of typical summer rainy period). Following almost a decade of moderate to severe drought. FRES No. 33 (Southwestern Shrubsteppe Shrubland Ecosystem). K-52 (Grama-Tobosa Shrubsteppe). SRM 508 (Creosotebush-Tarbush), a "persistent subclimax of the grama-tobosa shrubsteppe" (Herbel in Shiflet, 1994). Creosotebush-Tarbush Series, 153.21, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41). Creosotebush-Mixed Shrub Series of Dick-Peddie (1993).
137. Fourwing saltbush form of Creosotebush-Tarbush Chihuhuan Desertscrub- A calcerous plains basin typical of the Creosotebush-Tarbush Association (range dominance or cover type) with fourwing saltbush as local dominant was presented in these two photographs. Fourwing saltbush was the whitish-green- or silverish- or grayish-colored. shrubs scattered throughout in both views. In the first photograph the low-growing, spreading, darker green foremost shrub in lower right foreground was honey mesquite; small, light-colored (silverish) shrub to left of this mesquite was fourwing saltbush. The three pea-green colored taller shrubs in midground (left to right) of first photograph was tarbush as was the shrub of same color in left foreground of second slide. The taller, dark-green shrub in slightly right-of-center midground in second photograph was red-berry agarito (Berberis haematocarpa= Mahonia haematocarpa). Tallest plant in center background of first slide and left-of-center background in second slide was a small tree netleaf hackberry or pale blanco (Celtis reticulata= C. laevigata var. reticulata).
Mesa dropseed and plains bristlegrass were well-distributed throughout; these two grasses formed an irregular herbaceous layer. Tansy mustard was an annual cool-season annual brassica visible as dead, light-brown stalks.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. June, early estival aspect. FRES No.33 (Southwestern Shrubsteppe Shrubland Ecosystem). K-53 (Trans-Pecos Shrub Savanna). Fourwing saltbush variant of SRM 508 (Creosotebush-Tarbush). Saltbush Series, 153.26, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41). Chihuhuan Deserts- Low Mountains and Bajadas Ecoregion 24c (Griffith et al., 2004). Gravelly Outwash range site in Desert Shrub vegetation zone.
138. Fourwing saltbush series of Chihuhuan Desertscrub- Fourwing saltbush dominated a local area of a calcerous basin on what was otherwise a creosotebush flats or creosotebush plains form (range cover type) of the Chihuhuan Desert. In the concept from Landscape Ecology of landscape element types this fourwing saltbush range was a patch within the matrix of creosotebush-tarbush co-dominated Chihuhuan Desert Scrubland. This was a distinct range cover (= dominance) type, Fourwing Saltbush Chihuhuan Desert, even though it was small in spatial scale (acerage)
In right foreground and center foreground (directly behind two fourwing saltbush plants) there was a plant of honey mesquite (in contact with right margin) and two plants of tarbush (in line with and immediately to left of the honey mesquite).The two native perennial grasses, mesa dropseed and plains bristlegrass, formed a patchy herbaceous understorey.
Elephant Mountain Wildlife Management Area, Brewster County, TexJune. FRES No. 33 (Southwestern Shrubsteppe Shrubland Ecosystem). K-53 (Trans-Pecos Shrub Savanna). Fourwing saltbush variant of SRM 508 (Creosostebush-Tarbush). Saltbush Series, 153.26, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41). Chihuhuan Deserts- Low Monutains and Bajadas Ecoregion 24c (Griffith et al., 2004). Gravelly Outwash range site in Desert Shrub vegetation zone.
139. Netleaf hackberry (Celtis reticulata= C. laevigata var. reticulata)- This was the small netleaf hackberry tree presented in the two photographs immediately preceding the preceding photograph. This is a valuable browse species, and a rare tree species in the Chihuhuan Desert per se (not a tree in a wash plant community or riparian range vegetation. This tree was growing amid fourwing saltbush, creosotebush, tarbush, red-berry agarito, mesa dropseed, and plains bristelgrass.
Elephant Mountain Wildlfie Management Area, Brewster County, Texas. June.
140 Tarbush (Flourensia cernua)- Two plants of this woody composite (Heliantheae tribe) were part of population that comprised an associate species (along with creosotebush) on a Fourwing Saltbush Chihuhuan Desert range cover type described above. Large shrubs behind tarbush were honey mesquite.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. June.
141. Plains bristlegrass (Setaria leucopila)- This is one of the more widely distributed and more valuable of the native panicoid grasses (Panidoideae subfamily of Gramineae or Poaacaeae) in the Trans-Pecos Chihuhuan Desert. Plains bristlegrass does form consociations (single-species stands) like black brama, chino grama, and tobosagrass, but the scattered bunchgrassess of this cespitose species provide valuable forage for grazing animals. It could be expected that the grains would provide a concentrate for native birds.
According to Powell (2000, p. 306) S. leucopila is closely related to S. macrostachya, Texas bristlegrass (S. texana), and Scheeles bristlegrass (S. scheelei) and hybridization likely occurs among these species.At one time S. leucopila, S. texana, and S. macrostachya were included in a complex called plains bristlegrass (Gould, 1975, p. 559)
These specimens were growing on the same range that served as an example of Fourwing Saltbush Series of Chihuhuan Desert introduced above. Elephant Mountain Wildlife Management Area, Brewster County, Texas. June, seed-ripe phenological stage.
142. Mesa dropseed (Sporobolus flexuosus)- This lover of desertic sandy soils is one of the most valuable forage grasses of the Chihuhuan Desert, including anthropogenic disclimax Chihuhuan Desert. Most of the Sporobolus species produce only tillers (intravaginated or vertical shoots) and hence are cespitose (bunchgrass) species. That habit was illustrated in the two specimens presented. here.
These two plants were growing on the same range introduced above that provided an example of Fourwing Saltbush Series of Chihuhuan Desert. Elephant Mountain Wildlife Management Area, Brewster County, Texas. June, early spring "green-up" stage at beginning of summer rain period.
69. The following series of four slides provided an example of the Mixed Desert Scrub phase in the Trans-Pecos region of the Chihuhuan Desert. Scrub subdivision of the Chihuhuan Desert (MacMahon in Barbour and Billings, 1988, p. 249). (How's that for organization?) Unfortunately this woody species-rich range vegetation lacked the natural herbaceous understorey. This had most likely been grazed out, but it is perhaps always too convenient--even for pro-livestock authors like this one-- to blame overgrazing for every range not in the climax state. There was not, however, any evidence on this desert range of past farming, oil and gas development, or commercial trade or travel. What about fire? Would this range vegetation have carried fire hot and frequent enough to result in increased herbaceous growth?.Most diagnostic was presence of black grama, bush muhly, ever threeawn only under cover of shrubs. It was noted that there was more cover in shrubs that are used as sources of browse such as littleleaf sumac and catclaw or Gregg's acacia than cover of grasses (most of which was fluffgrass). There was physical evidence of past cattle grazing in "petrified" cattle dung, but not recent sign. This was circumstantial evidence of overgrazing by cattle, but maybe jackrabbits moved in and annilated the grass species. (That would still be overgrazing, and possibly induced by human impact). It was likely that this vegetation was a grazing disclimax on which most native grasses had been extirpated.
Who knows? Anyway not much grass, and about as sparse a cover of forbs. An amazing diversity of range shrubs, but of course creosotebush was the dominant. Very little honey mesquite. This range vegetation was not degraded to the point of what range ecologists describe variously as drastic disturbance, drastically altered, or devastated rangeland. Enough of that was shown later in this chapter.
This series of slides illustrated subtle differences in range vegetation with increasing elevation and transition from basin to bjada and tops of low mountains. Physiography of the Basin and Range physiographic province was obvious in each photograph.
Species composition was discussed for individual photographs all of which were taken of range vegetation in the Devil Ridge Eagle Mountains, Hudspeth County, Texas. June. FRES No.33 (Southwestern Shrubsteppe Shrubland Ecosystem). K-53 (Trans-pecos Shrub Savanna). No appropriate SRM (Shiflet, 1994) rangeland cover type period. Variant of Mixed Scrub-Succulent Series, 153.25, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41). Chihuhuan Deserts- Low Mountains and Bajadas Ecoregion 24c (Griffith et al., 2004). Gravelly Outwash range site in Desert Shrub vegetation zone was closest fit of published range site descriptions.
143A. Jackrabbits pack provisions- Amid water erosion of soil there was very high biodiversity, of shrubs that is. Overall dominant was creosotebush but in foreground woody species included purple pricklypear (Opuntia violacea), spiny allthorn, ocotillo, Gregg's or catclaw acacia (Acacia greggii), javelinabush or tecomblate (Condalia ericoides), and, what-else-but,.honey mesquite. Mesquite was the most limited of these listed shrubs.
Relict grasses in extreme right hand corner of foreground were a threeawn (of Aristida purpurea complex) and gnawed-off mesa dropseed. The photographer had to hunt "high and low" to get a shot with grasses other than fluffgrass. This was it. There were two forb species: tumbleweed or Russian thistle (Salsola kali-tenuifolia= S. imberica= S. tragus= S. pestifer= S. paulsenii) and scorpionweed (Phaacelia integrifolia).
143B. Jackrabbits have shade (little else)- Along a small wash with some accelerated soil erosion there was a rich tapestry of woody species including creosotebush (the dominant), javelinabush, spiny allthorn, catclaw acacia, whitethorn acacia, soaptree (Yucca elata), ocotillo, Englemann and purple pricklypear, littleleaf or desert sumac (Rhus microphylla), lechuguilla, and honey mesquite.
Forbs included tumbleweed or Russian thistle (a naturalized, Eurasian, warm-season annual) and scorpionweed (a native, warm-season annual). Enough fluffgrass to get one jackrabbit to the next slide.
143C. Fit only for jackrabbits, if them- Example of a "creosotebush flats" at base of a bajada below the Eagle Mountains where besides the dominant creosotbush there was ocotillo, catclaw acacia, and Englemann pricklypear. Only species of perennial grass was fluffgrass. Russian thistle and scorpionweed were widely scattered. The scattered dead forbs were degraded so as tob unidentifiable to this photographer-recorder of the range.
143D. Fit for scenery (anything else?)- Range vegetation on bajada and up to top of low mountain (more like a mountainette). Desert shrubland of remarkable species richness. Creosotebush, ocotillo, whitethorn acacia, catclaw acacia, honey mesquite, tasajillo, spiny allthorn, mariola, lechuguilla, broom snakeweed, soaptree yucca, Torrey Mormon tea (Ephedra torreyana), Englemann pricklypear, and the suffruticose species sweetbush (Bebbia juncea) were all visible in this slide upon projection. Only perennial grass species found was fluffgrass; the other grass was the annual sixweeks grama (Bouteloua barbata). Major forb was scorpionweed.
144. Whitethorn acacia, mescat acacia, or largancillo (Acacia constricta)- Specimen of whitethorn acacia growing on the degraded range of Mixed Desert Scrub phase presented in the preceding series of photographs. This is a common Acacia species and shrub throughout the Trans-Pecos Basin and Range area . Largancillo is browsed by livestock, including cattle, and native ruminants (probably to some extent by rodents and lagomorphs). Reportedly the seeds are an important feed source for quail (Powell, 1988, p. 184).
Devil Ridge Eagle Mountains, Hudspeth County, Texas. June, fruit ripe stage.
145. Whitethorn or mescat acacia or largancillo- This speciment of A. constricta was at peak bloom at edge of a saline basin. Presidio County, Texas. June, full-bloom phenological stage (and, as was shown below, also immature legume stage).
146. Leaves, inflorescences, and legumes of largancillo- Two photographs showing details of inflorescence and fruit (legume) of whitethorn acacia or largancillo. It is common to find flowers at anthesis, immature legumes, and ripe legumes on the same leader (branch) simultaneously. Is this species opportunistic or is it opportunistic? Vines
These photographs were of the specimen displayed in the slide before last (two photographs immediately above). Devil Ridge Eagle Mountains, Hudspeth County, Texas.June, bloom, immature-fruit, and ripe-fruit phenological stages simultaneously on same branch.
147. Bearing young (or "If we could only get our livestock to produce like this")- Apex of a leader of mescate acacia or largancillo flowering with immature fruit "standing by". Under the rigors of desert environment adapted plants have evolved different patters of resource allocation, many of which differ drastically for similar species growing in less severe habitats.
Detail view from the largancillo plant at edge of saline basin shown in photograph before last set of slides. Presidio County, Texas. June, full-bloom and immature fruit phenological stages simultaneously.
148. Catclaw acacia or Gregg acacia (Acacia greggii)- Powell (1988) reported nine species of Acacia just in Trans-Pecos Texas. The actual number of Acacia species in the Chihuhuan Desert, most of which is in Mexico, is perhaps still unknown. Vines (196) observed that cattle browse immature foliage of catclawacacia when grass is scarce. Otherwise foliage of this species is not palatable except to jackrabbits-- when other feed is scarce. Seeds are eaten by scaled quail (Callipepla squamata) accoreing to Vines (1960, p. 499). Vines (1960, p. 499) and Powell (1988, p. 186) reported that Indians of the Chihuhuan and Sonoran Deserts made a meal called "pinole" from the legumes of this species that was eaten as a mush or cake and that the lac insect (Tachardia lacca) feeds on sap of A. greggii and exudes some of the waste from this sap that can be gathered and used as commercial lac. Neither of these uses has been adapted to the industrial scale necessary to be profitable. So another Chihuhuan Desert shrub joins guayule, the composite that produces latex and has potential for commercial production. So far all these uses have nothing but potential, unless you are a pre-whiteman Indian.
The individual catclaw shown here was growing on the depleted range used as an example of the Mixed Desert Scrub phase. Devil Ridge Eagle Mountains, Hudspeth County, Texas. June, immature-fruit stage.
149. Leader of catclaw acacia- This branch of catclaw acacia was laden with a high yield of legumes. It was on the specimen shown in the preceding slide. Devil Ridge Eagle Mountains, Hudspeth County, Texas. June, immature-fruit stage.
150. Schott acacia (Acacia schottii)- Another of the nine Acacia species documented by Powell (1988) to grow in Trans-Pecos Texas. This specimen was photographed at edge of saline or alkali basin. Powell (1988, p. 184) reported that this species hybridizes with A. constricta and A. neovernicosa. Apparently this species is as indiscriminately promiscuous as many college students. Presidio County, Texas.
151. Javelinabush or tecomblate(Condalia ericoides= Microhamnus ericoides)- This species was described by Powell (1988, p. 273) as "a low spinescent shrub" with intricate branching. Javelinabush is a member of the buckthorn family, Rhamnaceae, which includes some of the most valuable browse plants on North American range including the Ceanothus and Rhamnus species. Condalia species are closely related to lotebush (Ziziphus obtusifolia= Condalia obtusifolia). Lotebush and javelinabush often grow in close association, even side-by-side as on the degraded range shown above as an example of the Mixed Desert Scrub phase of the Chihuhuan Desert.
Devil Ridge Eagle Mountains, Hudspeth Cunnty, Texas. June, bloom phenological stage
152. The following series of four slides of Chihuhuan Desert vegetation and landscape presented another range plant community within the Mixed Desert Scrub phase in the Trans-Pecos region of Chihuhuan Desert Scrub subdivision (MacMahon in Barbour and Billings, 1988, p. 249). This range vegetation was distinctly different from the vegetation shown in the preceding series. The range plant community featured now seemed to be best described in published range site descriptions as Gravelly range site in the Desert Shrub vegetation zone.
Another example vegetation of this range site was presented previously. Range plant communities varied greatly between these two example of the same range site in the same vegetation zone. One obvious difference was an average of 11 inches of annual precipitation versus an average of 13 to 14 inches in the previous example.There were not published county soil surveys for either location so differences in soil series or association could not be determined from the literature. The the range plant community presented below had developed on an extremely rocky soil in contrast to the combination gravelly and sandy soil in the previous example of a Gravelly range site.
Presidio County, Texas. June. FRES No. 22 (Southwestern Shrubsteppe Shrubland Ecosystem). K-53 (Trans-Pecos Shrub Savanna). No appropriate SRM (Shiflet, 1994) rangeland cover type. Still yet another variant of Mixed Shrub-Succluent Series, 153.25, of Chihuhuan Desertscrub, 153.2 (Brown et al., 1998, p. 41). Chihuhuan Deserts- Low Mountains and Bajadas Ecoregion 24c (Griffith et al., 2004).
152A. "Hard-scramble" Chihuhuan Desertscrub- This is about as "tough as it gets" barring solid rock, sand dune. or salt flat. This Mixed Desert Scrub phase was composed almost entirely of shrubs (most species of which are unpalatable) and with a few forbs (some rther unique). The herbaceous layer -- such as it was-- consisted almost entirely of fluffgrass (there were not annual grass species)and forbs that grew on or under shrubs.Shrubs were both succulent and non-succulent species. Succulents included dargon's blood or leatherstem, Spanish bayonet or Faxon yucc, pricklypear species of which Englemann pricklypear was most common, and tasajillo or pencil cholla. Ocotillo was present, and while easily identified not easily categorized as suculent or non-succulent. Non-succulent shrubs included creosotebush, the local and regional dominant, skeletonleaf goldeneye, spiny allthorn, a few whitethorn acacia, and, of course (though limited in this plant community) honey mesquite.
Forbs included three composites, wooly paperflower (Psilostrophe tagetina), slender goldenweed (Machareanthera gracilis), plains blackfoot (Melampodium leucanthum) that were well-distributed throughout. The suffruticose species sweetbush (Bebbia juncea), another composite, occurred in this range vegettion. Also present but limited to microsites where sand had accumulated was annual scorpionweed and bristly or curled fiddleleaf (Nama hispidum).
The only grass species present in this photographic field-of-view (at least that the photographer could find) was fluffgrass. On an adjacent parcel of range that was the creosotebush plains (= creosotebush flats) range type chino grama, black grama, bush muhly, and red threeawn were present but very limited and mostly restricted to the protective cover of shrubs. Rather this was protection from overgrazing, overheating (ie. shrubs provided shade), or some plant interactions could not be determined.
152B. Species-rich; feed-poor- Another view of the range that served as an example of Mixed Scrub Desert phase of Chihuhuan Desert gave a better presentation of the diversity of plant species and life or growth forms of this range cover type. This view also illustrated the nearly universal feature of the Chihuhuan Desertscrub: domination by creosotebush. Other shrub species included Faxon yucca or Spanish bayonet, skeletonleaf goldeneye, ocotillo, pricklypear species, tasajillo, leatherstem, whitethorn acacia, honey mesquite, and spiny allthorn.
Forbs were mostly composites including plains blackfoot, wooly paperflower, and slender goldenweed. Then there was--whether shrub or forb-- sweetbush. Fluffgrass was the only Gramineae member present.
152C. An interesting aggregation- Biodiversity of range plant species is often remarkable in desert vegetation, even under some conditions most hostile to plant life. Such was the example shown here. The center group of range shrubs (large yucca and lemon-green plant with yellow flowers) consisted of Faxon yucca, sleketonleaf goldeneye, creosotebush, and spiny allthorn, the latter of which was "hiding "behind others and not visible from this position. A weird forb (introduced in next photograph) hitched a ride. To the left of this group was honey mesquite, whitethorn acacia, and allthorn. To right of the "centerpiece" was creosotebush, leatherstem, and tasajillo.
Aggregation is a general term sometimes used to refer to a group of organisms living in close proximity at a point in time (eg. numerous numbers and species of plants in spatial arrangement) though not necessarily as an organized unit or an interacting assembly of numbers and/or species. The term perhaps could be traced back to Clementsian usage of the term to mean the clumping or thickening of plants as part of the ovrall process of invasion. Groups of plants consisting of more than one species were called mixed aggregations.
Assemblage is another and more commonly defined term that expresses the idea of groups of plants: "A collection of plants and/or animals characteristically associated with a particular environment that can be used as an indicator of that environment" (Allaby, 1998). The assembled or aggreagted plants (both kinds, numbers, spatial, and temporal as to life cycle) shown here and in the next photograph (in more restricted but more detailed view) provided an example of plant species diversity even over a small area in a 'big" ecosystem or landscape.
Desert biotic communities, ecosystems, and landscapes are usually thought of as being extensive and therefore not commonly having concentrations of species or numbers, but as Geroge Gershwin reminded folks in Porgy & Bess, "It ain't necessarily so". These desert range plants seemed to be getting along better together than most contemporary university faculties and administrators.
152D. Close-up of the "congregation"- This local group of range plant species was a close-up of some of the vegetation presented in the immediately preceding photograph. These photographs were of an example of the Mixed Desert Scrub phase of Chihuhuan Desert. Range plant species in this aggregation included Faxon yucca, skeletonleaf goldeneye, creoeotebush, spiny allthorn (behind other shrubs and not visible), and the forb, slender propellar-bush (Janusia gracilis), an odd perennial herbaceous vine. Actors in this desert play were introduced immediately below.
153. Slender propellar-bush (Janusia gracilis)- Photographs of an interesting little range plant were included to provide complete coverage of the range plant assemblage introduced above, and for readers' eduction (and amusement).
Presidio County, Texas, June.
154. Re-propellared- Another plant of slender propellar-bush, and while this plant might have been slender (thin, skinny, whatever) it was far from small and, instead, was twining, climbing, trailing all over a supportive guayacan for considerable distance. This epiphyte (one plant species that grows on or around another species of plant for physical support, nourishment, protection, etc.) was in the ceniza scrub (shrub) form of the Chihuhuan Desert, the Leucophyllum-Larrea-Prosopis climax community described by Kuchler (1964, p. 45), examples of which were presented above.
Big Bend National Park, Brewster County, Texas. Early October; peak standing crop, peak bloom phenological stage.
155. Skeletonleaf goldeneye (Viguiera stenologa)- A woody composite of tribe Heliantheae that provides browse for native browsers and even generally non-browsers like cattle. Powell (1988, p. 471) felt that this attractive shrub had ornamental uses. This would seem to be especially the case for those having interests in landscaping with native shrubs.
Skeletonleaf goldeneye is one of the more widespread shrubs on ranges in higher ecological status. This shrub is especially common on rocky soils like mountinous habitats. This specimen was the one in the "centerpiece" of range vegetation shown in the two photographs immediately before the propellar-bush. Presidio County, Texas. June, and blooming.
156. Skeletonleaf goldeneye- Shots of shoots in skeletonleaf goldeneye featuring the unique linear leaves and composite inflorescences. Same plant as shown above. Presidio County, Texas. June, peak bloom for this desert habitat..
157. Sweetbush (Bebbia juncea)- This aromatic composite (Heliantheae tribe) is mostly herbaceous though it becomes woody near its base. It was regarded as a shrub by Vines (1960, ps. 977-978) but as a forb by Powell (1988, p, 448). Sweetbush is widespread being native as far west as California and southward to Sinaloa and Sonora. Sweetbush is readily identified by its branches and general habit that bear resemblance to rushes (Juncaceae, Juncus), hence the specific epithet, juncea. Browse value was unknown, but bound to be of use for soil protection and as a bee plant.
Plant was growing on the range used as the example of Mixed Desert Scrub phase of Chihuhuan Desert. Presidio County, Texs. June, full-bloom stage.
158. Wooly paperflower (Psilostrophe tagetina)- This composite forb (also of the Heliantheae tribe) is easily identified by the triple-notched (three-toothed) ray flowers. Although this perennial forb is attractive to the human eye and adds diversity to the Chihuhuuan Desert range it is also attractive to sheep for which it is a poisonous range plant. The poisonous principle is psilotropin, a sesquiterpene lactone which can prove fatal to sheep in which it cuses regurgitation, caughing, depression, and coma, prior to death. Cattle are much less susceptible to paperflower poisoning so grazing infested ranges by cattle prior to introduction of sheep is one preventive practice. This is another example of the Fourth Cardinal Principle of Range Management: Proper Kind and Class of Range Animal.
Sources regarding toxicity of paperflower include Kingsbury (1964, ps. 420-422), Sperry et al. (1964, ps. 38-39), Schmutz et al. (1968, ps. 50-51), Fuller and McClintock (1986, p. 91), Burrows and Tyrl (2001, ps. 148-149, 187-189), and Hart et al. (2003, ps. 160-161).
Growing on the range used as an example of Mixed Desert Scrub phase of Chihuhuan Desert. Presidio County,Texas. June.
159. Plains blackfoot or arnica (Melampodium leucanthum)- Another composite forb of Heliantheae. This perennial is typical of many species of desert plants in that it blooms whenever conditions are favorable, and favorable is most commonly defined by "if and when it rains".
Growing on the range used as an example of the Mixed Desert Scrub phase of Chihuhuan Desert in Presidio County, Texas. June.
160. Slender goldenweed (Machaeranthera gracilis)- Still yet another composite species growing on the same range used as an example of the Mixed Desert Scrub phase of Chihuhuan Desert. This DYC (Damn Yellow Composite) was a member of the aster tribe, Astereae, rather than the more genus-rich Heliantheae. Apparently this species is like a lot of people: doesn't do anything real special, its just out there on the range. This one was on the same range as the other composite species in this section. There was a large number of sunflower family members on the range that was used as an example of one form of the Mixed Desert Scrub phase of Chihuhuan Desert. Presidio County, Texas. June, full-bloom phenological stage.
The above members of the sunflower or aster family (Compositae= Asteraceae) were presented to impress upon students of Range Management the contribution of this one family to range plants and range cover types. In North America there are more species of composites than of any other range plant family. In fact, on a planetary basis Compositae is second only to Orchidaceae (orchid family) in number of species. Orchids are of much less consequence on the ranges of North America. Composites are not as influencial as grasses or non-composite trees based on production of biomass (including wood and mast as well as forage and browse), cover, soil protection, etc., but from standpoints of number of species, poisonous plant problems, noxious plants (weeds and brush), health problems such as allergies and asthma, and feeds for many animal species the composites (both shrubs and forbs) are of utmost importance.
All real rangemen appreciate the contributions-- good and bad-- of composites.
161. Leatherstem, rubber-plant, dragon's blood, or sangre de drago (Jatropha dioica var. graminea)- One of the local dominants or, more commonly, associate species on Chihuhuan Desert ranges is this dioecious or, occasionally, monoecious species of the euphorbia family, Euprorbiaceae. A distinctive and unique shrub that has rubbery shoots covered with red, brown or, sometimes in older individuals, gray bark and that exudes a reddish or orangish watery sap when injured (hence, dragon's blood). There have been numerous mdeical values attributed to the plant sap (Vines, 1960, ps. 625-626).
J. dioica var. graminea (called grass-leaf rubber-plant) is the more common taxon in Trans-Pecos Texas.
On the range serving as example of Mixed Desert Scrub phase of Chihuhuan Desert. Presidio County, Texas. June.
162. Closer looks at leatherstem- "Closer-in" views of leathersterm or grass-leaf rubber-plant showing characteristic leaves, bark, and branching pattern of this interesting desert range plant. Photographs from plants on the range that served as an exampe of the Mixed Desert Scrub phase of Chihuhuan Desert, Presidio County, Texas. June, pre-bloom phenology.
163. Candelilla (Euphorbia antisyphilitica)- Candelilla (Spanish for "little candle") or wax euphorbia is one of the most unique and "talked-about" shrubs of the Chihuhuan Desert. Candellia grows from the Big Bend area of Texas south into many of the states of Mexico including Nuevo Leon, Coahuila, Hildago, and Chihuhua. The most notable attribute of this succulent species is its wax content which has long served as raw material for candles, soaps, various polishes, chewing gum, and general lubricants including use in insulation. Medicanal properties have long been attributed to candelilla including treatment for syphilis which explains the specific epithet antisyphilitica. The accolade was --as with many such allegeded remedies-- bogus, but the name stuck. Scientific names need not be based on actual scientific facts.
Powell (1988, ps. 241-242) presented a brief but thorough account of this species including discussion of candelilla wax operations. Maxwell (1968, ps. 95-99) noted that except for range grasses candelilla was the most commonly used plant of the Big Bend area of the Chihuhuan Desert. The interesting account (complete with era photographs) by Maxwell (1968, ps. 95-99) described harvest and processing of candelilla wax, .the latter of which consisted of mobile wax plants built around wax rendering vats. The primitive harvest of candelilla was simple: plants were dug up, bundled, and packed out on burros (Spanish for ass [Equis asinus]). Frontier harvest of many species (including those used for hides, pelts, robes, and plumage) was also primitive, but often successful in widespread extirpation of species. Ditto on candelilla. The species is still rare in some localities where it was once abundant prior to commercial harvest.
Candelilla wax is on the outside of shoots as an adaptation to prevent desiccation in the arid climate. This is just one of many species of Euphorbia native to the ranges of North America. Most are known by the generic noun, "spurge". Warnock (1974, ps. 83-87) presented photographs and described 12 Euphorbia species just in one area of Trans-Pecos Texas. All of these were known as a this-or-that "spurge".
Big Bend Ranch State Park, Presidio County, Texas. June.
164. Candles in the raw- Candelilla presented in two photographs that showed general habit and density of shoots. Big Bend Ranch State Park, Presidio County, Texas. June, prebloom stage.
165. Chihuhuan candles- Close-up photographs of candelilla shoots with developing floral buds. Candelilla is a monoecious species. Big Bend Ranch State Park, Presidio County, Texas. June, prebloom state.
166. Rio Grande saddlebush, sandpaper bush, or rough mortonia (Mortonia sempervirens subsp. scabrella= M. scabrella)- This unpalatable shrub of the stafftree family, Celastraceae, is noteworthy because it is the defining dominant of one of the biotic communities of the Chihuhuan Desert: Sandpaperbush Series. 153.25, of Chihuhuan Desertscrub, 153.2 (Brown et al, 1998, p. 41). The Sandpaperbush Series ocurs more in western portions of the Chihuhuan Desert (Brown, 1994, ps. 174, 176), but sandpaperbush is locally common in some mountains of Trans-Pecos Texas.
Big Bend Ranch State Park, Presidio County, Texas. June.
167. .Bristly or curled fiddleleaf (Nama hispidum)- This member of the waterleaf family, Hydrophyllacee, is most common on the sandier range sites and sandy microsites on stoney rangeland. A few scattered plants of this low-growing species are inconsequential, but where there are many such plants established on sandy range soil the land has a living carpet, and that is what it looks like. Obviously this provides a living, protective cover on soil highly susceptible to wind erosion. And it is yet another "nifty" desert range plant from another plant family that is uncommon on the ranges of North America.
El Paso County, Texas.
168. Gyp ringstem (Anulocaulis gypsogenus)- Gyp (from the adjective, gypseous, in reference to soil high in gypsum) is a member of another plant family tht is uncommon on range, the four-o'clock family or Nyctaginaceae. Basis of the common name can be seen in the more detailed secon photograph.
Big Bend Ranch State Park, Presidio County, Texas. June, immediate post-bloom stage.
169. A wooly amaranth- Wooly honeysweet or honeymat (Tidestromia lanuginosa), an annual forb, on a creosotebush-dominated grazing disturbance of a former creosotebush-grass (Bouteloua eriopoda-Muhlenbergia porteri) savanna in Trans Pecos Texas. Wooly honeysweet is a member of the Amaranthaceae (pigweed or amaranth family). Its fruit is an utricle, an indehiscent, single-seeded, sac-like (bladdery) fruit (Smith, 1977, p. 311).
This particular plant was growing on a severely overgrazed, depleted range from which much topsoil had been eroded. It had the good fortune, however, to grow in an extremely wet warm-growing season and had done quite well for itself.
Pecos County, Texas. Mid-October.
170. Wooly where most was grazed out- Foliage (first slide) and shoot apex (second slide) of a plant of wooly honeymat or wooly honeysweet, an annual and low-growing forb in the pigweed family (Amaranthaceae). This plant (and a lot more just like it) was (were) growing on nearly bare, eroded soil of a severely overgrazed former creosotebush-grass savanna in Trans Pecos Texas. Wooly honeymat is an annual invader that thrives under conditions of range retrogression.
Pecos County, Texas. Mid-October.
171. Fluffgrass (Tridens pulcehllus= Erineuron pulchellum= Dasyochloa pulchella; taxonomists better make up their minds on this one's name because they are running out ways to modify the root pulchel.)- This is one of the smallest, lowest stature perennial grass species on semidesert grassland. Fluffgrass has traditionally been interpreted as an ecological invader being lumped in the same company as annual grasses and forbs, most threeawns, and small perennials like red grama (Bouteloua trifida).
There is a twist to this oft-told story however. Dick-Peddie (1993, ps. 132) felt that fulffgrass served as an indicator species much like desert holly (explained above). Either of these herbaceous species might be relict species of semidesert grassland such their presence on Chihuhuan Desertscrub would indicate a desertscrub disclimax. While general occurrence of fluffgrass (and desert holly) was a very small (perhaps trace) proportion of climax semidesert grassland types (eg black grama grassland) this density, cover, etc. was extremely important as a clue to potential natural (= virgin= pre-Columbian) vegetation. Such is the value of an indicator species. It need not be a dominant, associate, or otherwise major species, just a diagnostic one.
El Paso County, Texas. June.
172. Fluffgrass at peak standing crop (such as it was)- This happy little semidesert dweller was "all swole-up" with the pride of any new parent. The "fluff" is the cottony pubescence on mature spikelets. Spikelets are arranged in fascicles, a term denoting a cluster or bunch as applied to culms, leaves, or, as in this instance, inflorescence branches (Gould and Shaw, 1983, p. 374). .Here again this enigmatic little range plant had another twist to its tale. The clumps of the inflorescence (fascicled spikelets) were themselves on clumps or bunches of shoots (and developing roots) that arose from stolons branching out from the parent plant. The little bunches of shoots topped with fascicles were ramets from the main (parent) plant which was an apparent genetic individual or genet. Each flowering module or clone was reproducing sexually (ie. there was prounced asexual and sexual reproduction simultaneously in the same generation).
In the theory of natural selection (= survival of the fittest) fitness is defined as the capacity to reproduce, specifically to reproduce deoxyribonucleic acid (DNA). The fittest organism (genotype, species, etc).is the one that reproduces the most offspring to perpetuate that genotype, species, etc., and that DNA. Increased fitness (more offspring; more DNA) can only come through genetic change. This requires recombination of genes which can only come from exchange and union (fertilization) of gametes (ie. sexual reproduction). The truest reproduction of existing superior genotypes (DNA having superior fitness) comes from cloning, which in plants is vegetative or asexual reproduction.
The fluffgrass plant shown here was hedging its bets and reproducing by both means so as to: 1) optimize the chances of producing improved genetic individuals (genets) and 2) perpetuation of proven (environmentally tested) genotypes through clones (ramets). And that was as good as the brushed twitch of any treasured tail.
The details of this phenomenon were readily visible in the second slide. Cute, hugh?
Presidio County, Texas. June, full-bloom phenological stage.
Anthropogenic (man-made) or, at very least, human-induced extensions of natural or climax vegetation of Chihuhuan Desert into range sites and rangeland cover types on which range vegetation other than Chihuhuan Desert is the potential natural plant community was discussed in considerable detail in the introduction of this chapter. This process of encroachment of Chihuhuan Desert (= Chihuhuan Desertscrub) into other climax or potential natural vegetation is one of numerous cases of desertification. Desertification is an on-going process on many areas of Earth. Desertification has tradtionally been interpreted as being the result (directly or indirectly) of human action. Desertification has probably been an anthropogenic-based process since prehistoric times, at least in areas such as the Mediterranean Region (ie. the Holy Land) as documented by numerous references in the Holy Bible.
There is nothing holy about human-caused desertifiction. It is an ecological disaster and, in this author's opinion, an unholy-- a sinful-- set of actions that has (continues) to violate the Abrahamic covenant. (See Eleventh Commandment at end of this publication.) Obviously desertification resulted from many human motives besides greed and selfishness. Ignorance would probably the primary cause of human-induced desertification.
In that context, and given that the mission of the professor is to declare war on and destroy ignorance (ie. "stomp out ignorance"), the following section was devoted to unnatural expansion of the Chihuhuan Desert. Most of this desertification in the Chihuhuan portion of the Basin and Range physiographic province has been and continues to be encroachment--noxious woody plant invsion-- into climax semidesert (Chihuhuan) grassland.
173. Creosotebush disturbance climax- The climax (pre-Columbian) vegetation of this range site was identified by Kuchler as Trans Pecos Shrub Savanna, a transition zone or ecotone between the semidesert grassland and Chihuhuan Desert. The pre-whiteman potential natural vegetation was a range community consisting of shrubs like creosotebush, tarbush , fourwing saltbush, mesquite, whitethorn acacia, lechuguilla (Agave lechuguilla), sacahuiste (Nolina texana), Mexican tea (Ephedra trifurca), skeletonleaf goldeneye (Viguiera stenoloba), mariola (Parthenium incanum), Yucca species, Rhus species, and Quercus species scattered among the dominant and more productive understorey of grasses like black grama, chino grama, sideoats gramas, tanglehead (Heteropogon contortus), and cane bluestem (Andropogon barbinodis= Bothriochloa barbinodis) as decreasers down to fluffgrass (Tridens pulchellus= Erioneuron pulchellum), burrowgrass (Scleropogon brevifolius) and perennial threeawns (Aristida species) as invaders.
Current vegetation is a creosotebush consociation, a disclimax that is perhaps "permanent" in human time scale. This was part of the expanding Chihuhuan Desert that had encroached onto the virgin semidesert shrub-steppe savanna. The desert pavement was partially a natural surface typical of arid landscapes and partially the product of a heavily eroded soil caused by human disturbances like overgrazing (but perhaps also by natural changes in climate) such that the pre-Columiban vegetation may no longer be the natural potential vegetation.
The characteristic wide-spacing and uniform distribution of desert shrubs was obvious in both of these slides. Students should also make note of the topography or local relief which consisted of the basin in the foreground that was surrounded by benches of mountain slopes. This is the classic basin and range physiography.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 508 (Creosotebush-Tarbush) variant. Gravelly range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
174. Chihuhuan Desert basin vegetation- In this basin floor adjacent to a desert mountain range (Elephant Mountain in background) creosotebush was the sole dominant species (ie. creosotebush consociation) with whitethorn acacia (taller shrub in center foreground) the associate. Climax vegetation for this range site was most likely primarily black grama, chino grama, sideoats grama, tanglehead, and cane bluestem as major decreasers with creosotebush, Mexican tea, tarbush, and other woody species like Yucca, Rhus, and Quercus widely scattered and more as associate than as dominant species. This gramagrass-shrub steppe savanna that had retrogressed to a creosotebush-dominated desert scrubland was a textbook example of desertification. The existing vegetation is probably the post-white man ecological potential (ie. a rangeland cover type of existing vegetation) and not the potential natural vegetation. That is, the existing range vegetation is a disturbance climax and not the pre-Columbian natural climax or what is sometimes known (redundantly) as the climatic climax.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 508 (Creosote-Tarbush) variant. Gravelly range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al, 2004).
175. Fluffgrass (Tridens pulchellus= Erineuron pulchellum)- Typical dwarf size and general habit of the smallest and most general stress-resistant perennial grass on the Chihuhuan Desert and semidesert grasslands. The pedestaled feature shown here is characteristic of highly eroded desertic soils: erosion (especially by wind) removes soil not bound by roots leaving pedestals of original root-bound soil several inches higher than the adjoining bare and unprotected (hence, eroded) land base that is often nothing but pebbles and other rock fragments. The latter remained because they were too heavy to become air-borne. All-in-all a sickening sight.
176. Trans Pecos grass-shrub savanna on igneous rock outcrop complex- There are various forms or "expressions" of the Chihuhuan Desert that are variants of range cover types, but that are not necessarily range sites or habitat types because they are not climax or potential natural vegetation. Rather, these forms are pre-climax successional stages that are permanent range plant communities in human management time scale. These are cover types of existing seral (vs. climax) vegetation that have to be managed as if they were climax. Such vegetation constitutes a disclimax (disturbance climax).
The range plant community presented here was one example of a range disclimax caused by the proceses of desertification. The range community shown in the preceding four slides (a creosotebush consociation on a Gravelly range site) was another example of a range disclimax that was the result of desertification. Specifically, components and features of the Chihuhuan Desert expanded into an area and onto a range site for which the combination of climatic, edaphic, topographic, and natural biotic factors had as climax or potential natural vegetation a grass-shrub savanna. That potential range plant community was an ecotone between semidesert grassland and Chihuhuan Desert scrub. The climax ecotone (trans Pecos shrub savanna having a dominant understorey of dominant mid- and shortgrass species) had been degraded-- to varying degrees-- into the range vegetation shown here.
The vegetation in this slide was similar to climax vegetation (ie. it was late seral stage vegetation) but with diminished cover and density of climax grasses like black grama, chino grama, sideoats grama, tanglehead, cane bluestem, and bush muhly and increased proportions of invader species like burrowgrass, threeawns, and fluffgrass. Shrub cover exceeded that of climax with excessive cover especially of mariola and, in local microsites, creosotebush and/or mesquite. Otherwise, shrub composition was similar to that of the likely climax with many decreaser shrub species present in relatively high percentages (cover). Relative abundance of ocotillo, yucca, and cholla cactus (Opuntia imbricata) was conspicuous and similar to that of the climax savanna. The shrub with shiny or glossy compound leaves at far left foreground was evergreen sumac (Rhus virens), a climax species and valuable browse plant. Details of the herbaceous component was presented in two slides following the next slides of the general (overall) plant community.
Elephant Mountain Wildlife Management Area., Brewster county, Texas. July (following recent plentiful rains). FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 505 (Grama-Tobosa Shrub). Igneous Hill and Mountain range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
177. Degraded trans Pecos grass-shrub savanna- Another section of the same hillside shown in the preceding photograph on which the range vegetation was ecotonal between semidesert grassland and the more xeric Chihuhuan Desert. Unlike the high seral stage vegetation shown immediately above, this local range plant community was a substantial departure from climax. Creosotebush had invaded this more mesic hillside from the xeric desert floor below. Mariola, skeletonleaf goldeneye, and mesquite (in that approximate order) were the major species on the deteriorated range presented here. The major grass species were still decreasers and increasers more than invaders. The grass layer of this vegetation was made up of chino grama, sideoats grama, cane bluestem, black grama, and vine mesquite (Panicum obtusum). Fluffgrass, burrowgrass, perennial and annual threeawns, and annual gramas were not common. In other words, the difference between this depleted range and climax range was in relative proportions of desert shrubs and decreaser grasses (greater and lesser abundance, respectively).
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Tran Pecos Shrub Savanna). SRM 505 (Grama-Tobosa Shrub). Igneous Hill and Mountain range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
178. Interior view of deteriorated Trans-Pecos grass-shrub savanna on igneous rock outcrop- Composition of this range type and site had departed from that of climax in having an increased cover of shrubs like mariola, creosotebush, mesquite, and skeleton goldeneye and decreased cover, density, frequency, etc. (as well as vigor) of dominant grasses (chino grama, sideoats grama, vine mesquite, cane bluestem, black grama, and tobosagrass). Proportions of certain shrubs like ocotillo and cholla cactus appeared to be similar to that of climax vegetation. (The lush foliage on the "centerpiece" ocotillo, a drought-deciduous species, indicated occurrence of recent heavy rains.)
Parent material of the soil of this site was igneous, most commonly rhyolite (volcanic rock consisting primarily of of orthoclase, which is potassium feldspar, and quartz with lesser quantities of biotite, hornblende or pyroxene). Rhyolite was the most abundant mineral comprising the boulders strewn across this hillside.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 505 (Grama-Tobosa Shrub). Igenous Hill and Mountain range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
179. Herbaceous layer of vegetation of trans Pecos grass-shrub savanna on igneous rock outcrop- Climax grass species dominated the herbaceous understorey of this ecotone between semidesert grassland and Chihuhuan desert. Ground-level vegetation was that of the range plant community shown in the immediately preceding three slides of a igneous hillside in trans Pecos Texas, the easternmost extension of the Basin and Range physiographic province.
The dominant grass in this photo-plot was vine mesquite followed closely by sideoats grama. Chino grama and cane bluestem (also climax species) were present in lesser quantities.
Rocks were mostly rhyolite (described in preceding caption).
Elephant Mountain Wildlife Mangement Area, Brewster County, Texas. Jully. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 505 (Grama-Tobosa Shrub). Igneous Hill and Mountain range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
180. Herbaceous understorey of trans Pecos grass-shrub savanna- Another view of the herb layer of range vegetation in an ecotonal area between Chihuhuan Desert and semidesert grassland. This was the same plant community featured in the preceding four photographs. This vegetation had deteriorated to considerable extent from the state of climax, but species composition of the grass-dominated understorey likely did not depart greatly from that of the virgin grass-shrub savann. Grass and shrub components had reversed in dominance with deterioration from climax such that the increased woody plant cover had become a case of invasion by brush (brush implies noxious woody plant and is never synonymous with browse, shrub, or woody plant). Proper management of this range should include the objective of reduction of the excessive cover of invading shrubs (ie. brush), but such intensive manipulation of this savanna would not be profitable under the low stocking rates that constitute proper use in this arid portion of the Basin and Range physiographic province.
Grasses in this photo-plot were mostly sideoats grama and chino grama. The blue-flowered forb was blue-eye grass (Sisyrinchium sagittiferum). Immediately adjcent to the right of the blue-eye grass and to the left of a rock of rhyolite was immature cane bluestem.
Elephant Mountain Wildlife Management area, Brewster County, Texas. July. FRES No. 33 (Souuthwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 505 (Grama-Tobosa Shrub). Igneous Hill and Mountain range site. Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
181. Chino grama (Bouteolua ramosa)- This is often the dominant decreaser grass species on hillsides in the Chihuhuan Desert and semidesert grassland region of the far western portion of the Edwards Plateau and the trans Pecos part of the Basin and Range physiographic province. Tobosagrass is the dominant on clay swales in this immense region. In fact, tobosa is often the exclusive species on these sites such that they are designated "tobosagrass flats" or "tobosa swales" (consociations of tobosagrass). These sites are usually the lowest points in the basins situated among surrounding foothills of the mountains (ie. basin and range physiography). On the higher or upland parts of basins black grama is the dominant, though it does not always form such exclusive homogenous stands as does tobosagrass. On the benches of the surrounding foothills chino grama often forms stands similar to those of tobosagrass and black grama, though typically with greater shrub cover (ie. a savanna in contrast to the grasslands or, at least, more grassland-like vegetation of the basins).
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.
One of the most pronounced (and best studied) examples of desertification in the Chuhuhuan Region has been encroachment of Chihuhuan Desertscrub into the climax--and, mostly, former-- semidesert (Chihuhuan) grassland along portions of El Camino Real, especially the Jornada Del Muerto. This was discussed in the introduction to Chihuhuan Desert. Readers wishing a historical background before viewing the following short section were referred back to that discussion. Presented below are textbook examples of Disclimax Chihuhuan Desert. As best estimated from long-term range vegetation studies, the pre-Columbian plant community was a mosaic of black grama grassland, tobosa grassland, and, probably most widespread, a grama- tobosa shrubsteppe (Bouteloua-Hilaria-Larrea) according to Kuchler (1964, unit 58) and Kuchler (unit 52, potential natural vegetation map in Garrison et al., 1977). Today it is... well, readers decide for yourselves.
182. All that's left- Broom snakeweed and honey mesquite (creosotebush, a distant third) dominated this deep, sandy soil on what was most likely a climax black grama-dominated semidesert grassland with scattered plants of longleaf Mormon tea, soaptree yucca, creosotebush, and honey mesquite (ie. a black grama shrubsteppe). Disclimax Chihuhuan Desert on the Jornada Del Muerto, one of the more dreaded reaches of the El Camino Real de Tierra Adentro. Overgrazing (primarily by draft animals) almost certainly took place on what was the first national highway (travel by Spanish explorers and traders began in 1598) in North America (Santa Fe to Chihuhua City).
The presence of longleaf Mormon tea or longleaf jointfir (foremost plant; in front of a large broon snakeseed) was a convincing clue as to what once was. Pre-existing range vegetation was estimated from small relict areas of pristine black grama grassland still present on this same range and based on numerous studies of this range vegetation (see Gibbens et al., 2005, including their citations of previous work). In the discussion that introduced the Chihuhuan Desert, it was emphasized that Dick-Peddie (1993, ps. 108, 116-117, 131-132, 140) reported that presence of certain shrub, forb, and/or grass species was "diagnostic" as to past vegetation. Presence of soaptree yucca, desert holly (Perezia nana), and fluffgrass and absence of other species like tarbush "might be considered" as indications of "new Chihuhuan Desert Scrub" or "used as indicators of recent succession [retrogression] from a grassland or desert grassland vegetation" (Dick-Peddie, 1993, ps. 131-132). Plant species were listed by Dick-Peddie (1993, as for eg. shrubs on ps. 116-117, 140141) that he regarded as diagnostic (climax) members. These species could perhaps be used as references to vegetation change. Presence of these indicator species-- especially if climax species-- might be evidence of pre-whiteman vegetation that differed substantially from existing vegetation. The presence of relict species (even just a few individuals of relict species) in Chihuhuan Desertscrub that are not climax species in desert but are climax in semidesert grassland strongly suggested that the existing range plant community was a deviation from climax (= pre-Columbian) vegetation. Such vegetation dynamics would have taken place by retrogression (the opposite process of plant succession). This would mean that existing Chihuhuan Desert was the outcome of desertification and that it was not natrual range vegetation (ie. present desert shrubland was vegetation in an ecological state or successional stage that indicated range deterioration). This is the essence, in management terms, of a depleted range and, in ecological terms, of a disclimax (= disturbance climax).
Longleaf Mormon tea and broom snakeweed are two indicator species, and their presence in the range plant community shown here indicated range degradation. Longleaf Mormon tea and broom snakeweed are climax species (ie. indicator species or diagnostic members) of semidesert grassland, but not climax species of Chihuhuan Desertscrub (Dick-Peddie, 1993, ps. 116, 140). Longleaf jointfir (and soaptree yucca) are almost always present on virgin black grama grassland range. Such range is a savanna on which longleaf jointfir and soaptree comprise the woody element (ie. these shrubs are decreasers). Broom snakeweed has traditionally been classified as an invader on abused or naturally stressed ranges (eg. those experiencing severe drought). Soaptree yucca is a member of both semidesert grassland and Chihuhuan Desertscrub (Dick-Peddie, 1993, ps. 117, 140). Thus, so presence of soaptree was not diagnostic even though it was present in the range plant community presented in this photograph.
On the depleted range presented here longleaf jointfir was a relict species and presence of this species strongly suggested that the range plant community that existed just before the current range vegetation (shown above) was the Ephedra trifurca-Gutierrezia sarothrae/Bouteloua eriopoda-Mixed Forb of the Shrub-Black Grama Series of Desert Grassland (Ecotone) given by Dick-Peddie (1993, Table 7.1, p. 111).
The range plant community shown in this photograph was a black grama-longleaf Mormon tea-broom snakeweed shrubsteppe (savanna) without the black grama and with broom snakeweed, a climax savanna (widely scattered) shrub that served as an indicator species, currently present as a local dominant. Broom snakeweed had so increased beyond natural proportions (cover density, etc.) in the climax vegetation that snakeweed had become a woody invader, hence a noxious range plant. Also present in noxious proportions was honey mesquite (one was present directly behind the foremost longleaf jointfir and broom snakeweed).Appropriately there was even some pricklypear of an unknown Opuntia species.
This semidesert grassland range was in a severe state of retrogression. Furthermore, range depletion was probably so far advanced in an arid climate that the climax plant community (or even higher seral stages thereof) could not be restored by proper grazing management or any management input except expensive, intensive range improvement practices like range reseeding followed by continued brush control measures.
If a state of retrogression would require such a long period of time before the range plant community could recover through secondary palnt succession the existing vegetation would be "permanent" or the "potential" in human time scale. If, for instance, the range site was so deteriorated due to extreme soil loss that the range vegetation could not recover faster than the rate of soil formation (geological time, in essence) the existing vegetation would be permanent for practical purposes, at least barring cost-prohibitive herculean practices to restore the former range vegetation. Instead, the present or new "permanent" plant community would be a human-caused (man-made) climax vegetation. This new "permanent" plant community caused by disturbance is a disturbance climax (= disclimax). That is the essence of disclimax (vs. natural) Chihuhuan Desert.
And that dear viewers is what was shown in this and the following slides.
New Mexico State University, Dona Ana County, New Mexico. June, early estival aspect (before beginning of summer rainy period). Potential natural (= climax) vegetation was most specifically described by Dick-Peddie (1993, p. 111): Ephedra trifurca-Gutierrezia sarothrae/Bouteloua eriopoda-Mixed Forb, Shrub-Black Grama Series of Desert Grassland (Ecotone). Disclimax range vegetation shown here was Shrub-Scrub Disclimax Series, 143.15 that was formerly the climax Grama Grass-Scrub Series, 143.11, of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40). No FRES, Kuchler, or SRM designations were presented because these were all of climax (vs. disclimax) vegetation. Even SRM 508 (Creosotebush-Tarbush) "is a persistent subclimax of the grama-tobosa shrubsteppe" (Herbel in Shiflet, 1994). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
183. Along the old El Camino Real- Range vegetation shown in this, the immediately preceding, and the immediately succeeding photographs was on a part of the New Mexico State University College Ranch that had been "smack dab in the middle" of the infamous stretch Jornada del Muerto stretch of the trade route, El Camino Real de Tierra Adentro. For three hundred years traders and other travelers moved along this route that wandered to and fro like a braided stream from Santa Fe to Chihuhua (now, Mexico) City. (Today part of the El Camino Real is paved and bears the designation of Interstate 25.)
This photograph was taken from one of innumerable ridges of sand ("rises") that have existed back in time measurable by the geologic calendar, including the centuries over which traders and travelers with numerous heads of livestock, especially beasts of burden, moved enroute through the Rio Grande Valley. Local folklore has long maintained that night camps were made whenever possible on such "rises" along El Camino Real. Camps on these sand ridges offered the advantage of "holding the high ground" so as to guard against marauding Indians. Depradations by Apaches were so common that the little but famous Fort Selden, both cavalry and infantry, was estblished near where the Jornada del Muerto stretch rejoined the main route of El Camino Real. Camping on sand ridges also offered such fringe benefits as greater exposure to cool breezes. Viewers are looking at one such sand "rise" on the Jornada del Muerto (ie. a Jornada "truck stop" or, same thing these days, public highway "rest stop"). The fuel of the times was of course forage and browse along the Royal Highway. It was "free for the taking" and such communal "filling stations" became what Garret Hardin so memorably coined "The Tragedy of the Commons". This range vegetation was about two miles from ruins of Fort Selden and about 80 years after 300 years of overgrazing.
When Anglo culture took this range from the Mexicans (who took it from the Spanish who took it from the Indians who took it for themselves) overgrazing of the grazing commons continued. Even original notes by land surveyors of the United States Department of Interior General Land Office were of range vegetation that had been subjected to European use and abuse (mostly the latter) for over two hundred years.
Is it any wonder that where black grama probably grew stirrup high (and even may have been used for hay) the range vegetation viewed here was disclimax Chihuhuan Desertscrub? Disclimax vegetation consisted of longleaf jointfir (foremost plant), a relict climax shrub; soaptree yucca, another relict from semidesert grassland; broom snakeweed, increased to co-dominant and noxious plant status; creosotebush, co-dominant second to snakeweed; honey mesquite; cane cholla (Opuntia imbricata), and desert sumac (Rhus microphylla), the one palatable browse species. Most common grass species was sixweeks grama (Boutelous barbata), the amber-colored little patches. Fluffgrass was the most common perennial grass; in fact, about the only one except for some "Lone Ranger" bush muhly plants growing under creosostebush. Black grama was not to be found. Gibbens et al. (2005, p. 664) reported greatest loss of black grama on deep sand sites and least on range sites of shallow sand. They hypothesized that this was due perhaps to perched water tables resulting from caliche layers on shallow sites.
New Mexico State University College Ranch, Dona Ana County, New Mexico. June (prior to initiation of summer precipitation period). Climax (= potential natrual) vegetation was-- at one time; now, "in your dreams"-- Ephedra trifurca-Gutierrezia sarothrae/Bouteloua eriopoda-Mixed Forb of Shurb-Black Grama Series, Desert Grassland (Ecotone) as described by Dick-Peddie (1993, p. 111). Grazing disclimax vegetation shown here was Shrub-Scrub Disclimax Series, 143.15, that was formerly the climax Grama Grass-Scrub Series, 143.11, of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40). No FRES, Kuchler, or SRM designations were given because they are of climax vegetation and inappropriate for this disclimax. Even SRM 508 (Creosotebush-Tarbush) "is a persistent subclimax of the grama-tobosa shrubsteppe" (Herbel in Shiflet, 1994). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
184. Stirring tales told in shifting sand- Yarns spun along the braided trail of El Camino Real have vanished like a desert breeze, but in the wind-shifted sand along the Jornada del Muerto stretch of the King's Highway the vegetation of an abused range speaks volumns. The range plant community that preceded what was shown here was grama-tobosa shrubsteppe (Kuchler, 1964, unit 58; Kuchler, in Garrison et al., 1977, unit 53). This pre-Columbian climax vegetation was a savanna dominated by black grama with some tobosagrass, bush muhly, red threeawn, and mesa dropseed with scattered shrubs of creosotebush, longleaf Mormon tea, soaptree yucca, broom snakeweed, honey mesquite, desert sumac, and other woody species. Forbs were not common.
The range vegetation presented here was disclimax Chihuhuan Desertscrub: semidesert grassland converted into desert scrubland at least partly by human impact of which propagule dispersal (eg. seeds of honey mesquite spread by livestock) and overgrazing have been regarded as one of or, even, the major contributing causes. On a small sand dune (or, in more precise terminology, a hummock) a plant of longleaf Mormon tea (left) and another of honey mesquite (right) were binding what would otherwise have been drifting sandy soil. Other major woody species included broom snakeweed, creosotebush, and soaptree yucca. Broom snakeweed, mesquite, and creosotebush were each ever-present and they "took turns" being the local dominant depending on whatever habitat variable was most critical (or perhaps on chance establishment from whatever germule happened to land on the sand).
This was not tarbush habitat. Tarbush is more mesophytic than these other woody species and does best on "adobe" (heavier clay) soils. That was discussed above when featuring the tarbush variant of the creosostebush-tarbush association. Likewise, the deep sand of this range site was not ecologically optimum for creosotebush. Creosotebush thrives on gravelly plains (the "creosotebush flats") and bajadas (as was also illustrated above). It is honey mesquite and broom snakeweed that thrive best on the deeper, heavier (= coarser)-textured soils. As such, the examples of disclimax range vegetation shown here that had developed along the former route of El Camino Real was typically dominated by broom snakeweed and mesquite with creosotebush as more of an associate species.
New Mexico State University College Ranch, Dona Ana County, New Mexico. June, early estival aspect (prior to onset of summer rains). Climax vegetation (former) was what Dick-Peddie (1993, p. 111) identified as: Shrub-Black Grama Series (Ephedra trifurca-Gutierrezia sarothrae/Bouteloua eriopoda-Mixed Forb) of Desert Grassland (Ecotone). Disclimax vegetation presented here was Shrub-Scrub Disclimax Series 143.15, that was formerly climax Grama Grass-Scrub Series, 143.11, of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40). FRES, Kuchler, and SRM units were not appropriate because they are of climax or potential natural vegetation whereas range vegetation shown here was disclimax. Even SRM 508 (Creosotebush-Tarbush) "is a persistent subclimax of the grama-tobosa shurbsteppe" (Herbel, in Shiflet, 1994). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
185. Wash along Jornada del Muerto- Jornada del Muerto (Spanish for Journey of the Dead) referred to approximately 90 miles of El Camino Real (Royal Highway from Santa Fe to Mexico City) between what became Las Cruces, New Mexico and Socorro, New Mexico. El Camino Real left the part of the Rio Grande River Valley where shifts in the river bed and quicksand made travel difficult to impossible, especially for woooden-wheeled carts. To avoid this situation El Camino Real permanently "detoured" through the dry but firm ground of the Tularosa Basin. Travel on the Jornada del Muerto through Tularosa Basin was little better due to greater scarcity of water and threat from Pueblo Indians and, a few centuries later, the Apaches. Hence this stretch of El Camino Real was known as Jornada del Muerto (ares, 1974, ps.9-10).
The landscape shown in this photograph was of a wash and wash vegetation along the southern end of the braided trail of Jornada del Muerto where El Camino Real re-entered the Rio Grande Valley. Location was approximately two miles from ruins of Fort Selden, and only 80 years after 300 years of overgrazing along Jornada del Muerto and, later, during the Anglo ranching heyday on this part of Public Domain range.
The landscape feature featured here was a dry wash, "a wash that carries water only at infrequent intervals and for short periods, as after a heavy rainfall"; wash is a general term used in the American southwest in reference to a relatively broad, sandy or gravelly, normally dry bed of an intermittent stream that is filled only occasionally by conditions like torrential rainfall or high runoff as from snowmelt (Wilson and Moore, 1998). Washes are prominent and unique features of the Chihuhuan and Sonoran Deserts.
Range vegetation that develops along washes is likewise prominent and, frequently, unique. The range plant community featured here was not unique but merely "more of the same" disclimax Chihuhuan Desertscrub. Plants were just larger individuals of the same major shrub species as on the rest of this sandy upland range situated between the San Andreas Mountains and the Rio Grande Valley. Honey mesquite, creosotebush, soaptree yucca, longleaf jointfir or longleaf Mormon tea, and broom snakeweed. Herbaceous species were rare being mostly sixweeks grama, and, maybe, a bush muhly plant growing under a creosotebush. There are-- on occasion --forbs on this range, some of which are conspicuous. Two were displayed in photographs below.
There is still seldom a time when water runs in this broad, dry channel. In fact, running water is so rare that there was no evidence of water movement down this wash. For example, there were no small channels of water-moved sand inside the large channel. It was possible that geologic sheet erosion might preclude such micro-channel formation. Nonetheless, in this arid zone having an average of eight or nine inches of annual precipitation this is still the Jornada del Muerto.
It seemed likely that in the virgin range vegetation, shrubs would have been more common along this wash. This was never a riparian zone under present climate, but greater periodic-- ephemeral --quantites of water perhaps permitted greater natural development of woody plants along washes like this one. Honey mesquite growing along such ephemeral water courses provided seed for potential dispersal to uplands such as sand ridges featured in the two immediately preceding photographs. Such potential dispersal was most likely seldom achieved in the pre-whiteman range evnironment because there were relatively few native animals (species and/or numbers) that consumed seed to disperse them. For example, North American buffalo (Bison bison) did not routinely migrate to and graze semidesert grassland ranges. All that changed beginning with travel on El Camino Real.
Result was spread of honey mesquite to the uplands such as sand ridges. Overgrazing of grass and palatable forbs and overbrowsing of shrubs such as fourwing saltbush reduced competition for water so un-defoliated shrubs like broom snakeweed and creosotebush increased in plant censity and cover so as to become ecological invaders and brush (noxious woody range plants). Woody climax plant species of intermediate palatabality (eg. longleaf Mormon tea) "held their own" under overgrazing by European livestock.
Total outcome of this human- induced range retrogression was the grazing disclimax shown in the three immediately preceding photographs.
New Mexico State University College Ranch, Dona Ana County, New Mexico. June, early estival aspect (prior to beginning of summer rainy period).
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186. Long on leaves- Large specimen of longleaf jointfir or longleaf Mormon tea (Ephedra trifurca). This is the more common and siedspread Ephedra species in the Chihuhuan Desert Region. This individual was growing on the same degraded range of man-made, expanded portion of disturbance climax form of Chihuhuan Desert shown in above (preceding) photographs.
New Mexico State University College Ranch, Dona Ana County, New Mexico. June, pre-cone phenological stage.
187. Yellow or soft globemallow (Sphaeralcea incana)- Indicator species: Dick-Peddie (1993. p. 119) listed yellow globemallow as a "diagnostic (climax) member of Desert Grassland". Presence of this plant of S. incana on range vegetatioin that was "from all outward appearances" Chihuhuan Desert was a critical, pivotal piece of evidence as to the actual nature of this plant community. S. incana was a relict species from semidesert (Chihuhuan) grassland. Presence of this species on this range strongly suggested that in actuality this plant community was man-made disclimax (vs. natural or climax) Chihuhuan Desert.
In addition, this plant was a "stand-out" specimen that demanded Kodachrome and inclusion in this publication. This specimen was over seven feet in height (in an eight or nine inch precipitation zone in which precious little of this had fallen). Not only that, the old girl (yellow globemallow is a perennial) was in full flower. There never was a Hibiscus plant that was "any purtier" given the growing conditions under which this extraordinary individual was reproducing.
New Mexico State University Colleege Ranch, Dona Ana County, New Mexico. June, full-flower aspect (before start of summer precipitation period).
188. Shoot of yellow or soft globemallow- Details of leaves and and inflorescence of yellow (but color is closer to orange) or soft globemallow. There are several species of Sphaeralcea native to the ranges of the Southern Great Plains and Trans-Pecos Basin and Range provinces. Wooton and Stanley (1915) listed 16 Sphaeralcea spp. for New Mexico.
The distinctive and, for most people, the key identifying characteristic of the Malvaceae, mallow family, of which Sphaeralcea is a member, is the staminal colume. The arrangement of the female organ, the gynoecium (the carpels, ovule-bearing structures of a flower, collectively), is also distinctive as there are typically numerous united carpels (Smith, 1977, p. 120). Cotton (Gossypium spp.) is the most important taxon of Malvaceae and the boll is a good mental model to visualize in thinking of mallow family members. While the fruit of cotton is a capsule, the fruit type in the Malveae tribe of Malvaceae (including Sphaeralcea spp.) is a schizocarp, defined by Smith (1977, p. 307) as "a dry indehiscent fruit derived from a syncarpous gynoecium which splits at maturity into one-seeded closeds sgements".
New Mexico State University College Ranch, Dona Ana County, New Mexico. June, but prior to beginning main season of precitpitation..
189. Spectacle-pod (Dithyrea wislizeni= Biscutella wislizeni)- Spectacle pod is not only one of the most apt-named range plants it is also one of most common species of the Cruciferae native to the ranges of the Southern Great Plains and Tran-Pecos Basin and Range. Coulter (1891-1894) wrote of this species as native to the Staked Plains (High Plains portion of the Southern Great Plains) and sandy soils along the Rio Grande. Wooton and Stanley (1915) presented the species range as from Colorado and Utan to west Texas and south into the Mexican states. Spectacle pod is thus a species of both Mixed Prarire and Shortgrass Plains grasslands as well as of the Chihuhuan Desert, but it is one of the most abundant and readily noted forbs in the disclimax Chihuhuan Desert as well.
Spectacle-pod appears to have a very versatile life cycle having been described by various taxonomists as annual, biennial, or perennial. This pattern of resource allocation is characteristic of plants of harsh habitats. Whle conducting reserch for his Master's thesis this author found spectacle-pod to one of the most densly populated of the larger forb species on the disclimax Chihuhuan Desert of the New Mexico State Universtiy College Ranch. This was during a period (the years of 1972-1973) of average or higher precipitation. Sebsequent visits to the same study ranges of the College Ranch following dry periods and severe drought revealed little and no evidence, respectively, of this cricifer. These findings were consistent with an opportunistic range species.
The specimen shown here was growing in a typically dense population in a sand shinnery oak (Quercus haavardii) shrubland in which there had been a recent surface fire. (Note small shinnery oak resprouts.)
Beckham County, Oklahoma. June.
190. Inflorescence and fruit of spectacle-pod- The fruit type of is a silique, defined by Smith (1977, p. 307) as a broad, longitudinally dihiscent fruit in which fruit walls part from a persistent internal partition called the replum.
The photographs of the flower cluster showed the prominent and clearly separate or unjoined four petals of the corolla.
Beckham County, Oklahoma. June.
191. Twinleaf senna (Senna bauhinioides= Cassia bauhinioides)- A readily identified (and another well-named) native of the Chihuhuan Region is this member of the Cassieae tribe of the Caesalpinioideae subfamily of Leguminosae. There are several members of this genus (irrespective of its correct name). Correll and Johnston (1979) listed 18 Cassia species in Texas. Kearney and Peebles (1969) described nine Cassia species for Arizona including twinleaf senna (or cassia). In this publication another Cassia species was featured for the Sonoran Desert in that Shrubland chapter.
The species introduced here was growing on semidesert grassland range and not Chihuhuan Desert, but this two-leaved legume thrives locally in both biomes or range cover type regions.
This is another taxon (or a group of closely relata taxa) that has considerable confusion regarding scientific names. For years this group of about 500 species (on a global basis) was interpreted as the large genus Cassia with three subgenera: Cassia, Chamaecrista, and Senna. As this was written the prevailing view was to elevate each of these subgenera to a separate genus (Burrows and Tyrl, 2001, ps. 540-542, 605-609). Of the 18 Cassia species listed by Correll and Johnston (1979) for Texas, there have been four species (currently included in the genus, Senna) that were reported as toxic to livestock. S. (or C.) bauhinioides was not one of these. Another source of confusion exists because there is another species, S. roemeriana, that also "goes by" the common name, twinleaf senna. In addition to Burrows and Tyrl (2002, ps. 605-609), Hart (2003, 190-197) also provided a good discussion (and great photographs) of these four toxic Senna species in Texas.
El Paso County, Texas. June.
192. Doom's Day approaches- The steady, fatal advance of "death and destruction" by honey mesquite on a black grama-tobosagrass semidesert prairie on the Jornada Trough (known also as Jornada Basin) above the Rio Grande Valley or floodplain. The "Desert Grassland" vegetation shown here was similar to grassland that according to local stories was cut for hay as late as the Nineteenth Century. Wooton (1916) observed that black grama was cut for hay in the near-by Mesilla Valley portion of the the Rio Grande floodplain..
Such pristine black grama-tobosa semidesert grassland was present in the fore-to midground of this photograph . This range vegetation was in high Good to Excellent range condition class. The range plant community was an example of the grama-tobosa shrubsteppe of Kuchler (1964, p. 58; in Garrison et al., 1977, map unit 52). Unfortunately, disaster was "looming on the horizon" as a brush invasion of honey mesquite (mostly) with some creosotebush was edging ever closer to the virgin range vegetation of semidesert grassland. The young soaptree yucca on the semidesert grassland portion of this landscape was part of the climax vegetation and not an invader.
Causes of such shrub encroachment have been studied for decades in the area of this photograph and there remain many unanswered aspects of the brush invasion problem. Readers were referred once more to the summary study by Gibbens et al.(2005), including their list of references. The classic analysis of vegetation changes of the Jornada Experimental Range by Buffington and Herbel (1965, p. 159-162) was again recommended. One of their conclusions was repeated: there is little if any possibility for grassland restoration following range site deterioration in which range vegetation has become so degraded that only shrub cover remains with accompanying on-going accelerated soil erosion and fierce competition from shrubs for any grass that might otherwise become established. "Protection from grazing at this point is useless..." (Buffington and Herbel, 1965, p. 161).
Semidesert grassland range cover types were treated elsewhere in this publication (Semidesert Grassland chapter).
Dona Ana County, New Mexico. June. FRES No. 40 (Deseert Grasslands Grassland Ecosystem). K-48 (Grama-Tobosa Prairie) at onset of brush (mesquite) invasion. Degraded variant of SRM 505 (Grama-Tobosa Shrub). Mixed Grass-Scrub Series, 143.14, of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40) at onset of brush (mesquite) invasion. Shrub-Black Grama Series, but no further sub-series was descriptive (Dick-Peddie, 1993). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
193. Too sad to show- A "zoom-in" focus showing replacement of black grama and tobosagrass by honey mesquite on the same range that was presented in the preceding photograph. Once invading shrubs have achieved this density and cover the climax semidesert grassland can be maintained only by expensive range improvement practices. Grazing management, including discontinuation of livestock grazing, will not rectify this ultimate stage of range retrogression. Even under such initial conditions of brush infestation as that shown here, grassland range can only be maintained by inputs of brush control (chemical control is about the only feasible practice where remnant black grama and tobosa like this is to be preserved and increased).
It is on the more productive range sites like the edge of this black grama-tobosa swale where there remains potential for range improvement so as to preserve some areas of semidesert grassland and halt the cancer-like encroachment of disclimax (= anthropogenic) Chihuhuan Desertscrub. Gibbens et al. (2005, p. 666) recommended limiting brush control to range sites that can, if "the planets come into favorable alignment", be restored. This means that the rest-- and vast majority-- of the once magnificant "Desert Grasslands" are relinguished to the **%@!!+ mesquite and a man-made mesquite dune desert as shown in the next photograph.
Dona Ana County, New Mexico. June. FRES No. 40 (Desert Grasslands Grassland Ecosystem). K-48 (Grama-Tobosa Prairie) at onset of brush invasion. Degraded variant of SRM 505 (Grama-Tobosa Shrub). Mixed Gras-Scrub Series, 143.14. of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40) at onset of brush (mesquite) invasion. Shrub-Black Grama SEries, but not a descriptive sub-series (Dick-Peddie, 1993). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
194. All is lost or, at least, all that remains- Where once black grama and tobosagrass reigned supreme a honey mesquite disclimax scrubland now maintains an ecological dictatorship. (Puts this author in mind of once marvelous universities now in the clutches of dictatorial administrations which have nothing but insatable appetites for ever-increasing enrollments supported by starry eyed innocents, increasingly financially strapped parents, and disillushioned tax-payers.) And there is no remedy in sight any time soon-- for either of these devastated ecosystems.
The vegetation and landscape sadly shown here was mesquite scrub on sand hummocks (Buffington and Herbel, 1965, p. 144). Most of these sand hummocks were two feet or less in height. There was few other plant species besides honey mesquite. Grass was limited to some mesa dropseed at edges of mesquite branches. Brown (dead) forb stalks were of tansy mustard and Russian thistle. No plant life existed on inter-dunal areas.
Soil crusting was caused by recent rain showers. Broken crust was by pleasure horse-riding, but no livestock grazing had occurred nor was any taking place. Evidence of mesquite bark removal by black-tailed jackbrabbits was evident. There were some burrows of kangroo rats within mesquite shoots on the sand hummocks.
Buffington and Herbel (1965, p. 159) reported that on a one-section (640 acre) exclosure of range that was transitional "between black grama grassland and mesquite sand dune type" ..."mesquite sand dunes advanced completely across the exclosure" within 30 years of livestock exclusion. Buffington and Herbel (1965, p. 161) concluded that "competition from brush is the main reason no changes have taken place with protection from livestock". This state is terminal in human time scale without cost-prohibitive range imporvement practices including mechanical control of mesquite and range reseeding.
The condition shown here is known variously as a drastically altered or severely damaged ecosystem; derelict, devasted, or drastically disturbed land; extremely disturbed landscape, etc. Rangeland is the condition presented here is not just overgrazed or even "go-back land" (an "old-field") following tillage that is undergoing secondary succession. Land in this degree of degradation is more like mined land or other forms of land so drastically perturbed that redevelopment of vegetation woulld be by primary (vs. secondary) plant succession. Natural recovery of vegetation and soil would require time period(s) measured in centuries.
Restoration of ranges, ecosystems, (or whatever else conceptual unit of management is appllied) in this state of depletion, degradation, or deterioration (all such terms would be appropriate) would require such intensity of inputs that it falls in the category of ecological restoration, "the process of assisting the recovery of an ecosystem that has been degraded, dmaged, or destroyed" (Society for Ecological Restoration International Science & Policy Working Group, 2004). In the context of Range Management inputs, irrespective of intensity, has long been known as range improvment. Hence such inputs are known as range improvement practices and the outcomes are, hopefuly, range improvements as defined by improved range ecological condition or rangeland health. "Rangeland health should be defined as the degree to which the integrity of the soil and the ecological processes of rangeland ecosystems are sustained" (National Research Council, 1994, p. 4).
Dona Ana County, New Mexico. June. No appropriate FRES, Kuchler, or SRM units for this degraded range. No Series designation in Dick-Peddie (1993). Shrub-Scrub Disclimax Series, 143.15, of Chihuhuan (Semidesert) Grassland , 143.1 (Brown et al., 1998, p. 40). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
195. Inside all that's left, and an otherwise moot point- Interior of a mesquite scrub coppice duneland (Buffington and Herbel, 1965, p. 144). Coppice sand dunes three to four feet in height with pronounced interdunal blow-outs characterized the ultimate stage degradation of former black grama-tobosa semidesert grassland. Here was the end of the "retrogressive spiral" resulting in a "retrogression subclimax, a new equilibrium eventually reached at the nadir of degradation" (Holechek et al., 2004). Same thing as disclimax (= disturbance climax).
This state of range vegetation is known among ranchmen simply as "mesquite dunes". This disclimax range vegetation should not be confused with the climax mesquite scrub (treated above) that developed naturally due to factors like gypsum soils or as part of the climax sand shinnery oak ecosystem (range cover type). Honey mesquite developed into the coppice growth form on both climax and disclimax (or natural and man-made) range vegetation. The distinction was an obvious one based on natural potential versus the "now" or "artificial" potential.
Or maybe it was not obvious. The old lyrics by Floyd Tillman and Jimmy Davis expressed :the practical sentiment for such a sad sucessional state : "I don't worry 'cause it makes no difference now". The final commentary on this vegetation was provided in Brown (1994, Fig. 101, p. 75): Classification of these hmmock forming Mesquite communities as disclimax semidesert grassland or Chihuhuan desertscrub is moot".
Dona Ana County, New Mexico. June. No FRES, Kuchler, or SRM units for this extremely degraded range. No Series designation by Dick-Peddie (1993). Shrub-Scrub Disclimax Series, 143.15, of Chihuhuan (Semidesert) Grassland, 143.1 (Brown et al., 1998, p. 40). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
Included below were several species from the cactus family (Cactaceae) that are found in the Trans Pecos Region of northern Mexico, Texas and New Mexico. People (from tourists to interested layman to serious students of vegetation) most commonly associate (picture in their imaginations) cactus with the Sonoran Desert more than with any other North American desert. This is both understandable and precisely correct from the perspective that cactus species are dominants of the Sonoran Desert (so much so that the Sonoran is often referred to as a "succulent desert") and not of neighboring deserts, at least not to that extent. The cactus (and unrelated succulents like Agave and Nolina species) are not dominants-- and they do not impart a picturesque feature to the vegetation (ie. are not an apparent dominant life or growth form in the physiogonomy)-- of the Chihuhuan Desert. What is often lost in this ecological fact is another fact: there is as much, if not more, species diversity of the Cactaceae in the general desert parts of Texas (the Trans Pecos and western parts of Edwards Plateau Vegetational Areas) than in the Sonoran Desert. This partly explains the fact that Texas has more species of cactus than does Arizona. It was appropriate to include some of the cacti of the Trans Pecos Region in this section on the Chihuhuan Desert.
Taxonomy of the Cactaceae is in a mess, in fact "one helluva of a mess". It seems that the more scholars there are who study a given group of plants, the longer such a group is studied, and the more publications that are generated by such scholarly study the more confusion and controversey is generated. "Insiders" appreciate that this often involves academic egos which are some of the most prima donnish of all vanieties. Whatever the explanation, treatment of cactus taxa remains in some state of disarray with different "experts" often placing the same kind of cactus in different genera. Some of the taaxonomic synonyms for the species presented below where given, but the synonymy was not complete. Common names of cactus are even more varied than scientific names.
There are at least three encyclopedias for North American cactus: Britton and Rose (1936, 1963 for Dover edition), Benson (1982), and Anderson (2001). All are excellent, but comparisons of a given specimen among these three typically resulted in a state of hands-in-the-air confusion for this non-specialist. The definitive authority for Cactaceae of the Trans-Pecos area and neighboring parts of the Chihuhuan Desert is Powell and Weedin (2004). This Trans-Pecos reference in the tradition of previous excellent encyclopedias and it went a long way toward resolving nomenclature of some long-disputed taxa (eg. Opuntia engelmannii vs. O. lindheimeri vs. O. phaeacantha) In addition to the encyclopedic tretments, there are several field guides devoted exclusively to the Cactaceae (eg. Weniger, 1984) or to the cactus along with other woody plants (eg. Vines, 1960; Warnock, 1970; Warnock, 1974).
196. Long-spine pricklypear or purple pricklypear (Opuntia macrocentra= O. violacea var. macrocentra)- This is one of the more common of several Opuntia species native to the Trans Pecos Region. The color and long spines rendered identifiction of this plant a "snap". This particular individual was growing at the base of a creosotebush, the sole dominant of a range community that was formerly part of the Trans Pecos Grass-Shrub Savanna (an ecotone or transition zone) but that had deteriorated to an eastward extension of the Chihuhuan Desert.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.
197. Purple pricklypear- Another specimen of purple pricklypear was presented. Big Bend Ranch State Park, Presidio County, Texas. June.
198. Englemann or Englemann's pricklypear (Opuntia englemannii var. englemannii= O. englemannii= O. englemannii var discata= O. phaeacantha var discata= O. discata)- Englemann pricklypear is the most common pricklypear cactus in the Trans-Pecos portion of the Chihuhuan Deser(Powell and Weedin, 2004, ps. 172-177). There has been terrific confusion in regards taxonomic treatment of numerous cactus, none more than between this taxon and the closely related O. englemannii var. lindheimeri (covered below). Differences between these two varieties was discussed immediately below after presenting the other variety.
Individuals of Englemann pricklypear are "everywhere" in northern parts of theChihuhuan Desert. Interestingly (and fortunately) these are less apt to reach population sizes that constitute noxious (either ecologically and/or economically) range plants. Fruit as well as stems ("pads" or, in Spanish, "tunas") are valuable for certain species, especially javelina or collared peccary (Tayassu tajacu). Fruit had already started to fall from this characteristic specimen.
Presidio County, Texas. June, fruit-ripe stge.
199. Texas pricklypear and, though often creating confusion (and perhaps errenous to boot), Englemann or Lindheimer prickly- pear (Opuntia engelmannii var. lindheimeri= O. lindheimeri)- Shown here and in details of the next three slides is one of the most widely distributed cactus species. It's range extends from the Gulf Coast to the Pacific and from southern Mexico to central Oklahoma. The specific epithet lindeimeri has been proven conclusively to be in error, but it is still commonly used. To add further confusion (to be expected with any species as wide-ranging as this one) some authorities have included varieties of other species (eg. O. phaeacantha var. discarta) in their interpretation of O. engelmannia.
Powell and Weedin (2004, ps. 172-181) may have cut the Gordonian knot and resolved the matter once and for all (but don't bet the ranch on it) by distinguishing Texas prickly pear (O. engelmannii var. lindheimeri) from Engelmann's pricklypear (O. engelmannii var. engelmannii synonyms of which include O. englemannii var. discata, O. phaeacantha var. discata, O. discata, and O. englemannii).
Whichever author(s) one follows this taxon remains one of the farthest-ranging cacti in North America. It is extremely common in the Rio Grande Plains and Trans Pecos Texas and throughout much of Mexico.
The neighbor to this specimen was the shrubby composite commonly known as mariola. Mariola was shown in full-bloom in several slides below under which it was discussed in greater detail.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.
200. Texas pricklypear (O. englemannii var. lindheimeri= O. lindheimeri)- According to some authorities this species was incorrectly named and described as Lindheimer pricklypear (O. lindheimeri) based on a mistaken description that was actually a combination of two species, pads of one and fruit of another (Weniger, 1984, p. 245). The probability of such an error was increased by the wide distribution-- and thus much ecotypic variation and phenotypic plasticity-- of this "often misunderstood" species (Weniger, 1984, p. 245). Hopefully Powell and Weedin (2004, ps. 177-181) straightened out the confusion.
The large individual shown here (about five feet tall) had produced a number of large but still immature fruits (along the top ridge of the pads). The "pads" (a common layman's term) are actually the broad, circular-shaped stems (shoot segments) that have two different forms of appendages or sharp outgrowths (ie. "stickers" to employ another lay term) and small, ephemeral leaves (see below). The more technically precise term for these highly modified shoots or stems is variously (depending on reference) that of cladophyll, phylloclade, phyllode, or cladode (a modified, often flattened, photosynthetic stem or branch). Different botanists use these terms in slightly different detailed meanings. (It would appear that almost everything of a scientific nature about these amazing plants is interpreted in various ways by various taxonomists.) By whatever name they are known these highly modified shoots or branches bear either no leaves or short-lived ones such that photosynthesis (the water-conserving Crassulacean-acid metabolism, CAM, pathway) takes place in the stem. This stem is a trunk or bole in some of the larger cacti. This feature is an obvious evolutionary adaptation to water shortage. One of the most spectacular examples of convergent evolution is development of this leafless and succulent stem feature or trait in the spurge family (Euphorbiaceae) and the milkweed family (Asclepiadaceae) as well as in Cactaceae. This is standard textbook fare (see for eg. Raven et al. 1992, p. 518).
The mature fruit of prickly pear is a many-seeded berry often known as a "tuna" (Spanish). These tunas are the source of some of the finest jellies imaginable. They are also used for making candy. The "pads" have sometimes been used for human food as well, first learned by American Indians of course and later passed on to Mexicans and gringos.
The main concern with this species of prickly pear is as a brush (= a noxious plant) species resulting from all of the standard causes ranging from overgrazing, underburning, oil and gas development to climatic shifts. Englemann (and numerous of the other Opuntia species) are major feed plants for wildlife. They provide both browse as in case of the javelina or collared peccary (Tayassu tajacu) and mast (the fruits) for birds, coyotes, coons, etc. as well as for javelina. Under emergency feeding conditions, especially drought, Lindheimer or Englemann pricklypear is one of the major species of "pear" from which the spines are scourced for use as a major survival feed source for cattle and sheep. "Burning pear" (by use of propane burners) has been a principal duty of otherwise proud vaqueros or cowhands during drought that is so recurrent in the Southwest. O. englemannia is a "mixed blessing" on southwestern and southcentral ranges.
The Englemann prickly pear in this photograph was growing on a Sandy Loam range site dominated by blackbrush (Acacia rigidula) in the Rio Grande Plains. Chaparrosa Ranch, Zavala County, Texas. May.
201. Fleshy or succulent shoots (cladodes or cladophylls) of Texas pricklypear- In the first of these two slides new "pads" (the succulent stems) of O. englemannia var. lindheimeri) had begun growth from the apical portion (meristem) of parent "pads". The new daughter cladophylls still had their ephemeral leaves (the slightly curved or bent nail-appearing appendages) present along their apices. These rudimentary organs are characteristic of Opuntia species.
Also visible in both of these slides are the epidermal appendages that are modified protective organs. These sharp outgrowths of the members of Cactaceae are of two major forms: 1) spines which are the long, sharp, usually woody, thorn-like "jaspers" and 2) glochids or spicules which are much smaller, hair- or bristle-like "stickers" usually having many tiny (almost microscopic) barbs. These appendages are usually interpreted as modified leaves or leaves reduced to spines as an obvious adaptation to reduce transpiration and increase survival in arid environments as well as adaptative defensive organs to protect these water-storing xerophytes from herbivores. Some cactus specialists and ecophysiologists interpreted spines, especially those resembling hairs (often even white in color), as adaptative structures to shade and insulate the fleshy shoots in order to prevent heat and/or wind injury as well as to reduce water loss by transpiration. Conversely, the insulation feature of these structures prevents heat loss and cold injury at night and in winter. Fluted trunks of cactus serve these same functions (Vankat, 1979, ps. 195-198).
One of the key characteristics of the Cactaceae is the presence of areoles, the area or location on the "pad" around which the spines and glochids (and ephemeral leaves) arise. Areoles are either raised areas (like a pimple) or depressions (ie. pits) which are openings in the epidermis. The areole is unique to the Cactaceae. Areoles are interpreted as buds because they are the source of leaves and the protective outgrowths of spine and glochid. Incidentially it is numbers of the latter organ which cause the most aggravation and irritation to animals (including man) which carelessly stray too close to these succulent species.The spines can obviously cause more injury, but the pesky glochids typically break off in the animal epidermis and are extremely difficult to remove due to the many tiny barbs arranged along the individual glochid.
Areoles, complete with conspicuous glochids and spines, were clearly visible on the pad shown in the second slide. Newly emerging ephemeral leaves were also visible around areoles below the apex of this shoot. Also clearly visible in this second photograph was a developing cactus flower in the center of the "ridge line" (apex) of the cladophyll.
Erath County, Texas. April.
202. Ephemeral leaves on a perennial shoot- A cladode or cladophyll of Texas or Englemann's pricklypear with characteristically small, ephemeral leaves called cylindroids. Such tiny, tubular (oblong and slightly pointed) leaves are shed soon after appearing prompting one to wonder for what purpose these short-lived organs evolved.
Ephemeral leaves (the only leaves of Opuntia species) grow near the aeroles or areolas, circular areas out of which grow the long, hard spines and the shorter, flexible (and much more troublesome to remove) appendages known as glochids.
"Pads" (cladodes) of the pricklypear species are flat and thinly circular (somewhat plate- or platter-like) so these Opuntia species are in subgenus Platyopuntia (in contrast to the cylindrical cholla species which comprise the Opuntia subgenus, Cylindropuntia).
Erath County, Texas. Late April.
203. Short-lived organs- Ephemeral leaves known as cylindroids of Englemann's or Texas pricklypear on the dorsal surface "spine" or "ridgeline" of a cladode (or cladophyll).
Erath County, Texas. Late April.
204. Blooming on the ridge- Inflorescences of Texas or Englemann's pricklypear atop immature fruits aligned along the dorsal edge ("ridgeline") of jointed units of shoots, each of which is a cladode or cladophyll.
In the first photograph there are three blooms each of which is a different stage of flowering: 1) immediate pre-bloom (will bloom tomorrow morning), 2) initiation of flowering (opening bloom) , and 3) flower fully open (peak bloom), right to left, respectively. The second photograph showed a large bloom with a reddish-colored corolla atop a fruit which was a fourth flowering stage: 4) immediate post-bloom (bloom in porcess of closeing; petals senescing/dying). Also in second photograph and to immediate left of post-bloom flower was an unopened flower that was about two days away from opening (ie. this floral unit was one day behind the rightmost floral unit in the first slide or just before 1) in first image).
Each of these inflorescences sat on an immature fruit. The cactus fruit is a many seeded berry (Smith, 1977, p. 104) or in common usage, a "fig",or (in Spanish), a tuna.
Erath County, Texas. Late April.
205. Flower of Texas pricklypear- An example of the beautiful inflorescence so characteristic of the Cactaceae. The circular arangement of numerous stamen is an obvious and attractive feature of the cactus flower. Unfortunately (from a human perspective) the blooms of most of the cactus species are notably short-lived, often persisting for only a few hours. Some of the most beautiful cactus inflorescences open solely at night when they are pollinated by nocturnal animals including insects, reptiles, birds, and mammals like bats. Even those that bloom at mid-day are opportunistic and infrequent as to their schedule, erratic precipitation events often dictating when sexual reproduction occurs. The more common and widely adapted species like many of those of Opuntia are less extreme in this regard. This example of O. englemannia var. lindhemeri was right "on schedule" by blooming in May in northcentral Texas (Erath County).
As is true for many perennial range plants, much (probably most) reproduction in Cactaceae is asexual by means of profuse production of cladophylls and their feature of rapid rooting upon physical separation of these fleshy shoots from the parent plant. Cactaceae members are yet other examples of clonal organisms in which individual segments of their fleshy stems ("pads") are modules or ramets of the genetic individual, the genet. A striking example of this was shown two slides below for the next species.
206. Beetles in the blooms- Two blooms (inflorescences) of Engelmann's or Texas pricklypear on the dorsal edge of a cladophyll (cladode). The inflorescence at left was a current (today's) bloom while flower at right was a "spent" (yesterday's) blossom. The currently open (today's) flower was shown at closer range (though from a different angle or direction) in the second slide.
Both of these flowers was occupied by a number of scarab beetles known as the common flower scarab or bumble flower beetle (Euphoria kernii), the topic of the next slide and its caption.
Erath County, Texas. Late April.
207. Scrounging scarabs- A "herd" of common flower or bumble flower scarab beetles (Euphoria kernii) in a flower of Lindheimer or Texas prickly pear. This ornate scavenger feeds on a wide array of spring flowers throughout southcentral and southwestern North America. It is a pollenivore. Grant et al. (1979) reported that E. kerni was "virtually ubiquitous" in flowers of O. lindheimeri in central Texas and that they "... do carry out some pollination, but not very much". Conversely, these scarab beetles were "highly destructive in some flowers" mainly through consumption of stamens (beetles cannot reach ovules of the inferior ovary so this much is safe from their voracious apetites). McFarland et al. (1987) reported that E. kerni was regarded as being of no more importance than as an accidental pollinator of cholla (Opuntia imbricata) in southern Colorado.
In other words, the flower scarab beetle is a showy, sort-of-cute little "bug" that gets one's attention but is of undetermined ecological importance. Sort of reminded the author of a lot of students he was plagued with over the decades; the difference being that the insects knew and (cared about) what they were doing, died cute, and were less of a burden on their environment.
E. kernii is in subfamily, Cetoniinae family, Scarabaeidae of tribe, Cetoniini.
Erath County, Texas. Mid-May.
208. Cactus Jack would be proud- Before leaving the cactus blossum the author included one last pair of nested photographs of Texas or Englemann's pricklypear inflorescences.
The beautiful cactus flower entered the folklore of American and Texas history via the personality of a Texas original, John Nance Garner, IV. Garner ultimately settled in or near Uvalde, Texas from which he was elected to the Texas House of Representatives. During the time that John Garner was a member of the Texas house the state legislature set out to select the Texas State Flower. The flower of the pricklypear cactus was one of several nominees for this honor, and it was the one that John Garner promoted with much colorful enthusiasm. As every Texan knows the cactus flower lost to the bluebonnet, but for the rest of his long life the pricklypear promoter was known as "Cactus Jack". "Cactus Jack" won election to the US House of Representatives and eventually became Speaker of the US House. After being re-elected for 14 consecutive terms Garner decided to run for the US Presidency. When "Cactus Jack" realized that he was going to lose this political contest (like the state flower battle) he cut a deal with the nominee-to-be and settled for position as Franklin Delano Roosevelt's running mate. "Cactus Jack" served two terms as vice-president of the United States, but concluded the vice-presidency was "not worth a bucket of warm piss". (Garner was a traditional--though progressive-- southern Democrat who became progressively at odds with New Deal welfare liberalism.) FDR chose Iowa corn-breeder Henry A. Wallace as his third-term running mate. Garner returned to private life in Uvalde County, Texas where he remained as "Cactus Jack" until he died shortly before reaching his 99th birthday.
Texans and southern conservatives like "Cactus Jack" could interpret these colorful inflorescences as paying tribute to a "yellow dog Democrat" and "cactophil" (or "cactophile"). Otherwise, these provided images of the corolla encircling numerous stamen that surrounded the single, columnar style with its several stigma (appearing as lobes of the style), a key charactistic of the Cactaceae.
Erath County, Texas. Late April.
209. Large Texas pricklypear (again, to avoid concusion: O. englemannii var. lindheimeri= O. lindheimeri) in fruit- This old "pear" plant was bearing fruit, but the most obvious mode of reproduction in this clonal plant had been by vegetative (= asexual) reproduction: simply growing more cladophylls. The versality of both asexual and sexual reproduction was illustrated. A county road cut provided a favorable microsite for this representative of it's species. Texas West Cross Timbers. Erath County, Texas. Late August.
210. Texas pricklypear bearing a "bumper crop" of fruit- This large specimen of Texas pricklypear (it is still O. englemannii var. lindheimeri) bore a fantastically high yield of nearly ripe fruit. It was growing in an area of disturbance in the Texas West Cross Timbers. Erath County, Texas. Late August.
211. Fruit of Texas pricklypear- The "ridgeline" of cladophylls (= cladodes) is location on which pear fruit is borne. The concave (dished) upper surface (dorsal or "top") of fruit is the umbilicus. It is the site where inflorescence had been attached. The fruit of the cactus family is a many seeded berry. A berry is a multiseeded, indehiscent, fleshy fruit in which the pericarp (fruit wall) is fleshy throughout; other examples of berries are grape and tomato. The cactus berry of many species, including both Englemann and Texas pricklypear, is used for making of jellies and candy. Texas West Cross Timbers. Erath County, Texas. Late August.
212. Small, but with all its underground parts- A seedling of Texas prickly pear (age unknown) with two tubers and characteristic at-the-soil-surface lateral roots. One of the evolutionary adaptations of this cactus is presence of a shallow root system admirably suited (via natural selection) to absorp soil water as soon as precipitation enters the soil. By this means, pricklypear (for that matter, essentially all Cactaceae members) can capture, transfer, and store absorbed water in its succulent shoots (another evolutionary adaptation) before soil water can evaporate.
Prickly pear tubers are food (photosynthate)-storage organs and the sites from which new shoots arise. Production of new shoots is thus both growth and asexual reproduction. Texas pricklypear also regenerates by sexual reproduction, that is from seed in its berries (shown in the immediately preceding two slides). The unit of Texas pricklypear shown in this slide was such a seedling (again, age unknown), and this product of sexual reproduction was "making plans" to regenerate further by its asexual mode.
Little wonder that Texas prickly is a survivor, and a survivor with the potential to become a brush species under certain conditions such as overgrazing and underburning.
Tarleton State university Hunewell Ranch, Erath County, Texas. Late April.
212. Blind pricklypear (Opuntia rufida)- This semi-defenseless cactus "is the only truly spineless native Opuntia species in the Trans-Pecos" (Powell and Weedin, 2004, 118-119). Although the trunk base and lower cladophylls often have a brown or bronze-like coloration (as in the specimen shown here), it is the reddishness or the glochids that are basis for the specific epithet, rufida, from the Latin rufulus meaning reddish (Powell and Weedin, 2004, p. 118). Another common of cinnamon pricklypear is even more apt for older individuals like the one presented here. Coloration and spineless make this one of the easiest cactus species to identify on the range.
Big Bend Ranch State Park, Presidio County, Texas. June.
213. Tasillo, pencil cholla, or Christmas cactus (Opuntia leptocaulis), creosote bush, and cyclic succession- This was an instructive and interesting slide that "pictured" or portrayed a textbook example of plant succession that has been interpreted as an exception to the classic model of linear and progressive development in plant succession (ie. the traditional Clementsian paradigm).
An individual plant of tasillo in full, ripe fruit (shown in detail in the succeeding slide) was growing "cheek-by-jowl" with a single plant of creosote bush. A single plant of mariola (Parthenium incanum) was growing to the side of these two species. The mariola was the shorter, grey-colored shrub in the extreme right foreground. Mariola is generally an invader, as are the two "featured" species, in the trans Pecos shrub-grass savanna which was the potential natural (= climax) range plant community of which this photo-plot was a part. Mariola is a composite shrub that produces latex enough to yield about two or three percent rubber. Mariola often hybridizes with guayule (P. argentatum) one of the potential new agronomic rubber crops which can yield as much as eight to 20 percent rubber Powell, 1988, p. 452-453). Latex from Parthenium species is one of the highest quality rubbers known. Latex rubber is produced from the bark of these Parthenium species.
Special attention should be given to the dead creosote bush to the left and slightly behind the tasillo and to the remains (trunk and major limbs) of the dead creosote bush between and just in front of the live creosote bush and the tasillo. These dead shrubs were explained in the quotation shown two paragraphs below. Viewers' attention is drawn again to the heavy fruit yield on the tasillo, the importance of which (including predictions to be drawn from this sexual reproduction) was explained in the quotation that followed.
The combination of species shown here was a textbook example of what F.E. Clements termed (after taking his cue from H.C. Cowles) "Dynamic Ecology" "dynamic plant ecology" or, as later popularized by Clementsian ecologists, "dynamics of vegetation" (Allred and Clements, 1949). Ironically, one form of plant succession in the Chihuhuan Desert (the creosotebush-tasillo example shown here) does not appear to play by Clementsian rules of Dynamic Ecology (the classic model known by some ecologists as directional succession) and instead is cyclic succession. Technically there is cyclic succession at smaller spatial and shorter temporal scales within overall directional (linear or curvilinear) succession (Barbour et al., 1999, p. 274-275).
This example of apparent exception was reported by Yeaton (1978) and described concisely by Barbour et al. (1999, p. 274) as followed:
"Shrub-dominated communities ofter exhibit cyclic succession. Open areas within desert scrub in Texas, for example, appear to go through a short cycle of invasion by creosote bush (Larrea tridentata) followed by invasion by a cactus, Christmas tree cholla (Opuntia leptocaulis), followed by a reversion back to bare ground (... Yeaton, 1978). Bare sites may be invaded by Larrea seedlings because the small seeds and fruits are abundant and may be widely wind-dispersed. Once a shrub is established, it may attract birds and rodents that scatter the seeds and fruits of Opuntia. As the cactus grows, its roots may compete for soil moisture with Larrea, leading to Larrea mortality. Now removed from the protective influence of a shrub canopy, the shallow root system of the cactus may be subject to erosive forces. Large Optuntia plants also attract burrowing rodents that further weaken the root system, and the plant dies. Now open space is available for Larrea seedling to invade".
Readers should note that this passage interpreting the work of Yeaton (1978) is another textbook example of a fundamental concept in Ecology whether emphasis is on the ecosystem, landscape, or climax plant community (and it's development). Barbour et al. (1999, p. 274) just described dynamic equilibrium which they had in the preceding paragraph ascribed as the state that is characteristic of the climax plant community (citing Huston, 1994). Thus, in final analysis even cyclic (vs. directional or linear) succession still supported the classic Clementsian paradigm even though initially it appeared to be an exception to it. It was not an exception, but rather short-term adjustment of the overall plant succession-climax vegetation model that has been dominant in the Anglo-American School of Plant Ecology for over a century (ie. once again Clements was triumphant).
It should be emphasized further that there are many examples in which creosotebush and tasajillo co-exist and co-dominate in the Chihuhuan Desert. Several photographs of this phenomenon were given above in this chapter on the Chihuhuan Desert. The important (maybe the most relevant) factor of time must be specified in discussions like the one presented here. If a time interval consistent with the career of a community ecologist (three or four decades) is resorted to the relationship between creosotebush and tasajillo appears cyclic. If the "climatic cycle" time frame of Clements was used the relationship seems to be one of dynamic equilibrium.
This sample of vegetation was part of a deteriorated hillside range on an Igneous Hill and Mountain range site of the Trans- Pecos shrub-grass savanna type: FRES No. 33 (Southwestern Shrubsteppe Ecosystem), K-53 (Trans Pecos Shrub Savanna), SRM 505 (Grama-Tobosa Shrub). Rather than the climax grass-shrub steppe, an ecotone (grass-shrub savanna) between semidesert grassland and Chihuhuan Desert, it had become an extension of the latter. It was an example of desertification (most likely primarily anthropogenic in origin) resulting in a disturbance climax that was the climax (= climatic climax) of conterminous but more xeric and generally harsher habitats. This photograph served as an example of one form or expression of the Chihuhuan Desert in addition to presenting an example of tasillo cholla cactus.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.
214. Tasillo or pencil cholla (Opuntia leptocaulis)- Entire young plant of Christmas cactus or tasillo uprooted and placed on ground to display habit and growth form of the cholla group of Opuntia which was formerly in the separate genus, Cylindropuntia.
Texas West Cross Timbers. Young County, Texas. April.
215. Tasillo loaded with fruit- This "heavy laden" specimen was in the Texas West Cross Timbers. The ecotypic variation has to be tremendous in a species whose range extends from desert to tallgrass prairie-deciduous forest ecotone. Young County, Texas. April.
216. Detail of tasillo, Christmas cholla, or Christmas tree cholla cactus- This terminal end of a branch or linear arrangement of linked shoot units ("pads") of O. leptocaulis had one ripe fruit (a many seeded berry) and many young cladophylls or cladodes. Tasillo is one of several species of Opuntia known as "cholla" which have a tree-like habit complete with limbs and branches. Several of these cholla species are called "jumping chollas" by those who work around them. In jumping chollas the individual cladophylls are readily detached from the the plant by anything that brushes against them. Often this is the vaquero or his horse with the result that numerous of the small "pads" secure themselves to the leggin's, boots, hands (gloved or bare) of rider and/or gear of the horse (eg. chinch, breast harness, head stall). For this reason tasillo is one of the most dreaded shrub species on southwestern ranges. Tasillo cholla is often a brush species whose populations increased as a result of human disturbances as in the case of the other noxious range plants. For instance, fire will readily eliminate most of the tasillo from routinely burned range. Fire is less likely on desert of course and tasillo often persist as a climax desert shrub (as was shown in the preceding slide).
This slide was an example of how important asexual reproduction is in the various cacti. In the caption for the Opuntia inflorescence (two slides above) cactus were described as modular or clonal organisms in which the individual cladophylls are ramets of the clone or genet (genetic individual). The importance of sexual reproduction was illustrated in the preceding slide showing tasillo with a heavy fruit yield. The quotation of role of cactus fruit in cyclic succession in that caption along with both of these photographs showed why (how) tasillo cholla persisted on arid and semiarid rangeland.
Waggoner Ranch, Wilbarger County, Texas. October.
217. Fruit of tasillo, pencil cactus, or slender-stem cactus- The cactus fruit is a berry which is a multiseeded, indehiscent fleshy fruit with a pericarp (fruit wall) that is fleshy throughout. The fruit of tasillo is undoubtedly fine fare for certain wildlife species, which then become agents of dispersal much to the distain and discomfort of any rangemen and their mounts who wander within "jumping distance" of this slender cholla whose stem segments detatch readily from the plant to become vegetative propagules (and horse and rider become unwilling agents of dispersal). Young County, Texas. April.
An example of speciation and biodiversity of flora in the Chihuhuan Desert was illustrated by inclusion of the following three species of hedgehog cactus (Echinocereus spp.).
218. King's cup, strawberry, or claret-cup cactus, one of many species known generically as hedgehog cactus (Echinocereus triglochidatus var. triglochidiatus)- The treple-hook spines from which the specific epithet and variety were derived were apparent in this photograph (at least before photo-quality was substantially diminished by the "cap-and-ball" equipment that was used to scan in the slide and save it as a Jpeg).
This slide also turned out to be a detailed photo-quadrant of Chihuhuan Desert vegetation. A young tasillo cholla was growing adjacent to E. triglochidatus (seen immediately to the right of the old hedgehog cactus). A small chino grama was growing to the right front of the hedgehog cactus while a robust plant of sideoats grama served as "rearguard" (far right background). The short, gray-colored, and flowering composite shrub in the left background was mariola.
Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.
219. Turk's head, bunchball, or aggregrate cactus, another of numerous cacti known generally as hedgehog cactus (Echinocereus coccineus var.conoideus)- Weniger (1984, p. vii-viii) that it was difficult to get photographs of wild cactii blooming in their native habitats concluding that "it was obviously impossible to be in a canyon of the Texas Big Bend on precisely the days when each cactus chose to bloom". To get photographs of inflorescences of specific cactus species one must either "live with" the cactuses or, as Weniger did, transplant specimens to a central convenient location. Thus it was that this large specimen of E. coccineus was not caught "doing it's thing", but it was at least representative and reflective of the fact that blooming is brief in these species that thrive in their "hostile environments".
This is also-- like the preceding slide-- a photo-plot of Chihuhuan Desert vegetation. E. coccineus was surrounded to it's left and rear by the shrub form of mesquite while a little chino grama was holding it's own in front of the hedgehog cactus. A profusely blooming mariola accented the left background such that a typical desert scrub community included woody species of both legume and composite families.
Elephant Mountain Wildlife Management Area, Brewster County, Teaxas. July.
220. Turk's head, bunchball, or scarlet hedgehog cactus (Echinocereus stramineus= E. enneacantyhus var. stramineus) in full-flower- The stark contrast of the bleak, barren-appearing desert environment coupled with the strikingly beautiful combination of spines and brillant cactus flower could be used as a "photo essay". The story would be even more detailed if it was explained that the body of a once large and now long-dead creosote bush served as a former nurse plant for a baby cactus that survived to reproduce by both sexual and asexual means. Your more scientifically inclined author chose to resort to his "desert rat" ways and let viewers write their own stories and draw their own ecological conclusions, or perhaps best of all, just enjoy another example of the beauty of the desert.
Big Bend National Park, Brewster County, Texas. July.
221. Gypsum Barrens or Gypsum Scrub- This is the dune front or foredune of the famed "white sands" of the Tulorsa Basin in southern New Mexico. This is actually "a vast gypsum sand area" (Dick-Peddiie, 1993, p. 128) with gypseous soils around its edges spreading out into an alkali sink. This huge gypsum "pile" occurs just above the alkali sink grassland vegetation dominated by alkali sacaton (included with the Grassland slides) and an alkali sacaton-fourwing saltbush-pale wolfberry savanna seen in the previous slide and at the base of the foredune (the alkali sacaton dominating the foreground of this photograph). Species on the foregune are soaptree yucca (Yucca elata) on the far left, fourwing saltbush in the center and rubber rabbitbrush (Chrysothamnus nauseosus) to the right of center. Gypsophiles or gypsophilous plants are those species which live or thrive in a gypsum-rich soil (Morris, 1992). All of the gypsum-dwelling species found here are widely distributed ones which more commonly thrive on non-gypseous soils. This suggests that the ones growing on this gypsum-rich habitat are unique gypsophilous ecotypes of species that are not usually gypsum-adapted plants. White Sands National Monument, Otero County, New Mexico. June. FRES No. 33 (Southwestern Shrub Steppe Savanna), one form or subunit of K-53 (Trans-Pecos Shrub Savanna) for the alkali sink vegetation and no K-unit for the foredune scrub. SRM 701 for the alkali sacaton-fourwing saltbush savanna but no SRM for the unique gypsum scrub (too many shrubs for SRM 701). Chihuhuan eserts- Gypsiferous Dunes Ecoregion, 24g (Omernik and Griffith, 2006).
222. Gypsum Desert Dune Scrub- This scrub vegetation on the gypsum foredune is a remarkably diverse range community in a small area. It is the point at which gypsum foredune meets the alkali basin or sink of alkali sacaton. The immediate foreground is dominated by alkali sacaton and soaptree yucca, the latter also extending up the lower and mid portions of the foredune. Rubber rabbitbrush and fourwing saltbrush occupy the mid-elevation of foredune while the top of the foredune (center ridgeline) supports skunkbush sumac (Rhus trilobata= R. aromatica). These are probably gypsophilous (adapted or surviving on gypsum-habitats) ecotypes. This vegetation is growing on a foredune on a less xeric and cooler east side. This is an example of the importance of aspect, the position facing a particular direction usually expressed as a compass direction in degrees or cardinal directions of north, south, east or west or breakdowns thereof such as a southeast or northwest aspect (Helms, 1998) or, more simply, the direction the slope of a hill or mountain faces as in a north-facing aspect (Morris, 1992). Influence of aspect is more commonly thought of as being important in the mountains, but this example illustrates that aspect can be just as much an abiotic factor at smaller scale in deserts. White Sands National Monument, Otero County, New Mexico. July. FRES No. 33 (Southwestern Shrub Steppe Ecosystem), but no K-unit or SRM description fits the gypsum dune shrubland. Chihuhuan Deserts- Gypsiferous Dunes Ecoregion, 24g (Omernik and Griffith, 2006).
223. Dwarf Rio Grande cottonwood on Gypsum Scrub Barrens- This part of the foredune is populated by Rio Grande cottonwood (Populus deltoides subsp. wislizenii). This is a subspecies of the eastern cottonwood which is so common on the eastern prairies (eg. the State Tree of Kansas). Such depauperate cottonwood trees are of limited browse value but they were shown to impress upon the student the importance of speciation and ecotypic variation as an expression of natural selection. White Sands National Monument, Otero County, New Mexico. June. FRES No. 33 (Trans-Pecos Shrub Steppe Ecosystem), but no K-unit or SRM designation for this unique desert dune scrubland vegetation. Chihuhuan Deserts- Gypsiferous Dunes Ecoregion, 24g (Omernik and Griffith, 2006).
224. Gypsum Desert Scrub- This is the interior of the immense gypsum dune barrens in the Tulorsa Basin of southern New Mexico. This is inside a barchan dune in the interior of the extensive gypsum dunefield. The large cespitose grass in the foreground is gyp (for gypsum) dropseed (Sporobolus nealleyi). The shrub immediately behind it on the near crest of the barchan dune is rubber rabbitbrush and the dark green shrubs in the background (the choppy dunes of the foredune crest) are skunkbush sumac. Gyp dropseed is another example of speciation as an adaptation to unique abiotic environments
Comparison of this immediate habitat with the alkali sink savanna (and the alkali sink grassland in the Grassland slides) illustrates vividly the concept of ecological niche and Gauses Competitive Exclusion Principle that no two species can occupy the same ecological niche. Sporobolus airoides dominates the alkali sink immediated adjacent to the gypsum dune fields while S. giganteus and S. wrightii form sacaton swales or flats in this same area but on non-gypseous, less-saline soils (cf. Grassland slides for these grassland range types). Mesa dropseed (S. flexuosus) is an associate species on climax black grama semidesert grasslands and a dominant increaser on deteriorated black grama ranges that are in immediate or close proximity to all these range sites/plant communities. Also refer to the true prairie and tallgrass prairie range types (Grassland slides) for dominance by prairie dropseed (S. heterolepis) and tall dropseed (S. asper). The Sporobolus species may not rival the speciation of Darwin's finches but these diverse bunchgrasses illustrate the concept of "fitness" (natural selection for those taxa whose genes are passed to the most progeny).
225. Chihuhan Desert- Climax vegetation.Creosotebush is clearly dominant and is seen here in full bloom. Outer edge of tobosagrass swale form of semi-desert grassland is in foreground showing the adjacent location of these two range types as shown previously. Understory of creosotebush is fluffgrass and six-weeks grama (Bouteloua barbata) and six-weeks threeawn (Aristida adscensionsis). Tarbush (Flourensia cernua), the lesser co-dominant of the Chihuhuan Desert, is at far right. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). Arch-type of K-53 (Trans-Pecos Shrub Savanna). SRM 508 (Creosotebush-Tarbush ), "a persistent subclimax of the grama-tobosa shrubsteppe" (Heerbel in Shiflet, 1994).Creosotebush-Tarbush Series of Brown et al. (1998). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
226. Co-dominants of Chihuhuan Desert: tarbush (left) and creosotebush (right). The Chihuhuan Desert is the easternmost desert in North America and a hot desert. Dona Anña County, New Mexico. June. Same community as preceeding scene. SRM 508 (Creosotebush-Tarbush), "a persistent subclimax of the grama-tobosa shrubsteppe" (Herbel in Shiflet, 1994). Creosotebush-Tarbush Series of Brown et al. (1998). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
227. Creosote bush- This member of the Zygophyllaceae is the dominant shrub of the Chihuhuan, Colorado, Mojave, and portions of the Sonoran Deserts. The basic anatomical/ morphological features of this shrub are more those of mesophytes than most xerophytes, but it is uniquely adapted to desert environments. This was an example of the Chihuhuan ecotype of creosotebush distinguished by Brown (1994, p. 172-173). "Plants with the 'typical' Chihuhuan growth form are shorter, have sparser foliage and straighter stems, and are more open at the base than their Sonoran counterparts" (Brown, 1994, Figure 99, p. 173).
228. Leader of creosote bush- Shoot apex with fruit, flowers, and leaves of the Chihuhuan ecotype of this major North American desert shrub.
229. Duel to the death in the desert- Interspecific competition between creosotebush and bush muhly (Muhlenbergia porterii) on the Chihuhuan Desert is a slow, silent fight to the death. The Chihuhuan Desert has substantially exapanded on ranges that 50 to100 years ago were semidesert grassland. There have been countless ecological studies conducted and subsequent papers published documenting this desertification and speculating as to causes for what most rangemen regard as retrogression. But in the drama presnted here on an apparent ecotone between Chihuhuan Desert and semidesert grassland "the tables were turned". Bush muhly is an associate species on black grama-, and sometimes tobosagrass-, dominated semidesert grassland. Its establishment appears to be sporadic. At the location shown here bush muhly became established and soon began to compete-- successfully-- with creosotebush for some key resource(s) such as water possibly.
New Mexico State University College Ranch, Dona Anna County, New Mexic. June. FRES No. 40 (Desert Grasslands Ecosystem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
230. "To the victor belongs the spoils"- Bush muhly outcompeted creosotebush for some critical resource(s) resulting in death of the latter. There are few sights that can do more to restore a rangeman's soul than skeletons of dead creosotebush, mesquite, huisache, juniper, and other brush on grassland.
New Mexico State University College Ranch, Dona Anna County, Mew Mexico. June. FRES No. 40 (Desert Grasslands Ecosystem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Chihunuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Omernik and Griffith, 2006).
231. Another example of bush muhly competitiveness- Another example of bush muhly-shrub competition except that this time the victim was tarbush.This battle-to-thedeath also took place in the Trans Pecos Basin and Range province. It was a cattle range on an ecotone between semidesert grassland and Chihuhuan Desert. The competitive adaptation of bush muhly was evident from death of the tarbush plant around which this bush muhly established and ultimately emerged as the victor in this grass-shrub interplant competition.
Observant students will note that there were four (or five) live plants of tarbush growing in close proximity around the dead tarbush. These live tarbush plants did not have to compete with bush muhly (= other tarbush plants did not have tarbush growing with them). Hopefully their time was coming.
Railway Ranch, Upton County, Texas. Mid-October; bush muhly was entering winter-dormancy.
232. Bush muhly (Muhlenbergia porteri)- This is unquestionabaly one of the most important climax perennial grasses in both the Chihuhuan and Sonoran Deserts. This native bunchgrass has a range from southern Mexico to Colorado, Utah, and Nevada and extending eastward to the Great Plains and even rarely into the Edwards Plateau of Texas. Bush muhly grows in sandy habitats in the Chihuhuan Desert, but also it also grows on rocky slopes in the Sonoran Desert. These rather depauperate specimens with their extra-dense clumps-- an atypical habit-- grew in a caliche pile on a calcareous soil in west Texas under severe drought conditions (which explained their stunted growth).
Shreve (1951, p. 13) described bush muhly in the Sonoran Desert in his typical terse coverage: "Under the original conditions of the desert lowlands, Muhlembergia porteri was abundant. This grass grows in the open in rounged bushlike clumps but is more abundant as a semiclimbing plant in cresote bushes. The stems are weak but when supported by stout bushes sometimes reach a height of 4 feet. This grass is very palatable, which accounts for its being much less abundant than formerly". Gould (1951, p. 202) also described bush muhly as "highly palatable", but had a somewhat different view of its association with shrubs: "Bush muhly originally existed in extensive stands on the open range lands of southern Arizona but now occurs for the most part in the protection of shrubs and subshrubs and is seldom locally abundant". Here "protection of shrubs" referred to shelter from excessive livestock grazing because animals are reluctant to graze close to woody, spiny, plants; it was not so much an allusion to the nurse plant phenomenon.
Humphrey (1960a, p. 68; 1960b, p. 99-100) wrote: "Bush muhly was formerly one of the most abundant and important grasses of southern Arizona", but that currently it was largely limited to microhabitats "growing under protection of shrubs". Humphrey further noted that bush muhly provides green feed all of most of the year given sufficient moisture. He recommended allowing bush muhly to set seed in summer (the main growing season) every second or third year and deferment in July and August on depleted ranges to allow restoration of bush muhly (Humphrey, 1960a, p. 69; 1960b, p. 100).
Emphasis on bush muhly by these workers was consistent with that Clements (1920, p. 177) who put this species first on his list of the most important grasses in the Sonoran Desert. Shreve (in Shreve and Wiggins, 1964) did not mention bush muhly; in his flora portion, Wiggins (in Shreve and Wiggins, 1964, 256-257) described the species withour comment as to ecological or economic importance.
An example of bush muhly growing (and outcompeting) creosotebush in the Chihuhuan Desert was presented in this publication in photographs and captions of Chihuhuan Desert, Shrublands.
Midland County, Texas. April, dormant in severe drought so still in hibernal aspect.
233. Panicles of bush muhly- These lacy, purple-flowered inflorescences of bush muhly are a "dead giveaway" of this species from a considerable distance. Midland County, Texas. April, but severe drought so still dormant in winter phase.
234. Spikelets of bush muhly- The exaggerated teardrop-like shape of the caryopsis with adhering lemma and palea is a prominent characteristic of mush muhly. Midland County, Texas. April (and drought).
235. Another community of the Chihuhuan Desert- Whitethorn acacia (Acacia constricta and/or A. neovernicosa)-dominated Chihuhuan scrub instead of the more common creosotebush form. Culbertson County, Texas. June. FRES No. 33 (Southwestern Shrubsteppe Ecosystem). K-53 (Trans Pecos Shrub Savanna). SRM 508 (Creosotebush-Tarbush) variant. Whitethorn Series of Brown et al. (1998). Chihuhuan Deserts- Chihuhuan Basins and Playas Ecoregion, 24a (Griffith et al., 2004).
236. Apical leader of whitethron acacia or largancillo (Acacia constricta)- Dominant central shoot of one of the major legumes of the Chihuhuan Desert. New Mexico State University College Ranch, Dona Anna County, New Mexico. June.
237. Leader of whitethorn acacia or largancillo- Lateral branch of A. constricta showing bark, leaves, and inflorescences of one of the widespread shrubs in the Trans Pecos portion of the Basin and Range physiographic province. Another Acacia species that is closerly related to A. neovernicosa is A. constricta. These two species (as recognized by most authors) probably hyybridize where their species ranges overlap. New Mexico State University College Ranch, Dona Ana County, New Mexico. June.
238. Twig and inflorescence of golden ball or littleleleaf leadtree (Leucaena retusa)- This attractive native member of the acacia tribe has been widely planted as an ornamental, especially for xeriscaping. The importance of the species as a range plant derives from its ecological status as a native member of the natural plant community--including the Chihuhuan desert--and as a valuable browse species for both livestock and wildlife. Shown here were details of a flowering leader and inflorescence, a head or capitulum which is a short, densely flowered spike typically haveding a rounded appearance or sphere-shape, of L. retusa.
Hudspeth County. September (when it rained).
239. Big-flowered or plains zinnia (Zinnia grandiflora)- The number one family of forbs in the Chihuhuan Desert is the same as that for most other deserts (and biomes): Compositae. This is one of the more conspicuous and widespread composites in the Trans Pecos portion of the Basin and Range physiographic province. Z. grandiflora is similar to wooly paperflower (Psilostrophe tagetina), but they are readily distinguished because there are three notches ("teeth") in ray flowers of paperflower and no such teeth in those of plains zinnia. This specimen was in Hudspeth County, Texas. June.
240. Trans-Pecos Disclimax, Subclimax, or Postclimax Scrub- This desert scrub is dominated by lotebush (Ziziphus obtusifolia= Condalia obtusifolia), background, and, in lesser proportions, fourwing saltbush (Atriplex canescens), javelina brush (Microrhamnus ericoides), and littleleaf sumac (Rhus microphylla). Honey mesquite is present but barely— if at all —as an associate species while creosote bush occurs in trace to small amounts. Understory dominants are plains bristlegrass (a taxonomic complex once ascribed to Setaria macrostachya, but now split with S. leucopila being the most descriptive for the dominant here), showy fingergrass (Chloris virgata), and, in depressions, white tridens (Tridens albescens). Shrubs present as associate species include such dominants of the adjacent Chihuhuan Desert as creosote bush, tarbush, mesquite, and broom snakeweed. Quite obviously the vegetation shown in this (and the next two photographs) differs in species composition and shrub density and cover (much greater) from that of the actual Chihuhuan Desert, at least as it has been interpreted.
Successional status of this shrub-dominated community is known but to God and certain to stir a spirited debate among rangemen. Range ecologists of the classical or purist Clementsian school of thought typically regard this as a disturbance climax induced by livestock overgrazing and/or cessation of fire and other activities to which species have not evolved such that the pre-Caucasian semidesert grassland dominated by black grama and tobosagrass was degraded into a grazing disclimax (ie. another example of Paul Sears Deserts on the March). Other ecologists, including those who are (or who consider themselves) primarily Clementsian ecologists interpret this as a climatic climax which had its origin about mid-Twentieth Century as a result of dramatic— and catastrophic— meteorological events including a combination of wet winters followed by the severe drought of the 1950s. Some of those expounding the latter view even read recent atmospheric phenomenon as being major climatic shifts, and this view was expressed and argued convincingly decades before "global warming" became the latest "ecology fad" or revisionist "paradigm". In the latter view, the beautiful black grama and tobosa grasslands that were literally used as hay meadows would have been post- climax while scrub vegetation like that seen here would have been the climax (= regional or climatic climax). Those of the disclimax hypothesis (who also have data and convincing arguments) simply cannot look at the nearly entire loss of the former soil (a mature soil) and its replacement by desert pavement (or sand dunes as in the range shown here) as being other than range deterioration (ie. retrogression induced by anthropogenic disturbance).
Either way (or some other way not even dreamt of), scrub vegetation like this now covers hundreds of thousands, if not mllions of acres throughout the Trans-Pecos Region. And, as just discussed, this vegetation is clearly different and distinct from the Chihuhuan Desert of creosote bush, mesquite, tarbush, and associated Acacia species such as that seen in preceding slides. That does not imply that this scrub type could not be an atypical or less common manifestation or phase of the Chihuhuan Scrub. It could well be just that. Alternatively, dominance by species like lotebush and plains bristlegrass, common species of the adjoining High Plains, and javalina brush, a species more typical of the Rio Grande Plains, suggest that this vegetation could be transitional (ie. an ecotone) between the three regional climaxes of Chihuhuan Desert, semidesert grassland, and Great Plains mixed prairie or short grass plains, or even of the Rio Grande Plains shrub savanna to the southeast.
Local abundance of more palatable browse species like fourwing saltbush (generally regarded as having high feed value for all kinds of livestock and big game) complicated interpretation of this shrub community as a grazing disclimax because the palatable species would be expected to be uncommon with overbrowsing. Although lotebush lacks the high browse value of fourwing saltbush, lotebush leaves are frequently eaten by ruminants including cattle (though less commonly than by deer, goats, and sheep).
Conversely, relict specimens of the climax plains lovegrass (which were restricted to protected areas outside this pasture and, inside the pasture, to small patches among shrub thickets and under less dense shrubs) could be interpreted as an indicator of overgrazing which supports the disclimax perspective.
One bit of evidence which this author cannot leave out is the ever-present prescience of the Clements-Nebraska school. Decades before this part of the Trans-Pecos became desert scrub Weaver and Clements (1929, p. 476-477) had already published this summation: "Subclimaxes of the Desert Scrub.—It was formerly supposed that this formation comprised two associations, an eastern and a western, but the former has proved to be a desert-plains savannah in which the shrubs Larrea, Flourensia, Franseria deltoids, Ephedra, Condalia, Opuntia, Acacia, and Prosopis have largely replaced the grasses in consequence of overgrazing and of fire, also, to some extent…
"In addition to the bronze scrub or Larrea-Flourensia associes is a taller and more massive subclimax found in southwestern Texas and adjacent Mexico. This consist of Acadia, Condalia, Celtis, and Prosopis as major dominants and has all the appearance of a true climax. A study of the effects of fire and grazing, however, and of the course of sucession makes it clear that this so-called mesquite, no matter how luxuriant and controlling, is really a subclimax associes that has greatly increased in extent during the historical period. In nature, it is essentially postclimax, and other postclimaxes occur on escarpments, talus slopes, and rocky hills from western Texas to Mexico and eastern California."
Reeves County, Texas. October.
241. Scrubland in Trans-Pecos Basin and Range- Disclimax, subclimax, or postclimax shrubland dominated by lotebush with javalina brush, fourwing saltbush, and littleleaf sumac apparently sub-dominants. This scrub cover type is in the eastern and less arid portion of the same region as the Chihuhuan Desert, but creosote bush, tarbush, and honey mesquite, which are the dominant shrubs of the climax Chihuhuan Desert, are present only as associate species or even in smaller roles and proportions. Likewise, the understory grasses such as plains bristlegrass, showy fingergrass, and white tridens are different from both dominant climax and seral grasses of the adjacent semidesert grassland and the climax Chihuhuan Desert. As discussed immediately above, if this scrub community is part of the desert climax it is quite obviously a different phase of it. Alternatively, this shrubland type may be either a disturbance climax induced by human action or a relatively new climatic climax brought about by a fairly recent combination of perturbations due to climate.
There is no obvious FRES or Kuchler designation for this range plant community as it does not fit either the creosote bush-tarbush desert shrub or the grama-tobosa grassland climaxes of this portion of the Basin and Range Physiographic Province. Neither is there an SRM rangeland cover type (Shiflet, 1994) that matches this vegetation. The closest SRM cover type appeared to be a drastically modified form of SRM 505 (ie. a deteriorated state of Grama-Tobosa Shrub). Depleted state of Chihuhuan Deserts- Chihuhuan Desert Grasslands Ecoregion, 24b (Griffith et al., 2004).
Reeves County, Texas. October.
242. Interior of a lotebush-javelinabrush-fourwing saltbush scrub- The abundant regeneration of the dominant lotebush and the absence of any herbaceous understory in much of this community are obvious in this slide. A grass understory occurs primarily in small openings among the much larger patches of shrubs. Reeves County, October.
243. Lotebush- Leaves, thorns, and fruit on branches of lotebush. Reeves County, Texas. October.
244. Lotebush in bloom- Blooming shoot (upper photograph) and detail of inflorescences (lower photograph) of lotebush or gray-thorn. Lotebush has a wide species range that extends from the Rolling Red Plains of Texas westward to the Colorado Desert of southern California and south into Chihuhua and Sonora. This species has to have tremendous ecotypic variation.
Maricopa County, Arizona. June.
245. Trunks of an oldster- Several woody shoots (trunks or boles) of an obviously old lotebush in the Rolling Red Plains of west Texas. Revealingly instructive views of the s;hoots of this shrub were possible at phenological stage of winter dormancy (leaves were shed).
Scurry County, Texas. Late February.
246. Squaw-bush or Warnock's condalia (Condalia warnockii= C. spathulata)- A range plant that calls both the Chihuhuan and Sonoran Desert's it's home. This delicate, diffusely branched shrub can attain heights of 10 feet. Like lotebush in the preceding photograph squaw-bush is in the buckthorn family (Rhamnaceae).
Pima County, Arizona. June.
247. Fourwing saltbush- A fruit-laden female plant of the dioecious Atriplex canescens. This is one of the most palatable and productivebrowse plants of the Chihuhuan Desert and Great Plains grasslands. Reeves County, Texas. October.
248. Apical portion of fourwing saltbush- Close-up photograph showing fall-colored fruit and leaves on branches of a female fourwing saltbush. Reeves County, Texas. October.
249. Plains bristlegrass- This mid-grass has presented agrostologists with taxonomic difficulties. Plains bristlegrass was long used as either a catchall name for closely related and hybridizing but morphologically varied grasses generally interpreted as a complex and identified as Setaria macrostachya. More recently some authors adopted S. leucopila as plains bristlegrass leaving S. macrostachya as a historic species complex. By whatever name (to borrow a concept from William Shakespeare), this grass is a climax species on most arid range sites and is generally regarded as having good forage value> However, it also usually has lower forage quality than black grama and lower yield than tobosagrass, the two more common climax dominant grasses of this arid region. Severely restricted relict stands of plains bristlegrass in this shrub-dominated community suggested the possibility of overgrazing which further suggested the possibility of this vegetation being a subclimax or disturbance climax.
250. Showy fingergrass, feather fingergrass, or showy chloris (Chloris virgata)- This flashy annual grows on varied habitats throughout much of southcentral and southwestern North America. As is typical of most annuals on North American range, this species usually is most common on disturbed areas (ie. where plants are subjected to severe stresses such as overgrazing, drought, trampling, denudation by construction projects). Feather fingergrass is therefore generally characterized as an ecological invader in the Clementsian model as explained by Dyksterhuis (1949). Showy fingergrass is a widely distributed grass with a global range of distribution (species range) throughout much of the tropics and warm parts of temperate regions (Gould, 1975, p. 321). C. virgata is locally abundant on ranges in the Chihuhuan Desert and westward into the Sonoran Desert including parts of southern California. It is apparently the native Chloris species that is most productive of forage on range and degraded agronomic pastures with Kearney and Peebles (1969, 125-126) noting that in Arizona: "It furnishes appreciable quantities of forage on the cattle ranges in the southeastern counties, where in favorable seasons it is cut for hay". Humphrey (1960, p. 34) explained that feather fingergrass was one of the first grasses to pioneer disturbed habitats, but that it produced abundantly only with favorable rainfall or runoff. When and where there is high herbage production of showy fingergrass "...this grass is valuable as forage ..", but it has low palatability (in spite of fine leaves and soft stems) so that livestock "... much prefer the perennial grasses when available" (Humphrey, 1960, p. 34). Previously, Gould (1951, p. 132) had reached a different conclusion as to forage value of feather fingergrass when, after remarking that the species frequently formed "dense stands on disrurbed soils in southern Arizona...", he concluded that it was "[o]f no particular value as forage". Hitrchcock and Chase (1950, p. 519) concurred with most workers and stated that C. virgata "furnishes considerable forage" when it is "locally abundant".
The local stand of showy fingergrass presented here was in full bloom on an overmowed railroad right-of-way in the West Cross Timbers of northcentral Texas (Erath County). Overmowing for purposes of conspicuous consumption had resulted in death and replacement of little bluestem (Andropogon scoparium= Schizachyrium scoparium var. scoparium) and Indiangrass (Sorgastrum nutans), native dominant tallgrasses, by this native annual invader. This is the typical ecological situation where even on Chihuhuan and Sonoran Deserts this prolific annual grass is most abundant on go-back land or old fields (previously tilled land) and on overgrazed ranges where it replaced native perennial grasses such as tobosagrass and the various sacaton species on more fertile, less xeric sites.
251. Showy cosmopolitan- Showy or feather fingergrass has such a large natural (vs. artificial in reference to anthropogenic or man-induced) geograpahic or species range that it can be interpreted as having a cosmopolitan (or nearly so) distribution. Also, this annual native grass is widely distributed over a wide array of range sites, especially in range vegetation that is in a state of range deterioration (some stage of plant retrogression), within its species range.
The inflorescence of Choloris species is unusual in having features of both raceme and panicle types. The spikelets (each with one perfect floret) of the fingergrasses are sessile and arranged in two rows on one side of a contiuous rachis (Hitchcock and Chase, 1950, p. 519). Gould and Shaw (191983, ps. 53-54, 295) explained that all grasses in the tribe Chlorideae have sessile (or short-pedicelate) spikelets on spicate primary branches that are arranged in a digitate pattern in the panicle, the entire of which is "[m]st striking of the panicle modifications" in the Gramineae.
Erath County, Texas.
252. Crawling plants and animals- Plant of trailing windmills or trailing allionia (Allionia incarnata) on floor of Chihuhuan Desert (first slide) and portions of shoots of of trailing windmills with leaves and flowers plus a feeding caterpillar of white-lined sphinx moth (Hyles lineata) on a shoot of same plant (second slide). These examples were growing in the lower basin form of Chihuhuan Desert scrub in the Big Bend area of the Trans-Pecos Texas vegetational area (eastern portion of the Basin and Range physiographic province).
Trailing windmills is a perennial forb that is widespread and, sometimes, locally abundant in the Chihuhuan, Sonoran, Mojave, and Great Basin Deserts (yep, all four), but the species (biological) range of this member of the four-", and purple-creepero'clock family (Nyctaginaceae) includes subhumid climates in central Texas as well as harsh, xeric habitats in the arid zone. Trailing windmills grows in drier, harsher edaphic habitats ranging from loamy to sandy although it typically does not occupy extremely sandy soils or dunes.
Numerous "wildflower" field guides treated trailing windmills as did all of the standard floras for states within the biological range of this species (Caifornia, Arizona, Nevada, Utah, Colorado, New Mexico, and Texas). Trailing windmills also made it into Notes on Western Range Forbs (Dayton, 1960, p. 108) so tht is the definitive source for this range plant. Dayton (1960, p. 108) reported that trailing windmills was frequently "of considerable value" on summer range s in New Mexico and Arizona where it "furnishes a palatable and nutritious food for sheep and cattle". In addition to providing palatable feed, trailing windmills withstandids grazing and typically has good yields of seed. Other common names for this trailing forb included "cartwheel", "trailing four-o'clock", and "purple-creeper" (Dayton, 1960, p. 108).
The phenomenon of an outbreak, a population explosion, of white-lined sphinx moth caterpillars--and their preference for trailing crtwheels--was covered immediately after presentation and brief discussion of trailing windmills.
Big Bend National Park, Brewster County, Texas. Early October (in a rare, wet autumn).
253. Trailing wheels of color- Portion of shoots with flowers (first slide) and two flowers (second slide) of trailing windmills or trailing cartwheels growing on a peppley or gravelly edaphic habitat in a lower basin of the Chihuhun Desert in the Texas' Big Bend area at the eastern portion of the Basin and Range physiographic province.
Relevant details of this perennial forb as a range plant were given in the preceding caption. Trailing windmills is also a common plant in semidesert grasslands, especially where these desert plains grasslands and the various desert scrublands, the Sonoran and Chihuhuan Deserts in particular, form a patchwork of range plant communities.
Big Bend National Park, Brewster County, Texas. Early October (in a rare, wet autumn).
An appropriate ending for this synopsis- Shown below was an example of desert plants and animals engage in the most basic interaction of these range organisms--grazing (feeding in general). Production and consumption. Reproduce, grow, and be eaten. The following short treatment showed one step in the food chain. This particular consumption involved the class of animal which has more species than all other animals combined. This short segment represented the present biological era of this group of animals-- the Age of Insects.
254. End of the season for one; mid-season for another- A plant of the perennial forb, trailing windmills (Allionia incarnata) which apparently had completed its annual growth cycle and entered dormancy. Dead herbage (primarily leaves) of this plant was being used as forage by numerous caterpillars of white-lined sphinx moth (Hyles lineata) in the Chihuhuan Desert in the Big Bend area of Trans Pecos Texas.
There was a population explosion of the larvae of white-lined sphinx moth during an extremely wet year (spring through autumn). It was a rare "Nikon moment" in life of the desert and the phenomenon was gladly shared with viewers in www. land. Times of super-abundant reproducttion insure survival of the reproducing species by providing a surplus of offspring which furnishes such a feast in the food chain that some progeny (seed, fruit, asexual shoots, eggs, larvae, gamete-producing adults) escape their predators and parasites to produce the next generation. In the instance recorded here, both the species of producer (trailing windmills) and consumer (sphinx moth caterpillars) yielded surpluses of feed for other consumers in the food chain (and for continuation of their kind). Surplus production of offspring is a survival adaptation, evolution in action.
Trailing windmills was able to complete its annual growth/reproduction cycle somewhat earlier in the warm-growing season and there were so many caterpillars that the trophic level above them was over-run with highly a nutritious feedstuff. This same phenomenon is at work with surplus enrollment of college students: fodder for slum lords, saloon keepers, and peddlers of luxuries (eg. over-priced dually pick-ups) in order to insure that are enough legitimate graduates (the small minority who know how to work, save, and learn) to perpetuate knowledge and meet needs of human society.
Trailing windmills is a member of the four o'clock family (Nyctaginaceae). It is a species of hot, dry habitats.
Big Bend National Park, Brewster County, Texas. Early October (in a rare, wet autumn).
255. Having a party- Shoots of trailing windmills being fed on by caterpillars of white-lined sphinx moth in the Chihuhuan Desert in the Big Bend area of Trans Pecos Texas during a record-setting year of precipitation (and that was during the growing season). This plant of the perennial trailing windmills had completed its annual cycle of growth relatively early and with a surplus of biomass and seed.
These two images were representative of the density of caterpillars on certain range plant species, especially trailing windmills which was a favorite of these lepidopteran larvae. It was obviously also a feeding heyday for those animals higher in the food chain with a preference for this nutrient-rich food source.
Big Bend National Park, Brewster County, Texas. Early October (in a rare, wet autumn).
256.Lines even as babies- Caterpillars of white-lined sphinx moth feeding on leaves or resting on stems of now-dormant trailing windmills in the Chihuhuan Desert in the Big Bend area of Trans Pecos Texas during a record-rainfall growing season. In a rare moment, it was a time of feast for all. For now, all was right in the desert world.
Big Bend National Park, Brewster County, Texas. Early October (in a rare, wet autumn).
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