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This article reviews the potential of Araucaria hunsteinii, Araucaria cunninghamii, and Agathis robusta for developing plantations in Papua New Guinea (PNG). The species are propagated from recalcitrant (A. hunsteinii) and orthodox (A. cunninghamii and A. robusta) seeds. The viable seeds are extracted from ripened cones and kept in controlled rooms to maintain seed quality. The seeds are raised in nurseries for seedlings and transplanted in the field. The Bulolo and Wau plantations (PNG) are managed on a 30–40-year cutting cycle. Silviculturally, a 3 × 4 m spacing (12 m2/tree) is applied with 833 trees/ha as initial stocking. Tending is executed in the initial stages and two medium- to high-intensity thinning operations are employed to boost the growth of residual stands. Also, synthetic fertilizers and termiticides are applied to enhance plant growth and control termite infestation in young plantations, respectively. Next, non-commercial (low) thinning is scheduled at 5–7 years with 416 stems/ha stocking (estimated volume 5.522 m3/ha) followed by commercial (crown) thinning conducted at 17–20 years with 208 stems/ha stocking (estimated volume 17.790 m3/ha). The 208 stems/ha is maintained as final crops up to 30–40 years with expected 30.206 m3 volume.
Forestry Department, Bulolo University College, PNG University of Technology, Papua New Guinea
*Address all correspondence to: benson.gusamo@pnguot.ac.pg
1. Introduction
The Araucariaceae is a member of evergreen coniferous trees (softwoods). There are several species of importance belonging to this family, which are confined to Asia and the Southern Hemisphere [1, 2]. Some members of Araucariaceae and their natural distributions in Asia and the Southern Hemisphere are given (Table 1). In New Guinea (Papua New Guinea (PNG) and West Papua of Indonesia), the three species (Araucaria hunsteinii K. Schum., A. cunninghamii Ait. ex D.Don and Agathis robusta F.M. Bailey var. nesophyla Whitmore) of Araucariaceae are found in the natural forests [1, 2, 15, 16, 17]. According to Havel [2], these conifers are mostly found in the lower and mid-montane rain forests between 660 and 2300 m above sea level. The species occur on the mountains of mainland New Guinea commonly in softer slopes and ridges in their natural habitat. These conifers have excellent wood properties and are among the top-listed timbers with other tropical broad-leaved species (hardwoods). Due to wood properties and economical value of the Araucaria spp. and Agathis robusta, the species are highly sought by the timber industries. Thus, the government via the PNG Forest Authority (PNGFA) restricted the export of round logs of these timbers since 1980 unless logs are converted into semi-finished or finished wood products [18].
Some members of Araucariaceae and their natural distributions in Asia and The Southern Hemisphere.
PNG and West Papua of Indonesia.
The scientific names, common names, and synonyms are checked and confirmed with International Plant Names Index [6].
The Araucaria spp. and Agathis spp. are propagated solely from seeds. The seeds from ripened cones are dispersed by wind and animals in the natural habitat [3]. The only threat to seeds on the forest floor or during storage are rodents who feed on them for food [17, 19]. The seeds of these coniferous species (Araucaria spp. and Agathis robusta) have low dormancy and can lose their viability quickly in natural conditions. For example, seeds of A. hunsteinii are dead within 8 weeks if left in the open and allowed to dry [19]. Also, seedling survivals are low in prolonged shadings under the forest canopy [3]. However, if there is no damage by rodents or infestations from insect pests and diseases on the fertile seeds, the species have good natural regeneration capabilities when exposed to environmental conditions (moisture, light, and temperature) conducive for germination. The species can easily be domesticated from their wildings either from seeds or from seedlings plucked up from the forest floor. Thus, these species are widely domesticated and cultivated on monoculture or mixed plantations and as ornamentals in the tropical environments of PNG and northern Australia. For silvicultural trials and plantation establishments, the seeds are selectively sourced from healthy parent trees with good vigor and stem forms. The seeds are stored in a controlled storage shed and raised in nurseries for seedling production until they reach a transplantable size for out-planting in the field. As far as timber processing and utilization are concerned, the softwoods are non-porous with desirable wood characteristics, that is, physical, mechanical, and working properties in terms of strength-to-weight ratio, sawing, peeling, gluing, seasoning, machining, and permeability to treatment with chemical solutions [16, 20].
The PNG government has developed a policy on reforestation for sustainable forest management due to depletion of forest resources as a result of industrial logging, forest clearance (deforestation) for agri industries, and shifting cultivations [21, 22]. The envisaged target is to achieve 800,000 ha of planted forest by 2050 via reforestation and afforestation activities of logged-over concessions and anthropogenic grasslands or degraded lands, respectively [23]. In the reforestation and afforestation programs, the softwoods Araucaria spp. and Agathis spp. (as well as other indigenous hardwoods of commercial value) are identified as prime candidate species for increasing the plantation capacity in the country. Apart from the production of a forest through plantation establishment, the reforestation and afforestation practices should address other sustainable development goals such as carbon sequestration and climate change mitigation.
This work provides a review on the three native coniferous species (Araucaria hunsteinii, A. cunninghamii and Agathis robusta) of Araucariaceae of PNG. Specifically, the article highlights the species’ natural distributions, flowering and seed characteristics, seed storage and viability, nursery techniques for seedling production, basic silvicultural practices applied in Bulolo and Wau plantations (PNG), and the importance (potential) of the species for developing plantations.
2. Botanical description and natural distribution of Araucaria spp. and Agathis robusta in Papua New Guinea
The Araucaria spp. and Agathis spp. come from the Araucariaceae family in the order Araucariales. The Araucariaceae is classified as seed-bearing (vascular) conifers belonging to Phylum Gymnospermae [24]. Unlike the angiosperms, the gymnosperms bear arborescent seeds with no enclosing carpellary structure [25]. The Araucaria spp. and Agathis spp. have male and female flowers (unisexual) in the crown and bear naked seeds in cone-shaped fruits [2]. Whitmore [4] said that the species have characteristics of growing huge in size (50–90 m tall and 2.0–2.5 m diameter) with straight and cylindrical bole as emergent trees in the natural forest canopy (Figure 1). The descriptions of tree taxonomy (based on natural stands) and natural distributions of Araucaria spp. and Agathis robusta in PNG (Table 2) are summarized from various literature sources [2, 15, 16, 17].
Figure 1.
Emergent trees of Araucaria hunsteinii with monopodial crown in a mixed forest of Bulolo.
Taxonomical descriptions
Araucaria hunstenii (Klinki pine)
Araucaria cunninghamii (Hoop pine)
Agathis robusta (Kauri pine)
Habit/Characteristics
A very tall tree (93 m height & 2 m diameter) with straight cylindrical bole, which continues to the tip. Branches whorled, horizontal, slender, with long leaf-bearing twigs crowded at the end. Young trees have a pyramidal crown but may change to round or flat tops in older trees.
Tall tree (66 m tall & 2 m diameter) with a straight cylindrical bole, which continues to the tip. Branches whorled, slender, horizontal, with leaf-bearing twigs along the whole length. Crown mostly irregular & sharply pointed in young trees.
A large tree (50 m tall & 2.5 m diameter) with a huge cylindrical bole & broad crown. Young trees with narrow pointed crowns.
Bark
Thickness: 3 cm. Outer bark: dark brown with large pustules & fissures, peeling off in thick corky flakes. Inner bark: red to pink, fibrous near the wood tissue, with thick, white resinous exudate.
Thickness: 3 cm. Outer bark: dark red-brown, rough, peeling off in papery layers, which often cling to the bole. Inner bark: brown & white, mottled, with thick, white resinous exudate.
Thickness: 2 cm. Outer bark: rusty brown, craterous & pustular, peeling off in rounded flakes. Inner bark: pink with thick, white exudate, corky, non-fibrous.
Wood
Straw colored with pink tinge, soft & light, non-porous with fine rays.
Straw colored, fairly soft & light, non-porous with fine rays & uniform texture.
Pink to light brown, soft & light, non-porous with narrow rays & fine texture.
Leaves
On shaded young trees: distichous, 3 cm long, relatively thin & lanceolate. On matured trees: crowded around the branches, thick, coriaceous, broadly lanceolate & 10 cm long. Both surfaces are glossy, medium to dark green.
On shaded young trees: spreading almost distichous, 2 cm long, sharp & pointed. On matured trees: shorter (1 cm) crowded, overlapping & awl shaped.
Sub-opposite. Almost without petioles, narrowly elliptical (8 × 2 cm) thick coriaceous, parallel venation, glabrous light green. The terminal bud is rounded & has pointed buds.
Flowers
Male flowers on lower branches, in pendulous spikes (15 cm long), consists of papery scales covering anthers; light green in color. Female flowers on upper branches, in short spikes & consists of pointed scales covering the ovules.
Male flowers on thin hanging branches in the lower part of the crown, in spikes (5 cm long). Cylindrical, composed of scales & anthers. Female flowers erect on the upper-most branches in small (2 cm long) spikes, consists of sharp pointed scales & ovules.
Male flowers in axillary spikes. Spikes ovoidal to cylindrical, consists of papery scales & anthers. Female flowers in short spikes, consists of blunt scales & ovules.
Fruit
A large cone, broadly ovoid (20 cm long & 12 cm broad), consists of numerous leathery, winged scales, with sharp points. Seeds (2 cm long) are contained in scale, with broad tip & pointed base, starchy.
An ovoid cone (7 cm diameter) composed of woody, winged scales, with sharp points, which contain the seeds.
A near-globose cone, which consists of spirally arranged woody scales & seeds. Scales blunt, seeds separate from scales, thin, with coat extended into 1 or 2 wings.
Habitat
In the mountains of Eastern New Guinea, especially on softer slopes of lower montane rain forests. Mostly occurs between 660 and 1650 m above sea level.
Throughout the mainland New Guinea & islands of Milne Bay Province, mainly on the ridges of upper (mid) montane rain forests. Mostly occurs between 1000 and 2300 m above sea level.
In the mountains of mainland New Guinea & New Britain island (Pomio). Occurs mostly between 660 and 1980 m above sea level.
Natural distribution (PNG)
It is found in Bulolo, Watut, and Waria Districts (Morobe Province); border valleys of Whagi (Western Highlands) & Jimi (Jiwaka); and borders of Eastern Highlands & Morobe Provinces.
Heads of Sepik River (Ambunti, East Sepik Province).
Inland Pomio (East New Britain Province). Occurs at 2000 m altitude in Watut, Morobe Province.
Table 2.
Taxonomical/botanical descriptions and natural distributions in PNG.
The genus Araucaria composes of 19 species and occurs along the eastern coast of Queensland (Australia), eastern half of New Guinea, New Caledonia, Norfolk Island, southern and eastern Chile, Argentina, and southern Brazil [3, 26]. On the other hand, the Agathis genus comprise about 20 huge timber trees [27] that have natural distributions in the Philippines, Malaysia, New Guinea, Australia, and New Zealand [3, 17, 26]. According to Whitmore [27], the genus Araucaria (18 species) and Agathis (13 species) compose the Araucariaceae, whereby the Agathis spp. has wide distributions than the Araucaria spp. In the tropical rain forest of the Far East (Table 1).
The three coniferous species Araucaria hunsteinii, A. cunninghamii, and Agathis robusta are endemic in PNG, and their distributions are indicated on the map (Figure 2). A. hunsteinii grows at altitudes between 500 and 2100 m in primary forests and are distributed mainly in Bulolo, Wau, Watut, and Waria (Morobe Province); Jimi Valleys (Jiwaka Province); and Central and Western Highlands Provinces (Figure 1). Meanwhile, A. cunninghamii is scattered along the eastern coast of Australia (northern New South Wales to north-eastern Queensland) and New Guinea (Figure 3). In PNG, A. cunninghamii occurs at altitudes between 600 and 1500 m often in sub-montane forests on leached soils in association with Podocarpus neriifolius, Prumnopitys amara, and Castanopsis acuminatissima. On the other hand, Agathis robusta occurs at altitudes between 700 and 2000 m in mainland New Guinea, for example, Watut in Morobe Province, and in New Britain Island, for example, Pomio in East New Britain Province [2, 15, 17]. The cultivated stands of A. robusta are shown (Figures 4 and 5).
Figure 2.
Map showing the distribution of three species of Araucariaceae in Papua New Guinea.
Figure 3.
A stand of Araucaria cunninghamii at Bulolo University College.
Figure 4.
A stand of Agathis robusta at Bulolo University College.
Figure 5.
An unthinned plot of Agathis robusta at Bulolo plantation.
The flowering and fruiting seasons and the characteristics of the three pines (Araucaria hunsteinii, A. cunninghamii and Agathis robusta) differ between the species and between different geographical localities. The species are reproduced sexually via pollination mainly by the wind. For instance, in Araucaria hunsteinii, the pollen from the male flowers on lower branches in pendulous spikes are carried by the wind to the ovules of the female flowers on the upper branches on short spikes [16]. In Bulolo and Wau, flowering begins from January to March, and the cones mature at the end of dry season (September to October) per year. On average, a single cone weighs ca. 850 g with 117 viable seeds, which produces approximately 5000–6000 seeds per kilogram (Figure 6B). Meanwhile in A. cunninghamii, flowering occurs between March and June every year. The fruit, in a single cone, matures from October to December for collection. The mature cone weighs ca. 200 g with 260 seeds, which yields between 4000 and 5000 seeds per kilogram [17]. In addition, Laufenfels [3] noted that individual trees of Araucaria spp. can produce >500 cones per year. Later in the year, the cones become ready (ripen), and winged seeds are dispersed early in wet seasons (Figure 6A). In contrast to 260 seeds produced per mature cone [17], Laufenfels [3] reported 800 seeds contained in a cone. The difference in the number of seeds produced per cone is suggested to be due to the size of cones from which seeds were extracted during the time of seed collection. In this case, the 800 seeds may have been extracted from larger cones sourced from the natural forest (old-growth) stands in the 1950s [3] compared to 260 seeds derived from the cones of plantation stands [17].
Figure 6.
Clean viable seeds: (A) Araucaria cunninghamii and (B) Araucaria hunsteinii.
There is insufficient information available on the flowering and fruiting seasons of Agathis robusta in PNG. Whitmore [27] described Agathis spp. As monoecious, but female cones are produced before the males. The male strobili are more or less sessile and comprised of a number of bracts that produce the microsporophylls. The female cones are heavily globose and borne on shoot tips with blunt scales, each having a single ovule. At maturity, the cones are shattered where flattened ovoid seeds with wings are dispersed (Figure 7).
In PNG, seeds of Araucariaceae are collected from seed trees of natural stands marked out in the field. Often these trees lose their vigor and health, and the ability for seed production declines over time. In order to maintain improved and quality seed sources, the best individual stands (healthy and defect-free) of Araucaria spp. and Agathis robusta are marked and selected as seed trees in few compartments of the plantations. Usually, thinning is conducted to remove the inferior layer of the stand and allow the superior layer of the stand to grow as seed trees for improving seed production and sourcing quality seeds. These seed trees in the compartment are not managed as part of a seed orchard as the seed trees are harvested during clear-cut operations. And, new seed trees are marked in established compartments. This is unlike other countries where seed orchards are permanently established and managed from genetically improved stands for the mass production of quality seeds [28].
4.1 Preparation of Araucaria hunsteinii seeds
The time for cone maturity and seed shedding is usually short; thus, it is important to understand cone maturity and plan seed collection promptly on time. The following methods are used to determine cone maturity: (1) the embryo should be 16 cm long with a well-developed and hard endosperm; (2) cut the tip of the cone to observe the brown color on the cone’s scale; and (3) use weight, as mature cones are usually lighter than immature cones. Cones are collected immediately using hooks attached to a bamboo pole, or use ladders to climb and collect cones from orchards or parent trees. Cones are transported in copra sack bags to an extraction shed and dried for 2–3 weeks on open racks or stored in bags for a week (note: longer storage in bags can result in fungal infestations). As the cone dries, it disintegrates into individual scales, making it easy for hand separation. The seed is de-winged by hand and dried for a week before storage. The matured seeds are recalcitrant with >53% moisture content (MC) and can tolerate desiccation below 32% MC during storage (Figure 6B). Seed viability reduces to zero after 4 weeks when stored at 25°C; however, viability can be maintained for 6–18 months if seeds are kept in air-tight containers at a constant temperature of 3–6°C [17]. For example, Evans [19] reported seed viability up to 8 weeks, while Havel [29] observed 50% seed survival for 18 months when stored in moist conditions in a sealed container. Next, McKinty [11] added that the seeds of A. hunsteinii lose viability at a rate of 10–12% per week.
4.2 Preparation of Araucaria cunninghamii seeds
The matured cones are collected before they open while on the trees. A hook is attached to a pole to dislodge the cones. Cone maturity is determined by cutting slightly the tip of the sample cone with a sharp knife where a dark gray–brown color indicates maturity. Also, full-sized dark green cones are considered mature and are collected. The cones are then air-dried by spreading on trays for 2–3 weeks under a heavy shade. The wings are moved with hands using gloves and a wire screen. Other cleaning techniques are winnowing or the use of domestic electric fans to separate light materials from the seeds. The seeds are orthodox unlike their counterpart Araucaria hunsteinii (Figure 6A). The matured seeds have 23% MC at the initial stage and can dry to 2% MC without damage. Seeds are stored best in a refrigerator (−18°C) where they can be stored for up to 6 years. Meanwhile, seeds placed in copra sack bags or in air-tight containers can be store at −10°C for up to 3 years. Additionally, the fresh seeds have 75–80% viability [11, 17, 29].
4.3 Preparation Agathis robusta seeds
There is little information available on its flowering/fruiting phenology, seed preparation, and viability in PNG. According to PNGFA’s National Tree Seed Centre (Bulolo, Morobe Province), A. robusta flowers every 6 months per year, and fruits are harvested from January to March in the same year. Tree climbers use ladders to climb the parent tree and use hooks to dislodge the cones. The collected fruits are dried in the open where cone scales are disintegrated, and seeds fall off (Figure 7). The seeds are separated by hand and winnowed before storage. The orthodox seeds are best stored in a refrigerator at a temperature of 3.5°C immediately as the seeds lose viability rapidly at ambient temperatures. Elsewhere in New Zealand, there could be documentation on the Agathis australis with regard to seed collection, preparation, and storage techniques as well as tests for viability [3, 5, 12, 27].
5. Plantation development and management with reference to Bulolo and Wau projects
Iverson et al. [30] reported that the plantation of Araucaria spp. began in Bulolo and Wau districts of Morobe Province after the gold discovery and extraction in the 1960s in Bulolo Valley during the Australian colonial administration of the Territory of New Guinea. As the gold deposit was depleting, a Canadian gold mining company (Bulolo Gold Dredging Ltd), which was renamed Commonwealth New Guinea Timbers Ltd. (CNGT), ventured into the timber-processing industry. The pure stands of Araucaria spp. in the Bulolo Valley were harvested for veneer production for plywood manufacture in the 1950s. The plantations of Araucaria spp. in Bulolo and Wau districts began in the 1950s, and the plantation capacity increased in the 1960s in order to maintain the raw material supply and sustain the plywood-making industry. CNGT was later changed to PNG Forest Products Ltd. in the 1970s and established as a sawmill complex (alongside the existing plymill) where plantation raw materials (Araucaria spp.) were fed for sawn boards and pole productions while maintaining plywood making [30].
Presently, the state through the PNGFA owns and manages 12,000 ha of pine plantations at Bulolo and Wau districts of Morobe Province. The plantations are composed of three major species: Araucaria cunninghamii, A. hunsteinii and Agathis robusta (including exotic Pinus carrbaea). A few area (ha) is planted with Agathis robusta within the plantations due to inadequate knowledge about its silviculture and longer cutting cycle as compared to Araucaria spp. However, A. robusta has huge potential for commercial cultivation on a plantation scale for veneer and lumber production given the favorable environmental conditions in PNG. Apart from Bulolo and Wau plantations, a few compartments of Araucaria cunninghamii can be found in Lapegu and Kainantu state-owned plantations in the Eastern Highlands Province (PNG). According to the PNGFA’s Corporate Plan 2021–2030, the annual target of the plantation management is to raise 500,000 seedlings of Araucaria spp., reforest 330 ha, and harvest 100,000 m3 volume of raw materials [23]. The PNGFA regards Bulolo and Wau monoculture plantations as a model project, and the project anticipates to achieve sustainable yield and high economic return on investment with prudent management and application of appropriate silvicultural practices.
5.1 Nursery techniques: Propagation and management
The Bulolo and Wau plantations’ nursery is designed to hold 800,000 plus seedlings of high quality (premium ‘A’ grade) at any one time per annum (Figures 8 and 9). Some specific tasks of the nursery management are to: (1) ensure seed tree locations are well-defined and take necessary measures to protect them (in order to protect gene erosion); (2) supervise collection, extraction, drying, and storage of seeds; (3) plan and implement nursery production of healthy seedlings to meet the target and on schedule; and (4) ensure high quality (disease-free) seedlings are dispatched for reforestation and afforestation activities. The major nursery activities undertaken in order to produce high quality materials for plantation establishments include seed and soil collections, seedling production, and seedling maintenance [17, 28].
Seed collection. Seeds are collected from parent trees marked out in the Bulolo and Wau plantations. The viable seeds are stored at PNGFA’s National Seed Centre, Bulolo.
Soil collection. The soils for nursery are usually top layer (humus) collected from the mid-montane forest. The soils are sieved and sterilized using fire to eliminate unwanted microorganisms that could infect seeds. The sterilized soils are then tubed using small- and medium-sized polythene bags.
Seedling production. The germination sheds and stand-out beds are prepared in advance to accommodate polythene tubes for germination. The propagation of Araucariaceae is from seeds through direct or broadcast sowing methods. In direct sowing, the seeds are directly sown into the tubes and allowed germination under sheds. Alternatively, the viable seeds are spread on the plastic trays with sterilized soils and allowed for germination under sheds (Figure 8). Gunn et al. [17] pointed out that fresh seeds of Araucaria cunninghamii take 12–20 days to germinate. The germinated seedlings are then plucked out carefully and transplanted into the polythene tubes. The tubes (with seeds or seedlings) are lightly sprinkled with water to encourage germination.
Seedling maintenance. The following maintenance activities are conducted in the germination sheds (green houses) and stand-out beds for seedling production.
Weeding—light weeding (0–5 months), medium or high weeding (5 months plus)
Fertilizer applications—3–4 g of inorganic fertilizers (NPK and boron) are applied to boost plant growth at the juvenile stage.
Shifting seedlings—after 2–3 months in the germination shed or green house, the seedlings are shifted to stand-out beds for hardening and culling processes.
Hardening/Culling/Sorting—seedlings are allowed to undergo hardening and culling (Figure 9). Dead seedlings are removed, seedlings are graded (A, B, and C), and slow-growing seedlings (B and C) are separated and treated with fertilizer to boost their growths. Seedlings can be in the stand-out beds for 1–2 years until they reach transplantable size.
Root pruning—tap roots that protrude out at the base of the polythene bags are pruned to avoid root coiling. Coiled root seedlings when out-planted in the field are subject to fall over (or uprooting) due to shallow penetration of the root systems (shallow rooting-habit) to withstand wind-throw incidents.
Pest and disease control—a synthetic pesticide (from Blitz chemical group) is applied to control snails that feed on young leaves of seedlings. Pesticides are applied to control insect pests (especially leaf chewing or defoliating insects) and fungi that cause blights and root rots.
Irrigation—continuous sprinkling of water is done on a daily basis. A good time for watering seedlings is in the mornings (7:00–10:00 AM). Watering is also done in the afternoons, particularly during prolonged dry periods [28].
Figure 8.
Araucaria cunninghamii seedlings stored under a shed in stand-out beds, Bulolo plantation.
Figure 9.
Saloon cloth is removed for seedlings to undergo hardening or culling. Seedlings are ready for out-planting in the field, Bulolo plantation.
5.2 Establishment of plantations
The current management of Bulolo and Wau plantations applies 3 × 4 m spacing (12 m2 per tree) for Araucaria spp. and Agathis robusta to attain 833 trees per hectare (ha) as initial stocking during establishment (Figure 10). Prior to planting, site preparatory works such as soil mobilization and brushing of vegetation are not usually conducted. Seedlings are immediately planted after a clear-cut operation when the site is cleared from the regrowth of vegetation for reforestation activity. For afforestation, brushing of spontaneous vegetation and control burning are done as site-preparation activities before planting. Most field plantings are planned and executed during rainy seasons to achieve a high survival rate with low mortality. After 4–5 weeks, tree survival counts are conducted for dead trees (mortality) at planted sites and replaced with new seedlings. Mortality count and subsequent replacement are important for maintaining the initial stocking (833 trees/ha) in the compartments.
Figure 10.
Three-year-old second rotation Araucaria cunninghamii crops, Bulolo plantation. Note the line tending done to control spontaneous vegetation, which will shade the young crops.
5.3 Application of silvicultural treatments and harvesting cycle
The main silvicultural treatments applied in plantations after establishments are tending, pruning, application of fertilizer and pesticide, and thinning operations. These treatments are given in order to improve growth performances of the stands and increase crop yield and productivity. The tending operations (clear and line brushing) are scheduled between 1 and 5 years of planting. The Araucaria spp. are often self-pruned; however, low pruning can be conducted together with line brushing at an early age. Occasionally, synthetic fertilizer (N, P, K, Mg or B) is applied when trees in certain compartments indicate symptoms of deficiency (yellowing of leaves, stunted growth) of certain macro nutrients. Likewise, pesticide is applied to young trees that show signs of termite (Coptotermese elisae) attack as a chemical control measure.
As per the current Bulolo and Wau plantation management decision, moderate-to heavy-intensity thinning activities are scheduled at the age of 5–20 years for the plantations in which non-commercial (thin-to-waste) thinning is conducted (5–7 years old), followed by commercial thinning (17–20 years old) and final harvest (35–40 years old). In thinning operations, theoretically, 50% is removed at each thinning interval, that is, non-commercial and commercial thinning until retained ca. 200 stems/ha for final harvest (Figures 11 and 12). Basically, low thinning or thinning from below is employed for non-commercial thinning where suppressed and intermediate trees are removed. While for commercial thinning, crown thinning or thinning from above is implemented where the intensity of thinning is expressed by specifying the number of stems or basal area (m2) per ha to remain after thinning [19, 28]. The present practice in thinning is that any tree that falls within the vicinity of 5–6 m radius from a residual stand is selected and removed. Types of thinning, age and their schedules, average diameter, residual stock, and estimated volume are provided (Table 3). The unthinned plots of Araucaria hunsteinii and Agathis rubusta are shown in Figures 13 and 5, respectively. Under the old management of the 1980s, the rotation age of Araucaria spp. was 35–40 years; however, the current management decides to allow one commercial thinning only (after non-commercial thinning) and retain the stocking of 200 stems/ha for the final harvest. The non-commercial and commercial thinning treatments create optimum conditions that stimulate prolific growths in residual stocks to reach harvestable size (ca. 55 cm diameter-breast-height on average) at 25–30 years (Figure 14).
Figure 11.
Commercial thinned compartment with 208 stems/ha as residual stock for final harvest, Bulolo plantation.
Figure 12.
Commercial thinning materials are stored at a landing awaiting log trucks for hauling, Bulolo plantation.
Treatment
Trees/ha
TTR1
Age2
EAD3
FSH4
EVH5
Non-commercial thin
833
50
5–7
10–15
416
5.522
Commercial thin
416
50
17–20
30–35
208
17.790
Clear cut
208
100
35–40
40–45
Nil
30.206
Table 3.
Thinning schedules, stocking and final harvest of Araucaria spp.
1TTR—Theoretical tree removal (%), 2Age (years), 3EAD—Estimated average diameter (cm), 4FSH—Final stocking (trees/ha), 5EVH—Estimated volume (m3/ha).
Figure 13.
An unthinned plot of Araucaria hunsteinii at Bulolo University College.
Figure 14.
A compartment of Araucaria cunninghamii due for clear-cut, Bulolo plantation.
As per the records of CNGT in the 1970s, the mean annual increment (MAI) for Araucaria spp. was 20 m3/ha/year at 40 years of rotation age [19]. According to present Bulolo and Wau plantation management practices, an average of 1.0 m height and 2.0 cm diameter growth increments are attained annually with prudent silvicultural treatments (nursery techniques, fertilization, brushing of vegetation, vine cutting, pruning, thinning) planned and executed on schedule (Table 3).
5.4 Final harvest and utilization
As far as harvesting and utilization are concerned, the current plantation management allows an annual allowable cut (AAC) of 63,000 m3 and 18,000 m3 from clear-cut (clear-fell) and commercial thinning operations, respectively, from its 12,000 ha forests. These volumes of raw materials (logs) are derived from various compartments of the plantation based on individual compartment history, that is, compartment scheduled for commercial thinning or clear-fell operations. The clear-cut materials are processed into veneer products for plywood manufacturing, while the thinning materials are converted into lumber products. In particular, the Araucaria hunsteinii (Klinkii pine) is managed for specific end uses, for example, core veneer in composing plywood and poles for electricity transmission. The Araucaria spp. poles and sawn boards are seasoned, machined, and pressure-impregnated with waterborne copper-based preservatives (copper chromium arsenic and alkaline copper quaternary) prior to marketing and utilization [2, 16, 20, 29]. In clear-cut compartments, immediate reforestation with second-cycle Araucaria spp. follows suit, while the regrowth of vegetation is still minimal in order to avoid costs involved in heavy brushing and control burning.
5.5 Fire, pests, and disease infestations
The Araucaria spp. And Agathis robusta are highly susceptible to fire incidents in Bulolo and Wau monoculture plantations. The species are intolerant to fire, with 100% mortality in any fire incidents particularly during the dry season, which falls between the months of June and September per year in PNG. The plantation management is fully equipped with fire-fighting equipment and tools, and the fire-fighting team is always on alert to combat fire. There are three fire lookouts (towers) built at higher locations within the plantations to monitor fire incidents. Any fire incidents are immediately reported to the fire-fighting crews to respond and suppress fire from spreading in the plantations. Huge losses of plantation crops were experienced in 1997 and 1998 El Nino-Southern Oscillation (ENSO) events in PNG [11].
Typical of any monoculture cropping systems, Bulolo and Wau plantations of Araucaria spp. are subject to the outbreak of pests and diseases with devastating effects on the crop productivity and economic value. Laufenfels [3] first reported the susceptibility of Araucaria spp. from a host of insect pests such as leaf branchlet-mining scolytid, wood-boring weevils, and termites. The major threat to the plantation crops at present is infestations from insect pests, namely Hylurdrectonus araucariae Schedl. (Coleoptera: Scolitidae) and subterranean termite (Coptotermese elisae) Desneux (Isoptera: Rhinotermitidae). Also, Gray and Lamb [31] reported infestation of the leaves of Araucaria cunninghamii by H. araucariae. According to Schneider [32], the larvae of H. araucariae bores into the leaves of A. cunninghamii and mines the cortex between the healthy green and wilt yellow or brown area of branchlets. The prime targets are 4–11-year-old crops that are confined to compartments located at cooler climatic conditions. The insect pest gradually kills the hosts (A. cunninghamii) over a period of time. On the other hand, subterranean termite (C. elisae) enters the hosts (Araucaria spp.) via injured roots or bark and bore (tunnel) into the cambium and heartwood (Figure 15). Once inside the wood, the termite intensifies its boring activity until killing the hosts. The symptoms on the termite-infested trees include yellowing or browning of tips of branchlets, defoliation at the upper crown, and mud galleries constructed at the base of the trees [32]. Often the main targets are young A. cunninghamii crops of 4–10 years old, while A. hunsteinii and Agathis robusta are unaffected by the termite. Usually, young trees growing under stress or weak trees as a result of disease and wound infliction release a volatile allelochemical (kairomone), which is sensed by the termite to initiate its attack [32]. At the moment, the plantation management applies a termiticide (trade name: Termido) as a chemical control measure with limited success. The application of Termido is an expensive exercise, and the control of the subterranean termite is difficult due to the fact that the termite colony lives underground and in most cases are unaffected by the termiticide [32]. A biological control measure undertaken now is the burning of tree residues (debris such as branches, tops, and stumps) after log extraction from clear-fell operations, which become a food source for the termite. The biological control measure looks promising, and further research works are required to substantiate the effectiveness of the technique.
Figure 15.
Subterranean termite (Coptotermes elisae) attack on young Araucaria cunninghamii stem, Bulolo plantation.
The three species Araucaria hunsteinii, A. cunninghamii, and Agathis robusta of Araucariaceae flowers all year round in the PNG’s environmental conditions. The seeds of these conifers have low viabilities and should be kept dry (avoid moisture uptake) during extraction from mature cones and refrigerated immediately at recommended temperatures to maintain the quality. The seeds have good dormancy in cool storage as long as they are kept dry and protected from rodents. The conifers are easily propagated from seeds with low mortality in nurseries if proper nursery techniques are applied to raise seedlings for plantation establishment purposes. The conifers have the ability to adapt well and grow prolifically (with 25–30 years cutting cycle) in Bulolo and Wau environmental conditions, except for Agathis robusta where its silviculture and cutting cycle are unknown. This opens up research opportunities for silviculture of A. robusta in order to promote the species for plantation cultivation. The species of Araucariceae have excellent working characteristics for lumber, treated poles, and plywood products. In PNG, the importance of the species as plantation crops will be maintained with timely application of silvicultural practices. The only threats to plantation of Araucaria spp. are fire and termite attack. Burning of forest biomass left behind after log extraction from clear-cut operations is a promising biological control measure for pest (subterranean termite). The global climate change phenomenon will influence the tree physiological processes (photosynthesis, respiration, phenology of flowering and fruiting characteristics) as well as outbreaks of fire, pests, and diseases in the plantations. For instance, climate change potentially affects biotic and abiotic factors, which in turn causes imbalances in macro/micro climatic conditions, ecological functions, soil properties, and forest hydrology that have direct bearing on tree growth and productivity. For sustainable plantation management in the future, one must have a fair understanding of the effects of climate change so that mitigating strategies can be adopted to address the potential impacts to tree crops.
I am grateful to the following staff of Bulolo University College: Charles Feriwok and David Tobesa for providing information on nursery techniques, Louis Veisami for forest measurement, Olo Gebia for plant taxonomy, Ryan Dagoro and Samson Aguadi for map work. Also, my appreciation goes to PNGFA’s Bulolo plantation officers: Steven Keki, Leo Tohichem, Timothy Sawaraba and Awasa Gebob for providing basic information on seeds and silviculture of PNG’s Araucaricaeae. Next, I thank forestry undergraduate Theophyllus Bogan for providing field photographs for the Araucaria spp. and Agathis robusta.
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Written By
Benson Kumuli Gusamo
Submitted: 23 August 2023Reviewed: 18 September 2023Published: 07 March 2024
Open access peer-reviewed chapter - ONLINE FIRST
