Figure 1.
Geographic location of the study region and of the research sites.
Table 1.
Grain size analysis of the soil samples was conducted using a particle size analyzer (LS 13 320, Beckman Coulter®).
Table 2.
Coordinates, mean annual precipitation (MAP), and plant community composition of the study sites.
Table 3.
Results of the analysis of covariance performed on the wet to dry biomass ratio, k, using tissue type (i.e., above ground or below ground biomass) as a factor and size of the wet sample as a covariate.
Figure 2.
Dry biomass density of roots in the four sites across the Kalahari aridity gradient.
The error bars indicate the minimum and maximum data values, unless outliers are present (shown as circles). The black line indicates the median, while the box boundaries are the lower and upper quartiles. Based on a set of 60 soil profiles sampled at each site.
Figure 3.
Linear root density (average root lengths per volume) across the Kalahari rainfall gradient in Botswana.
Kuke site exhibits the highest length/volume readings compared to the other sites. The error bars indicate the minimum and maximum data values, unless outliers are present (shown as circles). The black line indicates the median, while the box boundaries are the lower and upper quartiles. Based on a set of 60 soil profiles sampled at each site.
Figure 4.
Root diameter distribution along the soil profile across the Kalahari's rainfall gradient.
The error bars indicate the minimum and maximum data values, unless outliers are present (shown as circles). The black line indicates the median, while the box boundaries are the lower and upper quartiles. Based on a set of 60 soil profiles sampled at each site.
Table 4.
Parameters, a and b, and associated statistics from the fitting of an exponential distribution r(z) = a e−bz to the average root profile in the vertical (z) direction.
Table 5.
Z50 and Z95 root depths calculated assuming an exponential profile of root biomass.
Figure 5.
Measured average woody plant biomass (above and belowground) per unit area (top 1.1 m) across the Kalahari transect aridity gradient.
Inset: ratio of below to above ground biomass. The error bars represent ± standard deviation calculated for a set of 3 plot replicates at each site.
Figure 6.
Left: Fire frequency from 2000 to 2011 calculated from the MODIS Burned Area Product (MCD45) [72] in yr−1.
White areas experienced no fires during this period. Right: Average fire frequency (in yr−1) calculated along a longitudinal transect (21.3°) using a moving box of approximately 100×100 km.