要旨
The distribution of woody biomass in savannas reflects
spatial patterns fundamental to ecosystem processes,
such as water flow, competition, and herbivory, and is a key
contributor to savanna ecosystem services, such as fuelwood
supply. While total precipitation sets an upper bound on savanna
woody biomass, the extent to which substrate and
terrain constrain trees and shrubs below this maximum remains
poorly understood, often occluded by local-scale disturbances
such as fire and trampling. Here we investigate the
role of hillslope topography and soil properties in controlling
woody plant aboveground biomass (AGB) in Kruger National
Park, South Africa. Large-area sampling with airborne
Light Detection and Ranging (LiDAR) provided a means
to average across local-scale disturbances, revealing an unexpectedly
linear relationship between AGB and hillslopeposition
on basalts, where biomass levels were lowest on
crests, and linearly increased toward streams (R2 = 0.91).
The observed pattern was different on granite substrates,
where AGB exhibited a strongly non-linear relationship with
hillslope position: AGB was high on crests, decreased midslope,
and then increased near stream channels (R2 = 0.87).
Overall, we observed 5-to-8-fold lower AGB on clayey,
basalt-derived soil than on granites, and we suggest this is
due to herbivore-fire interactions rather than lower hydraulic
conductivity or clay shrinkage/swelling, as previously hypothesized.
By mapping AGB within and outside fire and
herbivore exclosures, we found that basalt-derived soils support
tenfold higher AGB in the absence of fire and herbivory,
suggesting high clay content alone is not a proximal limitation
on AGB. Understanding how fire and herbivory contribute
to AGB heterogeneity is critical to predicting future savanna carbon storage under a changing climate.
