Comparison of the impact of fire, floods, and large herbivore grazing on the 3-D structure and biomass of Mopane Woodland in Kruger National Park using Terrestrial Laser Scanning

We conducted a study to look at the impact of large herbivore grazing exclusion, fire, and flooding on the three dimensional (3-D) structure and biomass of Mopane woodlands using Terrestrial Laser Scanning (TLS). The study was conducted at the 42-ha Letaba exclosure that is located on the northern shore of the Letaba River in the northern part of Kruger National Park (KNP), South Africa. The study entailed comparison of 4 X 30-m diameter paired plots, with 4 treatment (no grazing) plots within the exclosure and 4 control plots outside. Additionally, the northern 4 plots are in upland savanna vegetation on a gravelly loam stream terrace that had been burned in 2010. The southern 4 plots are in riparian woodlands on sandy loam soils that had been flooded in 2007. TLS data was collected at 4-cm spacing with 30-m range at 4 scans per plot. Scans were registered and a 3-D virtual environment was created for each plot from which canopy cover, plant density, and vegetation height were manually measured and biomass was derived. We used discriminant analysis to test the hypothesis that 4 structurally distinct groups would be detected, i.e., burned ungrazed savanna, burned grazed savanna, flooded ungrazed riparian, and a flooded grazed riparian group. We found that point density of grass and trees across plots correlated significantly with plot biomass. We predicted that exclosure biomass would be greater than biomass outside the exclosure and that upland biomass < riparian biomass and this was confirmed. Structural parameters were distinct in riparian plots with > height and density in the canopy, shrub, and herbaceous layers within the exclosure compared to outside. However, though biomass was distinct, structural features were not in the upland pairs.