Megagrazer loss drives complex landscape-scale biophysical cascades

Wild animals can modulate ecosystem-climate feedbacks, e.g. through impacts on vegetation and associated carbon dynamics. However, vegetation cover and composition also affect land surface albedo, which is an important component of the global energy budget. We currently know very little about the influence of wild animals on land surface albedo and the resulting climate forcing of these albedo changes. Leveraging a unique, ecosystem-scale, semi-experimental approach, we study how the loss of the world’s largest, terrestrial grazer, white rhinoceros (Ceratotherium simum), affected the coupling between fire dynamics, woody encroachment and surface albedo in Hluhluwe-iMfolozi Park (HiP), South Africa. Our path analysis revealed that areas in the park where more rhinos had been removed showed a stronger increase in burnt area and woody encroachment compared to areas with fewer rhinos removed, which were both related to a decrease in surface albedo. Increasing burnt area was further associated with higher rates of woody encroachment, indirectly reinforcing the negative effect of rhino loss on albedo. Our study demonstrates that removing megagrazers in HiP were related to complex ecosystem-wide cascades with measurable impacts on land cover and surface albedo and consequences on climate forcing. This highlights the importance of restoring functional ecosystems by reinstating trophic processes.

Methods
We assessed changes in woody plant, fire and short-wave albedo dynamics along a gradient of rhino loss, including legal and illegal removals at a 1 km² spatial scale. Due to sensitivity around rhino poaching, our permit prohibits sharing or displaying spatial data on rhino removals or counts. See details for the experimental design in the methods section of of the article. 

We obtained data on mean annual rainfall, burnt area, woody cover and surface albedo across the park between 2010 and 2019. From these products we derived mean annual rainfall, rate of change in woody encroachment, mean annual burnt area, fire frequency and rate of change in annual surface albedo for each 1x1 km grid cell.