Herbivory and Drought Reduce the Temporal Stability of Herbaceous Cover by Increasing Synchrony in a Semi-arid Savanna

Ecological stability in plant communities is shaped by bottom-up processes like environmental resource fluctuations and top-down controls such as herbivory, each of which have demonstrated direct effects but may also act indirectly altering community dynamics. These indirect effects, called biotic mechanisms, been studied across gradients, few studies assessed the importance on mechanisms conjunction with processes. Here we use a long-term herbivore exclusion experiment central Kenya to explore joint drought herbivory (bottom-up limitation, respectively) three mechanisms: (1) species asynchrony, decline one compensated for rise another, (2) stable dominant driving overall stability, (3) portfolio effect, property distributed among multiple species. We calculated temporal herbaceous cover over 22-year time series moving window examine changes through time. Both additively reduced asynchronous dynamics, leading lower during droughts under high pressure. This effect likely attributed reduction palatable higher creates space subordinate fluctuate synchronously response rainfall variability. Dominant population promoted an that did not vary precipitation depended herbivory. The was important this system. Our results demonstrate system naturally dynamic, future increasing reduce its stability. However, these will turn be amplified or buffered depending their impacts