Responses of African Savanna Trees to Large Herbivore Extinction and Rewilding.

The global decline or extinction of large mammals over the last 50,000 years has caused sweeping changes in the ecosystems they once inhabited. Trophic rewilding holds promise for returning lost ecological function and restoring processes that support ecosystem resilience, but there remains considerable uncertainty surrounding the efficacy of rewilding. To address this uncertainty, we experimentally excluded a diverse African savanna mammal community from replicated plots for 18 years to simulate extinction. Herbivore exclusion caused a rapid increase in tree cover, which was underlain by shifts in community composition and increases in canopy area, growth rate and density. We then removed the exclosure fences, simulating rewilding. Reintroducing herbivores rapidly reduced tree cover and largely reversed individual phenotypic shifts, but tree density remained elevated despite increased mortality rates after reintroduction. Our results suggest that even short-term extirpation can cause complex shifts in vegetation communities, some of which may be resistant to rewilding.