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Disturbances in drylands: Interactions among herbivory, drought, and termite activity in savanna plant communities

Published Article

Africa

Publication date: April 10, 2025

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Extreme‑weather events are expected to intensify, yet their ecological impacts depend on interactions with biotic forces. Using 15 years of data from a 28‑year semi‑arid savanna experiment, this study shows that large herbivores exert the strongest influence on understorey vegetation—reducing cover, increasing richness and favoring annuals. However, these effects shift unpredictably with rainfall variation and the presence of soil‑engineering termites. A complementary enrichment experiment revealed that resource boosts cannot simply offset top‑down herbivore pressure. These findings underscore the power of top‑down forcing, the surprising robustness of savannas to drought and the irreplaceable value of multi‑decadal experiments for understanding interacting drivers of ecosystem change.

Subject Tags

  • Climate impacts
  • Savanna
  • Climate resilience

Abstract

  1. Climate models predict increases in the frequency and intensity of extreme-weather events. The impacts of these events may be modulated by biotic agents in unpredictable ways, yet few experiments cover sufficient spatiotemporal scales to measure the interactive effects of multiple extreme events.
  2. We used 15 years of a 28-year experiment spanning several significant droughts to investigate how rainfall, large herbivores and soil-engineering termites affect understorey vegetation in a semi-arid savanna.
  3. Herbivory was the dominant influence on community structure—decreasing cover, increasing species richness, and favouring occurrence of annuals relative to perennials—but these effects were contingent on rainfall and termitaria in non-additive (hence unpredictable) ways.
  4. A separate experiment showed that resource enrichment, mimicking the effects of termitaria, does not straightforwardly compensate for top-down effects of herbivory.
  5. Synthesis. Our study highlights the potency of top-down forcing in African savannas. It suggests impressive robustness to drought and underscores the value of multi-decadal experiments for studying interactions among multiple drivers of ecosystem dynamics.

Citation

Wells, H. B., Kimuyu, D. M., Odadi, W. O., Charles, G. K., Veblen, K. E., Porensky, L. M., ... & Young, T. P. (2025). Disturbances in drylands: Interactions among herbivory, drought, and termite activity in savanna plant communities. Journal of Ecology, 113(6), 1491-1503. https://doi.org/10.1111/1365-2745.70036

TNC Authors