Grazing herbivores reduce herbaceous biomass and fire activity across African savannas

Fire and herbivory interact to alter ecosystems and carbon cycling. In savannas, herbivores can reduce fire activity by removing grass biomass, but the size of these effects and what regulates them remain uncertain. To examine grazing effects on fuels and fire regimes across African savannas, we combined data from herbivore exclosure experiments with remotely sensed data on fire activity and herbivore density. We show that, broadly across African savannas, grazing herbivores substantially reduce both herbaceous biomass and fire activity. The size of these effects was strongly associated with grazing herbivore densities and, surprisingly, was mostly consistent across different environments. A one-zebra increase in herbivore biomass density (~100 kg/km2 of metabolic biomass) resulted in a ~53 kg/ha reduction in standing herbaceous biomass and a ~0.43 percentage point reduction in burned area. Our results indicate that fire models can be improved by incorporating grazing effects on grass b..., , , # Grazing herbivores reduce herbaceous biomass and fire activity across African savannas

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## Authors

A. Tyler Karp*
Sally I. Koerner,
Gareth P. Hempson
Joel O. Abraham
T. Michael Anderson
William J. Bond
Deron E. Burkepile
Elizabeth N. Fillion
Jacob R. Goheen
Jennifer A. Guyton
Tyler R Kartzinel
Duncan M. Kimuyu
Neha Mohanbabu
Todd M. Palmer
Lauren M. Porensky
Rob M. Pringle
Mark E. Ritchie
Melinda D. Smith
Dave I. Thompson
Truman P. Young
A. Carla Staver

*Corresponding Author: A. Tyler Karp
Institutions: Yale University and Brown University

## ABSTRACT

Fire and herbivory interact to alter ecosystems and carbon cycling. In savannas, herbivores can reduce fire activity by removing grass biomass, but the size of these effects and what regulates them remain uncertain. To examine grazing effects on fuels and fire regimes across African savannas, we combined data from herbivore exclosure experiments with remotely sensed data on fire activity and herbivore density. We show that, broa...,