Effects of large mammalian herbivory, previous fire, and year of burn on fire behavior in an African savanna

Abstract

AbstractFire, herbivores, and climatic factors are all major drivers of savanna and grassland dynamics, and they interact in complex ways, which are still in the process of being explored. In particular, herbivores can reduce fire intensity by removal of biomass, and this could be reinforced by herbivores’ attraction to recently burned sites, although grassland resilience may limit the temporal depth of such effects. Fire temperature is the most common fire metric reported for grassland fire, but additional aspects of fire behavior can also be measured. Using a set of controlled, replicated experiments, we examined the effects of year of burn, herbivory by livestock and wildlife, previous burn, and weather history on fire behavior in an African savanna. Multiple measures of fire behavior (minimum fire temperature, flame front speed, fire residence time, maximum flame height, and flame length) in 36 controlled burns were positively intercorrelated. Burns conducted in 2018 were significantly cooler, especially at heights >0.5 m above the ground, than those in 2013, a wetter year with more grass fuel. Grass fuel loads and fire temperatures were reduced by the presence of livestock and wildlife. Our sampling methods did not for the most part reveal expected differences in fire temperatures or other behaviors between the reburned plots and those burned for the first time in 2018, with or without herbivores, suggesting strong postfire resilience in this semiarid savanna rangeland.