Fire and Herbivory Interactively Suppress the Survival and Growth of Trees in an African Semiarid Savanna

Abstract

There has been a long-standing interest in understanding how interactions between fire and herbivory influence woody vegetation dynamics in savanna ecosystems. However, controlled, replicated experiments examining how different fire regimes interact with different herbivore groups are rare. We tested the effects of single and repeated burns, crossed with six replicated herbivore treatments, on the mortality and growth of woody vegetation in the Kenya Long-term Exclosure Experiment plots located in a semi-arid savanna system in central Kenya. Burned plots experienced higher tree mortality overall, but differences between burns and non-burns were only significant in plots excluding all wild herbivores and in plots accessible to megaherbivores. Cattle ameliorated the negative effects of repeat burns on tree mortality, perhaps by suppressing fuel load accumulation. Across all herbivore treatments, trees experienced a significant reduction in height within the first two years after fire (top-kill), which was followed by a gradual recovery. Saplings and coppices subjected to repeated burns regrew faster than those that were burned once, except in the presence of megaherbivores. This study highlights strong context-dependent interactions between fire and different herbivore groups, and extends previous approaches to understanding fire–herbivory interactions, which have tended to lump the effects of different herbivore groups, or study them separately.

Fire and herbivory – key drivers of temperate open ecosystems : Effects of consumer control on woody and herbaceous plant communities in temperate wood-pasture

“…The most probable reason for this is the low fuel load in the treatments, due to herbivory, leading to a low fire intensity, which is described in Paper III. Similar results were also found in a study by Ngugi et al (2022) in Kenya, where the amount of fuel was reduced by the cattle to the level where fire had no longer an effect on tree establishment and recruitment.…”

“…In a study from the African savanna, native ungulates prevented woody expansion and Capozzelli et al (2020) showed that introducing both fire and herbivory into the landscape decreased the woody encroachment on grasslands in central North America. Similar results were found in studies in the African savanna (Ngugi et al, 2022;. All of these studies show that fire and herbivores are important factors that can control woody vegetation.…”

Effects of simulated fire and browsing on the resprouting of subtropical dune thicket shrubs in the southeastern Cape Floristic Region

“…2005;Nzunda et al 2008). Even though re had a greater negative effect on resprouting vigour than browsing, the impacts of continuous browsing or sustained browsing of young post-re resprouts may have a greater negative impact on resprouting vigour than just re, whereby stored carbohydrate reserves become depleted(Schutz et al 2011;Ngugi et al 2022), but this is yet to be investigated for thicket shrubs.Pre-treatment shrub size had a strong positive in uence on survival and resprouting vigour after both defoliation treatments. This is unsurprising since larger plants can mobilize more carbohydrates post disturbance(Vesk 2006; Lawes et al 2011; Marais et al 2014; Strydom et al 2020;Staver et al 2009).…”

Ecosystem‐wide responses to fire and large mammal herbivores in an African savanna

“…2016; LaMalfa et al. 2019; Ngugi et al., 2022). We therefore have a limited understanding of the interacting effects of fire and LMH on savanna biodiversity and functioning.…”

“…Studies of top-down and bottom-up effects of fire and herbivores have quantified plant diversity, plant adaptations to fire and herbivory (Bond & Midgley, 2001;Bond & Keeley, 2005;Charles-Dominique et al, 2015), nutrient cycling (Coetsee et al, 2008;Coetsee et al, 2011;Holdo & Mack, 2014;Hempson, Archibald, Bond, Ellis, et al, 2015;Pellegrini et al, 2015), and changes in plant defenses (Chinder et al, 2020;Scogings et al, 2017). However, less attention has been paid to the influence of fire and herbivory on biodiversity broadly, and there are few fully factorial studies that evaluate the interactions between fire and large mammal herbivores (LMH; Levick et al, 2009;Burkepile et al 2016;LaMalfa et al 2019;Ngugi et al, 2022). We therefore have a limited understanding of the interacting effects of fire and LMH on savanna biodiversity and functioning.…”