Abstract
Grassland and savanna ecosystems, important for both livelihoods and biodiversity conservation, are strongly affected by ecosystem drivers such as herbivory, fire, and drought. Interactions among fire, herbivores and vegetation produce complex feedbacks in these ecosystems, but these have rarely been studied in the context of fuel continuity and resultant fire heterogeneity. We carried out 36 controlled burns within replicated experimental plots that had allowed differential access by wild and domestic large herbivores since 1995 in a savanna ecosystem in Kenya. Half of these were reburns of plots burned 5 yr previously. We show here that the fine-scale spatial heterogeneity of fire was greater in plots (1) previously burned, (2) accessible to large herbivores, and especially (3) these two in combination. An additional embedded experiment demonstrated that even small experimental burn-free patches can have strong positive effects on tree saplings, which experienced less damage during controlled burns and quicker postfire recovery. This work highlights the importance of simultaneously examining the interactions between fire and herbivory on fuel heterogeneity, which can have important impacts on the growth of woody saplings in savanna grasslands.
Highlights
In many terrestrial ecosystems worldwide, herbaceous-dominated communities persist where more woody-dominated vegetation could be supported by soil and climate conditions
Interactions among herbaceous vegetation, woody vegetation, and consumers play out dramatically in savannahs, which are defined by the co-existence of trees and grasses, and characterized by their potential for alternative states of either grass- or tree-dominated vegetation reinforced by fire and herbivory (Sankaran et al 2008, Touboul et al 2018)
Evidence from our experimental exclosures demonstrates that long-term use by herbivores increased plot-level burn heterogeneity and decreased burn severity in patches that were burned. The strength of these effects depended strongly on previous fire history: the effect of herbivores on proportion of the plot burned and unburned patch length was stronger in plots that had previously been burned
Summary
In many terrestrial ecosystems worldwide, herbaceous-dominated communities persist where more woody-dominated vegetation could be supported by soil and climate conditions. To better understand how herbivory and fire interact to modify fuel loads at small spatial scales, with concomitant impacts on tree seedling survival, we examined spatial burn patterns of prescribed fires in the Kenya Long-term Exclosure Experiment (KLEE). We hypothesized that saplings located within even small clipped patches (1 m diameter) experience lower fire severity (proportion burned) (H4a), and have higher above-ground survival rates and are larger post-fire (H4b).
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