Woody cover and geology as regional‐scale determinants of semi‐arid savanna stability

Abstract

Savannas, defined by a balance of woody and herbaceous vegetation, are vital for global biodiversity and carbon sequestration. Yet, their stability is increasingly at risk due to climate change and human impacts. The responses of these ecosystems to extreme drought events remain poorly understood, especially in relation to the regional variations in soil, terrain, climate history and disturbance legacy. This study analysed time series of a vegetation index, derived from remote sensing data, to quantify ecosystem stability metrics, i.e., resistance and resilience, in response to a major drought event in the semi‐arid savanna of the Kruger National Park, South Africa. Using Bayesian Generalized Linear Models, we assessed the influence of ecosystem traits, past extreme climate events, fire history and herbivory on regional patterns of drought resistance and resilience. Our results show that sandier granite soils dominated by trees have higher drought resistance, supported by the ability of deep‐rooted water access. In contrast, grassier savanna landscapes on basalt soils proved more drought resilient, with rapid vegetation recovery post‐drought. The effects of woody cover on ecosystem drought response are mediated by differences in historical fire regimes, elephant presence and climate legacy, underscoring the complex, context‐dependent nature of savanna landscape response to drought. This research deepens our understanding of savanna stability by clarifying the role of regional drivers, like fire and climate, alongside long‐term factors, like soil composition and woody cover. With droughts projected to increase in frequency and severity in arid and semi‐arid savannas, it also highlights remote sensing as a robust tool for regional‐scale analysis of drought responses, offering a valuable complement to field‐based experiments that can guide effective management and adaptive strategies.