Climate change, disturbance legacy and abrupt shifts in ecosystem functioning: what makes arid African savannas more resilient?

The accelerating pace of climate change has led to unprecedented shifts in surface temperature and precipitation patterns worldwide. Regions particularly susceptible to these changes include African savannas. With increased climate anomalies and human impacts, comes increased disturbance events in the form of fires, overgrazing from elephants, invasive species etc. Consequently, there is a continual, large-scale transformation in vegetation patterns. Long-term ecosystem characteristics, such as soil traits, topography, and species composition, also contribute to the susceptibility of ecosystems to these climate and disturbance pressures. Understanding the complex interaction between climatic pressures, local disturbance drivers and underlying ecosystem traits, and their impact on ecosystem functioning and stability, is thus crucial.

This research pursued a dual objective: firstly, detecting shifts in ecosystem functioning within the African savanna biome and analysing their spatial and temporal patterns; secondly, exploring the interplay between climate legacy, disturbance legacy, and underlying ecosystem characteristics, and how these factors influence savanna ecosystem resilience at regional and local scales in the context of global change. Remote sensing time series analysis and breakpoint detection algorithms were employed to identify change hotspots in the South African savanna biome. Combining this ethodwith survival analysis, a novel approach, also helped uncover large-scale climatic drivers and underlying ecosystem traits facilitating these changes. Bayesian hierarchical modeling, coupled with field data collected in the Kruger National Park of South Africa, was then utilised to delve into the complex interactions between disturbance legacy (e.g., drought legacy, history of extreme rainfall events, increased fire frequency, and elephant activity) and the resistance and resilience of the savanna landscape at a local scale. The outcomes of this research contribute to prioritising conservation efforts and enhancing our understanding of the future of savannas in the face of global change.