Climate variability as a dominant driver of post-disturbance savanna dynamics

How do climate variability and climate shifts influence vegetation patterns in dryland ecosystems? A landscape scale assessment of the effect of changes in precipitation on vegetation in three watersheds, spanning four southern African nations is undertaken and tests of statistical significance of vegetation changes developed. Concepts of resilience provide the framework for examining the influence of changes in both the mean and variance of annual precipitation on the ecological systems of southern Africa. They illustrate thresholds of change and their manifestation in the state of savanna ecosystems, which could previously only be postulated. Time series analyses indicate the fundamental role of precipitation mean and variability in modulating the states of savanna ecosystems. Here we show that the savanna dryland ecosystems have overall responded with increasing NDVI measures despite decreased precipitation since the mid to late 1970's. Areas which experienced diminished vegetative cover over time, are related to specific vegetation types, and declines in the variance of precipitation (even in the presence of overall increases in annual mean). The work highlights the importance of time-series analyses and explicit vegetation-precipitation linkages across this highly vulnerable region.