WHEN CHANGE IS MORE OF THE SAME: THE INCREASING IMPORTANCE OF HYDROLOGICAL VARIABILITY ON ECOSYSTEM STRUCTURE AND FUNCTION

Dryland ecosystems are well-known for characteristically large variation in seasonal rainfall. This inter-annual variability leads to highly dynamic systems and allows for a greater diversity of vegetation functional types than would exist in a less heterogeneous environment. However, despite being appreciated as a conceptual tool for understanding dryland function, the specific role of variability in governing the dynamics of drylands has received little empirical attention. Furthermore, the importance of hydrological variability within and between seasons of more mesic tropical systems is even less-appreciated. Most studies of variability in rainfall and soil moisture dynamics have attempted to capture either fine-scale spatial heterogeneity caused by vegetation structure (i.e. tree/grass/bare patch differences) or short-term impacts of shits in soil moisture distributions via experimental manipulations. In this talk, I will examine the larger-scale implications of understanding rainfall variability, impacts of variability on the partitioning of surface hydrological fluxes, and subsequent patterns and dynamics of vegetation across a range of ecological settings. Of particular interest is understanding how dryland, tropical, and substistance agricultural ecosystems will respond to shifts in rainfall climatology which may alter the frequency and depth of rainfall events without necessarily impacting average seasonal rainfall totals. Using examples from across the tropics - with a focus on sub-Sarahan Africa - I will highlight some recent work which explores shifts in ecosystem function driven by altered rainfall climatology and the potential impacts of increased variability on the structure and function of tropical ecosystems.