Same rainfall amount different vegetation—How environmental conditions and their interactions influence savanna dynamics

Abstract

Water limited ecosystems such as savannas are characterized by strong interactions between water fluxes and vegetation. However, the fraction of mean annual rainfall that is transformed into plant available water, is not only dependent on the prevailing vegetation cover, but also on abiotic factors such as soil texture and topography as well as intra-annual precipitation patterns. Most models projecting savanna vegetation cover dynamics have not accounted for these factors until now. Here, it is highlighted how and why spatial heterogeneity in water availability and vegetation cover is closely related to abiotic conditions. The role of soil texture, slope and precipitation patterns on water availability and emergent vegetation patterns are systematically tested by using the process-based, spatially explicit model EcoHyD. The analysis shows that the same overall precipitation will result in qualitatively different vegetation cover, depending on environmental conditions. This highlights that models of savanna systems should indeed resolve water dynamics and the feedbacks between water and vegetation with care. In addition the study discusses that future savanna models should go one step further and include phenotypic plasticity and demographic processes to better resolve individual plant responses towards water stress.