Savanna domain in the herbivores-fire parameter space exploiting a tree–grass–soil water dynamic model

The tree–grass co-existence in savannas involves multiple and sometimes connected biogeophysical conditions. The savanna domain, its boundaries, and transitions (gradual or abrupt) to other vegetation types (i.e., grassland or forest) are fundamental for the management of ecosystems and for preserving the biodiversity in present conditions and in future changing scenarios. Here we investigate the savanna domain within grazers-fire and browsers-fire parameter planes through a simple ecohydrological model of tree–grass–soil water dynamics. Stability maps allow to identify savanna domains and to show the behavior of vegetation under increasing pressure of grazing and browsing. Stability maps shed light on the causes behind possible vegetation abrupt transitions (e.g., forest collapse and bush encroachment). An application to 15 African savannas sites is presented and discussed with the support of a local sensitivity analysis of the model's parameters.

► We investigate the existence and stability of savannas in the herbivores-fire space.
► The analysis is based on a spatially implicit ecohydrological model.
► The results show the types of savannas as function of the disturbance levels.
► An application is discussed with the help of a local sensitivity analysis.
► The comparison between model and data supports the theoretical findings.