Hydrological minimal model for savanna fire frequency assessment

Savanna is the environmental state in between grassland and forest where trees and grasses coexist without one displacing the other. It is commonly accepted that limited resources, herbivores and fire are responsible for the maintenance of savanna, although, the origin and the dynamics of this ecosystem are poorly understood. A minimal model for soil moisture and biomass balance, based on the interdependence between moisture availability, biomass growth and fire regime has been formulated. Fire is modeled as a grass predator in a context where grasses are better adapted to drought and trees are superior competitor for light. The fire regime is not defined a-priori, but rather it is affected by species composition and fuel availability. The ecosystem itself self-regulates the tree-grass ratios dictating the frequency and intensity of fire and grazing, by reducing fuel availability, further affects the fire regime. In pastoral area, under water scarcity conditions fire frequency increases with grazing; under more wet condition, when tree seedling establishment is not limited by resources availability, grazing leads the system to a no-fire regime.