Understanding Tree–Grass Coexistence and Impacts of Disturbance and Resource Variability in Savannas

Savannas exhibit enormous spatiotemporal variability in woody and herbaceous biomass, structure, and plant functional forms; and the determinants of these are poorly understood (Bond, 2008; Lehmann et al., 2009). This is not surprising given that savannas are subject to an array of environmental drivers. Savannas occur over a huge range of climate conditions: mean annual precipitation (MAP) alone ranges from 150 mm to more than 2800 mm (Solbrig, 1996; Sankaran et al., 2005). Soil properties (fertility, texture, and depth) and irradiance also vary widely across savannas (Solbrig, 1996). Additionally, large areas of savanna are subject to defoliation by herbivores and fire, two quite different forms of defoliation on plants with consequent effects on their (re)growth, which also vary substantially over the biome (Olff et al., 2002; Bond and Keeley, 2005).