Double stress of waterlogging and drought drives forest–savanna coexistence

Significance Explaining the distribution of vegetation is a long-standing challenge in ecology. In the tropics, forests have been associated with areas of high rainfall and low fire occurrence, while savannas dominate where rainfall is lower, and fire is frequent. However, in many landscapes, both vegetation types coexist, with savanna (forest) pockets occurring within forest (savanna) dominated areas. Using modeling and remote sensing, we show that one mechanism driving this coexistence is hydrology. In areas where the water table varies seasonally from too shallow (waterlogging) to too deep (drought), savannas are favored even if rainfall is high. Considering this mechanism alters our predictions of forest–savanna dynamics under a changing climate.