In recent years the term "savanna" has become synonymous with African plainslands - grasslands studded with flat-crowned acacias and carrying a profusion of wild ungulates. In this chapter the term will be used in a wider context, to include all ecosystems in which C4 grasses potentially dominate the herbaceous stratum and where woody plants, usually fire-tolerant, vary in density from widely scattered individuals to a closed woodland broken now and again by drainage-line grasslands. Rainfall occurs in the warmer, summer months with a dry period of between two to eight months duration during which fire is a typical phenomenon at intervals varying from one to fifty years.