In this paper the term savanna refers to a vegetation formation and will include all vegetation types that are described as either bushveld, thornveld, lowveld, woodland or scrub. Booysen (1967) proposed a definition of bushveld in South Africa which will be used here to define savanna: "savanna is veld in which the dominants are trees and tall shrubs and in which most of the grazeable material is provided by grasses and/or dwarf shrubs which dominate the field layer."