The relevance of fire frequency for the floodplain vegetation of the Okavango Delta, Botswana

Abstract

The study investigates the relevance of fire frequency for the floodplain vegetation of the Okavango Delta in Botswana, considering species composition, species richness, vegetation structure and tree density. Based on flood and fire frequency data derived from a series of satellite images, active and drying floodplains were separated and study plots were selected with fire frequencies up to ten burns between 1989 and 2003. Both for drying and active floodplains, no typical species assemblage could be associated with fire frequency. On drying floodplains, fire frequency showed no effect on species composition, but rather on vegetation structure. While small woody species showed higher cover values on high fire frequency, large trees showed significantly lower cover values on high fire frequency. For active floodplains, a significant response to fire frequency, both positively and negatively could be determined for specific species. But as almost none of these species appear at low or high frequency only, no differences in species composition could be associated with fire frequency. Rather flood frequency and specific annual flood cycles could be described as the determining factors for the vegetation on active floodplains.