A PALEOECOLOGICAL PERSPECTIVE ON THE ORIGIN OF AFROMONTANE GRASSLANDS

This paper offers a review and reassessment of the biogeography of the Afromontane region. Much of the montane vegetation of Africa, especia lly in the southern part of its distribution (the southern Afromontane region) is characterized by a mosaic of forest 'islands' in a 'sea' o f grassland, with or without heathland elements. Controversy has arise n as to the origin of these grasslands and the view has emerged, based on a variety of phytogeographical, zoogeographical, ecological, pedol ogical and historical evidence, that the grassland element has been de rived, or at least markedly extended, in the recent past by forest cle arance through human agency. An alternative hypothesis holds that the grassland is a much older component of the Afromontane landscape. The paper assesses these two opposing viewpoints in the light of published palaeoecological and biogeographical evidence not previously brought to bear on the problem of Afromontane grassland origins in general. Th e physical environment and vegetation of the southern Afromontane.regi on is reviewed and the suggestions put forward to account for the wide spread occurrence of grasslands in the region are presented. The compe ting hypotheses are then tested against data on plant species richness and diversity from a number of upland areas within the region and aga inst published Quaternary palynological data from the Nyika Plateau, M alawi, the Inyanga Mountains, Zimbabwe and the Winterberg Escarpment a rea of South Africa. The resulting reassessment offers strong support for the idea that the grasslands have been prominent in the southern A fromontane region since before the permanent occupation of the mountai ns by people. Environmental changes, especially of the late Quaternary , are suggested as having been important in establishing the vegetatio n pattern and, while increased magnitude of human impact in recent tim es is apparent, the so-called 'relict' nature of montane forest patche s is questionable. It is argued that the southern Afromontane grasslan ds are themselves relict from a time, around the last glacial maximum, when the climatic conditions were more suited to these formations tha n to forest.