The Formulation of hypotheses on quaternary vegetation history: General approach and an example from the south eastern cape

An approach is presented for the formulation of hypotheses on Quaternary vegetation history. As a first step the approach requires the analysis of contemporary vegetation in terms of phytogenies, endemism and the environmental correlates biological and ecophysiological attributes of track components. Hypotheses formulated on the basis of these data are then tested using independently derived geomorphological, climatic, phylogenetic, palaeontological and palynological data. By acknowledging that both vicariance and dispersal are equally important processes governing the evolution and distribution of floras, the approach is not limited by the dictates of either of these paradigms. What is most important is that it leads to the formulation of explicit and testable hypotheses. To illustrate the approach, a hypothesis is presented on the history, during the Last Glacial to Holocene sequence, of Subtropical Transitional Thicket in the south eastern Cape. Using data on the contemporary thicket flora, it is argued that thicket would have become established in the south eastern Cape and elsewhere in the Cape coastal region, since the onset of Holocene warming. The thicket would have displaced a glacial karroid shrubland which would have been succulent in frost-free areas. The hypothesis yields many testable predictions. Both vicariance and dispersal events would have accompanied range expansion and contraction of thicket species in response to climatic oscillations.