Rainfall and topo-edaphic influences on woody community phenology in SouthAfrican savannas

Woody community phenology was studied in the central lowveld, South Africa, over a twelve month period at three sites along a rainfall gradient, with both toplands and bottomlands sampled at each site. Each month, individual plants, in replicated samples, were scored into a number of categories desc ribing their phenological state. Position on the rainfall gradient influenc ed: (1) onset and magnitude of leaf emergence, (2) onset and duration of ma ture leaves, and (3) the proportion of leafless trees. Generally. the moist site demonstrated earlier leaf growth than the intermediate or ac id sites . Emergent and mature leaves were recorded earlier, and in the case of matu re leaves, retained longer. Overall, there was a lower proportion of leafle ss trees during the dry season at the moist site, followed by the semi-arid site, followed by the arid site. Differences with respect to catenal posit ion were evident for the proportion of trees in winter with mature leaves, and the proportion of trees with senescent leaves. Bottomlands had a greate r proportion of trees with leaves during winter, but a lower proportion of trees recorded with senescent leaves. Both of these findings were a result of the greater proportion of evergreen species in bottomlands. as well as i ncreased leaf retention by the deciduous species. Phenological activity of leaves was related to plant stem size. In particular, there was greater lea f retention during the dry period by small stems, relative to large stems.