Rainfall and topo-edaphic influences on woody community phenology in South African 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 describing their phenological state. Position on the rainfall gradient influenced: (1) onset and magnitude of leaf emergence, (2) onset and duration of mature leaves, and (3) the proportion of leafless trees. Generally, the moist site demonstrated earlier leaf growth than the intermediate or arid sites. Emergent and mature leaves were recorded earlier, and in the case of mature leaves, retained longer. Overall, there was a lower proportion of leafless 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 position were evident for the proportion of trees in winter with mature leaves, and the proportion of trees with senescent leaves. Bottomlands had a greater 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 increased leaf retention by the deciduous species. Phenological activity of leaves was related to plant stem size. In particular, there was greater leaf retention during the dry period by small stems, relative to large stems.