Seasonal woody plant shoot growth in Burkea afrieana — Ochna pulchra savanna

Abstract

Seasonal changes in dry mass of shoots and their leaf and twig Components are described for Ochna pulchra and Burkea africana in a northern Transvaal savanna. Initiation of Shoot growth was found to correspond with a higher rate of temperature increase while time of leaf drop appeared to be affected by the rainfall of the current growth season. Later flushes of growth within a given season were relatively uncommon and where they did occur, they were of the order of half the magnitude of the first flush. Shoot growth per Ochna pulchra plant was found to relate to the previous season's rainfall and not to that of the current season of growth. In Burkea africana, a Similar relation was found, but only for rainfall toward the end of the previous season. From this and other evidence, it appears that shoot growth in these species depends more on carbohydrate reserves than on current photosynthate. The role of pleonanthic and hapaxanthic shoots in affecting relative growth of vegetative shoots per plant between seasons is discussed. Degree of syllepsis in Ochna pulchra affects aspects of canopy structure and the interseasonal changes in shoot growth. Plant size was found to relate inversely to individual shoot mass in Burkea africana and to relate directly to time of leaf fall in Ochna Pulchra. Shoot mortality between growth seasons was lower in Burkea africana than Ochna pulchra and was, in both species, greatest following a season of drought.