Survival, regeneration and leaf biomass changes in woody plants following spring burns in Burkea africana—Ochna pulchra Savanna*

Abstract

Effects of two intensities of spring burn on various aspects of woody plants of a Burkea africana—Ochna pulchra Savanna after one growth season are given. Mortality of woody plants was very low with, for example, that of individuals of Ochna pulchra being between 1 and 5%. Some species where the above-ground parts were often burned away completely, as in  Grewia flavescens, no mortality of individuals occurred. Basal regeneration shoot mass was found to depend parabolically on plant height while the ratio of leaf to twig mass in basal shoot regeneration varied inversely with plant height in  Ochna pulchra. The ability of  Ochna pulchra plants to produce new basal shoots appeared to not only depend on size of the plant but also on the number of basal shoots present prior to the fire. In live Ochna pulchra plants basal regeneration shoot biomass per individual was found to increase exponentially with greater reduction in canopy leaf biomass. This relation was also affected by possible direct heat effects. Basal shoot regeneration mass was found to vary greatly with species and varied from 0,7 g/individual for  Dichapetalum cymosum to 285,6 g/individual for Euclea natalensis. There was a clear tendency for non-suffrutex shrub species to have greater mean basal regeneration shoot mass per plant than that of most tree species. There was a compensatory effect in  Ochna pulchra between number and size of basal regeneration shoots. Standing dead woody plant individuals (before the burn) were either felled by fire or apparently unaffected by fire and there was no selectivity by species. Results of the present study are generally supported by other work on the effects of fire in savanna and some other vegetation types.