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.
Highlights
Les effets de brulage deprintemps de deux intensites sur les aspects varies de plantes ligneuses de savannes Burkea africana— O chna pulchra apres une saison de croissance, sont donnes
It is clear from the evidence that fire may be expected to reduce canopy leaf biomass, it appears that the effect on radial stem growth may be different since in the Kavango region o f South West Africa it was found that there was no significant effect of annual fire treatments on stem basal area increment over a nine year period in Burkea africana and other species investigated (Geldenhuys, 1977) while in Nigerian savanna it was found that controlled burn ing early in the dry season would permit an increase in established trees’ basal area (Kemp, 1963)
After a hot November burn in Burkea africana Savanna in South West Africa, data showed that a higher percentage of plants with canopies killed had basal regeneration shoots present than those with canopies that survived for all species investigated (Rutherford, 1975)
Summary
Fire has probably occurred regularly in the savan nas of southern Africa, initiated first by agencies such as lightning and later increasingly by man. Since the area had been unburned for some years and had a recent history of very low grazing pressure the graminoid fuel load was probably above average for the given type of vegetation the nutrient-poor sandy soils may be expected to result in a generally lower heat intensity and slower fire than in several other vegetation types (Anon, 1960). The main objectives of the present study were to determine the short term effects of two intensities of spring burn on the individuals of each woody plant species population in a selected area of the Nylsvley study site, with particular attention being given to mortality/survival, degree of canopy reduction, degree of basal regeneration, changes in leaf biomass and to relationships between these aspects
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