Short-term responses of shrub layer communities to dry season fires and tree thinning in semi-arid miombo woodlands of north-western Zimbabwe

Abstract

Short-term responses of shrub layer communities to dry season fires and tree-thinning were investigated in semi-arid miombo woodlands in North-western Zimbabwe. Fifty-four (54) plots, 50×50 m each, were demarcated at three miombo sites. Treatments applied were: no burn, no tree thinning; no burn, thinned; early burn, no thinning; early burn, thinned; late burn, no thinning; late burn, thinned. After three years, height structure of the shrub layer communities had significantly changed, with increases in proportions of plants below 10 cm in burnt plots due to height reductions of burnt plants and additions from natural recruitment. Non-burnt plants significantly increased in heights while frequent burning kept plants in a fire-trap. Reductions in heights were further exacerbated by herbivore browsing of new resprouts. Numbers of stems significantly increased in late burnt plants. This is a survival strategy inherent in the life history characteristics of plants in fire-prone environments to ensure quick re-establishment and regain their above-ground biomass for survival. Changes in heights of selected individual samplings did not differ among sites or between thinning treatments while burning led to increases in stems. Monotes glaber and Pseudolachnostylis maprouneifolia had above-average height increases. Mortality was low with only 5.1% in late-burnt, thinned plots, indicating good tolerance to fire.