Determinants of a forest-savanna boundary were investigated around Chirinda forest, south-eastern Zimbabwe. Vegetation data were collected in 60 plots along ten 200 m-transects demarcated across the forest boundary. Geology, soil properties, physiography and fire were recorded as explanatory variables. Species composition changed significantly across the boundary, with 100% species turn-over between extreme ends of the distance gradient, indicating a strong environmental influence on the transition from forest to savanna. Species diversity (F = 8.06, p < 0.01) and species richness (F = 16.73, p < 0.001) were significantly lower inside the forest than outside. Measured explanatory variables significantly (F = 8.4, p < 0.01) accounted for 52% of the variation in species data. Soil moisture, soil depth, fire, geology and slope were significant boundary determinants. All forest plots were on dolerite but not all dolerite areas supported forest. This indicates the importance of geology in determining the position of the forest edge but it becomes less important in some areas where altitude, soil moisture, soil depth and fire are more important. Therefore, Chirinda forest is not a relic of what was once a larger forest neither is it a progenitor of a larger forest-to-be, but the position of its boundary is determined by a complex hierarchy of interacting determinants.
Key words: Chirinda, determinants, ecotone, forest boundary, moist forest, species diversity, Zimbabwe.
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