A Preliminary Account of the Plant Ecology of the Chimanimani Mountains

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Abstract
A description is given of the plant communities of the Chimanimani Mountains, a range on the borders of Southern Rhodesia and Mozambique. The main environmental factors influencing these communities are outlined, the effects of climate, altitude, fire, soils and the type and availability of ground water being considered. The overriding factor distinguishing this montane flora from the non-montane ones nearby is clearly a combination of topography and altitude which combine to produce higher total rainfall in the dry season, lower evaporation rates and cooler temperatures. There is a clear distinction between those soils derived from schists, those serived from quartzites, and forest soils derived from either. Different plant communities are closely correlated with these distinctions. The plant formations themselves, which are broadly classified into fire-sensitive and fire-tolerant, comprise dry montane forest, woodland, scrub, grassland and certain less important associes. Dry montane forest occurs in the vicinity of perennial water, but where the soil is well drained. It only survives in fire-protected areas although such habitats become to a greater or lesser extent self-maintained. Dry montane forest produces its own type of soil, a brown forest soil over either schists of quartzites. It is a post-climax community. Woodland, dominated by Brachystegia spiciformis Uapaca kirkiana or Brachystegia tamarindoides, favors slopes of moderate angle, with sufficient soil to support tree growth but not a dense herbaceous vegetation. The soil is well drained and dries out in the dry season. Fires are not fierce due to the comparative paucity of the ground flora. Woodland is considered to be the climatic climax. Two distinct categories of scrub are distinguished. Ericaceous scrub, among quartzite crags and along streams in quartzites, is believed to be a more xeric counterpart of evergreen forest. It favors more or less fire-protected habitats in the "mist belt". The soils are somewhat intermediate between forest soils and those of well-drained quarzite grasslands. Proteaceous scrub, on the other hand, favors exposed sites among schist or quartzite grassland and only a marginal facies in the quartzites can be considered at all fire-susceptible, Grasslands are widespread on flat and gently undulating slopes and dominate the deeper soils due to interaction with fire. Well-drained grasslands are a fire-sub-climax and those on hydromorphic soils an edaphic sub-climax. All combinations of schistose, quartzite, hydromorphic and well-drained facies are distinguished. Lithophytic and aquatic floras are also mentioned. In the discussion the serai status of the plant communities described are considered based on the concept of fire as a normal factor affecting the vegetation. The presence of an otherwise inexplicable truly montane fire-derived element in the flora is used as evidence for the continual importance of fire effects during a series of climatic oscillations and before the advent of man.

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