Brief Note

Secondary succession in the Mopani veld of the Limpopo Valley, South Africa


Abstract

The long-term establishment sequences of the herbaceous and woody component of the Mopani veld of the Limpopo Valley were studied and documented. Based on vegetation surveys conducted at three enclosed sites at the Messina Experimental Farm during the period 1964 to 2001, no clear fixed grass species establishment sequence was observed. The classic plant succession model of the grass component, as usually found in other veld types, is absent in Mopani veld of the Limpopo Valley. Shallow, nutrient poor, gravelly, severely eroded soils with low moisture retention and a high runoff rate are mainly colonised by annual grasses and forbs. Perennial grasses take long to establish. This results in an unstable herbaceous component that is vulnerable to changes, which in turn depends on the erratic availability of soil moisture. Where the woody component is concerned, eight tree species appeared to be early colonisers, five intermediate colonisers and seven late colonisers. Tree numbers increased at sites with deeper soils, indicating that bush encroachment is a general, natural process that occurs irrespective of rest treatments applied to the herbaceous component. At a site with an extremely shallow soil, bush density decreased, suggesting that the bush encroachment process in the Limpopo Valley is much more affected by soil and climate than in other veld types and climatic zones of the Limpopo Province.

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