Fallow plant communities and site characteristics in semi-arid Niger, West Africa

From 1994-1996, 196 fallow sites in south-west Niger were surveyed using a plant sociological approach. Following a climatic gradient of 350 mm up to 650 mm precipitation, different geomorphologic units (dune, glacis, platt au, depression, dallol) were taken into account. Soils were sampled for each site and analysed for pH(H2O), C-org, N-total and Soil texture. The most important factors for the differentiation of the sites are soil texture and soil organic matter. Special sites like depressions, laterite sites or sites with compact soil surface layers due to heavy grazing can be easily distinguished with character species, but on sandy sites this becomes more difficult, and with different grazing intensities it is even more complicated. The fallow age has no importance for the differentiation of the plant communities which appear to vary according to a state-and-transition model which has yet to be described. (C) 1998 Academic Press.