Primary production is limited by water availability in the N Sahelian zone only; elsewhere in the region nutrient availablility is critical. Woody species influence the water balance via rainfall interception, the influence on evapotranspiration and the influence on water infiltration. The ultimate result for grasslands and crops depends upon local conditions. Processes that influence nutrient availability under trees are those acting via redistribution, those reducing nutrient losses and those increasing soil fertility. Of the latter processes, serious limitations exist in the region concerned: N-fixation is limited by P shortage mainly and deep rooting is very limited and so is possible uptake of minerals from deep soil layers. The positive influence from woody species on soil fertility and primary production varies with average annual rainfall and soil type. This positive influence is basically linked to the redistribution of nutrients and water, the internal nutrient cycling and the related enlarged plant-litter-soil nutrient cycle.
|Publication status||Published - 1991|