Effects of the shea butter tree (Vitellaria paradoxa) on soil fertility at different catena positions in South Mali

The role of the Shea butter tree (#Vitellaria paradoxa#) on soil fertility was analysed for a soil catenary sequence in the Fana region of south Mali. A descriptive analysis of the structure of the catena and of the parkland led to a structured sampling of the cultivated soil layer below and outside the tree crown at different positions in the catena. Measurements of leaf litter in the various parts of the parkland has enabled us to quantify the annual amount of leaf fall. Analysis of the soils shows variation in fertility according to the position in the catena and a different expression of the influence of the parkland on fertility depending on this position. Soil genesis and use of the environment by farmers may explain the observed fertility gradients and the different expression of the trees¿ influence. The effect of the trees on fertility is considerable within the zone of influence of the crown, but because of the sparseness of the trees, it is not great on the scale of the whole landscape except at the foot of slope, which is also the most fertile zone. Likewise, leaf fall alters the quality of the soil organic matter, mainly at the bottom of slopes where the localised additions are largest.