Tree vegetation patterns along a gradient of human disturbance in the Sahelian area of Mali

This study characterizes the tree vegetation around Bamba, a village adjacent to the northern part of the river Niger in Mali. Tree species are surveyed in an area of 1300km2. Two human activities in this area affect tree distribution: herd grazing and fuel-wood logging. The characteristics of this tree vegetation are related to the spatial distribution of villages, wells and the river Niger. Two tree vegetation gradients are identified: a North–South gradient in terms of tree density and logging intensity, and a radial gradient around wells in terms of regeneration. Species composition is similar throughout the entire area. Tree density and logging intensity increase from North to South. This gradient may be explained by the amount of ground-water due to the river Niger and by the distance to villages. Seedling density increases with distance from wells. This gradient may be related to herd trampling. Both gradients are non-linear: a threshold distance of 4 km is associated with the North–South gradient, whereas that for the radial gradient is 9 km.