Pterocarpus lucens Lepr. in the area of Banh (N.W. Burkina Faso, Western Africa). Pastoral importance and present status of stands

Abstract

Located in the Sudanese-Sahelian zone (14°05’ N and 02°30’ W with 550 mm annual rainfalls) the area of Banh is mainly devoted to pastoral activities. As the amount of rainfalls has dropped (400 mm annual average since 1970), rearing strategies have shifted - decrease in the cattle stock and a sharp increase in the goat stock - and vegetation is affected by the mortality of ligneous species. This is leading to a higher pressure on depleted browse resources. Pterocarpus lucens is one of the most palatable browse species especially at the very end of the dry season. On rangelands it can be directly browsed (seedlings, sprouts) but leaves are more often eaten after pruning. The structure of Pterocarpus stands was studied in relation to various ecological situations, i.e. gravelly glacis (with striped thickets), low parts of glacis (bush savanas), depression (woodlands). The second unit is heavily used during the rainy season and the other ones to a less extent. Collection of stand structure data was carried out through a systematic stratified sampling. Densities of living trees and mortality rates depend both on ecological situations, but this is less the case for regeneration which is rather abundant. However, for the majority of seedlings growth seems severely hindered by browsing. The status of Pterocarpus lucens is not so alarming as reported on other places in Northern Burkina Faso but only the implementation of shifting exclosures is able to prevent a further depletion of the stands in the middle run.