Forêts sèches au sud-ouest du Burkina Faso: végétation - sols - action de l'homme
[Dry forests in the southwestern part of Burkina Faso: vegetation - soil - human impact]
Neumann, Katharina; Müller-Haude, Peter
In 11 small dry forests in the southern Sudan zone of SW Burkina Faso (rainy season of six months and annual precipitation around 1000 mm) plant species composition and soil conditions have been investigated, focussing on the question which conditions enable the existence of these dense woody formations in a savanna environment. The forests are characterized by a dense cover of trees and shrubs, numerous lianas and the almost complete absence of grasses. Typical tree species are Anogeissus leiocarpus, Diospyros mespiliformis and the liana Saba senegalensis. Two plant communities can be distinguished, the Mimusops kummel-Malacantha alnifolia community on moister soils and the Fagara zanthoxyloides-Pterocarpus erinaceus community on drier, well-drained soils. The latter is further divided in two sub-communities correlated with different soils. A dense shrub layer and the absence of grasses prevent these forests from annual bushfires and favours accumulation of organic matter in the upper horizons of the soils. The small forests are imbedded in a cultural landscape, consisting mainly of fields and anthropogenic savannas, and their presence is due to cultural, economic and historical factors. The examined sites do not represent particular soils favouring the growth of forest formations. The soils are mainly shallow, with little reserves of nutritive elements and often high stone contents. Some of the forests are clearly secondary while others might be the relics of formerly larger primary dry forests. However, none of them can be called "virgin" forests as there is ubiquitous evidence for human impact.