Structure of natural Pterocarpus erinaceus poir. Populations in the Sudanian domain in Niger and Burkina Faso

Pterocarpus erinaceus Poir. is endemic to the Sahelo-Sudanian and Sudano-Guinean zones and much sought after for its wood, fodder and medicinal properties. As a result, individual trees are repeatedly mutilated, which is causing serious damage to the natural tree stands. This study assessed the population structure of P. erinaceus in the different pedoclimatic zones and the effects on tree numbers of the main environmental variables and intensity of use in Niger and Burkina Faso. Individual trees with a diameter of 5 cm or more were measured (diameter, total height, height of the bole, perpendicular diameters of the crown) at a height of 1.30 m above the ground in eigth forest formations. In each, the dendrometric measurements were made along two perpendicular transects. The density of P. erinaceus increases significantly (P < 0.003) from the Sahelo-Sudanian to the Sudano-Guinean zone: 1.2 ± 0.7 stems/ha in the Sahelo-Sudanian zone; 2.6 ± 2.2 stems/ha in the northern Sudanian zone; 6.1 ± 4.6 stems/ha in the southern Sudanian zone and 15.0 ± 1.1 stems/ha in the Sudano- Guinean zone. Our analysis of the stands by diameter and height shows an increasing frequency of young individuals along the pluviometric gradient. However, use intensity is greatest in the driest zones, where the species is under threat.