Abstract
Pterocarpus erinaceus is a popular tree for medicinal and fodder uses in the Sudano-Sahelian belt of West Africa. It is also used for its wood. P. erinaceus is one of the most exploited tree species in many countries in West Africa. Planks and logs have been exported towards the South-West Asian countries for ten years. This paper analysed the demographic structure, the ecological characteristics of natural stands of P. erinaceus and level of human pressure they suffer in two agro-ecological zones of Burkina Faso and Niger. Transects were installed in four forests of which two were in the Sahelian zone of Niger and two were in the Sudan region of Burkina Faso. Measurements and observations focused on the dendrometric parameters, soil type, vegetation type and the presence of termite mound. The traces of debarking and pruning were noted. Trenching traces have been categorized into 3 classes according to their intensity. The Sudanian zone shows higher densities than the Sahelian zone. The largest individuals of P. erinaceus (the mean diameter and the highest average height) are observed in the W regional park (57.7 ± 18.6 cm and 10.8 ± 2 m) although this park belongs to the Sahelian zone. In all areas, distribution of diameter classes are bells, characteristics of aging stands with predominance of older individuals. Dendrometric characteristics vary according to the agro-ecological zones, soil type and vegetation. Twenty-one percent of P. erinaceus inventoried in the Sahelian zone and 13% in Sudanian area are close to an anthill. P. erinaceus is a species of Sahelo-Sudanese areas, analysis of its demographic structure shows that individuals of small diameter are very poorly represented in all forests. The species is exploited much more in Sahelian zones for feed supplements. The soil type and vegetation type influence the growth of P. erinaceus. Indeed, the strongest individuals were observed on soil clay loam, sandy loam soil and woodland. Key word: Pterocarpus erinaceus, demographic characteristics, Sahelian and Sudanian zones, Niger, Burkina Faso.  
Highlights
In Africa, natural resources play a very important role in the lives of rural populations (Ouedraogo et al, 2006)
The analysis of this table shows that the largest individuals of P. erinaceus are observed in the W regional park (57.7±18.6 cm and 10.8±2 m) this park belongs to the Sahelian zone
The structure of stands of P. erinaceus shows that the best represented individuals are in the diameter classes between 15 and 45 cm and between 35 and 65 cm in Sudanian zone and Sahelian zone respectively (Figure 3)
Summary
In Africa, natural resources play a very important role in the lives of rural populations (Ouedraogo et al, 2006). Is widely appreciated for its wood, fodder and medicinal products (Ouedraogo et al, 2006; Sylla et al, 2002; Rabiou et al, 2015) it is belong to the species currently threatened in West Africa. The species is threatened in Burkina Faso and Niger where it undergoes severe pressure, affecting its capacity for natural regeneration (Touré, 2001; Ouedraogo, 2007). P. erinaceus foliage is the most widely sold forage in Niger and Burkina Faso (Sanou et al, 2011). The constant pruning operates as a hindrance to the development of buds towards flowers and fruits and dangerously compromises the ability of the species to disseminate its seeds and possibly the regeneration in natural condition (Rabiou et al, 2015)
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