Population structure and minimum felling diameter of Pterocarpus erinaceus Poir in arid and semi-arid climate zones of West Africa

Abstract

Pterocarpus erinaceus Poir (Fabaceae) is an endemic, highly exploited and threatened plant species in arid and semi-arid zones of West Africa. This study was conducted at the sub-regional level across three countries, namely Burkina Faso, Niger and Togo. These countries represent a spatial ecological gradient of P. erinaceus distribution to collect information on population structure and silviculture operating standards that could guide the industry, ensure species regeneration and establish appropriate management strategies for the species. Data were collected in P. erinaceus populations by means of forest inventories. Results showed that the average tree density was 1.17±0.75trees/ha in the Sahelian zone, 49.20±63.2trees/ha in the Sudanian zone and 110.9±1.15trees/ha in the Guinean zone. The average stem diameter values were 26.63±7.89cm (Guinean zone), 29.02±15.44cm (Sudanian zone) and 49.63±19.44cm (Sahelian) with noticeable variability (CV=53.6%). Significant differences for these parameters were noted between the zones (P<0.001). The average total height in the populations of the Sudanian zone (9.51±2.75m) were significantly less (P<0.001) than in the other two zones (10.18±2.27m for the Sahelian zone and 14.16±2.88m for the Guinean zone). The merchantable heights were between 4.08±1.35m (Sahelian zone) and 3.63±2.63m (Guinean zone) and varied significantly from one zone to another (P<0.001). The distribution of trees in diameter classes varied depending on the climate zone: modal distribution with most classes ranging from 30–65cm in the Sahelian zone and 15–45cm in the Sudanian zone and an “L” model distribution in the Guinean zone (most classes ranging between 10 and 25cm), while the distribution of height classes showed a modal form for all climate zones. Two minimum diameters of exploitation (MDEs) could be determined: 35cm for the Guinean and Sudanian zones (P=316.6% and P=53.4%, respectively) and 65cm for the Sahelian zone (P=111.9%) for a rotation period estimated at 20years for all the climate zones.