Tree population inventory, diversity and degradation analysis of a tropical dry deciduous forest in Afram Plains, Ghana

Abstract

Forest inventory and diversity assessments are essential to understand the tree population structure and diversity status of forests and to provide information for biodiversity recovery planning. But, unfortunately, the vast majority of forests in developing countries lack inventory data, particularly the dry forests and savanna woodlands where timber potential is considered to be low. Consequently the tree population structure and diversity status of these forests are often insufficient for sound management. In this study, the structure and composition of tree species were studied in a dry semi-deciduous forest in Afram plain, Ghana. The site’s status in terms of level of degradation/disturbance was also determined. Two-long rectangular plots (each 20m×2000m) were established, 200m apart, in five locations within a 40-hectare (ha) area. Each of the plots was sub-divided into 20quadrats (20m×100m). All tree species ⩾10cmdiameter at breast height (dbh) were identified and their diameters over bark measured at 1.3m. The forest condition was scored and habitat types classified. In total 44 tree species with 831 individuals belonging to 25 families were recorded at the study site. This corresponds to an average of 21 treesha−1 of which 17 haddbh ⩽30cm. Trees with dbh ⩾70cm were less than one tree ha−1 (mean 0.8ha−1). The Simpson (0.06) and Shannon (4.52) indices reveal a poorly stocked and less diverse forest. Five species (Lophira sp., Danielliaoliveri, Pterocarpuserinaceus, Terminalia glaucescens and Ficus sur) accounted for 50% of the total individuals recorded with the Fabaceae being the most species-rich family recording 22% of all the species in the studied area. Tree basal area (1m2ha−1) and volumes (13m3ha−1) were at least 49% lower than national means for dry semi-deciduous forest to which the study sites belong. Based on basal area cover, D.oliveri was the single dominant species. The mean forest condition score was 5.7 and vegetation cover type was largely open forests with less than 2% forest cover. These results suggest the area is highly degraded and the loss of biodiversity may be more significant than previously thought. This would indicate a need for rehabilitation interventions and doubling of conservation management efforts in the area. Three pathways of intervention have been recommended: (a) protecting intact native forest and ecological corridors, and undertaking enrichment riparian plantings to protect waterways, (b) developing agroforestry practices for biodiversity conservation in agroecosystems, and (c) establishing plantations in the severely degraded areas.