Effect of human disturbance and climatic variability on the population structure of Afzelia africana Sm. ex pers. (Fabaceae–Caesalpinioideae) at country broad-scale (Bénin, West Africa)

Abstract

Anthropogenic disturbances and climatic variations are presumed to alter species population structures. In this study, we assessed the population structure of the endangered species, Afzelia africana across gradients of climate and human disturbances. Dendrometric variables such as regeneration and tree density, mean diameter, basal area and height and stem diameter distribution were recorded at national scale in forest reserves located in three different climatic zones in Bénin. A canonical discriminant analysis was applied to describe the species' population structure across climatic zones and disturbance levels. Relationships between the principal components (structural parameters of A. africana stands) and climatic variables and disturbance levels were assessed using Pearson correlation. Significant differences were found in the structural parameters between the disturbance levels, mostly in the Guinean zone. Structural parameters also differed significantly across the three climatic zones, with the Guinean zone recording the highest values. The effects of disturbance levels on structural parameters depend on the climatic zone, and vice versa. The results imply an interaction between climatic zones and disturbance levels. In the Guinean zone, the tallest and biggest trees were found at the low disturbance level. However, along the climatic gradient (towards drier regions), trees were shorter and smaller irrespective of disturbance level. Further, the tallest and biggest trees were found at lower altitudes.