Human and Environmental Factors Shape Tree Species Assemblages in West African Tropical Forests

Abstract

Human activities exert a pronounced influence on forest ecosystems, impacting both biodiversity and function across multiple scales. Despite this, the consequences of low-intensity human activities on tropical forest ecosystems are difficult to assess and, therefore, remain poorly explored. Here, the influence of human activities and other site-specific variables on forest tree assemblages in central-west Africa was investigated. By dividing forest tree species into edible (from the perspective of humans) and inedible species, we aimed to assess the differential impacts of human resource use on different species; in particular, the greatest impact of human activity was expected to be seen on edible tree species. Tree data from 66 plots across Nigeria and Cameroon collected between 2002 and 2019 and Generalized Dissimilarity Models (GDMs) were used to assess pairwise beta-diversity between plots, accounting for candidate factors including proximity to human presence, elevation, and stem density. The analysis revealed that human activity significantly affects beta-diversity within the Nigeria-Cameroon forest region. The key variables that shape total beta-diversity included geographical distance between plots, plot elevation, stem density, proximity to human presence, and forest species composition. The forest species composition (monodominant or mixed forest) appeared to influence dissimilarity in beta-diversity, specifically for edible tree species. This pattern was not observed for inedible species, likely linked to the cultural practices in the region. While stem density contributed to the edible species models, elevation was more relevant for inedible species. These findings underscore the critical role of human influence in shaping tree species assemblages in African tropical forests and stress the necessity for further research in this area.