Degradation and Fragmentation Effects on Structural Complexity in West-African Forest Patches

Abstract

Tropical forests face alarming rates of deforestation and degradation, driven mainly by agricultural land expansion. West Africa is particularly affected by widespread forest fragmentation, leaving behind isolated forest patches in an agriculture-dominated landscape. Forest fragmentation and isolation can impact forest structural complexity, biomass, and species richness through various edge effects. The consequent loss of biodiversity and ecosystem services is expected to be more prominent in small and fragmented forests and closer to forest edges. We used terrestrial laser scanning to investigate patterns of forest structural complexity in 84 plots across seven forest patches in Togo, Benin, Nigeria, and Cameroon. We quantified forest structure using the stand structural complexity index (SSCI) and related it to tree species composition, distance to edge, and the modeled potential SSCI of primary forests as an ecological reference value to identify forest degradation. Spatial variability of SSCI within forest patches and plots indicates various areas of disturbance, ultimately accumulating to forest degradation. The overall trend suggests an increase in structural complexity, tree height, basal area, and tree species richness with increasing distance to the edge. However, these correlations were only significant for some of the forest patches analyzed. Comparison with the ecological reference value showed significant deviations for two forests, indicating degradation of forest structural integrity. Our results confirm and challenge theories of ecological dynamics in tropical forest patches in West Africa. Quantifying structural integrity helps to locate degradation and preserve the last remaining forest patches crucial for biodiversity, climate regulation, and forest products.