Mining matrix effects on West African rainforest birds

Globally, relatively low-contrast matrices are being converted to high-contrast through increases in land uses such as surface mining. Such conversion affects biodiversity not only at the impact site, but also potentially in adjacent remnant habitat, particularly for habitat types such as tropical rainforest. We investigated how the species richness of different functional groups of tropical rainforest birds varied in remnant rainforest patches embedded in two matrix types (mining vs. agricultural) at two distances to forest edge in fragmented Upper Guinean rainforest landscapes of southwest Ghana. We hypothesized that rainforest adjacent to high-contrast surface mining would support a relatively lower richness of forest-dependent birds than that adjacent to a lower-contrast agricultural matrix. Data from six point counts at each of 32 study sites were used to estimate species richness within ten avian functional groups based on (a) habitat preference (forest specialists, generalists, forest visitors, open country species); and (b) food preference (carnivores, frugivores, omnivores, nectarivores, insectivores and granivores). Species richness of each group was modelled as a function of adjacent matrix type, distance to patch edge and site-level vegetation characteristics using generalized linear mixed-effects models. Forest specialists and frugivores were most strongly negatively affected by adjacent mining, irrespective of distance to forest edge. Forest visitors were more common in forests adjacent to agriculture than mining, and they preferred edges to interior habitats. Forest specialist and frugivore richness also correlated positively with the density of large trees. This effect of a high-contrast matrix on forest birds suggests that even with no additional forest loss, increased surface mining in the Upper Guinea region is likely to result in population declines in forest-dependent birds. Preserving biodiversity in forest landscapes will require management of matrix quality. The widespread trend of increasing patch-matrix contrast from land use change in the matrix is likely to result in negative consequences for biodiversity in fragmented tropical forest landscapes.