Using a multifaceted approach to reveal avian community responses to natural and anthropogenic effects in a fragmented Southern Mistbelt Forest system, South Africa

Context Forest loss and fragmentation are major drivers of biodiversity decline globally. However, with the widely recognised notion that biodiversity is multifaceted, few studies have assessed the responses of different diversity metrics to forest landscape changes. Objectives Here, we used a multifaceted approach to assess the effects of landscape composition, forest fragmentation (patch-level) and local habitat heterogeneity on avian alpha-diversity (taxonomic, functional, phylogenetic and functional-phylogenetic diversity) of different ecological groups. Methods We conducted fixed-radius point-count surveys across 32 Southern Mistbelt Forest fragments of southern KwaZulu-Natal and northern Eastern Cape, South Africa. Using linear mixed-effect models, we related multiple facets of bird diversity to landscape composition (i.e., matrix quality), habitat fragmentation (i.e., isolation distance and fragment-size) and local habitat heterogeneity (i.e., forest-structural complexity). Results Matrix quality was a significant positive predictor of functional (FRic, sesFRic) and phylogenetic (sesPD) diversity of forest-dependent (forest specialist) species and functional diversity (FRic) of the whole community. Habitat fragmentation had significantly negative effects (i.e. increasing isolation distance and decreasing fragment size) on multiple diversity facets of all ecological groups, but non-forest-dependent (forest generalist) species showed no responses to isolation distance. Unexpectedly, diversity facets of forest-dependent species declined with increasing local vegetation complexity. Conclusions Large and connected forest fragments are vital for maintaining avian diversity facets and promoting local vegetation complexity could contribute to the loss of forest-dependent species (forest specialists) in the naturally fragmented Southern Mistbelt Forests.