Effects of a native, dominant tree, Colophospermum mopane, on diversity of plants, insects, and vertebrates in South African savannas

Abstract

Afrotropical savannas are biodiversity-rich ecosystems increasingly threatened by woody plant encroachment. In southern Africa, the leguminous tree Colophospermum mopane dominates over one-third of the savanna region and is projected to expand substantially under climate change. Yet, the consequences of its local dominance for biodiversity remain poorly understood. We conducted the first landscape-scale, multi-taxon assessment of mopanes bottom-up effects, analysing species richness and community composition of vascular plants, insects, birds, bats, and non-flying mammals across a gradient of mopane cover in Kruger National Park, South Africa. Our replicated plot-based study found that species richness of birds, mammals, bats, and insects declined significantly with increasing mopane dominance, with the steepest reductions in birds. Plant overall species richness was unaffected, although grasses showed a weak positive trend. We also revealed significant community compositional shifts in birds, bats, and mammals, while insect communities lost species without systematic composition change. Functional-group analyses confirmed species richness declines for herbivores across taxa, and for bird carnivores and omnivores, pointing to mopanes role as a strong ecological filter that reduces host plant and other resources availability, with consequences to the higher trophic levels. These results highlight mopane dominance as a potential driver of biodiversity simplification in African savannas, with cascading implications for ecosystem functioning. Given projections of mopane expansion and its socioeconomic value to local communities, management and policy must avoid promoting mopane dominance in land-use or restoration schemes. Safeguarding heterogeneous savanna mosaics will be essential for conserving biodiversity and ecosystem resilience under climate change.