Spatial incongruence among hotspots and complementary areas of tree diversity in southern Africa

Aim: Biodiversity hotspots have important roles in conservation prioritisation, but efficient methods for selecting among them remain debated. Location: Southern Africa. Methods: In this study, we used data on the dated phylogeny and geographical distribution of 1400 tree species in southern Africa to map regional hotspots of species richness (SR), phylogenetic diversity (PD), phylogenetic endemism (PE), species endemism (CWE), and evolutionary distinctiveness and global endangerment (EDGE). In addition, we evaluated the efficiency of hotspots in capturing complementary areas of species richness and phylogenetic diversity. We examined the spatial overlap among hotspots for each metric, and review how well one metric may serve as a surrogate for others. We then evaluated the effectiveness of current conservation areas in capturing these different facets of diversity and complementary areas. Lastly, we explored the environmental factors influencing the distribution of these diversity metrics in southern Africa. Results: We reveal large spatial incongruence between biodiversity indices, resulting in unequal representation of PD, SR, PE, CWE and EDGE in hotspots and currently protected areas. Notably, no hotspot area is shared among all five measures, and 69% of hotspot areas were unique to a single diversity metric. Areas selected using complementarity are even more dispersed, but capture rare diversity that is overlooked by the hotspot approach. Main conclusions: An integrative approach that considers multiple facets of biodiversity is needed if we are to maximise the conservation of tree diversity in southern Africa.