Phylogenetic diversity of the Coastal forests of Kenya: Role of sacred Kaya forests and Red listed species in the conservation of evolutionary history

The remnant forest fragments along the Kenyan coast constitute a globally important biodiversity hotspot, characterized by exceptional species richness and high levels of endemism. However, these ecosystems are increasingly threatened by habitat fragmentation, land-use change, and accelerating species extinctions. Despite their recognized ecological importance, limited understanding of the evolutionary history embedded within these forests constrains the development of effective conservation strategies aimed at mitigating biodiversity loss and sustaining key ecosystem functions. In this study, we assess patterns of phylogenetic diversity across coastal forest fragments in Kenya, examining their relationships with protection status, IUCN Red List threat categories, endemic species, and implications for conservation planning. Using data collected through standardized and intensive vegetation sampling, we calculated multiple phylogenetic diversity metrics, including mean pairwise distance (MPD), mean nearest taxon distance (MNTD), and Faith’s phylogenetic diversity (PD). To evaluate departures from random assembly, we applied null models to generate standardized effect sizes (sesMPD, sesMNTD, and sesPD). Our results provide the first comprehensive insight into the evolutionary history of plant species in Kenya’s coastal forests. We demonstrate that formal forest reserves alone are insufficient to conserve the full breadth of evolutionary history without incorporating sacred forest fragments. Notably, several sacred forests exhibited higher phylogenetic diversity than protected reserves, highlighting their critical role in conserving distinct evolutionary lineages and serving as seed sources for biologically unique species. Connectivity between sacred and protected forests therefore emerges as essential for enhancing dispersal and maintaining evolutionary processes. Furthermore, species classified under higher IUCN Red List threat categories contributed disproportionately to overall evolutionary history, with this contribution increasing with extinction risk. These findings underscore the importance of adopting phylogenetically informed conservation approaches that complement traditional taxonomic metrics and emphasize the protection of threatened species to prevent disproportionate losses of evolutionary history.