Revisiting Oligo-Miocene epoch through the altitudinal patterns study of plant species and phylogenetic diversity of Mt. Elgon in Africa

The variation in patterns of plant species distribution has been of interest to naturalists and ecologists. However, African mountains remain nature's laboratories least explored. This study aims to identify the altitudinal pattern of plant taxonomic and phylogenetic diversity, and community structure of Mt. Elgon, which is an isolated ancient volcanic mountain of the Oligocene-Miocene epoch in Africa, hosting a rare species pool. Species diversity data (1606 species) was obtained through random walk field surveys, herbaria collections and online data-bases. We calculated Faiths' phylogenetic diversity and its standard effect size (SES_PD), net related index (NRI) and nearest taxon index (NTI) among its four vegetation zones, six habitats and 28-100m elevation bands. Our results indicated that herbaceous plants had higher species richness than woody plants and they both assumed a monotonic decline pattern among vegetation zones, and a hump shaped pattern among habitats and 100m elevation bands. However, standardized phylogenetic diversity and structure (SES_PD, NTI and NRI) pattern differed and fluctuated between woody and herbaceous plants demonstrating a zigzag pattern. Mid-elevation phylogenetic overdispersion structure was observed based on NRI (clade level), while phylogenetic clustering progressively increased with elevation in NTI (taxon level). The complex phylogenetic diversity and structure in this study indicate a unique ecosystem worth conservation and more scientific exploration. Consequently, we recommend regions of phylogenetic over -dispersion structure for priority conservation.