Floristic diversity in fragmented Afromontane rainforests: Altitudinal variation and conservation importance

Question How does the floristic diversity of Afromontane rainforests change along an altitudinal gradient? What are the implications for conservation planning in these strongly fragmented forest areas that form part of the Eastern Afromontane Biodiversity Hotspot? Location Bonga, southwestern Ethiopia. Methods Based on evidence from other montane forests, we hypothesized that altitude has an effect on the floristic diversity of Afromontane rainforests in southwestern Ethiopia. To test this hypothesis, detailed vegetation surveys were carried out in 62 study plots located in four relatively undisturbed forest fragments situated at altitudes between 1600 m and 2300 m. Floristic diversity was evaluated using a combination of multivariate statistical analyses and diversity indices. Results Ordination and indicator species analyses showed gradual variations in floristic diversity along the altitudinal gradient with a pronounced shift in species composition at ca. 1830 m. Upper montane forest (> 1830 m) is characterized by high fern diversity and indicator species that are Afromontane endemics. Lower montane forest (< 1830 m) exhibits a greater diversity of tree species and a higher abundance of the flagship species Coffea arabica. Conclusions Our results provide crucial ecological background information concerning the montane rainforests of Ethiopia, which have been poorly studied until now. We conclude that both forest types identified during this study need to be considered for conservation because of their particular species compositions. Owing to the high degree of forest fragmentation, conservation concepts should consider a multi-site approach with at least two protected areas at different altitudinal levels.