Study area
Bioko Island lies on the continental shelf and is separated from the Cameroon coast by 32 km of shallow water (60m). Bioko was separated from mainland Africa 10, 000 years ago by the rise of sea level at the end of the last glacial period (Schabetsberger et al. 2004).
A recent study of the geochemistry of volcanic rocks from Bioko dates the main three strato-volcanoes at <1.3±0.07 Ma; K/Ar (Yamgouot et al. 2016). This dating indicates that the sky islands of Bioko (South and North) are very young without difference in age. Furthermore, a central depression with a maximum elevation of 500m separates Pico Basilé (3011m) in the North and the Pico Biao-Moka (2009m) and the Gran Caldera (2260 m) in the South (Schabetsberger et al. 2004). The vegetation of Bioko is arranged in elevational rings dominated by Guineo-Congolian tropical species with Afromontane elements appearing at higher elevations (Fa et al. 2000).
Mainland Cameroon comprises several Afromontane sky islands. In the southwest Mount (Mt.) Cameroon is the highest volcano (4085m) of West Central Africa. In the northeast, Mount Oku is another high peak with an elevation of 3011m. Likewise, Bamenda Plateau and Bambutos Mountains represent the orography of the North region. Mountains from the North Central, such as Mt. Oku and Bamenda-Banso highlands (2260m), uplifted during the Cenozoic (Oligocene to Miocene) (Missoup et al. 2016). Mainland southern volcanoes like Mt. Cameroon are the youngest with origins during the Pliocene to Pleistocene (Zimkus & Gvoždík 2013).
The vegetation is arranged in elevational bands within the montane forest and has been highly disturbed by grazing, fire, and human activities, except on Mt. Cameroon (Ineich et al. 2015).