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).