Vulnerability of montane forests of Cameroon in the face of climate change: Insight from the last glacial-interglacial transition

Aim

Afromontane forests of Cameroon are part of the West Africa Biodiversity Hotspot. Often located within or on the fringes of densely populated regions, they are currently highly threatened by the combined effect of climate change and of anthropogenic pressure. In order to provide bases for their conservation and management this article aims at studying the turnover of species and in particular the behavior of Podocarpus milanjianus/latifolius during the last glacial-interglacial transition, a period characterized by dramatic shifts in climatic conditions.

Location

Cameroon highlands, Lake Bambili, Lake Mbi, Lake Child and Lake Monoun.

Methods

Pollen analyses.

Results

The expansion of the post-glacial Afromontane forest took place in two main stages, coinciding with periods of increased precipitation. The first phase of development dates back to 14.5 ka. It was interrupted by the dry event of the Younger Dryas (YD) starting at 12.5 ka. The Afromontane forest then resumed its expansion from 11.5 ka, reaching its optimum between 9.8 and 8.5 ka. This was characterized by the massive expansion of Podocarpus in the northern sector of the Cameroon Volcanic Line (CVL) (Bambili, Mbi, Monoun). In the southern sector, closer to the coast, on the other hand, Afromontane forest elements declined in favor of sub-montane elements during the Holocene (Child).

Main conclusions

(i) Podocarpus experienced significant changes in abundance/extent within the current Afromontane forest belt during the post-glacial forest transgression. It was a fast colonizer in open and floristically poorly diverse areas where it benefited from the absence of competitors. In contrast, it has been a weak competitor within the Afromontane forest itself compared to more dynamic and fast dispersing tree taxa. (ii) The forest optimum was reached during the early Holocene, after a long period of gradual forest expansion characterized by a high turnover of species; (iii) Migration and stabilization times of the forest environment can be evaluated in centuries, even millennia, that has important implication for forest management.