Forest-savannah dynamics on the Adamawa plateau (Central Cameroon) during the “African humid period” termination : A new high-resolution pollen record from Lake Tizong

Due to its transitional position, located between the Guineo-Congolian rain forest and the Sudanian savannah, the Adamawa plateau of central Cameroon is ideally situated to record how forest and savannah composition and distribution responded to changes in climate and human interactions during the Holocene. We present a 4000-yr old pollen sequence derived from the Lake Tizong sediments (7°15′N, 13°35′E, 1160m a.s.l) analysed at high-resolution (50year intervals) that extends from the end of the African Humid Period to the present day. The last 4000years represents a critical period for understanding the environmental history of the region as it covers the period when people started to have strong impact on the surrounding ecosystems. The pollen sequence distinguishes two short-duration forested phases that lasted between ca. 3900 and 3000calyr BP, and ca. 1900 and 1450calyr BP; these were against a backdrop of overall forest degradation from the mid-Holocene. A critical ecological threshold occurred around 3000calyr BP when Poaceae reached higher percentages than forest taxa, and savannah was established until the present day with a brief expansion of lowland semi-deciduous forest, dominated by Myrianthus arboreus-type, between ca. 1000 and 700cal. yr BP. Although, human impacts and climatic factors driving vegetation change are difficult to differentiate, the late Holocene on the Adamawa plateau was characterized by a variable climate that resulted in significant vegetation transitions.