A contribution to the Holocene vegetation history of Nigeria: Pollen from Ohe Pond Nsukka, southeastern Nigeria

摘要

The pollen record from Ohe Pond (N 06° 50.156, E 007° 21.837) in Nsukka, Enugu State, southeastern Nigeria, provided strong evidence of existence of a Southern Guinea savanna in the mid-Holocene. Prior to 6417 ± 67 BP, there was a closed forest with strong Guinea savanna affinities with a more humid condition. However, after 6417 ± 67 BP, Southern Guinea savanna woodland became well established in the area. Considerable periods of high precipitation alternating with warm and dry climatic phases may have favoured the establishment and maintenance of this complex heterogeneous vegetation structure after 6388 ± 71 BP. Frequent natural fires, indicated by charred plant tissues throughout the mid Holocene, probably were important in promoting the expansion of savanna species in the vegetation. Furthermore, human impact associated with iron smelting from about 4005 ± 40 BP in the area may have contributed to depletion of the forest vegetation. The transition from the Southern Guinea savanna to derived forest-savanna mosaic vegetation became apparent at a latter part of the late Holocene around 1470 ± 79 BP. Although climate may have played a significant role in shaping the structure of the vegetation, human activities certainly played an important role in the late Holocene vegetation transformation.