Abstract:
The Tropical Rainforest (TRF) is the richest ecosystem in the world. In Nigeria, there are three varieties of this forest—the Lowland Rainforest (LRF), the Mangrove Swamp Forest (MSF) and the Freshwater Swamp Forest (FWSF). However, there is limited information about the vegetation history of the TRF and the antiquity of human occupation and interaction with it during the Holocene. Therefore this research was aimed at reconstructing the Holocene vegetation history of the LRF and MSF in selected sites in SW Nigeria, ascertaining the antiquity of human settlement and appraising human impact on both forests during the late Holocene.
Pollen analyses were carried out on sediment cores from Ogudu, Otolu and Ikorigho where the LRF and MSF still exist, and at Ahanve where only the LRF is present. Anthracological analyses were also carried out to determine the evidence of fire in the cores. Archaeological excavations were conducted on two mounds at Ahanve. These mounds, designated test pit1 (TPI) and 2 (TPII), were 2.1m and 1.1m deep respectively. Ahanve was selected for excavation with a view to ascertaining human antiquity and contributions, if any, to the disappearance of the MSF there. The recovered archaeological materials were classified according to types, decorations and functions.
The plant species in the LRF and MSF of all the sites were abundant and diverse in the Middle Holocene. They were characterised by wet forest taxa including Irvingia gabonensis, Pentaclethra macrophylla, Piptadeniastrum africanum, Rhizophora and Avicennia africana. The inferred climate was warm and wet. During the late Holocene, the LRF was reduced to secondary forest while the MSF drastically reduced in Ogudu at 2620± 30yrs B.P. and in Ikorigho at 1190±30yrs B.P., but it recovered thereafter. No significant reductions in the MSF were noted at Otolu. In contrast, mangroves disappeared from Ahanve at 3109± 26yrs B.P. and were subsequently replaced by secondary forest and coastal savanna. The causative factors for the vegetation changes were climatic, hydrological and salinity changes. A C14 date obtained from layer 130-140cm of TPI indicated human occupation of Ahanve at 360±40yrs B.P. This date does not indicate that humans contributed to the disappearance of mangroves there. Aquatic and terrestrial macrofaunal remains from the excavations included freshwater clam (Anodonta sp), catfish (Clarias gariepinnis), African giant snail (Archachatina achatina), cat-like animals and rodents (Rattus sp.). The occurrence of numerous charred palm kernels and charcoal indicated the utilisation of the oil palm (Elaeis guineensis) fruit for food on the one hand, and use of fire on the other. A high number of pottery, animal remains, iron slag and charcoal particles recovered from levels dated to AD1440–AD1800 suggested intensive human activities at those times. The occurrence of foreign smoking pipes between AD1800 and 1940 suggested that the Ahanve people had contacts, directly or indirectly, with Europeans.
Natural environmental changes were responsible for the reduction in the tropical rainforest during the late Holocene. Human occupation in the study area contributed to this reduction in the historic phase of this period.
Keywords: Holocene, Tropical rainforest, Environmental changes, Palynology, Human settlement
Word count: 493
