Assessment of recent changes from Kara community of Ogun State, South-Western, Nigeria: Inferences on Paleo Vegetation and Paleoclimate
Olusola Helen Adekanmbi, Okwong John Walter, Balquees Titilayo Jimoh
A 150 cm long sediment core from Kara community in Ogun state was studied to infer Holocene palaeoenvironmental and climatic change during the last 3610 years using fossil pollen, spores, and particle size. Late Holocene sediments were radiocarbon dated and subjected to standard palynological procedures. These analyses yielded palynomorphs which include pollen of Elaeis guineensis,Alchornea cordifolia, Tridax procumbens, Cyperus sp., Symphonia globulifera, Dryopteris sp., Fungi spore,etc. At 3610 yr B.P., the estuary was a brackish-water. By 1470 yr B.P., Poaceae (grass) pollen increased to high levels, suggesting that the rising level of the core site led to its colonization by Zea Mays (corn), the lowest-elevation plant type within regional estuaries. An increase in pollen and spores of moisture dependent species suggests a climate with more available moisture after 2600 yr B.P. This change is similar to that found at 106 yr B.P., implying that regional climate changes were time transgressive from west to south. Increased post settlement sediment input resulted from nineteenth-century land disturbances caused by farming, dredging, grazing and fire. Sedimentation rates increased further in the twentieth century due to closure of the estuarine mouth. The endemic Arecaceae family was present at the site throughout this 3610-yr interval but was less numerous prior to 1470 yr B.P. This history may have contributed to the low genetic diversity of this species and the disappearance of majority of the parent plants of the recovered palynomorphs.