Holocene pollen deposits and recent vegetation distribution of Obayi Lake,Nsukka

摘要

The palynological analysis of a core (116 cm) from Lake Obayi, Nguru, Nsukka yielded 78 pollen types belonging to 47 families. The results showed that discemable changes occurred in vegetation from 1845 ± 41 BP. Four pollen zones showing possible changes in vegetation were distinguished. Zone I was characterized by a considerable presence of forest species in association with some savanna components. The appearance of Podocarpus in this zone coincides with the decrease in Poaceae and ferns. There was no visible change in vegetation between pollen zone I and II. Zone III was marked by an expansion of savanna species and increase in human activities as indicated by agricultural activities. Savanna vegetation became abundant but never completely displaced the secondary forest species. In zone IV, there was a recovery of forest species although there was still a clear dominance of the savanna flora. The pollen diagram in general reflects a history of gradual transition from a forest dominated vegetation to that of mosaic lowland rainforest and secondary grassland, which became more pronounced after 1845 ± 41 BP. The frequent lowering of the lake level and the sudden disappearance of Podocarpus points to increasing drier environmental condition upwards. Human impact which became more prominent after 1845 ± 41 BP contributed to the vegetation change. The impact of climate on the vegetation must have been accentuated by the increase in human activities in the area.