ABSTRACT
A pollen record from a 22 m sediment core from Lake Elmenteita, reveals the vegetation history of central Rift Valley of Kenya during the last 30,000 years. The record shows a vegetation change at about 8500 yr BP, from one (Zone I) whose pollen assemblage shows mainly open vegetation with relatively little forest pollen transport from the distant highlands to one (Zone II) in which higher percentages of pollen from high altitude forest probably obscures the presence of pollen from lowland woody vegetation. The pollen assemblage in Zone I is dominated by Gramineae. Traces of a few short distance dispersal pollen like Anthospermum, Artemisia and Myrica, especially around 12,200 ± 180 yr BP are evident. This assemblage indicates a continuous period of aridity from before 29,320 ± 1100 yr BP.
The change to Zone II is characterized by a marked increase in the pollen of Podocarpus, Olea, Artemisia and Juniperus, accompanied by slight reductions in Anthospermum and Asteraceae pollen. The change is interpreted as an indication of relatively dry conditions, under which the increase in highland forest taxa may have been due to long distance dispersal from an expanding dry montane forest that obscured the existence of open grassland vegetation of the Rift Valley floor during this period.
