Late quaternary vegetation and fire dynamics on Mount Kenya.
Abstract Pollen and charcoal data generated from a 1469 cm core, radiocarbon dated to 26,430  14 C yr BP, recovered from Rumuiku Swamp on the southeast of Mount Kenya, are used to document changes in the distribution and composition of montane vegetation and fire regimes over the Late Quaternary. Throughout the transition from the Last Glacial Maximum (LGM), high resolution (sub-centennial scale) analysis documents a highly dynamic ecosystem and fire regime. The pollen record shows that under a cool, but rather moist LGM climate, Ericaceae and Stoebe species shifted down-slope more than 1000 m relative to the present day. Rather than simple altitudinal lowering of current vegetation zonation, these taxa formed a vegetation assemblage that mixed high altitude components with relatively lowland taxa; in particular Juniperus that is presently found at altitudes lower than the study site, but on the drier side of Mount Kenya. There is noticeable addition and co-dominance of Hagenia to the ecosystem from 20,500  14 C yr BP, until around 14,000  14 C yr BP when a mix of Ericaceous Belt and upper montane forest taxa, such as Artemisia , Polycias , Schefflera and Stoebe , dominated the initial development of montane forest. Reduced levels of Hagenia , Juniperus , Olea and Podocarpus are recorded about the time of the Younger Dryas with highly variable presence of more mesic taxa such as Polyscias and Schefflera . This development of montane forest over the Late Pleistocene to Holocene transition reflects a significant reorganization of the ecosystem composition that was heavily influenced by a variable fire regime. Shifts in vegetation composition reflect the onset of a warmer moist climate from the beginning of Holocene, as mixed montane forest became more established. The latter part of the Holocene registers human impact and forest clearance with increased anthropogenic impact marked by a transition to open vegetation and increased fire frequency.