SOIL CARBON ISOTOPE EVIDENCE FOR HOLOCENE HABITAT CHANGE IN THE KENYA RIFT-VALLEY

In eastern Africa the altitude of the boundary between montane forest and lowland savanna grassland changed substantially in response to climate change during the later Holocene, but this is not clearly reflected in regional pollen records. The carbon-13 to carbon- 12 ratios of tropical grasses are higher than those of most other plants, and this difference is preserved in soil organic carbon stable isotope ratios. Soil organic matter C-13/C-12 ratios in profiles along an altitude transect in the central Rift Valley of Kenya suggest that the forest-savanna boundary advanced more than 300 meters in altitude. This could have implications for understanding the effects of climate change on the configuration of floral zones, prehistoric hunter-gatherer land-use patterns, and the timing of the advent of Neolithic food production.