Late Quaternary fires and grassland palaeoecology of Mount Kenya, East Africa: evidence from charred grass cuticles in lake sediments
Abstract Multi-proxy evidence from Sacred Lake on Mount Kenya, including pollen and compound-specific carbon isotope data, indicates grassland expansion at the Last Glacial Maximum (LGM, circa 18,000 14C years BP), but lacks the taxonomic resolution with which to derive ecological inferences about past grasslands. Analysis of grass cuticles preserved in East African lake sediments is presented here as a palaeoecological tool for addressing this problem. Sub-fossil grass cuticles retain micro-morphological features that often permit identification to subfamily, supertribe, tribe, and in some instances genus or species level. A method for isolating and identifying this novel resource is presented, along with an analysis of Late-Quaternary to recent-age sediments from Sacred Lake, Mount Kenya. Data derived from 43 sediment samples and over 5000 graminoid cuticles support isotopic evidence for the presence of grasslands at Sacred Lake during the LGM. Size-class analysis of charred graminoid fragments indicates that relatively local, low-intensity fires occurred throughout the sequence. Current autoecological understanding of the taxa identified indicates that the grassland present at the LGM possessed specific adaptations to burning. We conclude that fire was an important landscape feature on Mount Kenya, reinforcing the impact of past variations in climate and atmospheric CO2.