Reconstruction of a subalpine grass-dominated ecosystem, Lake Rutundu, Mount Kenya: a novel multi-proxy approach
Palaeoecological reconstructions based on a single proxy are limited, but by combining pollen, biogeochemistry and grass cuticle analysis, ecosystem structure and function can be better understood. Lake Rutundu is a small, subalpine lake on the northeast flank of Mt Kenya. During the last glacial, pollen evidence suggests a shrub grassland dominated by Afroalpine taxa and Poaceae, representing a dry, cold, open environment. The δ13C values of terrestrial biomarkers imply a high proportion of C4 plants. Grass cuticle analysis allows resolution of the different C4 subtypes and shows that the vegetation was dominated by tall C4 panicoid grasses, prone to frequent fires. During the Holocene, Poaceae pollen declined while subalpine shrubs increased. The δ13C values of terrestrial biomarkers imply a C3-dominated vegetation. Together with an expansion of rainforest at lower altitudes, this suggests wetter conditions more favourable to C3 plants. Increased percentages of C3 pooid grass cuticles confirm a reduction in moisture stress.