Vegetation structure and composition of the Taita Hills Forests

Abstract

The structure and composition of the indigenous forest fragments of the Taita Hills of south-east Kenya were analysed. We collected data in all of the large forest fragments using Point Centred Quarter extensive surveys, supplementing these data with intensive surveys of 20 x 20 m plots. Our structural data on basal area per unit area, stem density, canopy cover, shrub density, stratification and extent of herbaceous ground cover clearly show that the largest fragment, Mbololo, is also the least disturbed. The next largest fragment, Ngangao, has suffered from intermediate levels of disturbance, and all other fragments have been very heavily impacted. Tree size class distributions show that nearly all of the large circumference trees have been lost from the smallest fragments, while the Chawia forest is selectively losing its small, easily-cut trees. Finally, we mapped the Importance Values (combined standard measures of abundance, biomass and dispersion) of each forest's tree species. The map indicates the forest biogeography of the region but also shows the extent to which all of the fragments except Mbololo and Ngangao are dominated by a very few secondary successional sub-canopy species. Only Mbololo and Ngangao may be viable forests in the long term.Journal of East African Natural History Vol. 87 (1&2) 1998: pp. 181-187