Vegetation types and diversity in Menegai caldera geothermal project area, Kenya

Abstract

The study was aimed at documenting the vegetation types in the Menengai Caldera. Line transects were established in each forest type and used as baseline upon which sampling plots were located. Plots of 20x20 m were placed at intervals of 50 m and marked along the transect and used to quantify species distribution patterns and vegetation dominance. Each block was divided into 4 (10x10 m) small plots within which vegetation parameters were determined. In each 10x10 m plot, all flowering plant species were enumerated. In addition, data on density, height and basal area of trees over 5 cm in diameter at breast height was estimated. The degree of forest or woodland cover was recorded on a five-point scale for three life forms i.e. trees, shrubs and herbs. The Daubenmire Cover Scale: 1:0-20%, 2:21-40%, 3:41-60%, 4:61-80% and 5:81-100% was used for determination of species population densities and frequencies. Species uniqueness (endemism, rarity, threat i.e. vulnerable, endangered) was analysed through literature review, voucher specimens and databases at the EA Herbarium. Plant species diversity for the first five plant community types was analysed using Shannon’s Diversity Index (H’=Σ Pi Ln Pi). Species Evenness analysed using Shannon’s Evenness Index (E=H’ / H Max).

Overall, 186 different species of plants were recorded in Menengai Caldera with a vegetation cover density range of between 15% and 65%. The caldera floor is classified into 8 plant communities. There were no endemic, rare or new plant species recorded in this study, though certain tree species like Rubus steudueri and Rubus apetalus are recognized Montane forest species which were recorded in Madrugada farm. This suggests that conservation of these areas is vital. In this regard, efforts are required to conserve the forest and mitigate potential impacts from the ongoing geothermal exploration project in Menengai caldera