Some environmental effects of small dams on vegetation dynamics; an assessment of Maomokeani reservoir in Kitui west, Kenya

Abstract

Data from transects on the shores and drawdown area of a small reservoir in Kitui, Kenya with a strongly fluctuating water level was used to illuminate a spatial and short-term temporal variation in the vegetation across ecotone-ecocline zones. Sampling and measurements were carried out between the months January 2001 to January 2002. The period was used to capture the vegetation changes in the study area over the bimodal rainfall pattern. The short rains were observed in the months of March to May while the long rains occurred in the months of October to January. Samples of the data obtained aimed at verifying the effects of reservoir waters in influencing vegetation dynamics in terms of distribution patterns, abundance, density and diversity. The terms were analysed with a view of using dominant species in assessing the reservoir's impact on the spatial vegetation distribution, composition and abundance. Dominance is taken to mean the most abundant species interms of numbers and diversity. The species were used in analysing the spatio-temporal variation of vegetation in the reservoir with a view of observation their patterns on ecotone-ecocline gradient basis. The drawdown area provided a characteristic matrix of an ecotone zone with dense perennial species of Echinochloa sp. and Polygonium sp. being common. The area above the drawdown used here to refer to ecocline zone was characterised by woody species interspersed with grass family species. The common species in this zone comprised of Acacia sp., Terminalia brownii interspersed with decreasing number of Echinochloa species. A number of species including Echinochloa sp. Acacia sp. and Terminalia brownii exhibited significant variations in terms of biomass, cover and composition.