Disturbances and species distribution of the riparian vegetation of a Rift Valley stream

Abstract

The Njoro River riparian vegetation species composition, distribution, disturbances and uses are presented and discussed. Montane Juniperus procera‐Olea europaea spp. africana and submontane Acacia abyssinica forests were identified as the main riparian vegetation groups. Approximately 55% of the riparian vegetation species are used for herbal medicine, treating more than 330 health problems, and only 11% of the plants are edible. Albizzia gummifera in the Syzygium cordatum‐Pittosporum abyssinicum‐Hibiscus diversifolius forest is cut selectively for herbal medicine preparations. Disturbances on the riparian vegetation zone are broadly classified as those induced by man, livestock and wildlife. Comprehensive effects of disturbance included loss of vegetation vertical strata, increase/decrease of species diversity, introduction of alien plant species, and reduction of plant sizes and vegetation hectarage. The effects of grazing on the vegetation were severe around livestock watering points. Grazing and browsing by wildlife were the main disturbances of the vegetation near the Njoro River estuary at the Lake Nakuru National Park. Periodic flooding, as a natural disturbance, regulates growth and survival of vegetation at the Lake Nakuru drawdown. Quantification of species diversity and the extent of disturbance by humans and livestock is important for future management of the vegetation and, consequently, the river.