Assessment of plant diversity, community structure and impacts of human activities in Mt. Marsabit forest, Kenya

Abstract

Mt. Marsabit forest is located in Marsabit district, northern Kenya. It is the main water catchment for the nearby Marsabit town and the immediate environs. It is also an important refuge for several endemic, rare and threatened species. Plant species diversity, community structure and impact of human activities were undertaken to inform its conservation and sustainable utilization of the forest resources. Three transects of 18 x 1.2, 12 x 1.2 and 5 x 1 km2with 400 x 400 m quadrats were laid out at different parts of the forest. Randomly distributed 154 sample plots of 20 x 5 m were used for the assessments. In each plot, all trees, shrubs, herbs, climbers and lianas were identified and enumerated. The numbers of individuals of each tree and shrub species were counted. The height and dbh (2::5 cm dbh) were measured to determine community structure. The following values were calculated for each tree and shrub species; relative density, relative frequency, relative dominance and importance value index. Diversity was determined using Shannon-Wiener and Simpson's diversity indices. Indicators of human activities in the forest and wildlife disturbance were observed. A total 'of 70 species were sampled, of which, 52 species were trees and shrubs, .12 were herbs and 6 were climbers. Rinorea convallaroides (8ak.f.}' Eyles ssp. marsabitensis Grey-Wilson (Violaceae), an endemic and rare species, and Drypetes gerrardii (Hutch.) (Euphorbiaceae), were the two most important species. Their dominance led to low species diversity in the forest. Several species of ecological concern were also found. Diversity was 2.735 (Shannon-Wiener), 0.880 (Simpson's) and 0.296 (Evenness). The structure had five strata corresponding to that of the Kenyan natural forest. There was variation among and within transects and eight plant species associations were identified. These were; Croton dichogamous community, Strychnos henningsiilTeclea simplicifolia association, Orypetes gerrardii/Rinorea convallaroides association, Cassipourea malosana community, Croton megalocarpus/Olea europaea association, Orypetes gerrardii community, mixed forest species and secondary forest species community. Profile diagrams were established for each association. There was strong evidence of overgrazing, destruction by wild herbivores and human extractive activities. In order to reduce further degradation of the forest, it is recommended that the forest adjacent communities be made aware of the appropriate agroforestry technologies and sustainable utilization of the forest. Creation of woodlots of indigenous species from Mt. Marsabit forest should also be introduced. This will provide timber, fuel wood, medicine and fodder to the people living around the forest.