VEGETATION COMPOSITION, REGENERATION AND ANTHROPOGENIC DISTURBANCES IN WESTERN MAU FOREST, KENYA

Abstract

Western Mau Forest is located at an altitude of 2,000 and 2,600 m and between the latitudes 00 10’ 46” S to 00 17’ 42” S and longitudes of 350 27’ 05” E to 350 39’ 42” E. It was originally 22,712 ha, but has been subjected to human encroachment such that it is now 21,676 ha. Tree harvesting was banned and any human population moved out of the gazetted forest land in 1987. A study was carried out between 2011 and 2012 on vegetation composition, regeneration and anthropogenic disturbances in the forest. The study sites were divided into three zones; forest, transition and grassland zones. Belt transects of 500 m long and 2 m wide were used in the forest zone; plots of 30 m long and 5 m wide were used in both in transition zone and grasslands. The forest zone transects were subdivided into 50 m by 2 m subplots, transition and grassland zone transects were subdivided into 5 m by 5 m subplots. In all subplots, a 1 m by 1 m quadrat was placed at the centre. Data were collected on occurrence of herb, fern, liana, shrub, seedling, sapling (DBH 1-9.9 cm) and tree (DBH ≥ 10 cm) species. The data were used to calculate abundance, diversity, importance value index, and regeneration. The data were analyzed using analysis of variance and chi-square statistic. Shannon-Weiner index was used to quantify species diversity. Two hundred and twenty three (223) vascular plant species belonging to eighty three (83) families were identified. The Asteraceae had the highest number of species (18) followed by Fabaceae (17). Forty (41) families had a single species each. There were more plant species in the transition zone than forest and grassland zone. The forest was dominated by seedlings and saplings (DBH ≤ 3 cm); the diameter size distribution was reverse J-shaped, indicating that the forest has a good regeneration potential. Species diversity was significantly higher in the forest (3.5 to 4.5) than transition zone (2.0 to 3.5) or grassland (1.5 to 3.0). There was a significant human disturbance and this affected the species composition, diversity and forest regeneration.