An Investigation of Forest Ecosystem Health in Relation to Anthropogenic Disturbance in the South-western Mau Forest Reserve, Kenya

Abstract

The dissertation describes investigations carried out from September 2005 to August 2006 to assess forest ecosystem health in relation to human disturbance in the South-western Mau forest reserve Kenya. The study involved the determination and comparison of tree species composition and structure, regeneration potential and capacity, litter production and nutrient fluxes between disturbed and undisturbed sites. A socioeconomic appraisal of the inhabitants was also carried out. Forest cover change analysis of the greater Mau forest was done for the period between 1984 and 2003 using Landsat satellite images. A total of 24 families, 34 genera and 37 woody species comprising mainly trees were enumerated. There were 20 families in the undisturbed sites while 21 were present in the disturbed sites. In undisturbed sites, 30 species belonging to 29 genera were recorded while 29 species from 27 genera were tallied in the disturbed sites. The mean species richness was higher in the disturbed sites. Undisturbed sites had a lower proportion of shrubs and under storey trees with a higher frequency of over storey trees. Both sites had high number of seedlings and wildings. Regarding survival and recruitment from seasonal seed rain, disturbed sites had significantly higher mean species richness. Germinations from seasonal seed rain indicated higher mean seedling species richness in disturbed plots while seedling density was significantly higher in undisturbed plots. No significant mean differences in species composition were recorded from the seed bank trials. A higher amount of fine litter was collected in disturbed plots with insignificant mean differences with regard to K, C and N content between the sites. There were no significant mean differences in the C: P, ratios whereas undisturbed plots had significantly lower mean C: N ratios. Within stand mean nutrient use efficiency for C, N, P, K, and Ca were lower in the undisturbed plots.Survey results indicated that several tree species that were once common or dominant in the area were increasingly becoming rare. Increase in human population, firewood collection, agricultural expansion, land subdivision among others were ranked as important causes of forest degradation. Positive significant correlations were reported between the definition of provision of services, forest condition, provision of goods, the adequacy of goods provided and ecosystem health. However, a significant negative correlation was reported for the values attached to the current land use. The presence of disturbance indicator species like Neoboutonia macrocalyx, Croton megalocarpus and Vernonia auriculifera in the vegetation community indicates considerable levels of human disturbance in the reserve representing retrogression in the vegetation succession. The vertical stratification of the forest reserve depicts secondary growth in the reserve. The potential for natural regeneration of trees after natural or anthropogenic disturbance exists despite a poor soil seed bank. High litter annual turn over in disturbed sites, coupled with lower nutrient content and nutrient use efficiency as well as higher fine litter C: N and C: P ratios defines them as poorer sites. A chronological degradation in the condition of the forest over time is apparent with current land uses having negative significant effects. Thematic change and image difference analysis indicated a significant change in closed canopy forest.