Impacts of indigenous and exotic tree species on ecosystem services : Case study on the mountain cloud forests of Taita Hills, Kenya
Year: 2012
Type: dissertation
Abstract: Although forest ecosystems are crucial for human survival they are constantly under threat from human interventions and natural disasters which reduce their capacities to effectively provide ecosystem services. As populations increase, incidences of forest encroachments become frequent to affect the provision of the services. The objective in this study was to assess some ecosystem benefits and to determine how the local communities used and value them. The benefits assessed were floristic diversity; biomass and soil organic carbon densities; and suitability of indigenous tree species for forest rehabilitation based on soil properties in four different forest types, indigenous and plantations of cypress, eucalypt and pine in Taita Hills, Kenya. The perceptions of local community regarding how they use and value these benefits were also assessed. The conceptual framework was based on the Millennium Ecosystem Assessment. Sampling design was based on a US Forest Service model used in the indigenous forests. For each forest area and forest type, a minimum of four plots were randomly selected and a total of 77 plots from 38 groups were sampled. In each plot, all juvenile trees of 5 cm or more in diameter at breast height were sampled for floristic diversity, biomass carbon stock and vegetation-soil relationship assessments. Soils were sampled at, 0-20 and 20-50 cm, for chemical and physical analyses to determine the soil organic carbon densities and vegetation-soil relationships. Tree species diversity, carbon densities derived from biomass and soil data were analyzed quantitatively. A qualitative analysis was done for the socio-economic part of the study, from data obtained using selected participatory rural appraisal tools and semi-structured questionnaires. Biodiversity analyses were accomplished using the Shannon-Weaver s Index. to assess the tree species composition. Tree biomass was estimated from allometric functions developed for tropical forests while soil organic carbon stocks were computed as a product of the analyzed carbon contents and bulk density values estimated using a pedotransfer function and measured particle size. Soil-vegetation relationships were determined by Principal Component Analysis, using CANOCO 4.5 software. The statistical analyses were accomplished by use of three versions of SPSS software for Windows (15, 16 and 20). The study established that indigenous forest was more diverse than plantations and regeneration of indigenous species significantly higher in exotic plantations of the most disturbed area than in the less disturbed areas. Some indigenous species correlated with sodium, phosphorus, carbon, pH and soil texture while some had no correlation with soil variables. Factors unrelated to soil variables, namely gaps were found to be important for the emergence and early establishment of seedlings. Total biomass C densities were generally higher in indigenous forest than in some exotic plantations, especially the cypress. Indigenous forest also had higher soil carbon stocks than plantations of exotic species. Community survey showed perceptions that exotics plantations contributed reductions of the forests to provide water and medicinal plants. Therefore, they are motivated to rehabilitate the forest by planting indigenous tree species. This study concluded that indigenous forest valuable for ecosystem services and that soil-vegetation relationships established be utilized along with soil analyses to select indigenous species to be planted in certain areas for rehabilitation. Such rehabilitation will enhance the floristic diversity and carbon sequestration and storage and therefore, contribute to restoration of the ecosystem services. Therefore, the initiated reforestation exercises with indigenous tree species to replace the exotic tree species are well justified. Key Words: Floristic diversity, biomass, carbon stocks, plantation, indigenous forest, Principal Component Analysis
Source: Työväentutkimus Vuosikirja
Author: Loice M.A. Omoro
Language: English
Subfield: Forestry
Domain: Life Sciences
SDG: Life on land
Open Access status: green
OpenAlex ID: W2110091162