Influence of forest fragmentation on tree fragmentation on tree speciesdiversity in the detachment portions of Kakamega Forest, Kakamega County, Kenya

Abstract

Forest fragmentation occurs when large continuous forests are perforated by small holes or broken up into edges and smaller patches to form a non-perforated matrix of open spaces. In various tropical developing countries, the twin pressures of poverty and increase in population are resulting in considerable fragmentation of forests, increasing the probability of extermination of many indigenous species. This results to the need of studying the effects of forest fragmentation on tree species richness and to highlight possible remedial actions. The process of habitat loss and fragmentation is widely considered to be one of the primary threats to global biodiversity. Few studies have analysed the effects of special physical dynamics of a fragment such as egde lenthg, area to edge lenth ratio and new fragment area to original size of forest fragments in determining the efects of fragmentation on tree species. The aim of this study was therefore to assess the diverse impacts of fragmentation on forest habitats by intergrationg the relationship between special land dynamics of a fragement to changes in species ricnhess and diversity along the edge in three fragments of Kakamega forest, Kakamega County in Western part of Kenya. We selected three frgments of the forest namely Malava, Kisere and Ikuywa for field sampling and analysis. A total of 20 plots of 0.04 ha each were randomly placed in each of the habitats whereby all trees with DBH ≥10 cm were inventoried in every plot and the average for the fragment calculated. Shannon-Weaner diversity index was used to analyse species diversity. A total of 39 species of trees were recorded from the three fragmnets with Funtumia africana being recorded as the most abundant species. Of the recorded species, 77.78% were common in the three fragments while 5.56%, 11.11%, and 5.56% occurred exclusively to specific fragments Kisere, Ikuywa, and Malava fragments, respectively. The Ikuywa fragment was significantly rich in terms of species abundance while in terms of diversity, Malava fragment was revealed to be the most diverse of the three at a mean average 3.79 Shannon Wiener diversity index. There was a significant linear correlation between edge density and edge length and species abundance. In summary, the results suggest that the three detached portions do not contrast significantly in terms of tree species richness, diversity, and relative tree abundnce. Moreover, the edge habitats of the three fragments were observed to be characterized by high anthropogenic activities with the edge density and edge length siginificantly affecting tree species diversity and richness respectively. This consequently leads to continued fragmentation as the distance from one forest fragment to another is likely to keep on increasing. The results of this research was important in understanding the ecological effects of the fragmentation in respect to tree species richness and therefore come up with viable recommendations on conservation. Data regarding the fragmentation will also be useful in assessing the potential risk of changes in the weather patterns on the surrounding region.