Topographic influence on Terminalia species diversity in Oluwa forest reserve, Ondo State (Nigeria)

Abstract

Most natural forests throughout the world have been destroyed and converted to human land uses to meet the ever growing demands for resources while the remaining forest landscapes consequently have a mosaic of human-modified land areas such as urban, agricultural, and plantation lands. Forest and forest products provide myriad of economic, financial and health importance. The threat to the rainforest compelled the establishment of forest reserves with the introduction of exotic tree species. The Oluwa forest is located between latitudes 6º37’ and 7 º20’ north and longitudes 4 º27’ and 5º05’ east in Ondo state, Nigeria. Species richness and abundance data are crucial for conservation priority setting, and long-term vegetation monitoring. Few studies have been carried out on the composition of Terminalia spp, diversity and richness in the institutional-based landuse. The aim of this work is to analyze the influence of topography on Terminalia species diversity for conservation purpose. Complete enumeration of the Natural forest was carried out to determine the varieties of Terminalia species in the study site. In all, two variety, Terminalia, superba and Terminalia ivorensis were identified. GPS coordinate their locations was overlaid on Elevation, Slope, Aspect and Hillshad. The area with low elevation, and low slope, high hillshade, and the west aspect showed maximum species abundance. The Shannon diversity index of Terminalia species was calculated and the result implies that the diversity/abundance is low in the study site. It was observed that the spatial distribution and relative abundance of these species was influenced by topographic factors. Despite the limited range of altitudinal variation (399 m), species richness increases with elevation. This work has provided evidence of variability in Terminalia species composition, richness and diversity across the topographic gradient. The information could be crucial for monitoring and providing conservative measure for management of species sustainability. A future study would be required to isolate proximate factors of tree species distribution.