Assessment of Tree Diversity and Abundance in Selected Forest Reserves in Osun State, Southwestern Nigeria

摘要

Studies have shown that forest has undergone different levels of disturbance due to anthropogenic activities which impacted tree diversity, abundance and species composition. Therefore, this study examined and assessed tree diversity and abundance in five selected forest reserves in Osun State, Nigeria with a view to ascertaining the present species status for mitigation decision. Primary data include measurement of floristic composition and Key Informant Interview (KII) focusing on species inventory. A total of five sampled plots of 10 m × 10 m were demarcated in each five selected forest reserves where total enumeration of tree species within the demarcated plots were identified and classified into families, while parameters like girth (diameter at breast height) and height were measured. The result showed that the maximum height in all the selected forest reserves was 15 m. The highest total number of individual woody tree species was found in Oba Hill Forest Reserve (112). The dominant tree species were exotic species, teak (Tectonagrandis) (98 stems) and gmelina (Gmelinaarborea) (36 stems) of verbanaceae family. Indigenous woody species identified to be highly threatened and at the brinks of extinction include Terminalia Africana, Albiziazygia, Miliciaexcelsa, Anogeissusleiocarpus etc. The Shannon-Wiener index (2.499) from Ikeji-Ipeu Forest Reserve was the highest among the five selected Forest Reserves which indicated that this forest was potential biodiversity hotspot. The highest mean basal area of 3.37 m3 and highest mean volume of 27.96 m3 both from Oba Hill Forest Reserve showed that matured woody trees were scanty. This study revealed that anthropogenic activities had set in greatly and the forest reserves were poorly managed which had led to the reduction in number of tree diversity. This study therefore, pro-vides baseline information for ecosystem management and control.