Assessment of tree species diversity status in some forest reserves of gombe state: strategy for ecosystems monitoring in arid regions of nigeria

The study assessed tree species diversity status of three Forest Reserves (Kanawa, Kaltungo and Wawa) in Gombe State, North-eastern Nigeria. Parameters determined were tree species diversity and composition, relative density and dominance, important value index, species richness and evenness in the Reserves. Five sample plots (100m2) were laid at random in each of the Reserves and tree species were enumerated by sample plot method. A total number of 196, 242 and 205 trees belonging to 15, 19, and 16 families and 28, 36 and 28 species were recorded in Kanawa, Kaltungo and Wawa Forest Reserves respectively. Families and numbers of species recorded in Kanawa Forest Reserve were; Combretaceae 6, Anacardiaceae and Mimosaceae 4 species each; Caesalpiniaceae, Fabacaea, Meliaceae and Myrtaceae 2 species each while all the other families had 1 each. In Kaltungo Forest Reserve Mimosaceae had 7 species, Moraceae 4, Caesalpiniaceae, Fabacaeaand Rhamnaceae had 3 each while Combretaceae and Malvaceae had 2 and the other families 1 each. In Wawa Forest Reserve, Mimosaceae had 6 species, Caesalpiniaceae and Moraceae had 3 each. Combretaceae, Meliaceae and Rhamnaceae had 2 each while the other families had 1 each. The highest Relative density, Dominance and Important Value Index of 24.50%, 24.43% and 24.97%; 9.09%, 10.28% and 9.68% were recorded for Azadirachta indica and Azanza garckeana in Kanawa and Kaltungo Forest Reserves respectively. Vitaleria paradoxa had the highest relative density and important value index of 11.21% and 10.09% while Anogeissus leiocarpus had the highest relative dominance of 11.38% in Wawa. Shannon’s diversity index was 2.49, 3.30 and 3.10 for Kanawa, Kaltungo and Wawa respectively. Species evenness (EH) was 0.75, 0.92 and 0.93, Species richness (d) 2, 2.31 and 1.96 and Shannon’s maximum diversity (Hmax) was 3.3, 3.6 and 3.3 for the three forest reserves respectively. It is thus concluded that the reserves had moderate diversity. Closure of the forests to exploitation and conservation efforts are thus recommended.