生物多様性管理と林業ジャーナル

Assessment of Tree Species Diversity Status in Some Forest Reserves of Gombe State: Strategy for Ecosystems Monitoring in Arid Regions of Nigeria

EE Dishan

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 (5) sample plots (100 m2) 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 Combretaceae had the highest number of species (6); Anacardiaceae and Mimosaceae 4 species each; Caesalpiniaceae, Fabacaea, Meliaceae and Myrtaceae families had 2 species each while all the other families had 1 species each in Kanawa Forest Reserve. In Kaltungo Forest Reserve Mimosaceae had the highest number of 7 species, followed by family Moraceae with 4 species, Caesalpiniaceae, Fabacaea and Rhamnaceae had 3 species each, Combretaceae and Malvaceae had 2 species each. All the other families had 1 species each. Family Mimosaceae had the highest number of 6 species in Wawa Forest Reserve, followed by Caesalpiniaceae and Moraceae with 3 species each. Combretaceae, Meliaceae and Rhamnaceae had 2 species each and all the other families had 1 species each. Azadirachta indica had the highest relative density, dominance and important value index of 24.50%, 24.43% and 24.97% in Kanawa, Azanza garckeana had the highest relative density, dominance and important value index of 9.09%, 10.28% and 9.68% in Kaltungo, and Vitaleria paradoxum 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. Consequently, closure of the forests to exploitation to allow for full regeneration is recommended. It is further recommended that efforts should be geared towards conservation so as to restore the reserves to their full potential