LOGGING IMPACTS IN TROPICAL LOWLAND HUMID FOREST ON TREE SPECIES DIVERSITY AND ENVIRONMENTAL CONSERVATION

This study assessed the effects of exploitations in natural forest ecosystem on tree species diversity and environmental conservation. This was achieved by comparing tree species diversity and yield in an unlogged forest (inviolate/strict nature reserve) and part of the forest reserve where active logging is in progress. Both forest types are located in Akure Forest reserve, Ondo State, Nigeria. Eight plots (20 x 20m) were located in each site using systematic sampling technique. All living trees with dbh > 10cm were identified in each plot and categorized into families. Ddiameter at breast height was measured from each of the trees in each plot. This was used to compute basal area and volume. Relative frequency, relative density and habitat occupancy were obtained and compared. Shannon-Weiner and species evenness indices were used to assess and compare tree species diversity and abundance. The result shows that the tropical humid forest is very rich in tree species diversity as a total of 54 different tropical hardwood species from 24 families were encountered in both forest types. There are 46 species distributed among 21 families in the inviolate forest while 24 species in 14 families were in the logged forest. Higher values of Shannon-Weiner (3.16 and 3.03 for inviolate and logged respectively) and evenness index (0.83 and 0.81) are also obtained for the inviolate and logged forest respectively. The stand density in the inviolate is 555 stems/ha and that of the logged forest is 132 stems/ha. A mean dbh of 39.35 cm and 14.24 cm, basal area of 10.34 m(2)/ha and 2.14 m(2)/ha and volume of 1235.04 m(3) and 14.81 m(3) were obtained for the inviolate and logged forests respectively. In the inviolate forest, the species with the highest number of occurrence is Mansonia altissima (80stems/ha) and Caesalpinoidae and Sterculiaceae families have the highest number of species (6). In the logged forest, Triplochiton scleroxylon (18 stems/ha) has the highest frequency and Caesalpinoidae family has the highest number of species (4). There are significant differences in all the variables estimated (P < 0.5) with result from the inviolate forest having the highest value. The study concluded that exploitation has affected species diversity in the ecosystem and subsequently, the roles of trees in environmental conservation are affected.