Volume equations for five economic hardwood species in Oluwa Forest Reserve, Ondo State, Nigeria
Tropical rainforest remains one of the most complex ecosystems in the world. Tree growth dynamics is a major technique in quantifying the forest composition. However, there is dearth of knowledge on tree volume equations of hardwood tree species in the tropical rainforest especially in Nigeria. Therefore, this study was carried out to develop tree volume equations for selected economic hardwood species (Lovoa trichiliodes, Celtis zenkeri, Picralima nitida, Buchlozia coriacea and Diospyros crassiflora) in Oluwa Forest reserve, Nigeria. Two transect (500m) were laid in the study area, in which distance between each transect was 400m. Systematic sampling technique was adopted to lay four temporary sample plots (TSP) on each transect making a total of Eight TSPs (size 50 x 50m) for the study. All tree species of the aforementioned hardwood species with dbh ≥ 10cm were identified in each TSP. Five models were selected as candidate models for the study. The result revealed that nonlinear model produced the best fit for Buchhlozia coriacea, Celtis zenkeri, Diospyros crassiflora and Picralima nitida while generalized nonlinear model produced a better fit for Lovoa trichiliodes. Residual analysis was carried out to validate the best fitted model for each species. The selected models (Nonlinear and Generalized nonlinear equations) can be very useful for sustainable forest management assessment of Lovoa trichiliodes, Celtis zenkeri, Picralima nitida, Buchhlozia coriacea and Diospyros crassiflora plantations in the study area and similar ecological areas.
Keywords: Volume Equation, nonlinear model, generalized nonlinear model