Tree crown ratio model for Hevea brasiliensis (A. juss.) plantation in Rubber Research Institute of Nigeria (RRIN) Edo State, Nigeria
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Crown ratio is a term used to describe the ratio of the crown length to the total tree height. The crown length emphasizes the distance between the crown apex and the crown point while the distance between the tree apex and the ground level defines the total tree height. The tree crown ratio are predicted by the use of empirical models which assist in the provision of accurate estimates for both individual, stand growth as well as yield that are veritable tools for evaluating numerous management and utilization decision. However, no single type of model can provide sufficient information effectively for all levels of decision making, thus the essence of modeling tree crown ratio for Hevea brasiliensis plantation in Rubber Research Institute of Nigeria (RRIN). Tree growth variables are such as diameter at the base (DB), diameter at the breast height (DBH), crown diameter (CD), crown length (CL), total tree height (THT) were measured from a six year old plantation of 402 trees, while tree attributes such as crown projection area (CPA), basal area (BA), tree slenderness coefficient (TSC), crown ratio (CR) were estimated using their empirical formula. The data collected from the plantation was analyzed using descriptive and inferential statistics such as correlation and regression analyses with non-linear models used in fitting the data into CR equations and other growth attributed with individual data fitted to evaluate the robustness of the models using the fit indices. The result of the study reveals that there were significant variations in the growth attributes within the plantation in the study area. The result of the correlation analysis between CR and other growth characteristics revealed significant associations. The best adjudged CR model was the logistics model which is represented as CR=a_0/(1-e^(^(1-a_(1 ) CL+a_2 THT)) ) ; (R2 = 0.96 and SSE = 0.1177). The study has shown that crown ratio models developed has significant relationship with CL and THT and this can be successfully used for predictive studies on crown attributes for Hevea brasiliensis plantations in Nigeria.
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