Abstract

Tree height is one of the basic growth variables in forestry through which several other variables essential to forest management and decision-making and stand development over time are dependent. To this end, a study was conducted to develop models for estimating tree height- diameter relationship for IITA forest, Ibadan, Nigeria.Systematic sampling design was used to lay three straight line transects, four temporary plots of 0.25ha (50 m x 50 m) were laid in alternating position along each transect at 100 m interval to make up a total of 12 plots for the study, total height and Diameter at breast height (Dbh) were measured for all trees with Dbh ≥ 10cm in every plot. A total of 299 trees, 46 species from 25 families were encountered. Mean Basal Area (Ba) ranged from 0.01 m² to 0.54m², mean volume ranged from 0.02 m³ to 11.93 m³, mean Dbh ranged from 10.00cm to 110 cm and mean total height ranged from 3.0 m to 34.40 m The Height- diameter relationship was modeled using R statistics. The data collected were split into two sets; the first set was the calibration set which was used for models’ construction and the second was the validation set. and Akaike’s Information Criterion (AIC), Bayesian Information Criterion (BIC) and Root Mean Square Error (RMSE) were the criteria used to select the best model. Based on these criteria, the power function (H = 1.3 + 29.275BH^0.724) was adjudged to be the most suitable model that best predict tree height for IITA forest because it has the lowest AIC and RMSE of 1387.598 and 5.616 respectively followed by Gompertz. Logistics and Ratkowsky has the same AIC and RMSE of 1394.859 and 5.697 respectively. T-test carried out to validate the best model at 95% probability level revealed that there was no significant difference (P>0.05) between the mean of predicted height (12.402m) and mean of the observed height (12.378m) with p-value of 0.976. However, close and low values of AIC and RMSE for all models tested suggest that all the models can adequately predict tree height for IITA forest and an indication that the models’ estimators are efficient.

Keyword: Tree height, Diameter at Breast Height, Models, IITA, AIC