Heigth-diameter modelling of mixed tree species in Ibadan
Accurate tree height and diameter at breast height (dbh) are important input variables for growth and yield models. Height-Diameter models adequately describe the relationship between both tree characteristics at stand level. This study was carried out to model height-diameter relationships of mixed tree species in and around the departments of Forest Resources Management and Wildlife and Ecotourism, University of Ibadan. Five commonly used non-linear growth functions were selected as candidate base models and were fitted to individual tree height-diameter data of mixed tree species. The study area hosts about 24 tree species dominated by Eucalyptus camaldulensis, Eucalyptus tereticornis, Nauclea diderichi, Terminalia superba, and Terminalia randii. Complete enumeration was carried out in the study area. A total number of 115 trees were identified and measured. The sampled trees were used to estimate the 5 nonlinear model parameters for about 24 species of trees pooled together. Model 1 had a RMSE, SEE, AIC and R2 value of 4.256, 4.295, 122.8979, and 0.920 respectively. Model 2; 4.083, 4.122, 122.4568 and 0.927 respectively. Model 3; 4.096, 4.135, 172.8217 and 0.926. Model 4; 5.194, 5.239, 123.2952.and 0.881 and model 5; 4.088, 4.127, 122.8179, and 0.926 respectively. Among the Five models, Shreuder model (M2) demonstrated the best fit and accounted for the greatest proportion of total height variations (RMsup>2= 92.7%). Residual plots were plotted for each model as a means of verifying the validation of the equation.
Keywords: Height-Diameter Models, Mixed Tree Species, University of Ibadan