Rangika Bandara and Upul Subasinghe
However, at present, there is no method for estimating the stem volume of this species. Therefore mathematical models were built in this study to predict the individual stem volume of the selected species grown as plantations and in homegardens.
Hawari nuga is sidely found in wet zone of Sri Lanka and therefore the study sites were selected from Kalutara and Galle Districts. For the non-forest areas, sampling was carried out in individual basis and ten 0.02 ha circular plots with slope correction were randomly laid out for each plantation in order to measure the necessary parameters.
Dbh, total height and height to the crown base of the trees were measured. Necessary measurements were also taken to calculate the stem volume using Newton's formula.
A theoritical model structure was developed using the relationship between form factor, volume, basal area and total height. Regression analysis was used to fit the data into the model. Untransformed as well as transformed combinations of the model structures were tested in order to select the best models. After examining the statistical performances of the resultant models, two models were finally selected for plantation grown trees and open grown trees. Those models had very high modelling efficiencies and negligible bias. When validated with the reserved data at the beginning of the modelling procedure, the selected models proved the capability of predicting stem volumes of Alstonia macrophylla grown in plantations and homegardens.