CONSTRUCTION OF AN INDIVIDUAL TREE TOTAL VOLUME PREDICTION MODEL FOR Pinus nigra var. maritima (Ait.) Melville (CORSICAN PINE) IN GREAT BRITAIN
A total volume prediction model for individual trees was constructed using total height anddiameter at breast height (dbh) as explanatory variables for intermediate and neutralthinning types using the data obtained from the British Forestry Commission.
The key question used was V, = g, * h, * J, where v, g, h, andf represent the total volume.basal area. total height and form factor of an individual tree. Form factor is the mostdifficult variable to measure because, it is highly correlated with species. age. site.variations, stand density, crown growth and competition from the neighbouring trees.
Assuming hasal area and total height of the particular tree will indicate the competition andage, direct functions were not constructed for competition. However, it was tested indirectlyusing crown parameters, stand density (N) and total basal area (G). Top height relatedfunctions were used to represent the site quality. The final equation tested was\' =Tts. h. s, G. N, crown growth).
For each thinning type, 75('k of plots were used for model construction and the remaining25'Yr for the validation of the constructed models. Data were divided by thinning type andthen by age in order to fit the models to one year at a time.
Crown parameters, site parameters, total number of trees or total basal area were notstatistically significant when fitted and the standard residual distribution indicated noimprovement. Basal area and total height were the significant variables. Finally, basal areawas replaced by dbh. For the final model at each age Rl was between 0.972-0.999 andstandard residuals were distributed without showing any particular pattern. Quantitativetests indicated negligible bias and very high modelling efficiency for all ages. Lack of fittest indicated the model was adequate.
There was an attempt to construct parameter prediction models with age which was notsuccessful because the estimated parameters for all ages were distributed around 0.5. Finallyan averaged value of the parameter which replaced the form factor was selected for all agesfor both thinning types. The finalmodcl is given below.
v = 0.5040 * h * (;rdbh2 1400(0)