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ŠUMARSKI LIST 3-4/2012 str. 29     <-- 29 -->        PDF

Conducted partial correlation confirmed the statistical significance of all independent variables (crown diameter, crown area and tree height) planned for model creation (Table 1). Multiple regression analysis confirmed the statistical significance of all created models – both model types (dM1 – Table 2 and dM2 – Table 3) and all tree species (Sessile oak, Common beech, European hornbeam and Black alder). Modelling results have shown that independent variables crown diameter and tree height from the first model (dM – Table 2), as well as the crown projection area and tree height from the second model (dM – Table 3) explain the variability of diameter at breast height with high values of determination coefficients (R2 > 0,76). By comparing the results based on tree species between different model types, it was determined that the first model for Sessile oak and Common beech shows better results – 4% higher values of determination coefficient, and lesser error values in dbh estimation, expressed through root mean square error (RMSE), were obtained. For European hornbeam and Black alder both models produced almost identical results regarding R2 and RMSE values. Since crown diameter and tree height variables in Common beech model (dM1) increase the explained dbh variability by only 3%, using the simpler model with crown diameter as the only independent variable is recommended for estimating Common beech diameter at breast height, especially if tree height is not measured during the photogrammetric measuring.

Based on the obtained results and regression analysis parameters for each individual model (Table 2 and 3), as well as the results from graphic (Figure 3 to 5) and analytic (Kolmogorov-Smirnov test) testing of each individual model, we can conclude that created regression models can be used for dbh estimation in "Donja Kupčina–Pisarovina" forest management unit of uneven-aged, privately owned forests located at hilly regions, and also in forest stands with similar characteristics. In order to confirm the possibility of practical application for created regression models it is necessary to conduct a photogrammetric measurement of forest stands in "Donja Kupčina–Pisarovina" forest management unit, and to compare the obtained results and the costs of its application to terestrial measurements.

Keywords: diameter at breast height, crown diameter, crown projection area, tree height, modelling, multiple regression analysis