DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 9-10/2023 str. 43 <-- 43 --> PDF |
coefficients were estimated using nonlinear regression (Gauss-Newton method) in the Statistica software package. The comparison of regression models based on the criteria shown in Table 6 indicates approximately the same estimation accuracy, that is, the usability of the tested regression models with two and three independent variables, except for the Swiss NFI model (with d1.3, h, and d7 as independent variables). Due to approximately same values of the presented criteria for comparing the tested regression models, except for the mentioned Swiss NFI model, the ranking of the models was not performed. Based on the observed criteria, the Swiss NFI model enables greater accuracy in estimating the volume of the tree, but at the same time implies a greater scope of field work when collecting the necessary data. In addition to measuring diameter at breast height and tree height, it is necessary to measure the diameter at the height of seven meters with special instruments (Finnish parabolic caliper, Bitterlich’s mirror relascope, Bitterlich’s telerelascope, Wheeler’s pentaprism, etc). Regarding the accuracy of the obtained model with the diameter at 7 meters high as the third variable, the fact that in this research the specified diameter was measured with a standard diameter on a felled tree must be taken into account. It is to be expected that the same accuracy of the survey cannot be |