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ŠUMARSKI LIST 1-2/2021 str. 37     <-- 37 -->        PDF

Since the fitted data for each site class could produce inappropriate culmination ages and values of the maximum current height increment (CAIh) that do not correspond to the biological growth characteristics of the site classes (the more productive the site the earlier the culmination of the CAIh and the higher its value at the time of culmination), a parameter prediction procedure was conducted. This procedure involved a new fitting of the model parameters of the growth functions representing all five site classes depending on their height at the reference age. For this purpose, b and c parameters of the tested growth functions were related to the fitted height of the dominant trees at the age of 100 for each site class and the parameters bSI and cSI and, consequently, parameter aSI per site class were calculated according to the aforementioned biological precondition. When balancing these coefficients, the intension was to obtain the final models in line with the empirical data on the value and age of the CAIh culmination obtained by the stem analysis procedure (Table 4) as possible.
Table 3 shows the prediction of the model parameters used for fitting the shape and the slope coefficients of growth functions per site class.
Generally speaking, the prediction of model parameters from ŽA performed better than the prediction for RU for all three functions used. It can also be seen that the slope and shape coefficients are best predicted by the CHR function for both areas. The parameters of the Korf and the Korsun models are well predicted for ŽA, while for RU the value of the adjusted coefficient of determination is negative, which calls into question the validity of these models.