Ocena możliwości zastosowania tablic Bergela dla daglezji zielonej (Pseudotsuga menziesii (Mirb.) Franco) w Polsce

There are no original local yield tables for Douglas fir stands grown in Poland. In the presented study we attempted to answer the question whether it is possible to successfully use the German yield tables for Douglas fir developed by Bergel [1985]. Based on the data from these yield tables we developed the height growth model (site index curves) for Douglas fir in the form of the polymorphic equation with variable asymptotes. This model appeared to be, as expected, far better than the anamorphic model. We applied the elaborated equation for calculation of the site index for 63 randomly selected research plots located on the typical Douglas fir habitat types (fresh mixed broadleaved forest and fresh broadleaved forest) in western Poland. We concluded that the mean site index values are significantly higher in younger stands than in the older ones. To determine the reason for this phenomenon, we tested the resulting model using the published data from the permanent research plots. We found out that the pattern of site index changes with age varies for stands in different age classes. Moreover, we noticed, that regardless the age of the stand, in the recent decades there is the increasing height growth rate, which can be attributed to the change in environmental conditions. On the other hand, the analysis of the other characteristics of the sample plots revealed, that there is no significant relationship between site index values and site and plot location, as well as between the productivity level, expressed by the value of the EN coefficient, and age class, site and location of the stand. Bergel yield tables can be used in Polish conditions taking into account the age−dependency of the site index values.