The BDq method as a tool supporting the development of diversified structure in silver fir Abies alba Mill. stands in the Bieszczady Mountains, Southeastern Poland
Metoda BDq jako narzędzie wspierające kształtowanie zróżnicowanej struktury drzewostanów jodłowych Abies alba Mill. w Bieszczadach, w płd.−wsch. Polsce
Abstract: Silver fir
Abies alba is one of the most important tree species found in Polish forests. In this study, the BDq method was used as a tool supporting the development and maintenance of the diversified structure of silver fir stands in the Bieszczady Mountains, by the example of the Lutowiska and Stuposiany Forest Districts. The role of study sites was played by 5 experimental control/sustainability units with an area of 20−30 ha each. In each of these units, 11−15 permanent circular sample plots of 0.04 ha were established. Based on the data collected from these plots, the basic parameters of the stands were calculated including total stem density, basal area and stand volume. Next, the numerical parameters of the model (target, desirable) tree diameter distribution (B, D and q) were determined. The derived theoretical distribution was compared with the empirical size distributions of individual control units in order to determine the intensity and diameter structure of selection cuts. The next stage included constructing an average tree diameter distribution for all control units and comparing it with the adopted target distribution in order to develop general guidelines for regulatory activities. The calculated (average for all sustainability units) value of the total intensity of selection cuts was 11% according to the number of trees (
i.e. 37 trees/ha) and 24% according to the basal area (
i.e. 8.9 m²/ha). In terms of volume, this corresponded to 120 m³/ha. The majority of trees intended for removal were in the 43−87 cm range of DBH. Every third tree in this range should be selected for removal,
i.e. approximately 25 trees/ha. The rules for performing the designed selection cuts were presented in an illustrative diagram. In the discussion, the importance of using appropriate methods of regulating silvicultural activities in stands with complex structures was emphasized. In this context, the BDq method was assessed as a relatively simple and practical tool. At the same time, the importance of the proper selection of numerical values for individual parameters determining the form of the target tree diameter distribution was underlined. While in the initial period of implementing this method into practice, decisions must be rather arbitrary, over time they should increasingly take into account the reaction of forest stands to the treatments, in particular the regeneration and recruitment of trees into the stand layer.
Key words: multi−aged silviculture, q−ratio, selection system, stand basal area, stocking control, target diameter, tree diameter distribution