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ŠUMARSKI LIST 1-2/2018 str. 57     <-- 57 -->        PDF

its relatively short history under state protection (thirty years). The managed forest deadwood volume was 10-20 times smaller than in the virgin forests. The research in Finland, Sweden, Germany, France, Belgium and Switzerland showed that the average volume of dead wood was less than 10 m3 ha-1 (Christensen et al. 2005). Compared to this result, the determined average volume of dead wood per hectare in specific managed beech forests in Serbia (Koprivica et al. 2013a) was almost twice as high, which can be assessed as important for the conservation of the general biological diversity.
In specific managed beech forests in Serbia other important research studies were conducted. Matović (2012) found that, in addition to significant dimensional diversity, these forests were characterized by heterogeneous spatial and age structure. Trees were usually randomly distributed in space, although they were often grouped in clumps and in a regular pattern. The age structure of these forests was strongly pronounced and represented by trees aged from one year to over 400 years in some stands. Koprivica et al. (2012, 2013b) found that the average values of basal area, volume, volume increment, biomass and carbon in these forests were relatively high and that these forests preserved their production potential.
The research conducted within this study and previous studies of the same authors suggest that although these forests have often been under inadequate and inconsistent forest management, they have preserved their production potential, structural diversity and naturalness. Moreover, in the context of the proclaimed approach to forest management in the future in Europe, these forests can be considered much closer to the original natural forests by many criteria. In comparison to other beech forests in Europe that are predominantly even-aged and more homogeneous in structure, managed forests in Serbia are uneven-aged and spatially heterogeneous.
It is important to emphasize that major natural disturbances such as wind or ice forest storms haven`t made any greater damage in managed beech forest in Serbia so far. Hanewinkel et al. (2014) found that uneven-aged forests had significantly higher resistance to heavy storms than even-aged forests. Furthermore, no significant insect calamities, epiphytotic attacks, fires and visible negative impact of long-term drought have been observed in beech forests in Serbia, which is due to their marked uneven-aged structure. We should bear in mind that Serbia is relatively close to the European Mediterranean Basin, one of the world’s climate change hotspots (Luterbacher et al. 2012). In the neighboring Hungary, Lakatos and Molnar (2009) found a mass dieback of beech forests in even-aged beech forests in the period of drought (2000-2004). Using the regional climate model and the biometeorological index, Stojanović et al. (2013) found out that by the end of the twenty-first century the majority of existing beech forest in Serbia may be beyond their 20th century ecological niches. In this context, it is of critical importance to implement adequate management measures to conserve the pronounced structure, uneven-age character and naturalness of beech forests in order to create better conditions for natural adaptation of these forests to the anticipated climate change in the future. Brang et al. (2014) defined six  adaptation principles to climate change (“increase tree species richness, increase structural diversity, maintain and increase genetic variation within tree species, increase resistance of individual trees to biotic and abiotic stress, replace high-risk stands and keep average growing stocks low”) and concluded that they are already largely contained in close-to-nature forestry.
CONCLUSIONS
ZAKLJUČCI
Having compared the stand structure of managed and virgin stands on the best beech sites in Serbia, as well as their stand structure with the beech virgin forests in Central, Eastern and Southern Europe in accordance with the aims of this research, the fol­lowing conclusions can be drawn:
1. The impact of previous forest management in beech high forests in Serbia on Structural diversity of trees is twofold. The greatest differences were found in the dimensions of the largest trees in the managed forests and in the stands of virgin character (dbh and heights). Certain differences were found in the shape of Height curves and Diameter distribution and the values of Slenderness coefficient. However, the Gini index and the Coefficient of variation show that the managed beech forests in Serbia substantially preserve Structural diversity, which is very important for these forests from the aspect of low tree species diversity and maintenance of the overall biodiversity.
2. The impact of previous management on the change in the average value of the forest estimation elements of managed beech high forests in Serbia in comparison to the virgin forests is clearly pronounced and statistically significant regarding production characteristics.
3. Comparison of forest estimation elements of stands of the virgin forest type in Serbia on the most productive sites with the equivalent forest stands in Central, Eastern and Southern Europe showed that the biggest differences were in the number of trees per hectare and the stand quadratic mean diameter. Basal area and volume and the volume of dead wood per hectare were quite similar.
4. The existing environmental stability of the managed beech forests in Serbia in the near past and present (after severe droughts) leads to the general conclusion that close-to-nature forestry may provide long-term conservation of these forests in the future within the limits of their current range in European terms.