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Wskazniki zroznicowania struktury drzewostanu

100%
Sylwan
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2002
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tom 146
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nr 04
69-79
Sylwan
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1995
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tom 139
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nr 03
53-65
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100%
Białowieża Forest (BF) is widely known for its outstanding natural values. The debate about the management/protection model, able to maintain all relevant values of BF on a sustainable basis, has a very long history. Currently, the main role in this debate is played by groups and organizations claiming that the major threat for the biological richness of BF is related to local forest management. In this paper, an attempt is made to verify this thesis. The extensive literature research reveals that vascular plants are one of the most threatened (and best documented) groups of organisms occurring in BF. It was found, for example, that in case of Serratulo−Pinetum (one of the most important woodland community type occurring in BF) the floristic diversity declines at the rate 0.6 species per year. However, similar situation concerns many other groups of species (e.g. lichens) as well. The recession of many species does not take place in the managed part of the BF only. This problem concerns also the areas which, since a long time already, have been subjected to the strict protection, like the ‘Strict Reserve' of the Białowieża National Park (comprising ca. 7% of the BF, under strict protection since ca. 100 years). Several factors and agents responsible for the general deterioration of natural values of BF were identified. Among other things, many authors underline the negative impacts of natural, successional processes taking part in areas which were ‘liberated' from the direct human impacts. Such processes are a direct cause of loss among many herbaceous species, particularly helio− and termophilous plants. Another important reasons for decreasing trends in many important elements of the local biodiversity are: strong reduction of open and semi−open areas (disappearance of the so called ‘cultural landscapes'), climate change, air pollution, deer overabundance, compositional impoverishment of many tree stands, invasive species of plants and animals. In conclusion, there are many factors responsible for decreasing diversity of BF and most of them have nothing to do with the local forest management. To preserve possibly high levels of the natural values of BF for future generations, a wise and complex conservation strategy is needed. As many other similar examples from different places over the world clearly show, the core element of such a strategy should be the principle of active management approach and not the out of action principle of ‘doing nothing'.
Growth and mortality of oak (Quercus robur L.) in young mixed stands with various admixture of hornbeam (Carpinus betulus L.) in the period of 9−13 years after planting were examined. The trial stand is located in central Poland (51.827023° N, 19.922315° E). It was established in 2004 on a moderately fertile site. Four experimental variants with different participation of oak (O) and hornbeam (H) were established: W1 – an oak monoculture (control variant, 100% O), W2 – a mixed stand consisting of two rows of oak and one row of hornbeam (67% O, 33% H), W3 – a mixed stand consisting of one row of oak and one row of hornbeam (50% O, 50% H), W4 – a mixed stand characterized by a single tree mixture, with three oaks and one hornbeam alternately occurring in each row (75% O, 25% H). During the first two years of the study period the height increments of oak trees were significantly larger in the study variants with hornbeam (the biggest in W3 variant), while during the next two years, the largest values of height increments occurred in the control variant (W1). Through the second part of the study period, the most pronounced, negative effect of hornbeam on the dbh increment of oak trees took place in the W3 variant. During the first nine years after planting the survival rate of oak trees in the variants with hornbeam were similar (82−94%) as in the control variant (85%). However, during the next four years, three times more oaks died in W3 variant (16,5%) than in other variants (5−7%). In general, the results obtained suggest that in order to create mixed oak stands with hornbeam as a nursery species, the share of hornbeam should not exceed 20−25% of all planted trees. The above value appears to be acceptable from the point of view of the negative competitive effects of hornbeam on oak trees during the initial stages of stand development.
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