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Badania wlaściwości geometrycznych nasion jodły

88%
Sylwan
|
1993
|
tom 137
|
nr 08
57-64
Numerous examples of silver fir stands growing outside its geographical range in northern Poland suggest that this species could be used in a greater extend in creation of managed forest stands. Climatic conditions could potentially constrain the use of this species in some parts of country. The objective of this work was to determine the potential climatic range of Abies alba in Poland. The bioclimatic envelope models were used to identify areas in which selected climatic variables show the same range of variability as observed within natural range of this species. Climatic data with 10' spatial resolution were used. The outcome of the analysis depends to large extent on the demarcation of natural range (in which the variability of tolerable climatic conditions is assessed). The model basing on the climatic conditions in whole natural range of silver fir in Europe suggest that almost whole area of Poland is suitable to fir, but models basing only of climatic conditions in Polish part of its natural range are much more conservative. In the last case the difference in extent between natural range and potential climatic range was smaller. As genetic variability of Polish fir populations is rather low, they are supposed to have constrained adaptative abilities. Forest managers should not focus on planting silver fir outside its natural range, but they rather should consider reintroduction of fir in parts of natural range from where it retreated in 20th century.
In Poland, the majority of silver fir stands is characterised by a single−layer stand structure. The current silvicultural activities aim at obtaining multilayer stands, which requires a clearer definition of the structure, and more precisely, a better knowledge of the pattern of diameters at breast height (DBH) distribution. The aim of the research was to develop a pattern of DBH distribution of trees in a multilayer silver fir stand in the Świętokrzyskie Mountains (central Poland) using the BDq method, through the mathematical determination of function parameters, including the productive capacity of the habitat. The application of this pattern will allow the selection of the management methods aimed to obtain and then maintain model stands with a different layer structure. The research was based on the empirical material collected in 56 stands that were characterized by both a single− and a multi−layered structure. They grew in coniferous forest habitats, mostly in the upland mixed coniferous forest, upland mixed deciduous forest and upland deciduous forest or mountain forest. One big (up to 1 ha) or 3−5 smaller (0.04 ha) sample plots were established in each stand in which diameters at breast height of all trees and heights of usually 25 trees, selected from the entire range of diameters, were measured. These were used to determine the height growth curve equation coefficients and then the height of each tree. For each stand the basal area was calculated and a graph for DBH distribution was prepared. Site index was established using the original empirical equation. In order to develop a model for multilayer fir stands, individual parameters of the equation 5, such as the basal area (B), the target diameter at breast height (D) and the coefficient q were to be determined using the BDq method. Taking into consideration only stands with one−tailed DBH, individual parameters of the function were found to be associated with site index. Empirical equations were developed for the determination of B and D, and, based on the DBH distribution graphs, coefficient q associated with site index was also calculated (tab.). The developed DBH distribution pattern is a mathematical description of the target fir stand. When the value of stand parameters approaches those of the model stand, it should be managed using the shelterwood cutting system, which results from the spatial variation in the stand height structure, and consequently from the need for different silvicultural treatments in different stand fragments.
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