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The paper presents the comparison of the influence of the season (winter and summer) on the level of damage to trees remaining after the timber harvest during early thinning in young alder stands. The study was carried out in black alder stands aged 38 and 40 years located in north−eastern Poland (Płaska Forest District). Chainsaw logging was performed in the cut−to−length harvest system, while timber was extracted using an agricultural tractor with a trailer with manual timber loading and unloading. The number and share of damaged trees and stand damage rates were estimated in a particular season of the year. Logging resulted in the damage of 8.3% to residual trees. Almost twice as many trees were damaged in summer as in winter (p=0.001). Significantly higher share of trees in 3rd, 4th, and 5th damage classes was found. Only the damage of timber fibers (6th class) did not differ significantly between analyzed seasons. The stand weighted damage rate (W) ranged in winter from 0.12 to 0.38, and in summer between 0.12 and 0.80. In turn, the value of weighted coefficient of damaged trees in the remaining stand amounted to 10.24−60.15 in winter, and 19.07−119.64 in summer. Both W (p<0.01) and WDI (p<0.05) indices were twice higher in the summer than in the winter period.
The study presents the assessment of the accuracy of two generalized height−diameter models, such as skwB [Bruchwald et al. 2001] and skwO [Orzeł et al. 2014], developed in Poland for black alder (Alnus glutinosa (L.) Gaertn.) stands. Verification of these models was conducted on empirical material that was collected in 127 alder stands located in the western part of Sandomierz Basin (southern Poland). Selected alder stands aged 6−89 years, while average breast height diameter ranged from 4.5 to 43.0 cm and average height from 6.3 to 32.7 m. The stand density varied from 222 to 4360 trees/ha. The accuracy assessment for uniform height−diameter curves was based on the analysis of single tree absolute error distributions. Synthetic indicators of goodness−of−fit, such as: average and standard errors, coefficients of variation and determination were calculated based on absolute errors. The final evaluation of the compared uniform height−diameter models results from the structure of the goodness−of−fit measures that was observed within all analyzed stands and within age classes of 20 years. The efficiency of uniform height−diameter models was also compared with stand height−diameter curve, which was developed based on the Näslund function. General height−diameter models overestimated height in alder stands on average from 0.26 (1.67) to 0.19 m (1.39%), based on skwB and skwO models, respectively. Bias depended on the age of stand and decreases from almost 3% in I age class to nearly 0.5% in IV and V age class. For both analyzed models, a positive systematic error was observed for the standardized breast height diameter. Bias in estimating the height of single stand depended on the accuracy of stand height estimations. In case of estimation based on the measurements of three trees height, bias in single stand can range from –13% to +14%. Due to the range and nature of observed systematic errors, uniform height curves should be applied to groups of stands that have different age and breast height diameter structure, as it allows for partial reduction of the error.
Black alder Alnus glutinosa (L.) Gaertn. is an important forest−forming species in Poland, with more than 5% participation in the species structure. It is a typical lowland species, especially in the river valleys, on the banks of the lakes and in the land depressions. It is one of the main species in the following habitats: boggy mixed broadleaved forest, alder and alder−ash forest, riparian forest and moist broadleaved forest. As a valuable admixture alder is introduced in the habitat of boggy coniferous forest and boggy broadleaved forest. Until recently black alder was considered in Poland as a species with a very low level of danger from the pests and diseases. The situation changed at the turn of the centuries, when the deterioration of the health status of the alder stands began, which led locally to the mass dieback of the trees, mainly in the stands which are over 20 years old. In the following years, the phenomenon was intensified. The largest number of such stands was recorded in 2006. The strongest deterioration of health condition of the trees was observed in five regional directorates of the State Forests: Białystok, Lublin, Torun, Wrocław and Olsztyn. The study gives information on lignicolous fungi found on black alder in 62 alder stands, which exhibited the most severe signs of the dieback. The research was conducted in 14 forest districts and in Poleski National Park (fig.). The surveys revealed the presence of 49 taxa of the lignicolous fungi (44 Basidiomycota and 5 Ascomycota). The most common species were Xanthoporia radiata, Stereum hirsutum, Daedaleopsis confragosa, Armillaria pp. as well as S. subtomentosum (tab. 2). The disease contributing to the local dieback of black alder in the stands (mainly in the Lublin Regional Directorate of the State Forests) is the root rot caused by Armillaria species. Many species of lignicolous fungi (e.g. Fomes fomentarius, Fomitopsis pinicola, Ganoderma applanatum) penetrate into previously weakened trees, causing decay of wood, which can accelerate the dying of single trees.
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