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ŠUMARSKI LIST 5-6/2018 str. 17     <-- 17 -->        PDF

temperatures had a significant effect on the amount of evaporation and transpiration in forest gaps and thus on soil moisture.
The forest regeneration process is one of the basic issues in natural silviculture and forest ecology, particularly in applied ecology. In the forest gaps of the present study, silver fir as the main forest tree species was poorly regenerated. Apart from the poor regeneration in gaps created by tree dieback, poor regeneration was also observed in the gaps of old-growth beech-fir forests (Rozenbergar et al. 2007). According to Albanesi et al. (2008) regeneration in artificially created forest gaps was more pronounced than regeneration in gaps formed by the dieback of silver fir trees. The shape and dimensions of artificially created gaps are determined by forestry experts, while the dimensions and shapes of gaps formed by tree dieback depend on the degree of tree degradation and intensity of dieback. The area of artificially created gaps is smaller than the area of gaps formed by tree dieback. According to Schugart (1984) and Mazur (1989), silver fir can cover only a part of the gap.
With respect to silver fir regeneration in forest gaps, a microlocation with a high level of direct light is less favourable (Rozenbergar et al. 2007). In the present study, the best sites for silver fir regeneration were the forest gap edge areas and forest stands (control plots). As the canopy density of forest stands is incomplete due to tree dieback, the necessary conditions are provided for the appearance of silver fir seedlings. According to the present study, regeneration of common beech is more pronounced within the gaps. The density of sycamore maple was highest in gap edge areas, while its density was the same in the control forest stand and in the gaps. Regardless of gap size, a larger number of silver fir plants were found in the class of small seedlings, while a larger number of common beech plants were found in the class of larger seedling and saplings.
In the present study, there were no significant differences in the number of silver fir plants between the large and small forest gaps. A significantly larger number of silver fir plants were found in the large forest gap edge areas as opposed to the edge areas of small forest gaps. In the large gap edge areas and within those gaps, a significantly larger number of sycamore maple plants were found than in the small forest gap and its edge areas (Table 5).
One of the possible outcomes of competition is that the population of one competitor is increased, while the population of the other is decreased or eliminated. Analogous to this, in the large and small gaps, a significant and negative correlation was found between the number of young seedlings of silver fir and common beech. Dobrowolska (1998) stated that the reason for the poor regeneration of silver fir is the competition of plants for nutrients. Young silver fir plants appear in forest gaps while there is a lack of older plants. One of the causes of high mortality of silver fir plants lies in the changing microclimate and microbiological conditions, and competition between tree species.
Microclimate, in particular air temperature, relative air humidity and soil temperature, has a significant affect on the number of young seedlings of silver fir and common beech. Common beech requires higher air and soil temperatures than silver fir and does not tolerate excessively dry soil (Seletković et al. 2003). In terms of its ecological requirements, silver fir is a species with a narrow ecological valence (Prpić et al. 2001). Given the ecological requirements of these two species, and the correlations outlined in Table 6, silver fir prefers lower air and soil temperatures, while common beech, as a species with a broader ecological valence, is found at sites with higher soil and air temperatures. For that reason, there was a higher density of silver fir seedlings around the gap edges, and a higher density of common beech seedlings within the gaps. Since common beech and sycamore maple are more successful in regenerating the gaps, forest gaps are habitats where the change of tree species occurs.
Silver fir dieback and salvage cutting of these stands create larger or smaller gaps in beech-fir forests. The creation of forest gaps causes changes in certain microclimatic elements and changes in the abundance of seedlings of various species. Forest gap size does not significantly affect air temperatures. Changes in forest gap size significantly affected soil temperature changes and soil volumetric water content. Favourable microclimate conditions were found in the small forest gap compared to the large forest gap. The density of silver fir plants in large and small forest gaps was insufficient for the species influx into higher layers of the stand. At the edge of the large and small forest gaps, the number of small seedlings of silver fir was significantly higher than that of broadleaf species. Microclimate had a significant influence on the number of small seedlings of silver fir and beech in the large gap. The results of this study could be applied in developing better silvicultural plans for the rehabilitation of forest gaps.
Albanesi, E., O.I. Gugliotta, I. Mercurio, R. Mercurio, 2008: Effects of gap size and within-gap position on seedlings establishment in silver fir stands, iForest, Vol. (1): 55.−59.
Anić, I., M. Oršanić, M. Detelić, 2002: Revitalizacija degradiranog ekosustava nakon sušenja hrasta lužnjaka – primjer šume Kalje, Šumarski list, Vol. (11−12): 575.−587.