DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 3-4/2013 str. 17 <-- 17 --> PDF|
volume of dead trees was 33 m3 ha–1, or 4.1 % of the total growing stock. Wild pear and hornbeam had a higher percentage in density of dead trees than live trees, while conifers had lower percentages, spruce in particular. Almost 80 % of dead trees were in the 2nd and 3rd diameter classes (Figure 8). The frequency distribution of dead fir trees was similar to a reverse-J shaped distribution, with the mode in the 2nd diameter class. Large dead trees were almost completely absent, which is another sign of overall stand vitality and that the trees had not yet reached the terminal phase. However, some individual trees showed signs of ageing such as transparent crowns, heavy moss and lichen cover on the trunk, fruiting bodies of fungi, and a secondary crown. Almost all broadleaves were snags, followed by fir (80 %) and spruce (47 %).
The upper canopy layer was very dense and allowed only a small amount of light to reach the forest floor; therefore, the shrub layer, woody regeneration, and ground vegetation were poorly developed. Top heights of fir and spruce were 35.8 m and 37.4 m, respectively. Height curves of fir and spruce were comparable with indication of slightly taller spruce in the range of mean diameters (35–60 cm; Figure 9).
The stand structural parameters on the permanent research plot were similar to those recorded on the whole reserve area, with the exception of higher growing stock (881.7 m3ha–1) and basal area (60.3 m2 ha–1).
Regeneration plots were on average 28.0 % covered with stones and rocks, 7.6 % with woody debris, 50.6 % with ground vegetation, 1.3 % with spruce and fir regeneration, while the rest was litter, soil, or roots of adult trees. We recorded 10,944 fir and 171 spruce one-year-old seedlings ha–1, respectively, and 10,260 fir and 2,394 spruce small seedlings ha–1, respectively. Within small seedling density, fir prevailed with 80 %, which is a slightly higher percentage compared to its share in density of trees or growing stock. Due to small seedling size, no browsing damage was recorded.
This study presents indirect evidence suggesting that fir stands represent a successional stage in the course of spontaneous forest expansion on former pastures as suggested in the first management plan for the region (Anon. 1961). This was supported by the following: the reserve position on an old military map, the presence of early successional broadleaves in the medium layer and their reduced vitality (hornbeam, wild pear), the comparable age of the oldest dominant trees, and the pattern of radial increment and overlapping bell shaped diameter distributions of individual tree species. Mlinšek (1968) reported that in the submontane belt in nearby Kočevje, many climax trees species were involved in secondary succession on abandoned agricultural lands, especially spruce, fir, maple, lime, and hornbeam. The sequence of immigration differed greatly; it depended on sites and also on chance. The exception was fir, which abundantly regenerated under dense crowns of hazel and pioneer species.
The growth pattern of dominant trees with slow growth in the initial phase, low vitality of broadleaves in the medium layer, and great age variability in fir indicate that the stand did not originate from a completely open space. It is likely that pioneer species such as hazel were the first colonizers, followed by maple, lime, hornbeam, fir and spruce. Shade tolerant fir can colonize sites under pioneer species and overgrow them when they gradually start losing vitality (Motta and Garbarino 2003). At the time of the study, pioneer species were already decomposed, while other, more long-lived broadleaves were still present. The greater light demand of Norway spruce compared to fir was indicated by the absence of rejuvenation and linkage to the larger diameter classes, i.e. dominant canopy trees.
However, we cannot exclude the possibility that stands were at the forest border or even within forest limits, but still under the heavy influence of grazing and other human activities (collection of firewood for lime production). In particular, the age spread of dominant firs may indicate a continuity of forests or long lasting succession stadia. Yet, progression of vegetation was confirmed, namely broadleaved species were in regression, and spruce was also confined to the upper canopy layer only. There is substantial evidence of landscape changes due to socio-economic changes. Several waves of emigration were reported from Poljanska dolina, especially during the "Long" and "Great" depression which triggered spontaneous expansion of forests (Anon. 1961, Prelesnik 2011).
The stand was characterized by a high growing stock and basal area of live trees and a large number of dead trees which were restricted mainly to the 2nd, 3rd and 4th diameter classes, while large diameter dead trees were almost completely absent. All this indicates high competition