DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 7-8/2018 str. 34     <-- 34 -->        PDF

14.46%. Significantly positive growth response (over 40% of trees) was two times recorded (1970, 1993) and negative only once (2015).
Discussion
Rasprava
The evaluation of basic biometric characteristics reveals that grey alder creates homogeneous stands in terms of species composition and vertical and diameter structure. The average age and diameter of surveyed individuals ranged between 28 and 47 years and 24.4 and 36.3 cm and the height ranged between 14.7-20.9 m (Table 1). The number of individuals also varied only in the narrow range of 490-570 pcs.ha-1. Similar results in the assessment of the height and diameter variations of the alder natural populations were gained by Bugala and Pittner, (2010) and Bugala and Parobeková, (2016) in other regions of Slovakia. They stated that the alder’s growth strongly depends on the light, so decreasing growing space of individuals starts processes of autoreduction and dying of the undersized trees. These processes result in a single-layer composition with the low height variation in all studied stands. Vacek et al., (2016) confirm homogenous vertical and diameter structure even with a much higher number of individuals per ha (556-828 trees per ha) in Sudetes Mts. in the Czech Republic.
Radial increment strongly depends on age and altitude. Fast-growing features of grey alder lead to the very intensive growth between 5-20 years of age and to a shortened lifespan at the level of 50-60 years (Pagan, 1996). In the surveyed basin, the radial increment in the first 20 years markedly fluctuated (1969-1989) and in the next 26 years decreased relatively fast until it dropped to less than one-quarter (Figure 3 above). Mentioned fact manifests favourable environmental conditions, which allows faster growth in early years but accelerates the onset of senescence. Higher ability of young individuals (up to 20 years) to respond to the external factors was also manifested. Young trees might respond faster to the changes in temperature due to higher growth rate and earlier onset of xylogenesis (Li et al., 2012). At the same time, Fang et al., (2015) describe the sensitivity of the young trees to the drought caused by low precipitation, although this would not be a threat to the riparian stands of the surveyed region, since mountain watercourses are permanent there (Blaškovičová et al., 2011).
Along the rising altitude, the highest average tree ring width is noticed at altitude of 605 m (4.1 ± 1.8 mm). Influence of altitudinal gradient is well portrayed by the trend of average basal area increment (Figure 2). In the observation of the BAIav along the altitudinal gradient, obviously, it ranges between 736.7 ± 330 mm2y-1 at an altitude of 685 m and 1660.7 ± 975 mm2y-1 at an altitude of 605 m, where it evidently culminates. Advancing of trend curve in the lowest and the highest elevation (P8, P1) is probably due to the proximity of debris dams affecting the microclimate conditions, a level of ground water-table and also an amount of nutrients. According to obtained results, the production optimum of the grey alder in the studied river basin is situated at the altitudes around 605 m (volume increment 6.41 m3ha-1y-1), but neither here its production does not reach the production of other commercial tree species. The average volume increment of the investigated river basin - 4.59 m3ha-1y-1 is comparable with average volume increment