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ŠUMARSKI LIST 7-8/2013 str. 22     <-- 22 -->        PDF

shallow root system creates preconditions to uprooting. Due to its shallow depth, the roots are often unable to stabilize the tree in soil on extreme steep slopes. Lack of silvicultural interventions resulted in dense forest structure where the process of auto-reduction and gradual reduction of crown make the individual static stability more susceptible to wind damage.
Despite all listed damaging factors, the wind disturbances are considered to be the crucial natural force driving the dynamics and development of subalpine spruce forests according to comprehension of many forest ecologists (e.g. White, Pickett 1985; McCarthy 2001; Splechtna et al. 2005).
The main goal of this paper is to evaluate whether the large-scale wind and bark beetle disturbances are the phenomenon of the last decade, or if they are the ordinary part of subalpine spruce forest development in the conditions of Slovakia. Following tasks will be analyzed in detail:
Age structure and tree recruitment in time;
Intensity and periodicity of disturbances – reconstruction of disturbance regime;
Role of disturbances in development of forest.
Materials and methods
Materijal i metode
Site description – Opis staništa
The study was conducted in the Low Tatras Mts. Regarding the orography unit, the mountain range belongs to Western Carpathians. The research plots were established on the northern slope of the Mt. Veľký Bok. The elevation of the site ranges from 1450 to 1550 m above sea level, with NE aspect. The prevailing soil type is skeletal cambisol with the average depth to bedrock of 20 cm throughout the site. Typical mountain forest of the 7th vegetation altitudinal zone(group of forest types Sorbeto-Piceetum) is almost exclusively dominated by Norway spruce (Picea abies L. Karst) but tree species composition also includes less abundant tree species, such as silver fir (Abies alba Mill.) and rowan (Sorbus aria L.).
In the past, the set of permanent research plots (PRP) was established to capture the structural changes of subalpine forest ecosystem in this locality. However, after the bark beetle outbreak in 2010, the locality was completely harvested. Our study was focused on the dendroecological analysis of the stand dynamics as well as the reconstruction of disturbance regime. Following the approximate location of former research plots (location of plots was not GPS positioned) we established a 20×200 m transect ranging from the position of former lowest PRP toward the upper tree line.
Sample collection and processing – Prikupljanje i obrada podataka
Transect was divided into 20×20 m subplots for systematic sampling. At each subplot approximately five stumps were cored (one core per stump) regarding the decay state of stump. Across entire transect we obtained the cores over a complete range of diameter classes. Following this procedure, also suppressed trees were included into analysis, because there was no opportunity to estimate the former height position of tree after it was cut. The perimeter of each sampled stump was recorded as well. All obtained increment cores (N=60) were air dried and sanded according to Cook, Kairiukstis (1996). Rotten and fragmented cores were excluded from further analysis. Rest of the samples was scanned using the Epson Expression 10000XL scanner and the ring widths were measured (WinDendro® software). In the cases the core missed the pith (N=14), we approximated the prior growth according to average width and curvature of five innermost rings. The tree ring series were crossdated according to marker year method (Yamaguchi 1991). We confirmed the accuracy of crossdating by COFECHA software (Holmes 1983). All crossdated series (N=47) were used for further analysis.
Data analysis – Analiza podataka
At first, all tree cores were inspected for the prospective gap origin. We calculated initial growth rates as the 5-yr average radial growth for each core at the point where the tree was 4 cm at sampling height. Result should be compared to threshold value assessed experimentally using the growth rates of suppressed and gap originated saplings at the site (Lorimer, Frelich 1989). In our case, all trees were cut therefore we used the threshold rate (1.93 mm year-1) proposed in the work of Svoboda et al. (2012) for the ecologically comparable spruce stand in Šumava National Park. Trees that passed the given threshold were considered "gap established".
For the quantification of abrupt growth events, we calculated the percent-growth changes as a running comparison of sequential 10-yr annual ring widths (Nowacki, Abrams 1997). This approach allows discounting the short-term growth pulses caused by climate events and gradual change of growth patterns due to tree ageing. We were focused on positive growth releases that are considered to be the indicator of removal of overtopping canopy tree.
For evaluation of growth changes we followed the procedure proposed by Black, Abrams (2003).
Obtained growth changes were plotted with respect to prior growth values and boundary line recently developed for Picea abies by Splechtna et al. (2005). However, the growth change data failed to reach the used boundary line at almost all levels of prior growth (Fig. 1, top) therefore we