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Th e research deals with the description of basic characteristics of stand structure and regeneration processes according to affecting factors. Characteristics are described before and aft er large-scale bark beetle outbreak in the high mountain spruce forest of the National Nature Reserve (NNR) Kotlov žľab. In 1968, a series of three permanent research plots (PRP) with the size of 0.50 ha was established at an altitude of 1400– 1500 m. Measurements of the stand structure and regeneration processes were carried out in 1968, 1978, 1988, 1998 and 2019. Before the largescale disturbance, the high mountain spruce forest was little differentiated and was dominated by single tree layer with stagnant regeneration. Th e development in PRP 3, which had initially the lowest number of trees, the highest variability of tree diameters and was located at the lowest altitude, responded best to the effect of disturbance. However, taking into account the forest development aft er disturbance, we can state that in 2019 there was a sufficient amount of advanced spruce regeneration in all PRPs, which will ensure that development does not take place through early successional stages. In the initial stage of the forest development, rowan could be expected to fill openings among remaining spruce trees. [ABSTRACT FROM AUTHOR]

Disturbances of different spatial extent and intensity play an important role in the Western Carpathian Norway spruce forests. These forests are shaped mainly by severe winds, often followed by bark beetle infestations. Their intensity varies substantially, resulting in variability of disturbance regimes. Low- and moderate-severity disturbances create small-scale dynamics associated with small- and medium-sized gaps resulting from the death of individual trees or groups of them. Large stand-replacing disturbances are much less frequent but affect larger areas. In spite of such large variability of disturbance regimes, the structure of old-growth spruce stands varies less, with unimodal diameter distributions being the most common ones. In this review we discuss the possible natural mechanisms behind the relationship between the varied disturbance regimes and the rather uniform tree stand structures. We reviewed a large number of studies done in well preserved spruce stands throughout the Western Carpathians in Poland and Slovakia, which included analyses of the diameter and age distributions of stands and their short-term dynamics, as well as dendroecological reconstructions of disturbances over the last 200 years. The regeneration niches of spruce and accompanying tree species are also analyzed. Two models of the relationship between stand dynamics and stand structure are proposed for Western Carpathian subalpine spruce stands. In the first one, severe stand-replacing disturbances hit forests over a large area, resulting in low variability of the age and size of trees recruited synchronously over extensive areas. In the second model, gap-phase dynamics produce spruce stands composed of distinct age cohorts of trees that originated over extensive areas. In our models, different trajectories of forest dynamics can yield similar stand structures, which will not be good indicators of disturbance regimes. We suggest that the abundance of rowan and European larch is a more reliable indicator of past disturbance regimes, because rowan benefits most from gap dynamics, while European larch is connected with extensive stand-replacing disturbances. [ABSTRACT FROM AUTHOR]

In order to gauge ongoing and future changes to disturbance regimes, it is necessary to establish a solid baseline of historic disturbance patterns against which to evaluate these changes. Further, understanding how forest structure and composition respond to variation in past disturbances may provide insight into future resilience to climate-driven alterations of disturbance regimes. We established 184 plots (mostly 1000 m 2 ) in 14 primary mountain Norway spruce forests in the Western Carpathians. On each plot we surveyed live and dead trees and regeneration, and cored around 25 canopy trees. Disturbance history was reconstructed by examining individual tree growth trends. The study plots were further aggregated into five groups based on disturbance history (severity and timing) to evaluate and explain its influence on forest structure. These ecosystems are characterized by a mixed severity disturbance regime with high spatiotemporal variability in severity and frequency. However, periods of synchrony in disturbance activity were also found. Specifically, a peak of canopy disturbance was found for the mid-19th century across the region (about 60% of trees established), with the most important periods of disturbance in the 1820s and from the 1840s to the 1870s. Current stand size and age structure were strongly influenced by past disturbance activity. In contrast, past disturbances did not have a significant effect on current tree density, the amount of coarse woody debris, and regeneration. High mean densities of regeneration with height >50 cm (about 1400 individuals per ha) were observed. Extensive high severity disturbances have recently affected Central European forests, spurring a discussion about the causes and consequences. We found some evidence that forests in the Western Carpathians were predisposed to recent severe disturbance events as a result of synchronized past disturbance activity, which partly homogenized size and age structure and made recent stands more vulnerable to bark beetle outbreak. Our data suggest that these events are still part of the range of natural variability. The finding that regeneration density and volume of coarse woody debris were not influenced by past disturbance illustrates that vastly different past disturbance histories are not likely to change the future trajectories of these forests. These ecosystems currently have high ecological resilience to disturbance. In conclusion, we suggest that management should recognize disturbances as a natural part of ecosystem dynamics in the mountain forests of Central Europe, account for their stochastic occurrence in management planning, and mimic their patterns to foster biodiversity in forest landscapes. [ABSTRACT FROM AUTHOR]

Abstract: The study presents the results of long-term observations in seven old-growth beech-dominated forest reserves of the northwestern Carpathians. Investigated forests cover a variety of forest sites within the natural range of common beech (Fagus sylvatica L.) in Central Europe. The main goal of the research was exploring the magnitude and the character of the changes of basic stand characteristics over time. Only those old-growth beech forests were included in the study, where the proportion of beech was higher than 90% according to the last measurement. In each investigated reserve, usually three rectangular plots of 0.5ha were located and measured periodically every 10years. Within each plot, we recorded all living and dead (standing and lying) trees. Basic stand characteristics (stem density, basal area, growing stock, volume, and proportion of deadwood) were calculated for each old-growth forest and measurement year. The temporal variability was quantified by the relative change (%) between subsequent decades. In addition, the differences of diameter distributions between particular reserves and measurement years were analysed. The long-term average stem density ranged in the investigated old-growth forests from 226 to 401ha−1 and the average growing stock from 452 to 744m3 ha−1. The highest temporal variability was recorded in stem density (mean relative change of 9–17%), whilst the changes of basal area and growing stock were significantly lower (less than 10%). The long-term average deadwood volume fluctuated amongst the reserves between 91 and 345m3 ha−1 and the deadwood proportion between 17% and 51%. The mean relative change of the deadwood volume reached 7–42%. The comparison of diameter distributions between the reserves showed a high variability of diameter structures, whereas no identical distributions were observed. In individual reserves, the diameter structure was relatively stable over time and it remained unchanged for at least three decades in most cases. The majority of analysed diameter distributions had a bimodal shape and the best fit was performed by a finite mixture of two Weibull functions. The results showed that old-growth beech forests of northwestern Carpathians can be considered very stable ecosystems and therefore the return of beech to the native sites can promote the overall stability of managed forests in Central Europe. [Copyright &y& Elsevier]