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ABSTRACT:The article describes natural, combined and artificial regeneration on 38 permanent research plots in both Czech and Polish part of the Krkonoše Mts. The attention is paid to species composition, spatial (horizontal and vertical) and age structure of forest regeneration according to different stand and site conditions. Concerning the structure and dynamics of forest stands and their regeneration, the potential and prospects of regeneration according to particular developmental stages and stand types (beech stands; mixed stands: spruce-beech, fir-beech, spruce-firbeech; spruce stands, stands in the ecotone of the upper forest limit and relict pine woods) were evaluated. In many aspects the plots show several similarities, nevertheless the regeneration in different site and stand conditions show clear differences in dynamics of development. The main differences are result of different ecological conditions, environmental limits and biological characteristics of dominant tree species.Keywords: forest ecosystem; forest regeneration (natural, combined, artificial); Krkonoše Mts.; site and stand conditions; structure and development of forest stands Increasing the ratio of natural regeneration is in present days considered as one of the main challenges of the Czech forestry and nature protection. The use of natural regeneration is commonly accepted as essential part of close-tonature forest management based on ecological principles. Beside lower establishment cost, natural regeneration is important measure in conservation of forest genetic resources and establishment of forest stands with appropriate tree species composition and ecological stability. In the Krkonoše National Park the ratio of natural regeneration is constantly increasing (Fig. 1) with simultaneous decrease of artificially regenerated areas, usually of conifers (mainly spruce). Issue analysisNatural regeneration, its age, species and height structure have a key role in regeneration of tree layer in forest ecosystems. Regeneration processes and their dynamics largely influence stability and functionality of forest stands. The advantages of natural regeneration lie mainly in maintaining of autochthonous or well-established allochthonous populations of forest woody plants with presupposition of preserving desirable qualities of maternal forests, i.e. individuals of regeneration that well adapted to more extreme site conditions; it enables to use effectively differences in site conditions (Korpeľ et al. 1989;Vacek et al. 2010a).The regeneration development in forests with natural or near-natural structure is related to the occurrence of disturbances in the forest development. The success of natural forest regeneration depends on a number of factors. Worsening conditions for existence of a forest in mountain areas (climatic and soil extremes) result in decreasing generative reproduction ability of forest woody plants. Continuous regeneration is dependent on

Abstract:The paper deals with the structural diversity and production of a less frequently studied type of alder stands originated on former agricultural lands in the 1950s, established partly by plantation and partly by natural succession in the area of the Krkonoše Mts. and the Orlické hory Mts. (Czech Republic). Four permanent research plots (PRP) were established at sites where Black alder (Alnus glutinosa L. Gaertn.) and Grey alder (Alnus incana L. Moench.) naturally occurs, each plot of 0.25 ha in size. The aim of the study was to evaluate the structure and development of the alder stands with respect to biodiversity, horizontal, vertical and species structure, diameter increment with emphasis on climate factors, and the quantity and quality of timber production. The results document low diversification of the studied stands in the PRPs. The horizontal structure is defined as random and clumped at sites at the highest altitude with high water table. The number of living trees with DBH ≥ 4 cm ranges between 556 to 828 trees ha -1 with the relative stand density index (SDI) 0.67-0.77. The stand volume ranges from 247 to 393 m 3 ha -1, and decreases with higher altitudes. Low temperatures is limiting factor for radial growth in the high mountain areas, respectively low precipitation in the middle lands. Owing to a rather specific site character, as especially the spring area, the stands exhibit only average production, but the production quality is generally high. The quality timber is suitable for industrial use; the rot-affected trunk base parts usable for fuel represent only approximately 16%.

ABSTRACT:The research is focused on structure and development of forest stands from 5 th to 8 th forest vegetation zone in the Krkonoše Mts. The forest stand diversity according to tree species composition and representation, horizontal and vertical structure was evaluated by using following indices: Clark-Evans aggregation index (Clark, Evans 1954), standardised Arten-profil index (Pretsch 2005) and index of complex diversity after Jaehne, Dohrenbusch (1997). Growth model SIBYLA (Fabrika, Ďurský 2005) was used for visualizations and growth predictions of forest stands on particular plots. Based on research results, management recommendations were evaluated.

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