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In spruce windfalls incurred in the autumn and winter season the synusia of cambioxylophagous fauna was evaluated in the profile of a whole stem and crown branches according to the species spectrum, tree cover and intensity of attack. The fauna of windfalls in the area with the basic level of Ips typographus and in the gradation area differed by species diversity. In the gradation area, frequency of the occurrence of Ips typographus (L.) was higher by 20-40%. P. chalcographus (L.) showed decreased stem cover in the gradation area. In the area with the basic state of Ips typographus, windfalls were intensively colonized by secondary species Hylurgops palliatus (Gyll.), Isarthron fuscum (Fabr.), Monochamus sp. With the increasing dbh (diameter at breast height) of windfalls the colonization of stems by Ips typographus was positively affected, H. palliatus, I. fuscum, Polygraphus poligraphus (L.) responded the other way round.

Studies were carried out in southern Poland during 2002-2006 in Scots pine stands under the effect of an outbreak of pine shoot beetles. The qualitative aspects of beetle feeding in tree crowns, studied on the basis of fallen shoots collected on experimental plots, are presented in this paper. The beetle numbers affected the age distribution of damaged shoots and the proportion of multiple attacks. The proportions of one-year-old shoots and the numbers of shoots with more than two attacks increased in the marginal part of the stand in the year of intensive feeding of beetles and in the subsequent year. A similar proportion of shoots with two attacks in both stands under investigations in individual study periods, with no relation to beetle numbers, does not permit to use this characteristic for forecasting purposes. The average length of tunnels in shoots attacked once reached 20 mm at maximum. The average length of tunnels (measured from the place of shoot disruption) was greater in shoots with two attacks than in shoots with a single one (P < 0.0001). The difference was not significant (P = 0.3429) only in stand B during the study season 2004-2005. The majority of the tunnels made in apical portions of shoots with two attacks damaged the tissue of apical shoots. The distance between the base of the second tunnel and the shoot apex in shoots with two attacks, and its significant (P < 0.01) linear relationship with the length of beetle tunnels, indicated a high nutritional quality of apical portions of shoots.

The paper analyzes the effect of whole-area site preparation by ploughing and of alternate field and forest crops on the understorey, soil biological activity and physical and chemical characteristics in the commercial forest. Another factor of the study was to assess the effect of the clearcut size on forest stands. Analyzed were 20-years-old stands of pedunculate oak (Quercus robur [L.]) on alluvial sites 1L9 (Fraxino pannonicae-Ulmetum). It can be deduced from the conducted analyses that after twenty years neither different site preparation nor clearcut size affected the understorey and soil biological activity. Field crops and forestry in alternation had a significantly adverse effect on porosity and water-retention capacity in the lower layer of top-soil (25-30 cm). Whole-area ploughing had a negative influence on the loss of organic substances due to accelerated mineralization. Nevertheless, the observed differences are not significant; the values did not fall below critical limits and in no case did they affect other studied site parameters or the development of root systems and aboveground parts of oak trees.

Natural mixed beech-fir forests were quite widely replaced by spruce dominated stands in Slovakia. Given the demands on the assessment of the forest status as well as on stopping the biodiversity loss it is required to evaluate the influence of Picea abies (L.) Karst. on the species composition. In a case study from the Veporské vrchy Mts. natural beech dominated forests were compared to stands with different spruce proportion. Within three groups of relevés with no, less and more than a half proportion of Picea abies the species diversity and Ellenberg indicator values were compared. The response of particular species to the proportion of Picea abies was evaluated by partial relation in direct gradient analysis. The increasing spruce proportion causes particularly higher occurrence of acidophytes and a decrease in nitrophytes. Species with the highest positive response to spruce are mostly shallow-rooted or characteristic of natural spruce forests. Greater richness along with the highest diversity was found in mixed stands with less than a half proportion of Picea abies. The most significant difference in species composition was between natural and spruce dominated stands. However the proportion of Picea abies does not reduce the species diversity in general, it causes significant changes in the species composition. As the results show, to avoid the negative effect and loss of phytodiversity it is required not to grow spruce dominated stands out of the natural occurrence of Picea abies.

Runoff generation under various natural conditions has often been studied in forested watersheds for a long time. In 1967, Hewlett designed a variable source area model. The model is based on the expansion and shrinkage of variable source areas and consequent changes in a drainage network during a discharge event. The runoff investigation was carried out in a forested watershed situated in the summit area of the Orlické hory Mts. The watershed has a drainage area of 32.6 ha with the land-surface elevation ranging from 880 to 940 m a.s.l. Runoff components, their amounts and ratios were calculated using a simple graphical-mathematical method of the hydrograph recession limb analysis according to a reservoir model representing the particular components (base flow, subsurface flow and overland flow, in other words slow, accelerated and rapid flows). Comparing the amount of slow and rapid runoff constituents (89.5-99.4% and 0.6-10.5%, respectively), the greater amount of slowly moving water confirmed that overland flow was absent under conditions of forest environment. Not even the drainage treatment altered this positive ratio of the runoff constituents. During the third period, under stabilized hydrology and stand conditions, the accelerated and rapid runoff increased again, however maximally by 10% and 4%, respectively, not reaching the initial size of the calibration period.

We provide fundamental information about the future development of selected climate elements in relation to anticipated threat to forests in the Czech Republic. All analyses were carried out in relation to four elevation zones with specific potential forest vegetation - up to 350 m a.s.l. (oak dominance), 350-600 m a.s.l. (beech dominance), 600-900 m a.s.l. (beech-fir dominance), 900-1,100 m a.s.l. (spruce dominance). We found out that while the projected increase in mean annual air temperature is almost constant over the Czech Republic (+3.25-3.5°C in the distant future), the frequency of heat spells at lower elevations is expected to increase dramatically compared to higher elevations. The precipitation totals during the vegetation season are projected to increase in the near future by up to 10% and to decrease in the distant future by up to 10% over all vegetation zones. In general, drought is presumed to become a key limiting factor at lower elevations, while increased temperature along with the prolonged vegetation season at higher elevations can be beneficial to forest vegetation. Consequently, northward progression of forest tree species and retraction of the species lower distribution range are a generic response pattern. Such impacts are presumed to be accompanied by changes in the distribution and population dynamics of pests and pathogens. Mainly the impacts on two key forest pests, Ips typographus and Lymantria dispar, are discussed.

The paper is the 6^th report on the production potential and stability of mixed forest stands in uplands. A mixed beech/larch stand that was established by natural regeneration in 1934 to 1942 is assessed. The stand is situated at an altitude of 460 m above sea level. It has been left to its natural development since 1961. At that time, the stand was characterized as an individually mixed, diameter- and height-differentiated 25-year pole-stage stand. The proportion of larch and beech amounted to 40% and 17%, respectively. Hornbeam (25%), oak (11%) and to a lesser extent birch (5%) and spruce (3%) also occurred in the stand. In the course of 42 years, the proportion of larch in this stand without planned thinning measures decreased to 35%. On the other hand, the proportion of beech increased to 39%. During all 5-year inventories, the stand could be characterized as a stabilized one with high production potential. Its initial growing stock 63 m³/ha at an age of 25 years increased to 497 m³/ha at an age of 67 years in 2003. At present, current volume increment amounts to 9.8 to 12.5 m³/ha/year.

Biotic agents driven spruce decline has been observed over several regions in Europe. We studied the spatial pattern of spruce stands mortality due to biotic agents in three spruce dominated regions in Slovakia - the Kysuce, Orava and Low Tatras regions. Regularly reported data on sanitary felling were used for the analysis. Geostatistical techniques and other spatial modelling tools were used to design the zones of biotic hazard for each region. Zone A stands for the totally disintegrated stands with extremely elevated activity of biotic agents. Zone B represents the buffer zone around the zone A. Its width depends on the spreading potential of biotic agents and related stand mortality observed during the last years. Zone C stands for the background areas, with more or less healthy stands. Zone-specific forest protection measures are proposed. Such a system allows for the priority rating of unnatural spruce stand conversion and optimal allocation of forest protection measures.

The Bruks mobile chipper was tested for chipping extracted non-merchantable stemwood at the roadside in Pine plantation in Victoria. The elemental time study method was used to evaluate the system productivity. The productivity, cost, biomass yield, remaining slash, chip quality (size classification and energy content), and fuel and energy consumption were analysed. Chipping extracted small logs at the roadside yielded a productivity of 43.88 GMt.PMH₀^-1 (19.4 BDT.PMH₀^-1). The average cost was about 16.96 USD.GMt^-1 (38.36 USD.BDT^-1).

Differences between the oak lepidopteran communities were studied in Slovakia in 1993 and 1994. Sampling was undertaken between April and October on 3 oak species. Biological traits of larvae were examined in order to explain differences in seasonal guilds among oaks. Cluster analysis shows similarities between communities in the flush feeder guild where the results were influenced mainly by temporal variability; in the late spring guild mainly by site; factors influencing summer feeder and autumn feeder similarities remain unclear. Detrended Correspondence Analysis (DCA) was used to investigate the main gradients explaining variability in communities. Results indicated that the host specificity along axis 1 (A1) and larval ballooning along axis 2 (A2) were important in the flush feeder guild; larval feeding strategy along A1 and the degree of defoliation by Lymantria dispar along A2 were important in late spring feeders; the year of study along A1 and host specificity along A2 were important in the summer feeder guild; and adaptation to lower quality of food along A1 and host specificity along A2 for the autumn feeder guild. The results are discussed.

Climate change is expected to influence the distribution and population dynamics of many insect pests, with potential severe impacts on forests. Spruce bark beetle Ips typographus (L.) (Col.: Curculionidae, Scolytinae) is the most important forest insect pest in Europe whose development is strictly regulated by air temperature. Therefore, climate change is anticipated to induce changes in the pest's distribution and development. We used the PHENIPS model to evaluate climate change impacts on the distribution and voltinism of spruce bark beetle in the Czech Republic. Two future time periods - 2025-2050 (near future) and 2075-2100 (distant future) - are addressed. The period 1961-1990 is used as the reference. We found that while a two-generation regime dominated in the Czech Republic in the reference period, significant three-generation regime regions are projected to appear in the near future. In the distant future, the three-generation regime can be expected to occur over all existing coniferous stands in the Czech Republic. The analysis of altitudinal shift of n-generation regime regions indicates noticeable expansion of Ips typographus development to higher elevations, leading for example to disappearance of one-generation regime regions in the distant future. Uncertainties and limitations of the presented findings are discussed as well.

A road network in forest lands provides easy access to forest resources for extraction, regeneration, protection and recreation activities. Erosion from forest roads and skid trails is a major concern in forest management due to the capability to cause adverse environmental effects. The objective of this paper is to introduce two methods for reducing erosion on forest roads and skid trails: water diversion and vegetation cover. Factors affecting erosion on forest roads and skid trails are climate, quality of forest road surfacing material, traffic, slope and vegetation cover. There are several management practices to mitigate the impact of logging and forest road and skid trail construction on stream water quality. Sediments delivered to streams from roads and skid trails lead to a number of dramatic effects on water quality and aquatic life. These management practices were found to be effective in controlling and reducing the runoff volume and soil erosion. Therefore, management and maintenance of forest roads and skid trails are essential elements to mitigate erosion.

The aim of this study was to compare the degree of root rot damage in two large complexes of Norway spruce stands established on former agricultural land at fertile sites. The root rot infection was observed on the stump cutting area on both intended and salvage clear fellings. Stands in Kružberk area in the Nízký Jeseník Mts. established on arable land showed very poor stability and large root rot damage at the age of 40-50 years. In contrast, stands in Lužná area in the Javorníky Mts., founded on former sheep pastures, were markedly much less damaged at the age of 90-110 years and proved to be able to provide quality timber, although they were damaged by the root rot as well.

The investigation of foliage biomass development including LAI and the growth of spruce and beech stands in the juvenile stage (age 1 to 21 years) represents a special complementary study to long-term research of water balance components on the experimental forest hydrology area Deštné Mountainside. The experiment is located in the Orlické hory Mts. at the altitude of 900 m on a clear-felled area. In 1982 the spruce plantation was established at 1.5 ´ 1.5 m spacing (4,600 plants/ha) and the beech plantation at 1.0 ´ 1.0 m (10,000 plants/ha). According to tending programs applicable to forest stands in the Czech Republic, two improvement fellings were carried out (1995 and 2001) in spruce and none in beech. In 2002, some 1,550 spruce trees/ha (mean height 10.1 m) and 7,440 beech trees/ha (mean height 4.8 m) were recorded. At the end of the first vegetation season in 1982, the dry matter (DM) of foliage in spruce and beech amounted to 35 and 70 kg/ha, respectively. Five years later (1987), these values increased to 770 and 360 kg/ha in spruce and beech, respectively. At a stand age of 21 years, foliage DM was determined to be 11,940 kg/ha for spruce and 3,050 kg/ha for beech. At the same time, the leaf-area index (LAI) was calculated to be 5.55 and 5.94 in spruce and beech, respectively. The method of foliage biomass quantification, based on the determination of foliage DM of mean sample trees and stand density, enabled to acquire complementary data usable in long-term research of the water regime of spruce and beech and simultaneously to provide information on the potential of biomass production and LAI value of both main commercial species in mountain forests of the Czech Republic.

The bark beetle Hylastes cunicularius was studied in the Tatra Mountains, West Carpathians, to clarify its role in transferring phoretic uropodine mites during dispersal in a mountain spruce forest. Emphasis was placed on the proportion of beetles vectoring deutonymphs of uropodine mites, and on assemblage structure, frequency distribution and placement of uropodids on the bark beetle vector. A total of 3,302 adults of H. cunicularius were caught into flight interception traps, of which 529 (16%) vectored a total of 1,020 individuals and four species of uropodine mites: Trichouropoda pecinai Hirschmann & Wisniewski, Trichouropoda obscura (C.L.Koch), Uroobovella vinicolora (Vitzthum), Uroobovella ipidis (Vitzthum). The uropodine mite assemblage was dominated by T. pecinai, which represented 94.6% of the collected mite individuals. T. pecinai and U. vinicolora were documented as new associates of H. cunicularius. Frequency distribution of uropodids on the beetle was L-shaped. The number of vectored mites and the number of dispersing individuals of H. cunicularius were positively correlated.

Coarse woody debris (CWD) is an important structural and functional component in forests in Northern Iran. In this study we determine the temporal patterns of CWD in Kheyroud Forests by examining the CWD volume in different decay classes and size classes along a chronosequence of secondary forest succession. The volume of CWD followed the general "U-shaped" temporal trend: the highest in the late successional forest (51.25 m³.ha^-1), lowest in the middle successional forest (25.95 m³.ha^-1) and intermediate in the early successional forest (37.05 m³.ha^-1). The late successional forest had a larger amount of logs, snags and stumps than the other two forests. In contrast, the snag volume did not differ between the late and middle successional forest. CWD in decay classes III and V was greater in the late successional forest than that in the other two forests, while CWD in decay classes II and I did not differ among the three successional forests. CWD in class II and I was significantly higher in the early successional forest than that in the middle successional forest. In the early and middle successional forests, CWD in early decay class was dominated by Carpinus betulus L. followed by Fagus orientalis Lipsky. In the late successional forest, CWD in early decay class was dominated by Fagus orientalis while CWD in the late decay class was dominated by Carpinus betulus. While forest succession had a large influence on the amount of CWD in different decay classes, it had no effect on CWD distribution among the different size classes. Our results suggest that both anthropogenic and natural disturbances have had a long-term effect on the distribution of CWD among three forests.

Although examples of payments for ecosystem services (PES) can be traced back at least as far as the 1980's, it is still a relatively new instrument, and the hitherto experience in many parts of the world is not extensive yet, or based on a very long timeframe. In addition, PES is being introduced in more and more sectors (agriculture, water supply, carbon sequestration, biodiversity conservation, etc.) and in relation to more and more ecosystems (surface water, groundwater, forest, etc.). But such PES can work only with good governance in place, comprising an effective political, legislative as well as institutional system. Nevertheless, an effective introduction of PES system into national legislation calls for an appropriate analysis of the current legal system so that duplications can be excluded and only valuable measures can be added. The main goal of this paper is to analyze if the current legal framework of the Czech Republic provides an appropriate basis for establishing payments for a forest ecosystem services scheme.

Small mammals cause serious damage to forests but there is only little knowledge of their ecology and possibilities of plantation protection. The objective of our study was to collect information on the damage caused by rodents to plantations of forest tree species. Data were obtained from a survey conducted in 2008 that was aimed at damage caused by small mammals. Questionnaires were sent mostly to foresters engaged in the Lesy CR state enterprise. We obtained usable data from 316 foresters. The response rate was 81%. It was confirmed that rodents cause significant damage all over the Czech Republic and that the occurrence of damage cannot be easily predicted with certainty as significant damage may appear perhaps in a small part of the threatened plantations where the key conditions for small mammals have been fulfilled. The main factors which affected probability of damage include: presence of a woody species attractive to rodents; suitable structure of ground vegetation enabling the pest species to breed sufficiently during the vegetation period; and also long-lasting snow cover. The current approach of forestry practice to damage by small mammals is considerably passive and we are missing an alert system of threat to stands and a methodology of dealing with problematic situations. Most of the foresters are uninterested in small mammals and many have only very smattering knowledge of the dangerousness of individual species and their ecological requirements. The use of rodenticides is expensive and the most effective and economic measure to lower damage by small mammals is to support forest management favouring natural regeneration of forest stands.

The noctuid C. trapezina (CT) has been considered an occasional predator of other Lepidoptera larvae. Functional/numerical response of predator and/or prey was estimated using 27 years of time-series data from Slovakia and stepwise multiple regression models (SMRM). SMRM were used to examine a possible delayed density-dependent feedback. We constructed 12 order-three autoregressive models [AR(3)] for CT and candidate prey. Independent variables were abundance of C. trapezina and abundance of candidate prey in lags 1, 2, and 3. Model variants were: (1) predation on free feeder models (FFM); (2) predation on shelter feeder models (SFM); (3) predation on the sum of 8 species models (S8M); (4) predation on all Lepidoptera models (ALM). Models were constructed for three areas (created by grouping sites based on significant correlations among CT populations). Additional comparative models were constructed for another three noctuid species and one geometrid species to compare their regression parameters under the same conditions as for CT. In total, 48 AR(3) SMRM were constructed for comparative species. A negative response of shelter feeders was found in models mainly for CT. We also found the positive response of CT growth rate to abundance of shelter feeders in lag 3 on two out of three models. This pattern was not found for any other comparison of species in the analysis. Possible mechanisms for these results are discussed.

The aim of this study was to investigate the wood density of Turkish hazel (Corylus colurna L.), an introduced species in the Czech Republic. Sample trees coming from a Czech site were tested for basic wood density and oven-dry density according to Czech national standards. Four sections were taken from each tree to evaluate the variability of wood density along the stem height and along the stem radius. The mean values for the basic density and the oven-dry density were 544 kg.m^-3 and 627 kg.m^-3, respectively. The results show that the highest density can be found in the bottom part of the tree, followed by a decline with the increasing height of the stem. For the radial direction from the pith to the bark, the pattern of density variability was more complex, reaching its highest value close to the cambium. Practically no correlation between annual ring width and density values was found out.

Comprehensive analyses of soil properties of sites of native Scandinavian broadleaved tree species were performed in 36 habitats in East Norway. The material consisted of stands of silver birch (Betula pendula Roth.), white birch (Betula pubescens Ehrh.), black alder (Alnus glutinosa Gaertn.), speckled alder (Alnus incana Moench.), European ash (Fraxinus excelsior L.), pedunculate oak (Quercus robur L.) and sessile oak (Quercus petraea [Matt.] Liebl.). The main objective was to describe the vertical characteristics and variations in some selected soil variables of the soil profiles. Particular soil horizons of 15 Brunisolic soils, 11 Regosolic soils, 6 Gleysolic and 4 Podzolic were sampled and analyzed for soil texture, bulk density, specific density, porosity, oxidizable carbon, total nitrogen content, pH in water, exchangeable acidity, exchangeable cations and anions (Mg, Ca, Mn, Al, S, Fe, B, P and K), cation exchange capacity and base saturation. No regular patterns were found in selected soil properties when tested between various soil units in silver birch stands. Furthermore, silver birch stands were found on sites, which topsoil (i) significantly differed in their cation exchange capacities, (ii) did not differ significantly in their pH values, and (iii) mostly differed in their clay contents and (iv) mostly did not differ in BS. Differences among the Humic Regosols, Luvic Gleysols, Sombric Brunisols, Eutric Brunisols and Humo-Ferric Podzols for silver birch stands in their topmost horizons of humified organic matter intimately mixed with the mineral fraction horizons and differences among particular soil horizons for the main soil properties under all the selected broadleaved tree species stands are discussed.

This paper presents research results of the performance of HSM-904 grapple skidder using a full tree harvesting method in a non-native aspen Populus deltoides plantation in even terrain conditions in Shafaroud, Northern Iran. Patch cutting as a silvicultural method was used in the plantation (2,000 ha). To evaluate the newly introduced machine to a ground skidding system in the aspen plantation and the possibility to increase the production rate, an empirical time study was conducted. The elements of the skidding work phase were identified and 58 cycles were recorded for the study. The models for effective time consumption, total productivity and work phase models are calculated. The average load per cycle was 2.2 m³, the average one-way skidding distance was 253 m. The average travel speed of unloaded skidder was 5.53 km.h^-1 and the average speed of loaded skidder was lower than the speed of the unloaded one by 2.94 km.h^-1. The average output in the study was 7.1 m³ per effective hour and the unit cost was 13.9 USD.m^-3.

The results of research on the production of raw timber assortments for the stands of poplar clones Robusta and I-214 in Slovakia are presented in this paper. Models of assortment yield tables were constructed, separately for each clone, in dependence on the yield class and stand age. The construction was based on the models of yield tables, stand assortment tables, models of external quality and damage to stems. Robusta clone produces by about 15-20% higher proportions of the highest quality assortments than I-214 clone. I-214 clone produces faster and higher proportions of average- and below-average quality assortments.

Toxic pollution of soils is a major environmental problem in the Czech Republic. Most contemporary remediation approaches do not provide acceptable solutions. For environmental clean-up, the use of specially selected and engineered plants capable of effective restoration and stabilization of contaminated sites is an emerging technology called phytoremediation. Aspen (Populus spp.) trees represent optimal plants for absorption, accumulation, storage, and degradation of environmental pollutants such as heavy metals, pesticide residues, and other waste products. The first aim of this study was to verify possibilities of micropropagating selected elite European aspen (Populus tremula) and hybrid aspen (Populus tremula × Populus tremuloides) mature trees growing in polluted areas. The primary cultures were established from 24 years old trees from provenance plots. Dormant buds were sampled from selected trees in spring. After sterilization of dormant buds, the shoot tips were extirpated and put on nutrient media. MS medium with a higher concentration of BAP (1.0 mg/l) and IBA (0.1 mg/l) showed to be suitable for induction of organogenesis. MS medium with lower concentration of BAP (0.2 mg/l) and higher concentration of glutamine (100 mg/l) in agar medium was used for multiplication. A high number of adventitious shoots (20-30) was produced per multi-apex culture. The losses during rooting and acclimatization were minimal, around 2%. Currently, the plantlets grow on the outside bed of the experimental nursery. Twenty-five clones were established in the gene bank. Secondly, standardization of the efficient transformation of hybrid aspen was investigated with the aim to facilitate production of transformed hybrid aspen with valuable genes for increased capability of phytoremediation in the near future. Four gene constructs of Agrobacterium tumefaciens comprising different promoters (bearing two genes, NPTII coding resistance to kanamycin, and GUS coding glucuronidase synthesis allowing histochemical and fluorometrical identification) were used for transformations of aspen hybrid stem segments. A promoter suitable for transformations was selected on the basis of GUS activity assay. The highest activity was estimated in transformants with construct 148 controlled by promoter CAMV 35S.

The paper presents results from a study of sycamore maple development, health condition and growth in forest altitudinal vegetation zones (FAVZ) 6 and 7 occurring in pollution damage zones A and B in the air-polluted region of Krušné hory Mts. as compared with the trees of identical height in FAVZ 4 and 5 occurring in pollution damage zone D in the Bohemian-Moravian Upland. Sycamore maple develops a fully diversified root system. On spread mounds it creates only a superficial root system and its growth is retarded. The growth of sycamore maple is limited by the layer of humus horizons. If the layer thickness is over 20 cm, the sycamore roots would grow into mineral horizons.

A field production study was conducted for a manual harvesting system using a chainsaw in a Caspian hardwood forest site. A selective cut was performed on a 42-hectare tract with an average slope of 30 percent. Felling time per tree was most affected by diameter at breast height and by the distance among harvested trees. The gross and net production rate was 20.6 m³ and 26.1 m³ per hour/one person, respectively. The unit cost considering the gross and net production rate was 1.05 USD/m³ and 0.81 USD/m³, respectively. The significant variables included diameter at breast height (D) and distance among harvested trees (L) for the time expenditure model. This regression function is statistically significant at α = 0.01.

In the spring of 2000, field experiments were begun on three 20-year old grand fir (Abies grandis) to influence the elasto-mechanical behavior of the stem, as well as the distribution of the assimilate crown production. The aim was to analyze, and then describe and model the expected resulting change in stem growth. Three stem sections of one fir were reinforced by rigidly attaching T-shaped steel bars to reduce bending stresses. Preliminary calculations with an elasto-mechanical tree and force model (that had been developed for a different tree, but was adapted by taking the size differences into account) gave first indications for the experimental design in regards to the necessary number of the bars and their dimensions required to guarantee that the stem rigidity would be highly increased. Furthermore, the simulations proposed no increased risk of stem breakage in the non-reinforced stem parts. The stability of the second tree was decreased by hanging sand bags with defined masses on the branches. Directly after loading, a significantly changed swaying behavior could be observed, which should cause correspondingly higher stress in the fibers. As for this load case, the simulated results prognosticate only a negligible increase in stress. The roughly-adapted model used, is seemingly invalid for this tree. In regards to the third tree, the bark at the base of all branches of the eastern half of the crown was removed to prevent any import of assimilates into the stem. The branches were not cut off because the mass distribution and thus, the mechanical behavior, of the tree was to be influenced as little as possible. The experiment will be concluded in the winter of 2003, after a four-year growth period. In addition to detailed stem analyses, the spatial crown structure with its needle and branch mass distribution, as well as the mechanical wood properties of the stem will be measured.

Frost cracks which originated in birch due to bending during long-term icing in winter 1995/1996 became the place of entrance for the attack of birch stems by Piptoporus betulinus (Bull. ex Fr.) Karst. and subsequently for one of the causes of birch stand disintegration in the Krušné hory Mts. The hypothesis is substantiated on the basis of regularities of the frost crack dispersion in the stem profile, frequency of occurrence related to the stand age, altitude and cardinal points. The number of frost cracks increased with the transect profile altitude 700-850 m. One crack on the birch stem predominated (73%) while the higher number of frost cracks occurred at altitudes > 800 m. In stands younger than 20 years, frost crack damage was higher (34-47%) than in older stands (14%). Frost cracks occurred in the lower part of stems with the highest bending stress.

In summit parts of the Orlické hory Mts., massive dieback of forests occurred during an air pollution/ecological disaster in the 70s to the 80s of the 20^th century. Destroyed stands were cut down and deforested areas were planted by more resistant species including mountain pine (Pinus mugo Turra). The aim of the paper was to assess effects of mountain pine on the prosperity of other tree species. Four localities with mountain pine stands were selected at altitudes from 1,000 to 1,115 m. In 2003-2005, growth analyses of shrubs were carried out there and basic parameters of stands were determined such as: height; cover of mountain pine, other tree species and herbs; radiation transmittance and temperature gradients. Results show the importance of the height of mountain pine stands in mitigating climatic changes in the ground layer of air, identification of the light compensation point for the mountain pine prosperity, the dependence of a growth type on outer and inner conditions of mountain pine including partly its age. Under given conditions, the present stands of mountain pine on top parts of the Orlické hory Mts. show their justification because they create a good protection for young seedlings, self-seeding and newly planted tree species. If forest spreads there, the markedly heliophilous mountain pine will recede similarly as in case of more than hundred-year-old mountain pine in the Sowie gory Mts. in Poland.