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Summary: Preliminary results of an investigation of the thinning effect on Norway spruce tree growth in terms of xylogenesis and phloemogenesis are presented. Three plots were selected where the stand densities were reduced by pre-commercial thinning to 1800 trees/ha (plot A; mild thinning) and 1300 trees/ha (plot C; heavy thinning) in February 2020. Plot B had no silvicultural intervention and represented a control variant (4500 trees/ha). Three dominant 14-year-old Norway spruce trees were sampled (micro-cored) for studying the xylem and phloem formation in the 2020 growing season. The total differentiation duration was determined to be around 169.7 ± 12.7–179.3 ± 4.0 days. The average number of xylem cells formed in control plot B was only 140 mature cells, plots C and A were determined to have 175 and 200 mature cells, respectively. Plot A had the fastest growth rate of all the plots studied. In all three plots (A, B, C), the beginning of the early phloem, late phloem sieve cells, and axial parenchyma cells coincided. Nonetheless, in terms of total phloem cell increase, plot C displayed the fastest growth rate among the three plots studied. The first results showed that the rate of total increment in both xylem and phloem cells, as well as the total number of produced tracheids and sieve cells, seem to be positively affected after the thinning application. [ABSTRACT FROM AUTHOR]

Norway spruce stands are established and managed along various site conditions in central Europe. Currently, spruce often grows at locations outside of its ecological optimum, resulting in extensive damage elicited by harmful abiotic and biotic factors, which relatively shortens the time to change this adverse status in the adaptation frame by foresters. Except for the rapid change in species composition through clear-cuts, another way is possible, i.e., stabilising current (especially young) spruce stands to extend the time required to implement adaptation measures. The assumption that different site conditions will have to be respected as part of this adaptation was confirmed by our study based on NFI data of the Czech Republic. A semiparametric generalized linear model (GAM) was used to model the relationship between the height-to-diameter ratio and forest stand age, differentially considering particular forest vegetation zones. Spruce stands with lower elevations attain a lower stability (expressed by their height-to-diameter ratio; HDR) than those in the mountains. The HDR culminated in lower and middle altitudes in the first half of the rotation period, representing the most critical timing and effectivity of silvicultural measures. Contrary to previous findings, we found higher HDR values at nutrient-rich sites than those at acid ones, especially up to 50–60 years old. Therefore, more research should be devoted to the issue concerning the same thinning regime under different site conditions. [ABSTRACT FROM AUTHOR]

Although the ongoing global climate change elicits a shift in tree species composition along the vertical gradient, very extensive areas of pure Norway spruce [Picea abies (L.) Karst.] stands still occur out of their ecological optimum in the Czech Republic and Central Europe. Adaptive measures should be applied in these stands to promote productivity and stability. All measurements were performed in the 2018–2021 period on three permanent research plots located in the North-East part of Bohemia (Czech Republic). Based on the results, the most favourable way to increase solar radiation use efficiency expressed by canopy production index (CPI) and leaf area efficiency (LAE) is in-time heavy pre-commercial thinning application. Th e highest CPI and LAE values were observed in the Norway spruce stand aft er heavy pre-commercial thinning application (CPI = 2.00 and LAE = 1.59). In contrast, CPI = 1.26 and LAE = 0.99 were observed aft er the mild one, and CPI = 0.73 and LAE = 0.60 were reported in the control treatment with no silvicultural intervention. Overall, the presented results indicate a positive effect of heavy pre-commercial thinning on CPI and LAE in pure young Norway spruce stands. However, more eff ort should be devoted to studying the impact of different pre-commercial thinning intensities on solar radiation use efficacy across a broader gradient of site conditions, and future work should also be extended to other tree species. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the influence of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.) on the vertical distribution of Cd, Cu, Pb and Zn in forest soil. Soil samples were taken from six beech- and six spruce-dominated mature (80–100-year-old) forest stands. In total, 420 composite soil samples were collected from the organic horizons, and at depths of 0–2, 2–10, 10–20 and 20–30 cm in the mineral soil, of 84 plots in a hexagonal sampling design. A direct influence of forest type was confirmed for Zn, which showed increased soil accumulation under beech. In spruce stand soils, Zn is likely to have leached more due to lower pH levels. While a minor influence of tree species on the vertical distribution of Cd, Cu and Pb was also confirmed, particularly as regards accumulation in the F + H layer of spruce stands, the results suggest a more dominant effect of other site-specific conditions at the scale studied, such as topography and atmospheric deposition, despite homogenous forest stand conditions. Furthermore, the C:N ratio had a significant impact on both Cd and Cu content, regardless of forest type, highlighting the importance of specific site conditions for driving decomposition of organic matter, a primary factor affecting Cd and Cu mobility in soil. [ABSTRACT FROM AUTHOR]

(1) Background: The growth and morphology of Norway spruce (Picea abies (L.) Karst.) juveniles were observed under different light conditions due to overstory canopy openness. The aim was to investigate the photo-morphological responses of juveniles for the development of a desirable forest structure. The research was located in a higher altitude zone in central Europe. (2) Methods: Light was estimated using hemispherical photographs. Eight different parameters of natural regeneration were measured on individuals within 1 × 1 m around each point on a 3 × 3 m grid. A total of 1214 sapling measurements (from 10 to 431 cm in height) were taken. (3) Results: Light affected the growth and morphological development of juveniles, resulting in variation in the lateral crown growth and crown length. Acclimations manifested as trade-offs between height and lateral crown growth. Similar shifts were found within relative height growth (the terminal length to the total height) and apical dominance ratio (the terminal length to the branch length). The crown length was proven to be highly capable to acclimation. Light influenced the density weakly, however, when a regeneration index (density × median height) was considered, significant relations with light conditions were discovered. [ABSTRACT FROM AUTHOR]

Heavy thinning is supposed to be helpful for maintaining more favorable water balance in forest stands, and thus mitigate impact of drought episodes. To investigate impact of thinning on topsoil (10–13 cm) moisture conditions, a two-year soil sampling campaigns were conducted in 2019 and 2020. The soil moisture was calculated using a water-weight loss approach based on dry/fresh sample weight ratio. The samples were collected using metal capsules of known weight from totally 8–9 experimental series monthly during growing seasons of 2019 and 2020, respectively. Each series included thinned and un-thinned young growth stands of Norway spruce monoculture, spruce mixed with broadleaved tree species and mixture of sycamore maple with rowan. However, the statistically significant differences were not found in topsoil moisture between thinned and un-thinned young growth stands, thinned ones showed slightly better water balance conditions during both investigated years. Reduced number of trees and canopy closure had not depleted water throughout evaporation from upper soil profile. Therefore, thinning of young growth should be recommended especially at drought-endangered sites. Forest health decline and following die-off are exhibited in large areas of monospecific stands of Norway spruce and Scots pine in the Czech Republic. This development is attributable to shifts of conditions such as high air temperatures in growing seasons and different distribution of precipitation amounts over year, which resulted in hydrological drought in 2015–2019. Thinning is a deliberate measure that helps us control future stability, health and resilience of young forest stands and also impacts on species composition, environment and nutrient cycle in the stands. Heavy thinning is supposed to affect hydrological balance as interception is reduced (lower LAI) and more soil water is expected to be available for the trees left on site. On the other hand, such thinning intensity can increase evaporation from inside the stands and it also increases temperature amplitudes. The drought stress is even attributable to increased transpiration rates from released trees in case the soil below canopy has been dry for a long time. If true frequently, one can doubt a usefulness of heavy thinning at drought-endangered forest sites. This article deals with topsoil moisture below thinned thickets of tree species that were compared with moisture conditions below unthinned thickets. The objective of the study addressed a research question whether the thinning affected availability of water in soil, and thus proved a beneficial effect of the heavier thinning on the young drought-endangered forest stands. The sampled stands were monospecific spruce, spruce mixed with other, mainly broadleaved tree species and sycamore maple with rowan (Table 2). The thinning aimed at releasing crop trees of better quality and removal of both the unhealthy ones and wolf broadleaves; the thinned treatment was always accompanied with the unthinned one. 10–13 cm mineral topsoil samples (20 per thinned-unthinned series i.e. 10 per the treatment, see Table 3) were taken monthly in May-September periods in 2019–2020. Larger stones were excluded from the samples, and each sample was placed into metal capsules (of known weight) and covered with lid. The closed capsules were then delivered to laboratory where a water weight loss was measured as ratio of dry (dried at 105 °C) and fresh sample weights; this allowed us to determine a soil sample moisture. Arithmetic means were calculated from 10 values representing thinned and unthinned moisture conditions. The differences were tested using a pair t-test and 95% confidence intervals of difference were computed using R 3.6.3 (R Core Team 2020). In 2019, topsoil moisture was affected negatively by low precipitation at depth of 10–13 cm; minimum values were shown in July. Following 2020 showed more favorable conditions with maximal values in May and July. Soil moisture showed also higher variability in 2020 compared to 2019 (Fig. 1). The differences between control and thinned treatments were very small and even negligible. In 2019, the sites benefited from thinning slightly except for May values when 0.4% higher soil moisture was found below unthinned canopy. No statistically significant (α = 0.05) differences excepting for the thinned treatment in September (1.5% higher moisture, p = 0.02) were found in 2019. The topsoil moisture was 0.6% higher insignificantly (p = 0.27; 95% confidence interval 0.6 ± 1.1 %) under thinned treatments in 2019. Next year, the soil moisture values exhibited small differences reflecting also benefit from thinning; the only zero difference was shown in August. The highest moisture attributable to removal of trees amounted 1.8% higher moisture compared to control in July. No statistically significant (α = 0.05) differences were found significant though July values were at limit of significance (p = 0.05). The topsoil moisture was 0.9% higher insignificantly again (p = 0.16; 95% confidence interval 0.9 ± 1.3 %) under thinned treatments in 2020. Based on the two-year measurement campaign and data analysis it can be concluded: • More favorable precipitation conditions of 2020 affected 10–13 topsoil moisture values positively compared to precipitation-poorer 2019. • The topsoil moisture below thinned thickets showed slightly higher values compared to conditions without thinning; the differences were found insignificant mostly. • Removal of trees and following broken canopies, however, did not show depleted topsoil water due to higher evaporation from exposed forest floor surface. The early thinning of the thickets should not, therefore be ignored at drought-endangered sites. [ABSTRACT FROM AUTHOR]

Topsoil contents of cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn) and related soil properties such as pH and carbon (C) and nitrogen (N) contents were studied in the two main forest types of the Archbishopric forests in the area of the Jeseníky Mts., Czech Republic. Statistical comparisons were carried out between mature Norway spruce (NS) and European beech (EB) stands, separately for the forest floor (horizons FH) and the mineral (0–2 cm depth) soil. The FH horizons under EB showed higher contents of Zn, as compared to NS. In comparison, potentially higher contents of Cd were found under NS. The mineral topsoil under EB showed higher contents of Pb and Zn as compared to NS. In contrast, the pH was higher and the C:N ratio lower under EB, as compared to NS in both soil layers; the latter due to higher C under NS in organic horizons, while higher N under EB in the mineral soil. The results indicate that the species composition of managed forests may have conflicting impacts on soil quality and the accumulation and persistence of heavy metals in forest soils. [ABSTRACT FROM AUTHOR]

Plant growth is affected by light availability, light capture, and the efficiency of light energy utilisation within the photosynthetic uptake processes. The radiation use efficiency (RUE) of four even-aged, fully stocked mature Norway spruce stands along a temperature, precipitation, and altitudinal gradient of the Czech Republic was investigated. A new straightforward, methodological approach involving an analysis of digital hemispherical photographs for RUE estimation was applied. The highest annual RUE value (0.72 g MJ−1) was observed in the stand characterised by the lowest mean annual air temperature, the highest annual amount of precipitation, located at the highest altitude, and with the lowest site index reflecting site fertility. From the viewpoint of global climate change mitigation, this stand fixed 4.14 Mg ha−1 and 13.93 Mg ha−1 of carbon units and CO2 molecules into above-ground biomass, respectively. The lowest RUE value (0.21 g MJ−1) within the studied growing season was found in the stand located at the lowest altitude representing the site with the highest mean air temperature and the lowest amount of precipitation where 1.27 Mg ha−1 and 4.28 Mg ha−1 of carbon units and CO2 molecules, respectively, were fixed. From the tested meteorological variables (mean air temperature, the monthly sums of temperature, precipitation, and air humidity), RUE was only significantly dependent on air temperature. Therefore, global warming can lead to diminishing RUE and carbon sequestration in Norway spruce stands, especially at low altitudes. [ABSTRACT FROM AUTHOR]

The paper analyses stand structure and production on two experimental forest stand series of mature pure and mixed Scots pine stands, growing on natural Scots pine sites in the Czech Republic. Sessile oak was the main admixed species. In mixed stands, Scots pine constituted the dominant level of the stand, admixed species grew mostly as subdominants. Admixture increased stand densities and aboveground biomass production compared to pure stands. Sessile oak with the 20-30% number share within the Scots pine stand led to an increase of the Scots pine tree dimensions and mean stem merchantable wood (DBH ≤ 7 cm) volume compared to the pure Scots pine stand of similar density. The Scots pine and sessile oak slenderness ratios increased in mixed stands compared to monocultures, however, the stand mechanical stability was not threatened. [ABSTRACT FROM AUTHOR]

Fast and precise leaf area index (LAI) estimation of a forest stand is frequently needed for a wide range of ecological studies. In the presented study, we compared side-by-side two instruments for performing LAI estimation (i.e. LaiPen LP 100 as a "newly developed device" and LAI-2200 PCA as the "world standard"), both based on indirect optical methods for performing LAI estimation in pure Norway spruce (Picea abies (Linnaeus) H. Karsten) stands under different thinning treatments. LAI values estimated by LaiPen LP 100 were approximate 5.8% lower compared to those measured by LAI-2200 PCA when averaging all collected data regardless of the thinning type. Nevertheless, when we considered the differences among LAI values at each measurement point within a regular grid, LaiPen LP 100 overestimated LAI values compared to those from LAI-2200 PCA on average by 1.4%. Therefore, both instruments are comparable. Similar LAI values between thinning from above (A) and thinning from below (B) approaches were indirectly detected by both instruments. The highest values of canopy production index and leaf area efficiency were observed within the stand thinned from above (plot A). [ABSTRACT FROM AUTHOR]

One of the main ideas of non-native tree species introduction into forest stands is to replace declining native species. The same is also valid for industry; the wood of native species should be replaced by a wood of the same or even better quality. Douglas-fir is often compared to other coniferous tree species based on its production. This study compared Douglas-fir wood properties with European commercial species, namely Norway spruce, Scots pine, and European larch. Trees representing different sites and ages were tested for wood density, shrinkage, and compression strength. In all cases, Douglas-fir outclassed spruce and pine in density and strength. The difference was striking, especially for spruce, where the density was surpassed by Douglas-fir by more than 100 kg.m−3 (above 25%). In the case of compression, the strength of Douglas-fir was up to 12.3 MPa higher (above 33%) compared to spruce. The only species that obtained higher figures was larch. Wood shrinkage was comparable to European softwoods. Therefore, Douglas-fir wood can be regarded as an excellent and promising substitute for the European processing industry. • Douglas-fir represents promising non-native species for Europe. • It should be a substitute, especially for Norway spruce in industry. • We tested some of the properties important for applications. • In contrast to previous studies, tested species grew together in the same stand. • Douglas-fir exceeded not only spruce but also Scots pine. [ABSTRACT FROM AUTHOR]