Norway Spruce Stands Research Articles

Remote Sensing Assessment of the Expansion of Ips typographus Attacks in the Chuprene Reserve, Western Balkan Range

The Chuprene Reserve was created in 1973 to preserve the natural coniferous forests in the Western Balkan Range in Bulgaria. The first infestations by European spruce bark beetle (Ips typographus) were registered in Norway spruce (Picea abies) stands in the mid-1980s. The aim of this study is to assess the damages caused by I. typographus in the Chuprene Reserve using remote sensing techniques – unmanned aerial vehicle (UAV) images, airborne images, and satellite images of European Space Imaging (EUSI), combined with terrestrial verification. High-resolution images in four bands of the electromagnetic spectrum and in a standard RGB channel were taken in 2017 via a multispectral camera ‘Parrot Sequoia’, integrated with a specialized professional UAV system eBee ‘Flying Wing’. The health status of Norway spruce stands in the reserve was assessed with the normalized difference vegetation index, based on the digital mixing of imagery captured in the red and near infrared range. The dynamic of bark beetle attacks was studied in GIS on the basis of maps generated from photographic surveys, airborne images taken in 2011 and 2015, and satellite images from 2020. In the UAV-captured area (314.0 ha), the size of Norway spruce stands attacked by I. typographus increased from 7.6 ha (2.4%) in 2011 to 44.9 ha (14.3%) in 2020. The satellite images showed that on the entire territory of the Chuprene Reserve (1451.9 ha), I. typographus killed spruce trees on 137.4 ha, which is 9.6% of the total area.

Growth, Yield and Carbon Sequestration of Even-Aged and Uneven-Aged Norway Spruce Stands – Evaluation and Application of a Process-Based Model

Growth, Yield and Carbon Sequestration of Even-Aged and Uneven-Aged Norway Spruce Stands – Evaluation and Application of a Process-Based Model

Spruce forest afforestation leading to increased Fe mobilization from soils

Increasing exports of Fe and DOC from soils, causing browning of freshwaters, have been reported in recent decades in many regions of the northern hemisphere. Afforestation, and in particular an increase of Norway spruce forest in certain regions, is suggested as a driver behind these trends in water chemistry. In this study, we tested the hypothesis that the gradual accumulation of organic soil layers in spruce forests, and subsequent increase in organic acid concentrations and acidity enhances mobilization of Fe. First generation Norway spruce stands of different ages (35, 61, 90 years) and adjacent arable control plots were selected to represent the effects of aging forest. Soil solutions were sampled from suction lysimeters at two depths (below organic soil layer and in mineral soil) during two years, and analyzed for Fe concentration, Fe speciation (XAS analysis), DOC, metals, major anions and cations. Solution Fe concentrations were significantly higher in shallow soils under older spruce stands (by 5- and 6-fold) than in control plots and the youngest forest. Variation in Fe concentration was best explained by variation in DOC concentration and pH. Moreover, Fe in all soil solutions was present as mononuclear Fe(III)-OM complexes, showing that this phase is dominating Fe translocation. Fe speciation in the soil was also analyzed, and found to be dominated by Fe oxides with minor differences between plots. These results confirmed that Fe mobilization, by Fe(III)-OM complexes, was higher from mature spruce stands, which supports that afforestation with spruce may contribute to rising concentrations of Fe in surface waters.

Forest stand structure and cone crop affect winter habitat use by Eurasian red squirrel (Sciurus vulgaris)

Food resources are one of the important components of high quality habitat. One way to better understand the behavioral decisions made by animals to select foraging patches is focusing on the important forest stand structure characteristics. In this study we investigate the relationship between red squirrel habitat preferences, forest characteristics, i.e. distance to forest edge, canopy closure, cover of understory and undergrowth, and estimated cone biomass. We explore for the first time a methodology to predict cone biomass based on allometric equations and the extent to which this parameter affects habitat choice by red squirrels. Using tree measurements to predicted cone biomass at the plot level which is located in a given stand provides a usefulness proxy of food resources and it is not time-consuming compare with the traditional annual cone count. We selected sixty 30-by-30 m plots in mature Norway spruce forest stands where we measured percentage understory cover, percentage undergrowth cover, distance to forest edge, number of Norway spruce trees, diameter at breast height and height of each Norway spruce tree, number of other tree species and percentage of canopy closure. Within each plot, we counted all Norway spruce cones stripped by red squirrels. Results showed that both forest characteristics (i.e. distance to forest edge and canopy closure) and estimated cone biomass were significant predictors of red squirrel feeding signs on Norway spruce. Our study revealed the potential usefulness of cone biomass as a parameter to determine cone productivity of Norway spruce stands. The effects of food abundance and forest stand structure characteristics are crucial for habitat selection by red squirrels. Estimation of cone biomass based on the tree measurement can be useful for predicting potential foraging habitats for red squirrels regardless of the seed year and can be simple to use for conservation practice in order to locate potential sites for protection of this species.

Potential relationships of selected abiotic variables, chemical elements and stand characteristics with soil organic carbon in spruce and beech stands

Increasing attention is given to carbon sequestration in forest soil with regard to climate change and the mitigation of its impacts; therefore, it is very important to know which parameters and variables could influence carbon sequestration and throw light on their relationships. The aim of this study is to assess the role of abiotic variables, chemical elements and stand parameters in soil carbon sequestration, and clarify which of these could affect soil organic carbon (SOC) content in the surface mineral horizon in Norway spruce and European beech stands in Czech Republic. We analyzed 81 monitoring plots within pure and mixed stands of spruce and beech with different degrees of forest naturalness. In each monitoring plot, SOC content, chemical elements (content of bound forms of oxides: tFe, tAl, tCa, tMg, tK, tMn, tP, tN) and related variables (BS, pH, C/N) were measured. The effect of these variables, including abiotic variables (elevation, temperature, precipitation, duration of growing season and soil group) on SOC content was tested, and differences between represented stands (natural vs. unnatural, pure vs. mixed, spruce vs. beech) were analyzed. The results showed that elevation has a positive relationship to SOC content. Of the studied chemical elements and related variables, only tN content was significantly related to SOC content. A positive relationship was also demonstrated between forest naturalness and SOC content. The highest SOC and tN contents were observed in pure natural Norway spruce stands, which likely play a very important role in SOC sequestration. In the context of the current issue of unnatural Norway spruce stands in the Czech Republic, a higher SOC content was found in mixed natural European beech stands than in either pure or mixed unnatural Norway spruce stands. Therefore, replacing the unnatural Norway spruce stands in the study area with mixed natural European beech stands could represent a viable alternative to current forest management in terms of soil carbon sequestration, especially in the context of global climate change and spruce dieback.

Growth response to thinning in two-storied mixed stands of Scots pine and Norway spruce

ABSTRACT The influence of thinning on growth, development, and yield of a spruce understory and a pine overstory was examined based on an experiment including five stands in southern Finland. Two thinning intensities (regular and heavy) were applied to the pine overstory. They were combined with four treatments in the spruce understory: total removal, retention of 800 and 1600 stems ha−1, and untreated. The plots were remeasured at 5-year intervals during the monitoring period of 10–15 years. The results indicated that thinning of the pine overstory significantly promoted the diameter growth of the spruce understory trees throughout the 10–15-year study period without notable delay, and height growth with a substantial lag during the first 5-year period. The influence was swifter and greater with heavier thinning. Thinning of the understory did not influence the height growth of the dominant understory spruces or the growth of the overstory. Complete removal of the understory resulted did not consistently influence growth of the overstory. It was concluded that a spruce understory seemed to thrive and grow relatively well under an overstory of pine, but repeated thinnings in the overstory were required to sustain understory vitality and growth in a prolonged two-storied situation.

Effects of fertilization on soil CH4 and N2O fluxes in young Norway spruce stands

Climate change mitigation strategies have increased the demand for wood products, resulting in an urgent need to increase wood production. One approach is to fertilize forest land, but this can influence greenhouse gas (GHG) fluxes within the ecosystem. The aim of this study was to examine the effects of forest N fertilization on soil CH4 and N2O fluxes in young Norway spruce (Picea abies (L.) Karst.) stands in southern Sweden. The gas fluxes were measured using flow-through non-steady-state dark chambers. In the first, long-term, experiment, half of the stand was fertilized twice (once in 2014 and once in 2016) with 150 kg ha−1 of N, and gas flux measurements were taken throughout 2014–2017. In the second, dose, experiment, 0, 150, 300, or 450 kg ha−1 of N was added to the stand in April 2016, and gas flux measurements were taken during April-December 2016. The dose experiment showed that the sink strength of CH4 decreased with increasing amounts of N; the long-term experiment indicated that repeated fertilization decreased the CH4 sink strength over time. Additionally, the long-term experiment indicated that, while significantly higher N2O emissions were recorded in the fertilization years, this was not detected in subsequent years, suggesting the effect to be short-lived. In the dose experiment, fertilization tended to increase the N2O emissions relative to the amount of fertilizer. However, despite the significant effects of fertilization on these GHGs, the summed fluxes were a fraction of the net uptake of C at the sites, as recorded in another study. These findings suggest that fertilizing forest land with commercial NP or NPK fertilizers corresponding to 150 kg ha−1 of N, the level used in operational forestry in Sweden today, can be conducted without changing CH4 and N2O fluxes to any great extent.

Magnitude and timing of density reduction are key for the resilience to severe drought in conifer-broadleaf mixed forests in Central Europe

Key messageWe applied a modified forest gap model (ForClim) to depict changes in stand water transpiration via density reduction as a forest adaptation strategy. This approach is the key to analyzing the ecological resilience to drought, stress-induced mortality, and economic efficiency of managed mixed forest stands in Central Europe. The results show that specific geographic conditions and forest composition define the optimal stand density of drought-resilient forests.ContextReducing stand density has been recognized as a valid strategy to increase forest resilience to drought. Moreover, to develop adaptive management strategies (AMS) under climate change, it is crucial to consider not only drought resilience but also the economic efficiency of alternative AMS proposed to alleviate drought effects.AimsTo analyze how decreased inter-tree competition among overstorey trees affects stand vulnerability to drought and its expected yield.MethodsWe integrated experimental thinning data and historical responses to drought years in a climate-sensitive forest gap model, ForClim. We tested a business as usual (BAU) and three alternative AMS (“do-nothing,” low- and high-intensity overstorey removal) in mixed stands of Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica) along an elevational gradient of 520–1020 m a.s.l. in Central Europe.ResultsHigh-intensity overstorey removal in mixed stands of all three species considerably increased forest volume growth resilience to drought and decreased stress-induced mortality by two-thirds vis à vis a “do-nothing” strategy. In sites including only conifer species, forest resilience was equally improved by high- and low-intensity overstorey removal compared to that in the BAU strategy. Regarding the timber economy, high-intensity overstorey removal resulted in a higher economic revenue of mixed stands (~ 22% higher net present value than other strategies) on the high-elevation sites (> 1000 m a.s.l.).ConclusionModifying forest density and structure by overstorey removal is principally suitable to increase forest resilience to drought and improve its economic efficiency. The magnitude of the effect however depends on the geographical setting and forest composition.

Imitated Whole Tree Harvesting Show Negligible Effect on Economic Value of Spruce Stands

The increased removal of forest-derived biomass with whole-tree harvesting (WTH) has raised concerns about the long-term productivity and sustainability of forest ecosystems. If true, this effect needs to be factored in the assessment of long-term feasibility to implement such a drastic forest management measure. Therefore, the economic performance of five experimental plantations in three different forest types, where in 1971 simulated WTH event occurred, was compared with pure, planted and conventionally managed (CH) Norway spruce stands of similar age and growing conditions. Potential incomes of CH and WTH stands were based on timber prices for period 2014–2020. However, regarding the economics of root and stump biomass utilization, they were not included in the estimates. In any given price level, the difference of internal rate of return between the forest types and selected managements were from 2.5% to 6.2%. Therefore, Norway spruce stands demonstrate good potential of independence regardless of stump removal at the previous rotation.

Control of Heterobasidion in Norway Spruce Stands: The Impact of Stump Cover on Efficacy of Urea and Phlebiopsis gigantea and Implications for Forest Management

This study investigated the efficacy of Rotstop®, a native Latvian Phlebiopsis gigantea strain and 35% urea solution in combination with a stump cover treatment to control against natural spore infection by Heterobasidion spp. upon precommercial thinning of Norway spruce in three stands growing on former agricultural lands. The major findings were that (i) infection rates of Heterobasidion spp. on stumps treated with the native P. gigantea strain, Rotstop® or urea are similar when stumps are uncovered, and (ii) stump cover promotes stump colonization by the Latvian P. gigantea strain and Rotstop®, leading to a significantly smaller relative area colonized by Heterobasidion spp., as well greater efficiency against Heterobasidion in comparison with urea. Covering of stumps appears beneficial for controlling Heterobasidion stump colonization and may be valuable to forest owners if used in small-scale operations, but it is impractical in automatized thinnings, where managers should consider using regular Rotstop® without covering the stumps.

Effect of Plant Growth Regulators on Protease Activity in Forest Floor of Norway Spruce Stand

Soil proteases are involved in organic matter transformation processes and, thus, influence ecosystem nutrient turnovers. Phytohormones, similarly to proteases, are synthesized and secreted into soil by fungi and microorganisms, and regulate plant rhizosphere activity. The aim of this study was to determine the effect of auxins, cytokinins, ethephon, and chlorocholine chloride on spruce forest floor protease activity. It was concluded that the presence of auxins stimulated native proteolytic activity, specifically synthetic auxin 2-naphthoxyacetic acid (16% increase at added quantity of 5 μg) and naturally occurring indole-3-acetic acid (18%, 5 μg). On the contrary, cytokinins, ethephon and chlorocholine chloride inhibited native soil protease activity, where ethephon (36% decrease at 50 μg) and chlorocholine chloride (34%, 100 μg) showed the highest inhibitory effects. It was concluded that negative phytohormonal effects on native proteolytic activity may slow down organic matter decomposition rates and hence complicate plant nutrition. The study enhances the understanding of rhizosphere exudate effects on soil microbial activity and soil nitrogen cycle.

Forest floor bryophyte and lichen diversity in Scots pine and Norway spruce production forests

Bryophytes and lichens are two main components of the forest floor vegetation. They provide essential ecosystem services, including nutrient recycling and water regulation. Here, we contrast the species richness, cover and community composition of forest floor bryophytes and lichens in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) dominated production forests. The study sites were located in the hemiboreal zone of southern Sweden, and represented early-, mid- and late rotation stands. Our aim was to examine the potential consequences for forest floor biodiversity from the decreasing use of Scots pine production forests in this region.Whereas Scots pine and Norway spruce stands did not differ in bryophyte cover, we found a higher cover of lichens in Scots pine stands, and highest in the intermediate aged stands. Also the species richness of lichens was higher in the Scots pine stands, while bryophyte species richness was higher in the Norway spruce stands. Differences in canopy cover and associated light transmittance to the forest floor appears to be important drivers for distinctive different forest floor communities in the Scots pine and Norway spruce stands, as revealed by Non-Metric Multidimensional Scaling (NMDS). Mean Ellenberg indicator values for bryophytes and lichens showed that species associated with Scots pine stands were characterized by their tolerance of brighter conditions, higher insolation, and better adaptation to a continental climate. Norway spruce stands instead had a comparably larger proportion of species tolerating lower light, but also indicators of higher available nutrient levels, humidity, and pH. The outcome of the Ellenberg indicator species analysis, as well as the larger cover of lichens,and adaptations to drought found among some mosses, revealed that forest floor communities are shaped by different environmental factors in Scots pine and Norway spruce production stands. These environmental differences, and the quantified shifts in forest floor communities identified in this study, indicate the large shifts in understory bryophyte and lichen species composition and abundance that is likely to occur if Scots pine stands are converted to Norway spruce.

Effects of Moderate Nitrate and Low Sulphate Depositions on the Status of Soil Base Cation Pools and Recent Mineral Soil Acidification at Forest Conversion Sites with European Beech (“Green Eyes”) Embedded in Norway Spruce and Scots Pine Stands

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, Ca2+, Mg2+, K+) pools and fluxes at forest conversion sites over 80 years old in Central Germany with European beech (so-called “Green Eyes” (GE)). The GE are embedded in large spruce and pine stands (coniferous stands: CS) and all investigated forest stands were exposed to moderate N deposition rates (6.8 ± 0.9 kg ha−1 yr−1) and acidic soil conditions (pHH2O < 4.7). Since the understanding of forest soil chemical and macronutrient status is essential for the evaluation of forest conversion approaches, we linked patterns in water-bound nutrient fluxes (2001–2018) and in predicted macronutrient storage in the herbaceous and tree layer to patterns in litter fall (2016–2017) and in forest floor and mineral soil macronutrient stocks at GE and CS assessed in 2018. Our results exhibited 43% (Nt) and 21% (S) higher annual throughfall fluxes at CS than at GE. Seepage water at 100 cm mineral soil depth (2001–2018) of CS is characterized by up to fivefold higher NO3− (GE: 2 ± 0.7 µmolc L−1; CS: 9 ± 1.4 µmolc L−1) and sevenfold higher SO42− (GE: 492 ± 220 µmolc L−1; CS: 3672 ± 2613 µmolc L−1) concentrations. High base cation (∑ Ca2+, Mg2+, K+) concentrations in CS mineral soil seepage water (100 cm depth: 2224 ± 1297 µmolc L−1) show significant positive correlations with SO42−. Tree uptake of base cations at GE is associated especially with a Ca2+ depletion from deeper mineral soil. Foliar litter fall turns out to be the main pathway for litter base cation return to the topsoil at GE (>59%) and CS (>66%). The litter fall base cation return at GE (59 ± 6 kg ha−1 yr−1) is almost twice as large as the base cation deposition (30 ± 5 kg ha−1 yr−1) via throughfall and stemflow. At CS, base cation inputs to the topsoil via litter fall and depositions are at the same magnitude (24 ± 4 kg ha−1 yr−1). Macronutrient turnover is higher at GE and decomposition processes are hampered at CS maybe through higher N inputs. Due to its little biomass and only small coverage, the herbaceous layer at GE and CS do not exert a strong influence on macronutrient storage. Changes in soil base cation pools are tree species-, depth- and might be time-dependent, with recently growing forest floor stocks. An ongoing mineral soil acidification seems to be related to decreasing mineral soil base cation stocks (through NO3− and especially SO42− leaching as well as through tree uptake).

Distribution of the timber quality attribute \u2018knot surface\u2019 in logs of Fagus sylvatica L. from pure and mixed forest stands

Research on mixed forests has mostly focused on tree growth and productivity, or resistance and resilience in changing climate conditions, but only rarely on the effects of tree species mixing on timber quality. In particular, it is still unclear whether the numerous positive effects of mixed forests on productivity and stability come at the expense of timber quality. In this study, we used photographs of sawn boards from 90 European beech (Fagus sylvatica L.) trees of mixed and pure forest stands to analyze internal timber quality through the quality indicator knot surface that was quantitatively assessed using the software Datinf® Measure. We observed a decrease in knot surface with increasing distance from the pith as well as smaller values in the lower log sections. Regarding the influence of neighborhood species identity, we found only minor effects meaning that timber qualities in mixed stands of beech and Norway spruce (Picea abies (L.) H. Karst.) tended to be slightly worse compared to pure beech stands.

Simulating conversion of even-aged Norway spruce into uneven-aged mixed forest: effects of different scenarios on production, economy and heterogeneity

Despite a general lack of knowledge on the effects of different strategies, conversion of even-aged stands to uneven-aged forest is ongoing across Europe. Conversion of Bavarian Norway spruce stands under the present climate scenario was simulated using the individual tree simulator SILVA. Three conversion strategies initiated at two different stand ages, 30 and 60 years, were simulated to develop uneven-aged mixed stands of Norway spruce, silver fir and European beech: gap creation, shelterwood and passive conversion. The three conversion strategies were furthermore combined with different harvesting rates. These conversion scenarios were compared with maintaining the even-aged Norway spruce management as reference. Scenarios were evaluated in terms of mean annual increment and structural development over a 150-year conversion period as well as the expectation value (EV) for eternal future rotations. Compared to the reference scenario, conversion scenarios reduced mean annual increment (6–43%) and also generally EV (−5–78%), except for some scenarios when stand age at conversion was 60 and applying a 3% discount rate. Conversion by shelterwood always reduced EV (both compared to the reference and other conversion scenarios) when initiated at age 30. With passive conversion, the effect on EV was dependent on the assumptions regarding regeneration costs. Gap conversion generally resulted in high EV and increased stand heterogeneity fastest among the different strategies. Other scenarios, especially passive conversion, were dependent on heavy thinning for developing heterogeneity faster (although still slower than with creation of gaps). Most conversion scenarios eventually resulted in similar structural heterogeneity, but the time it took to get to this stage varied greatly (50–120 years). Conversion by creation of smaller gaps in combination with a high rate of target diameter harvesting resulted in a favorable conversion in terms of economic returns and development of stand heterogeneity due to early income and differentiated regeneration.

Tree marking versus tree selection by harvester operator: are there any differences in the development of thinned Norway spruce forests?

ABSTRACT In Europe, Norway spruce forests are facing challenges due to climate change. One possible adaptive option is to enhance the resilience of forests by thinning. Usually, thinning requires two working steps: (i) tree marking by a forest manager and (ii) the harvesting operation. Since the typical tree selection procedure by forest managers is expensive and time consuming, the integration of the tree selection process in the harvesting operation is of high interest. In this paper, we examined four tree selection methods on 21 experimental plots located within eight Norway spruce stands and assessed their impact on the future stand development. The future stand development by tree selection methods was examined by means of a simulation study using the tree growth model MOSES (MOdeling Stand rESponse). The selection methods were (i) tree selection by forest managers, (ii) tree selection by the harvester operator as part of a fully mechanized harvesting system. Since we used the tree growth model MOSES, we additionally employed (iii) a random tree selection process implemented in MOSES, and (iv) a control simulation assuming no thinning. The Norway spruce stands are located in Lower Austria. The results show that 70% of the trees selected by the forest managers were identical to those chosen by the harvester operator and thus no significant differences in the key stand parameters after a 50-year simulation is detectable. Our study suggests that the tree selection for thinning by a trained harvester operator is a cost-efficient and fast method.

Effects of Fertilization on Wood Formation in Naturally Regenerated Juvenile Silver Birch in a Norway Spruce Stand in South Sweden

This study investigates wood density and anatomy of juvenile silver birch stems in Sweden, grown in mixed conifer stands. Our aim is to investigate if fertilization provides increased growth, as well as an eventual reduction in stem wood density. Measurements of basic density, ring width, cell wall thickness, and vessels are analyzed for 20 birch trees. Bark to pith radial sections are analyzed using a light microscope and the freeware ImageJ to compare treatments and ages. The results show that trees with fertilizer treatment have wider growth rings and thinner cell wall thickness compared to unfertilized trees. The fertilized trees also have a lower cambium age at the same height and the same diameter, and a slightly lower stem mean density (420 kg m−3) than the unfertilized stems (460 kg m−3). Fertilizer is a significant determinant of density and cell wall thickness in nonlinear models. The fertilized trees have increased growth and reached a fixed diameter earlier. The age difference between the trees likely explains some of the differences in cell wall thickness. This study supports the use of fertilizer as a silvicultural option for increasing the growth rate of silver birch for a relatively small reduction of wood density.

Do pheromone trapping always reflect Ips typographus (L.) population level? A study from the Tatra National Park in Poland

Abstract Pheromone traps are used for monitoring I. typographus populations in Norway spruce stands of the Tatra National Park (TPN) in Poland. The presented study is based on the set of pheromone traps of precisely known location (23) located in the whole area of the TPN and operated continuously in 2010–2019. The data on the captures of beetles were compared with two kinds of data concerning the mortality: the area covered by standing dead trees (airborne photographs) in the no-intervention zone, and the volume of trees infested by bark beetles processed in the active protection zone. No relationship was found between the mean numbers of beetles captured yearly in all pheromone traps in the whole TPN area and the volume of infested trees removed from the stands in the active protection zone. The captures in the two selected study areas were correlated with the area of spots with dead trees in the 500 m circle around the traps, however, this correlation is not statistically significant. There is no relation of captures to the volume of processed infested trees. The captures decreased in the growing seasons after the wind damage, and increased markedly after the drought started in 2015. The results of pheromone trapping are affected by several factors, as wind damage and defence potential of trees resulting from their physiological status. Pheromone traps represent valuable source of information about the bark beetle I. typographus population dynamics, although the collected data do not enable direct definition of its population level, especially in the protected areas with different and unstable (changed in 2017) approach to the protection of stands. As most of the information on beetles is captured in the first half of the growing season, the data collected till the end of July are sufficient for monitoring purposes; thus, the trapping should be reduced to the period May–July.

Storm legacies shaping post-windthrow forest regeneration: learnings from spatial indices in unmanaged Norway spruce stands

The anticipated increase in extreme disturbance events due to climate change is likely to expose Norway spruce (Picea abies (L.) Karst.) dominated forests in northern Europe to new conditions. Empirical data on the resilience of such natural (unmanaged) forests to disturbance and the long-term patterns of regeneration in its aftermath are currently scarce. We performed a quantitative assessment of natural forest stands in north–western Latvia to identify and characterise the patterns of stand structure 44 years after a stand-replacing disturbance and investigated the effects of legacies on regeneration. The spatial distribution of tree species and their dimensions were assessed in 71 circular sample plots (500 m2 each) in natural forest areas, where Norway spruce dominated prior to the windthrow and salvage logging was not carried out. Spatial indices (species mingling index, size differentiation index, and aggregation index) were used to characterise stand structure and diversity. The different initial states (age and coverage of surviving trees) of stands affected eventual tree species dominance, size differentiation, degree of mingling and aggregation. Our results demonstrate a close relationship between disturbance legacies and spatial indices. The pre-storm understory and canopy survivors decreased species mingling, whereas survivors increased size differentiation. The size differentiation increased also with a higher degree of species mingling. Leaving differential post-storm legacies untouched promotes a higher structural and species diversity and therefore supports the management approach of preserving canopy survivors.

IMPACT OF WINDTHROWS DISTURBANCE ON CHEMICAL AND BIOLOGICAL PROPERTIES OF THE FOREST SOILS FROM ROMANIA

The present study investigates the influence of windthrows on the chemical and biological characteristics and respiration processes of forest soils from Romania. Three pure Norway spruce, common beech, and sessile oak stands were chosen together with control plots, where the forest and soils were not affected by windthrows. Soil samples were taken from two soil layers: 0 10 cm and 10 20 cm. Soil carbon dioxide fluxes or soil respiration was monitored at 20 randomly selected points for each sample surface. Soil temperature and soil water content were also measured at these points. Furthermore, the total number of heterotrophic bacteria and the total number of fungi were also measured. We found that abiotic factors lead to the modification of the chemical and biological properties of forest soils: soil pH was higher in the areas affected by windthrows, while humus and nitrogen quantities were lower in these areas. However, these changes were observed only in the first 10 cm of the soil profile. Underground microclimatic conditions were found to influence soil respiration, with higher respiration values observed in the surfaces affected by windthrows. In the Norway spruce and common beech stands, aerobe heterotroph bacteria and fungus were more abundant in soils that were not affected by windthrows because the uprooted trees remove top horizons of soils and the creation of leaf litter, roots and fungal hyphae, stops. In this situation, organic matter, in the soil, begins to decay.