Search

Knowledge regarding tree species dynamics is essential to understand forest responses to the environment, and to evaluate management options in adapting forest ecosystems to future climates. As maintaining tree species diversity and promoting structural stand heterogeneity are among the strategic elements in adapting forest management to climate change, the monitoring tree diversity is an ongoing challenge. Large-scale forest inventories have been proposed as a suitable basis for forest diversity analysis on large spatial and temporal scales. We used Swiss forest inventory data (NFI) to analyse temporal changes in tree species richness on small plots from 1983 to 2006. For two size groups of trees (‘small’ trees with dbh from 12 to 35 cm from plots with 200 m2 area, and ‘large’ trees with dbh ≥ 36 cm from plots with 500 m2 area), we identified the number and the tree species appearing (‘gains’) or disappearing (‘losses’) from each plot during the study period, and related these changes to site, stand and management characteristics. We found that species richness change was size-dependent and varied largely due to regional differences in the past land-use history of the Swiss forests. ‘Gains’ of ‘small’ trees were higher in stands with diverse vertical structure, with less competitive pressure as well as in warm environments, whereas ‘gains’ of ‘large’ trees were mostly related to climate and were highest in warm and moderately moist habitats. ‘Losses’ in both tree-size groups were mainly promoted by management. Our analysis suggests high vulnerability of Picea abies and high competitiveness of Fagus sylvatica, and underlines the potential of Abies alba in forming future Swiss forests. Despite of the silvicultural paradigm to create more species rich forests, most silvicultural interventions decreased small-scale species richness. This calls for further studies on the effect of management on tree species diversity.

The European beech (Fagus sylvatica L.) is a competitive and shade-tolerant species, with its natural regeneration in closed-canopy stands affected by a number of variables. The study aimed to identify factors related to beech regeneration by focusing on two main questions: (1) can we identify environmental and stand structural characteristics that promote beech regeneration or indicate suitable conditions for regeneration under closed canopy conditions, and (2) do environmental and stand structural characteristics favorable for beech regeneration differ among the ontogeny of seedlings and saplings? To answer these questions, we sampled four beech-dominated forest complexes in northern and southern Poland. Study plots were established in sites with varying overstory composition, including beech-dominated, mixed, and conifer-dominated stands. In the analyzed forest complexes, regeneration consisted mostly of beech seedlings and saplings with admixture of shade tolerant or intermediate light-tolerant species—Norway spruce (Picea abies (L.) Karst.), silver fir (Abies alba Mill.), hornbeam (Carpinus betulus L.), and sycamore maple (Acer pseudoplatanus L.). The average density of beech regeneration was 9047, 10,305, 5198 and 8972 trees ha−1 in forest complexes 1, 2, 3 and 4, respectively; however, the inter-plot variation of the regeneration density was high. Beech regeneration occurrence were determined by stand structural characteristics. Beech regeneration decreases as stand density increases and increases with stand basal area and the percentage of beech in the dominant canopy layer. The ecological prerequisites favorable for beech regeneration abundance differ with the ontogeny of seedlings and saplings—the smallest seedlings regeneration was determined by stand structural variables to a greater extent, while more advanced regeneration abundance was also associated with light-demanding species regeneration abundance. Under closed canopy conditions, beech regeneration abundance was weakly influenced by intra/interspecific competition from surrounding vegetation; however, canopy openings may increase it, therefore, competition aspects should be taken into account in the selection of forest management practices.

Norway spruce (Picea abies), European beech (Fagus sylvatica), silver fir (Abies alba) and Scots pine (Pinus sylvestris) typically co-occur in European forests, but show contrasting response to climate and environmental change. Sustainable forest management therefore depends on species- and regional-specific information. Here, we use tree-ring width measurements of 334 beech, 280 fir, 144 spruce and 63 pine trees from 75 inventory plots in Slovakia to assess the predominant factors that control radial stem growth of Europe’s economically most important forest species. All four species exhibit significant shifts in stem growth over the past 100 years. Ring width patterns were, however, not significantly affected by tree species diversity and site elevation. The resistance, resilience and recovery of all species to the extreme summer droughts between 1950 and 2003 suggest that spruce is the species most unsuitable for the predicted warmer and drier future. Silver fir may benefit from warmer conditions, although we cannot conclude that it will not suffer from predicted increased frequency of climate extremes. Forest management in this locality should aim to avoid significant loss of forest cover by replacing Norway spruce monocultures with mixed stands of silver fir and European beech.

We studied the effect of coarse woody debris (CWD) on the soil nutrient status in two beech (Fagus sylvatica) dominated forest reserves in Flanders, Belgium: Wijnendale Forest, on a sandy soil and Kersselaerspleyn in Sonian Forest, on a loamy soil. More specifically, we looked at the chemical composition of beech logs of different stages of decay. In addition, we examined the chemical composition of the organic and the mineral soil at five distances from the decomposing logs. We considered the concentrations of the following elements: C, N, P, S, Ca, K, Mg, Mn, Fe, and Al. The results indicate a difference in wood and soil chemical composition between the two forest sites. The soil and the aboveground biomass of Wijnendale had the highest total N concentration and the lowest concentrations of P and base elements (Ca, K, Mg, and Mn). There is an increase in element concentrations in CWD of both forests during the decomposition, except for K and C. The higher N concentration in Wijnendale, explained by high atmospheric nitrogen deposition in this forest, persisted during decomposition. By contrast, the concentrations of P, Ca, K, and Mg in dead wood of both forests became similar when decomposition proceeded. The effect of CWD was more pronounced in the organic soil layer than in the mineral soil. The organic soil in the proximity of CWD had a higher pH and higher concentrations of C, N, P, Ca, Mg, and Mn (in Sonian forest) and a lower Al concentration (in Wijnendale forest) and this is highly significant for Ca, a limiting nutrient in moderate to highly acidic forests. The percentage of the soil surface impacted by the logs is 0.92% and 0.36% for Sonian and Wijnendale respectively, which is expected to increase with time, considering the fact that both reserves are only recently left unmanaged. The results of this study highlight the contribution of CWD in sustaining the nutrient status and buffering capacity of forest sites, in particular on soils sensitive to acidification and exposed to high nitrogen deposition.

We studied the fine root system of Fagus sylvatica in six mature stands on different bedrock down to the rock surface (or to 2 m) to investigate whether (1) the stand total of fine root biomass (FRB) increases, while the fine root live:dead ratio decreases, with decreasing soil base richness, (2) specific root area (SRA) and root tip frequency increase with a decrease in base richness, and (3) FRB is related to profile depth. The three beech stands on deep soil (>2 m profile depth) had on average by 38% larger FRB totals than the stands on shallow soil (60–80 cm), suggesting that limited root space is an important determinant of fine root system size in F. sylvatica. Despite large variation among sites, soil chemistry influenced root morphology only little: fine root diameter depended on soil C/N ratio and root tip frequency on base saturation in a few soil horizons. Much larger morphological differences were found between topsoil and subsoil roots within a profile. We conclude that the fine root system of F. sylvatica varies under similar climatic conditions remarkably little between base-poor and base-rich sites, in contrast to the pronounced topsoil-subsoil differences in root morphology and fine root density.

Despite improvements of dendrochronological techniques in many forest ecosystems, studies describing the growth responses of trees following disturbance events including comprehensive data on factors and processes behind tree-growth release are rare, especially for European temperate forests, limiting the interpretation and generalization of dendroecological studies. Here we examine the effect of key factors on the growth reaction of Fagus sylvatica L. to disturbances in 8 old-growth forests in the Czech Republic, independently dated using three different data sources – tree censuses, dendrochronology and historical aerial photographs. Using 117 increment cores, we studied four parameters of radial tree-growth surrounding canopy gaps: magnitude, duration, abruptness and response shift, in relation to factors of different spatial scales, i.e. tree-, gap- and stand-level variables. Our results indicate that the beech growth response to gap formation strongly differs across a complex of factors at diverse spatial levels, frequently occurring in noteworthy interactions. A positive trend for the gap size * radiation interaction in the analysis of magnitude was found, suggesting that the effect of gap area differs among topographical features. As for duration and abruptness, the interaction of distance and mortality mode was identified, indicating a longer and more gradual reaction along with increasing distance of the cored tree from the gap centre, varying by the type of the gap maker’s death. In addition, an altitudinal gradient was found to predict the magnitude of growth changes and the time interval between the disturbance and the reaction of nearby trees. Surprisingly, the diameter of the surviving trees was not a good predictor of radial growth, with a significant positive relationship to just abruptness. An effect of locality was not observed, facilitating the broad applicability of our findings across a wide range of beech-dominated temperate forests. Our results emphasize the general limits of dendrochronological data in disturbance spatial pattern studies, as indicated by the considerable variability in the responses of neighbouring trees to identical disturbance event. A detailed examination of the growth reaction, considering not only the response magnitude but also other important parameters, plays a key role in the precision of detecting growth releases as well as in reducing the sample size required for summary disturbance history evaluations. In focusing on this issue we believe we contribute to future dendroecological research by demonstrating the need for more precise disturbance history evaluations.

To better understand natural regeneration of trees and forest dynamics it is important to gain insight into the drivers of invertebrate herbivory. In mature forests, associational resistance of trees resulting from a high diversity of neighbouring trees is common, and can have cascading effects on tree growth through resource concentration effects or through changes in top-down control. While the underlying biological processes are known to be influenced by the forest’s spatial properties, we lack insights on how resource concentration, top-down control and fragmentation jointly affect sapling performance in fragmented landscapes. We therefore experimentally quantified effects of the proportion of conspecific trees in the overstorey (resource concentration), avian top-down control (natural enemies) and distance to the forest edge on invertebrate herbivory levels and sapling growth. The assessments were made on planted saplings of Fagus sylvatica, Quercus robur and Quercus rubra in 53 experimental plots and birds were excluded by means of exclosures from a subset of these saplings. Excluding avian top-down control increased herbivory on each tree species. Increased herbivory led to decreased sapling growth in F. sylvatica and Q. rubra. On Q. robur saplings, top-down control was stronger closer to the forest edge. Furthermore, in this species, herbivory inside the exclosures increased with an increasing proportion of conspecific trees in the overstorey, while such a resource concentration effect was not observed outside the exclosures. Our results show the importance for forest management of conserving insectivorous birds and promoting a mixed overstorey, which can decrease sapling herbivory when bird abundance is low. More generally, our study provides insight into the complex, multitrophic interactions that drive sapling growth in forest stands located within fragmented landscapes.

Fine-scale spatial point-pattern analysis can give insights into the underlying pattern-creating biological processes in an environmental context. However, there are few studies comparing the spatial distribution of trees in managed stands and unmanaged forests that take into account their developmental stage. The main aim of this study was to assess and model the spatial patterns of Abies alba Mill. and Fagus sylvatica L. trees in managed and unmanaged forest patches in the early developmental stage. This study investigated tree communities dominated by A. alba and F. sylvatica in the Świetokrzyskie Mountains in Central Europe. From 2016 to 2018, 60 sample plots representing the growing-up developmental stage were randomly selected: 30 from managed stands and 30 from unmanaged forests. Models of the fine-scale spatial distributions of the trees were distinguished using hierarchical cluster analysis (HCA), analysis of group similarities (ANOSIM), and multiple response permutation procedures (MRPP). Indices based on the K-function and the O-ring statistic, I L r and I O r , respectively, were developed and used as clustering variables. The proposed indices assume values from −1 to 1 for random patterns; values > 1 indicate aggregation, and values Models of the fine-scale spatial distributions of the trees differed only slightly between the managed and unmanaged patches. These models suggest that in the investigated sample plots, the fine-scale spatial patterns (with distances among the trees not exceeding 10 m) were usually random. Only in a few patches were the tree distributions found to be aggregated, from 5 to 10 m and from 7 to 10 m in the managed stands and the unmanaged forests, respectively. The relatively similar models of the fine-scale spatial distributions of the trees in the managed and unmanaged forest patches in the growing-up developmental stage show that early successional forest dynamics follow a parallel trajectory of recovery. The long-term application of the shelterwood system as well as self-regeneration and self-regulation natural processes led to the creation of the similar spatial structures of the trees. This observation may be helpful in the design of planting patterns and/or harvesting schedules.

Upon the occurrence of acidic deposition-driven damage to forests at the beginning of the 1980s, large-scale liming has been applied to acidic forest sites in Germany. Due to possible negative consequences on soil chemistry and on (soil) fauna and flora, this measure was discussed highly controversially right from the beginning and is disputed until today. In investigations of liming effects on the forest understory vegetation, very few studies covered a time period of more than two decades with intermittent releves. We analyzed releves of the herbal understory on limed and control plots in one pine (Pinus sylvestris), one oak (Quercus robur), two European beech (Fagus sylvatica) and five Norway spruce (Picea abies) stands at permanent observation sites in south-western Germany. These releves had been repeatedly conducted during approximately 25 years. The number of herbal plant species was generally low. An increase in the herb layer's plant cover with time was found at six out of the nine study sites and was mainly due to spreading of two grass species (Milium effusum, Deschampsia flexuosa) and of the subshrub Vaccinium myrtillus, which might have benefitted from continuous nitrogen deposition. Only two species (Agrostis stolonifera, Stellaria media) with a main distribution in open landscapes were found in the years of investigation and their occurrence was restricted to only four sites and some few years. Across all sites, the average Ellenberg indicator values of nutrient (nitrogen) supply (N-values) were significantly increased on the limed plots ten years after liming, and at Year 10, the N-values of the limed plots were significantly higher than that of the control, presumably due to increased decomposition rates after liming. At the spruce sites, the average Ellenberg indicator values of soil reaction (R-values) of the limed plots 10 years after liming were significantly higher than at the beginning (Year 0) and at the end of the investigation (2013). We found no significant differences among the Ellenberg indicator values of light condition (L-values). In conclusion, liming had a significant, but only transient effect on the composition of the understory species. Therefore, our results do not support arguments against liming of acidic forests that are based on long-term changes in the herbal flora. In managed forests for wood production on acidic soils, liming can continue contributing to buffer the soils against ongoing acidification and accompanying cation leaching caused by anthropogenic deposition of nitrogen.

Temperate forests with shade-tolerant canopy tree species can develop vertical structures of varying complexity. Forests with Abies alba Mill. and Fagus sylvatica L. can be composed of one-, two-, and multi-storied patches and selection patches. A dominant view in forest ecology is that unmanaged forests tend to have greater structural heterogeneity than managed stands. Structural integrity, however, may differ among forest developmental stages. The main objective of this study was to compare the tree diameter complexity in managed and unmanaged patches during the early developmental stage. Data were collected between 2016 and 2018 in the Świetokrzyskie Mountains in Central Europe. The investigated tree communities were dominated by A. alba and F. sylvatica. Sample plots representing the growing-up developmental stage were randomly selected; of these, 30 plots were in managed stands, and 30 plots were in unmanaged forests. The diameter at breast height (DBH) distribution patterns were determined using hierarchical cluster analysis (HCA), clustering indices, and finite mixture models. Three main DBH distribution patterns were identified for the managed stands (K-A, K-B, and K-C). These patterns consisted of three or two sub-populations. The patterns represented structurally diversified patches composed of trees of all ages with multi-, three- or two-layered canopies and with intensive natural processes of regeneration. Two main DBH distribution patterns were identified for the unmanaged forests (S-A, and S-B). These patterns consisted of two clearly separated sub-populations. They are typical in patches with two-layered canopies, and the trees from the upper layer had a large share (40–60%). The distinguished DBH distribution patterns indicated there was greater tree size diversity in the managed stands than in the unmanaged forests. When comparing managed versus unmanaged patches, it is important to consider the developmental stage.

Litter fall and the associated nutrient return are a significant supply of resources in forest ecosystems. In mixed stands both litter quantity and quality can change under different species compositions. Spatial heterogeneity inherent in mixed stands, defined by stand structure and the present species, will affect the litter composition around a tree of interest. Therefore spatially explicit information will be needed to determine how neighbourhood characteristics in a mixed stand have an effect on litter composition and nutrient return. Using a leaf dispersal model, we determined litter production and leaf shedding parameters of four different tree species. Results from this model indicated that the proportion of litter that originated from the neighbourhood was 86% and 77% at the local tree level for oak and beech respectively. Using this information we found that the presence of accompanying species birch or hornbeam had beneficial effects on local return of N, P, Ca, Mg and Mn. Return of K was optimal with only beech trees in the neighbourhood. These results could give an indication on how to use stand establishment, structure and management to optimize nutrient return.

The growth of forest trees under given environmental conditions is assumed to depend mainly on their age, stem and crown size, and competitive position in the stand. The current stem and crown size are commonly recognized as adequate proxy markers for the tree's ecological memory of the past. In contrast, tree ring structure, crown whorl morphology, or other biographical patterns are rarely used for predicting growth. Here, we asked how the latter affect tree growth. Our main hypothesis was that the growth in the longer past significantly co-determines the present growth. To test this hypothesis we derived metrics which quantify the social position, course of growth, and annual variation of trees in their past. We further selected variables for quantifying the trees' present stem and crown size and competitive status. Finally, we selected the approximately 200-years-old thinning experiment in European beech (Fagus sylvatica L.) Fabrikschleichach 15 in South Germany as our study object because it provided all required information. To examine the dependency of the current growth on the present growing conditions and the past tree development more closely, we applied linear mixed models. They revealed that (i) trees with similar age, size, crown and competitive status at present grew better if they were subdominant in the past. (ii) Ceteris paribus, slow starting trees with progressive growth trajectories were associated with higher growth than quick starting trees with degressive growth trajectories. (iii) Trees with lower interannual variations of growth in the past had significantly higher growth rates at present than trees with higher interannual variations of growth in the past. (iv) Including information about the trees' past reduced the RSME of the diameter growth model by 17–27% and increased the R2 by 15–30%. Thus, the diameter growth model could achieve R2 values of 0.76–0.79. (v) The contribution of past information for estimating present growth was higher in periods without thinning. We suggest that in the analysed European beech stands, even at parity of stem diameter or crown size, different courses of growth created different internal stem structures and crown morphologies. Such past structural and morphological formations may affect the tree's light interception and hydraulic conduction. These differences in structure may cause specific differences in the present tree functioning and growth. Of course these findings based on only one long-term experiment should not yet be generalized. However, the revealed relationship between the past and present growth deserves further investigations. We discuss the relevance of the ecological memory embedded in the past growth and in the tree ring pattern. We stress the consequences of the ecological memory for the monitoring, inventory, and modelling of tree growth and its implications for the development of silvicultural prescriptions.

Tree mortality is caused by complex interactions between multiple biotic and abiotic factors. Processes of tree mortality that are not induced by natural disturbances are often reflected in distinct radial growth patterns of trees, which typically serve as reliable indicators of impending tree mortality. However, it remains unclear whether empirical mortality models that are based on tree size and growth result in more realistic projections of forest succession in dynamic vegetation models (DVMs). We used a combination of tree-ring and inventory data from unmanaged Swiss natural forest reserves to derive species-specific survival models for six Central European tree species (Abies alba, Fagus sylvatica, Larix decidua, Picea abies, Pinus cembra and Quercus spp.). We jointly used 528 tree-ring samples and inventory data from eight forest reserves. We implemented the estimated parameters of the survival models into the DVM ForClim and performed simulations of forest succession that were validated using the inventory data of the forest reserves. Size- and growth-dependent variables (i.e., diameter at breast height and mean ring width) over the last few years prior to tree death were reliable predictors to distinguish between dying and living trees. Very low mean ring widths over several preceding years as well as small and large trees, respectively, reflected low survival probabilities. However, the small sample sizes of small and large trees resulted in considerable uncertainty of the survival probabilities. The implementation of these survival models in ForClim yielded plausible projections in short-term simulations and for some sites improved the predictions compared to the current ForClim version. Stand basal area, however, tended to be overestimated. Long-term simulations of ForClim based on the empirical survival models resulted in realistic predictions only if the uncertainty of the predicted survival probabilities was considered. We conclude that the combination of different data sources in combination with the consideration of intra-specific trait variability yields robust predictions of tree survival probabilities, thus paving the way towards better tree mortality models and more reliable projections of future forest dynamics.

Despite its dominance in Central Europe, beech cultivation is not without risks, because drought periods and direct solar radiation of the stem are suspected of causing branch dieback, sunburn and predisposition to attack by the European beech splendour beetle Agrilus viridis. Outbreaks of this beetle occurred in Germany in the early 1950s and in Hungary between 2003 and 2006 following severe precipitation deficiencies and extraordinary high temperatures. Leaf loss and an unusual accumulation of dead branches at the top of the crown of beech trees prompted us to initiate in 2010 a three-year study to investigate whether and to what extent A. viridis infestations are involved in this damage pattern. In eight differently damaged beech stands in Bavaria (south-eastern Germany) we measured the prevalence of A. viridis with flight interception traps in relation to the vitality status of beech, checked the oviposition behaviour of females on trap trees, and investigated the infestation frequency of beech trees depending on stand structure. The prevalence of A. viridis was significantly enhanced in sample plots with more heavily damaged beech trees. At lying trap trees, females preferred parts of the bark for oviposition which had been exposed to south or west when the trees had been standing. Particularly, trees in open stands, distant to neighbours in the south and west as well as damaged by sunburn are predisposed to attack by A. viridis. It was proved that survival of A. viridis occurred in branches at the top of live beech trees from where outbreak situations may be initiated due to climatic conditions like drought and/or extreme temperatures. Prevention of A. viridis infestation consists of avoiding sudden exposure to intense solar radiation of the beech trunk by silvicultural measures.

This study investigated the response patterns of aboveground macrofungal communities to different management stages representing a forest conversion from Norway spruce (Picea abies) to European beech (Fagus sylvatica) in the Eifel National Park, Germany. We used a space-for-time substitution approach with three replicate study sites for each forest conversion stage: (I) even-aged single species Norway spruce, (II) unmanaged Norway spruce windthrow, (III) salvage-logged Norway spruce windthrow, (IV) single Norway spruce tree selection cutting (close-to-nature managed) with European beech underplanting and (V) old-growth, uneven-aged European beech (as reference). We assessed environmental variables and macrofungal sporocarps, while the latter were categorized into functional groups to link taxonomic information to potential ecosystem functions. Overall, we observed 235 macrofungal species. The highest species richness was found in the European beech reference stage, followed by the close-to-nature managed spruce/beech stage, while the Norway spruce stage showed approximately half the species richness, similar to the species level of both windthrow stages. Non-metric multidimensional scaling (NMDS) ordination separated each forest conversion stage into distinct fungal communities, while both windthrow stages could not be distinguished from each other. Beside tree species composition change and forest management, nutrient availability and microclimate were the main drivers of fungal community changes among the five differently-managed stages. Further, different functional groups responded in different patterns to forest management and to explanatory environmental variables. We reinforced the assumption, that old-growth, uneven-aged European beech forests (>120 years) can act as a refugium for unique forest type specific fungal communities with a higher functional structure, especially contrary to non-native, even-aged Norway spruce forests (∼70 years). Single Norway spruce tree selection cutting with further introduction of European beech trees can be an adequate strategy to allow a spruce forest conversion without necessarily reducing the macrofungal species richness and its functional structure. We displayed that ecological consequences of windthrow events can be a depression of fungal species richness and a collapse for the functional structure of fungi, especially after salvage logging. Our study underlines the need of including fungal conservation in forest conversion plans to optimize forest ecosystem integrity and resilience against biotic and abiotic agents, such as windstorm events.

In the past few decades, high nitrogen emissions have reversed the nitrogen limitation of trees. Meanwhile, phosphorus (P) appears as a primary limiting nutrient of many forests in Europe. However, a simple and economic standard method for the determination of the plant-available phosphorus in forest soils, which drives the P supply of the trees, is not yet available. Therefore, we tested two soil extraction methods [citric-acid extract (Pcit), according to Hoffmann et al. (1991) and sodium bicarbonate extract (PHCO3), referring to Olsen et al. (1954)] for analyzing all Bavarian soil samples of the second German National Forest Soil Inventory (NFSI), resulting in a big data set with 342 forest sites and 2232 samples. We combined these results with the standardly gathered soil parameters and tested them as predictors for P nutrition indicated by the foliar P concentrations of the four most important tree species: Norway spruce (Picea abies), European beech (Fagus sylvatica), Scots pine (Pinus sylvestris) and pedunculate/sessile oak (Quercus robur/petraea). During the statistical process, we stepwise reduced the complexity of the prediction models. In our analyses, we achieved the best prediction of foliar P using soil information from the organic layer and mineral soil down to depths of 10 cm and 20 cm. Pcit stocks provided by far the best predictions in nearly all cases. Based on this parameter, we derived parametric regression functions to estimate the P nutrition (spruce: R2 = 0.52∗∗∗; beech: R2 = 0.49∗∗∗; pine: R2 = 0.39∗∗∗; oak: R2 = 0.35∗∗∗). Based on logistic regressions, threshold values were deduced for Pcit stocks down to 10 cm soil depth (spruce: 33 kg ha−1; beech: 43 kg ha−1; pine: 32 kg ha−1; oak: 41 kg ha−1), above which P deficiency becomes unlikely. Since these models are based on a large number of sites with diverse geologies and soil conditions, they can be used to estimate the P availability of most forests in Bavaria. Furthermore, the applied methods can be extended to other soil inventories. Estimated P availability based on such functions and thresholds can support sustainable nutrient management of temperate forests.

Mast seeding, the synchronised occurrence of large amounts of fruits and seeds at irregular intervals, is a reproductive strategy in many wind-pollinated species. Although a series of studies have investigated mast year (MY) patterns in European forest tree species at the regional scale, there are few recent evaluations at a European scale on the impact of weather variables (weather cues) and resource dynamics on mast behaviour. Thus the main objective of this study is to investigate the impact of specific weather conditions, as environmental drivers for MYs, on resources in Fagus sylvatica L., Quercus petraea ( Matt.) Liebl. , Quercus robur L., Picea abies (L.) Karst . and Pinus sylvestris L. at a European level and to explore the robustness of the relationships in smaller regions within Europe. Data on seed production originating from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) were analysed. Three beta regression models were applied to investigate the impact of seasonal weather variables on MY occurrence, as well as the influence of fruiting intensity levels in the years prior to MYs. Resource dynamics are analysed at three different spatial scales (continent, countries and ecoregions). At a European scale, important weather cues for beech MYs were a cold and wet summer two years before a MY, a dry and warm summer one year before a MY and a warm spring in the MY. For spruce, a cold and dry summer two years prior to a MY and a warm and dry summer in the year before the MY showed the strongest associations with the MY. For oak, high spring temperature in the MY was the most important weather cue. For beech and spruce, and to some extent also for oak species, the best fitting models at European scale were well reflected by those found at smaller scales. For pine, best fitting models were highly diverse concerning weather cues. Fruiting levels were high in all species two years before the MY and also high one year before the MY in the oak species and in pine. In beech, fruiting levels one year before the MY were not important and in spruce, they were inconsistent depending on the region. As a consequence, evidence of resource depletion could only be seen in some regions for spruce.

Forest stand growth dynamics in Central Europe have accelerated since 1870 due to a rise in temperature, extended growing seasons, and other components of climate change. Based on wood samples from the oldest existing experimental plots in Central Europe, we show that the dominant tree species Norway spruce (Picea abies (L.) H.Karst. ), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.), and sessile oak (Quercus petraea ( Mattuschka ) Liebl .) exhibit a significant decrease in wood density since more than 100 years. While stand and trees grow faster with respect to wood volume, we can show that wood density decreased by 8–12% since 1900. These results object a naive direct transformation of volume growth trends into an accelerated biomass production. Since 1900, stand biomass increment increased 9–24 percentage points less compared to volume increment (29–100% increase reduces to 20–76%). For a given stem diameter and annual ring width, tree stability against windthrow, wood strength, energy content and C sequestration are even reduced under recent conditions. The generally decreased late wood density, partly going along with an increased early wood fraction, suggests the observed extension of the growing season and fertilization effect of dry deposition as the main causes. Our results indicate that current increased wood volume growth rates must not be straightforwardly converted into sequestrated C and biomass harvest potentials assuming historic values for wood density. This should be taken into account in monitoring, modeling, and utilization of carbon and biomass in forests under global change.

International audience; Tree-related microhabitats (TreMs) are important features for the conservation of biodiversity in forest ecosystems. Although other structural indicators of forest biodiversity have been extensively studied in recent decades, TreMs have often been overlooked, either due to the absence of a consensual definition or a lack of knowledge. Despite the increased number of TreM studies in the last decade, the role of drivers of TreM profile in primary forests and across different geographical regions is still unknown. To evaluate the main drivers of TreM density and diversity, we conducted the first large-scale study of TreMs across European primary forests. We established 146 plots in eight primary forests dominated by European beech (Fagus sylvatica L.) in the Carpathian and Dinaric mountain ranges. Generalized linear mixed effect models were used to test the effect of local plot characteristics and spatial variability on the density and diversity (alpha, beta, and gamma) of TreMs. Total TreM density and diversity were significantly positively related with tree species richness and the proportion of snags. Root mean square tree diameters were significantly related to alpha and gamma diversity of TreMs. Both regions reached similarly high values of total TreM densities and total TreM densities and diversity were not significantly different between the two regions; however, we observed between the two regions significant differences in the densities of two TreM groups, conks of fungi and epiphytes. The density and diversity of TreMs were very high in beech-dominated mountain primary forests, but their occurrence and diversity was highly variable within the landscapes over relatively short spatial gradients (plot and stand levels). Understanding these profile provides a benchmark for further comparisons, such as with young forest reserves, or for improving forest management practices that promote biodiversity.

This study estimates the present and future distribution potential of 12 thermophilic and rare tree species for Europe based on climate-soil sensitive species distribution models (SDMs), and compares them to the two major temperate and boreal tree species (Fagus sylvatica and Picea abies). We used European national forest inventory data with 1.3 million plots to predict the distribution of the 12 + 2 tree species in Europe today and under future warming scenarios of +2.9 and +4.5 °C. The SDMs that were used to calculate the distributions were in a first step only given climate variables for explanation. In a second step, deviations which could not be explained by the climate models were tested in an additional soil variable-based model. Site-index models were applied to the found species distribution to estimate the growth performance (site index) under the given climate. We find a northward shift of 461 km and 697 km for the thermophilic species over the regarded time period from 2060 to 2080 under a warming scenario of 2.9 °C and 4.5 °C, respectively. Potential winners of climatic warming have their distribution centroid below 48°N. Fagus sylvatica and Picea abies will lose great parts of their potential distribution range (approx. 55 and 60%, respectively). An index of area gain and growth performance revealed Ulmus laevis, Quercus rubra, Quercus cerris and Robinia pseudoacacia as interesting alternatives in managed temperate forests currently dominated by F. sylvatica and P. abies. The 12 investigated species are already in focus in forestry and it has been shown that the changing climate creates conditions for a targeted promotion in European forests. Nevertheless, area winners exhibited lower growth performances. So, forest conversion with these warm-adapted species goes hand in hand with loss of overall growth performance compared to current species composition. So, the results are a premise for a further discussion on the ecological consequences and the consistency with forest socio-economic goals and conservation policies.

The high structural heterogeneity of primary forests is assumed to positively affect various ecosystem traits and functions, e.g. biodiversity, resilience and adaptability. Against this background, old-growth forest structures are emulated in many managed forests. To properly emulate such structures, quantitative reference values are required, through which primary forests are characterized. In this study, we used the stand structural complexity index (SSCI), derived from terrestrial laser scanning (TLS), to characterize and compare the structures in European beech (Fagus sylvatica L.) dominated forests along a management gradient, ranging from differently managed stands, over formerly managed but now unmanaged stands to primary forests, which have never been managed. The study objective was to quantify and compare the structural complexity of these forests to give insight into possible reference points for an improved prospective handling of managed forests. The highest stand structural complexity was found in primary forests. While there were no significant structural differences between the managed forests, they were more complex in structure than formerly managed forests that have been set aside as National Parks now. The results also showed that structural complexity significantly differed between the investigated stand age classes. Next to primary forests, thickets growing below sheltering overstory trees in managed forests resulted in high structural complexity values. The findings suggest that specific silvicultural management practices can increase the structural complexity in beech forests. This study may facilitate a ‘management for complexity’ in silvicultural practice and might lead the way towards a more precise promotion of three dimensional forest structures that are associated with specific forest functions as part of the stand management objectives.

Production of wood charcoal is a traditional form of forest use that lasted for millennia in most temperate regions, vanishing only some decades ago in the Mediterranean countries. Here, the abandoned charcoal hearths form a network of microhabitats with peculiar vegetation and soil conditions. Previous observational studies showed that establishment of woody species at these sites is severely hindered for unknown reasons. To test the effects of charcoal hearth soil on tree growth we used a common garden experiment with three major Euro-Mediterranean forest trees with different traits and ecology, one evergreen (Quercus ilex, holm oak) and two deciduous (Fagus sylvatica, beech, and Quercus cerris, Turkey oak). These were sown on control and charcoal-enriched soil collected in forest hearths abandoned since decades. Seed germination, seedling growth, photosynthetic efficiency and mortality were measured over a period of two years. Some responses were species-specific, while others were possibly associated to key traits such as evergreen vs. deciduous habit. Although charcoal soil effects were mainly positive on growth rate (height increase), they were mostly negative on germination of beech seeds, survival of holm oak seedlings, and photosynthetic efficiency. Although total biomass was not significantly affected, the root:shoot ratio was increased as a possible effect of physiological drought on hearth soil. These results support field-based evidence that the long persistence of charcoal remains in the soil may be not a favourable condition for forest regeneration. Management implications concern the use of biochar practices to promote forest restoration, which should be further tested on a wide range of species in different life-stages before applications in the field, also considering its long-term consequences.

Canopy gaps play a crucial role for forest dynamics processes, as they largely determine light transmission to lower canopy strata, thereby controlling the turnover of tree individuals in the stand. Even though their functional importance is undisputed, quantitative data on the rate of gap creation and gap closure, and the temporal change in gap size distribution patterns in temperate virgin forests are scarce. We used a repeated inventory (line-intercept sampling) of gap size frequency and fraction in a virgin beech (Fagus sylvatica) forest in the Slovakian Carpathians over a 10-year interval (2003–2013) to test the hypotheses that (i) disturbance intensity and thus gap creation and gap closure rate change only little over time, (ii) gaps persist or even expand, until they are filled primarily by vertical ingrowth of trees from lower strata, and (iii) gap creation promotes the height growth of released saplings and sub-canopy trees. In the 2003 and 2013 inventories, 37 and 30 gaps >20 m2 size were mapped along a total of 3217 m transect line investigated. The large majority of gaps was 500 m2 were very rare. Gap fraction decreased significantly from 13.6% in 2003 to 8.2% in 2013 (associated with a reduction in mean gap size from 261 to 96 m2), indicating considerable variation in disturbance intensity in the past decades. Before 2003, both large gaps (probably caused by wind throw) and small gaps (from dying trees) have been formed, while only small gaps developed in the period 2003–2013. Small gaps were closed within a few years through rapid horizontal canopy expansion of neighboring beech trees, while vertical gap filling through ingrowth of lower canopy layers and regeneration was the dominant process in larger gaps. Saplings and trees in lower canopy layers formed a heterogeneous understory in large parts of recently formed gaps and responded to this process with increased height growth. We conclude that, despite considerable variation in disturbance intensity over time, this beech virgin forest responds to gap formation with high resilience through rapid lateral canopy expansion in small gaps and ingrowth of saplings and sub-dominant tree layers in larger gaps.

The frequent occurrence of very large trees (diameter at breast height DBH ≥ 80 cm) is a typical element of both primary and secondary old-growth forests. We analyzed the characteristics of very large trees in one of the few stands of lowland old-growth beech forest in Northwestern Europe, regenerated around 1775 and left unmanaged since 1986. We examined their density, diameter range, increment, mortality rate and spatial distribution, based on repeated full dendrometric surveys. In order to evaluate the results, we compared them to original datasets from primary and secondary old-growth beech forests in Europe, and an extensive reference table, compiled from inventories and literature. In our study site, the density of very large trees increased from 31.5 to 34.3 trees ha−1 over the last 25 years, reaching a median DBH of 97 cm (mean 98.9), with the largest tree attaining a DBH of 159 cm. Although the trees were over 240 years old, they still showed an average DBH increment of 4.75 mm year−1 and a low mortality rate (0.89% year−1), indicating that they were still vital. These figures are remarkably high compared to other old-growth beech forest reference sites, where the density of very large trees generally varies between 5 and 20 trees ha−1 (median value 13.1), with a median diameter of 85–90 cm and maximum DBH for beech trees rarely exceeding 100–130 cm. The regular spatial distribution pattern of the very large trees in the studied stand clearly differed from a typical old-growth stand, in which very large trees are randomly distributed. Over the last 25 years though, because of random mortality and ingrowth, the spatial distribution gradually became more random. The extraordinary densities and sizes of the very large trees in our study site can be explained by the favorable climate and site conditions that promote high increments, in combination with the former management interventions of tending and thinning that resulted in continuous non-suppressed growth. Although derived from a very specific case with particular conditions, our observations may be relevant to other beech forests, as they tend to reset certain baseline assumptions for tree size and longevity potential of beech in Northwestern Europe.

The light environment of trees is a strong driver for their growth and morphology. Manipulating the light regime in forests is one of the main tools available to control the forest development. This study analysed the effect of a drastic light addition through gap creation on beech saplings (Fagus sylvatica L.) that had initially established under the canopy of mature trees. Altogether 6 gaps of varying size were created on an area of 4 ha. A total of 51 saplings were incorporated in this study. The saplings’ above- and belowground biomass compartments were destructively harvested along a light gradient. Relationships between light availability and growth increment, stress relief, biomass allocation, and growth morphology were analysed. Along the gradient of increasing light availability, beech saplings responded with an increased diameter growth, whereas the height growth remained unaffected. Also the root mass fraction increased at the expense of the leaf mass fraction. Other biomass compartments showed no significant trend. The mean branch weight also increased and the specific leaf area decreased. Other morphological traits were not affected by the light availability. The results lead to the conclusion that the morphological plasticity of the beech saplings towards light was not as high as initially expected. Furthermore, the sudden increase of light availability did not impose stress on the saplings. Finally, managing the light regime is appropriate to achieve specific goals.

More frequent and intensive droughts are projected to affect the vitality of major European tree species. Therefore, it is important to search for alternative, more drought-tolerant species to ensure ecological stability, biodiversity, and productivity of forests in future. Based on their relative abundance at very dry and warm sites, the otherwise rare and little-known, minor broadleaved species like Sorbus torminalis, S. domestica, Acer campestre, and A. platanoides are thought to be drought-tolerant. However, there is so far only limited scientific evidence to support that notion. Here we quantified the effect of extreme droughts (1947, 1976, and 2003) on radial growth of mature trees of the minor broadleaves in relation to the common companion species Quercus petraea and Fagus sylvatica in southwest Germany. Based on tree-ring analyses with a commensurate sample size for such rare species, the ability to resist and recover from drought, as well as the medium-term resilience of mature trees was studied. Likewise, the sensitivity of the species to temperature and precipitation was assessed. Radial growth was positively related to spring and summer precipitation for all species, whereas high summer temperatures led to decreased growth rates for A. platanoides, S. domestica, and F. sylvatica. Whereas S. torminalis appeared to be resistant and resilient in relation to drought, S. domestica and A. platanoides were also resilient but less resistant to drought stress. A synoptic ranking of the drought tolerance of all tree species suggests that the minor broadleaved tree species are not more drought-tolerant than Q. petraea, except for A. campestre. We conclude that cultivation of these minor species as well as Q. petraea should be expanded on xerix sites, where F. sylvatica reaches its growth limits.

Natural regeneration of European beech (Fagus sylvatica) and Norway spruce (Picea abies) plays a crucial role in the future of many European mountain forests. It is affected by various soil and stand-related factors whose relative importance, especially in mixed stands, is still not known. In this study, we assessed the importance of stand composition, soil wetness, disturbances and different microsites and seedbeds for regeneration of beech and spruce in a mixed old-growth mountain forest. We also focused on how the effects of these factors change as regeneration gets older. We sampled all regeneration in 563 plots from different microsite types (deadwood, intact soil, treethrow pits and mounds), distinguishing three seedbeds (mosses, beech litter, bare substrate) for seedlings. We used soil survey and tree census data with generalized linear mixed models and variance partitioning to identify the main factors driving tree regeneration and their relative importance. Although beech was slightly less abundant in the canopy than spruce, it strongly outnumbered spruce in regeneration. Beech regeneration showed an affinity for beech litter-rich microsites and drier soils, while spruce was more common on deadwood and moister soils and its response to the seedbed was microsite-specific. The regeneration of both species was positively related to the proportion of their own species in the canopy, but more so in seedlings than in older regeneration cohorts, where soil wetness was more important. The overall pattern of tree regeneration thus resulted from a complex interplay between site conditions and their alterations by current and former generations of canopy trees through the creation of new microsites (deadwood, uprooting mounds) or litter production. Where beech regeneration is not suppressed by excess soil wetness, it is much more successful than spruce due to its shade tolerance and ability to be established in the beech litter that dominates the forest floor. On the other hand, spruce regeneration is mostly restricted to elevated microsites with lower litter accumulation, such as deadwood and treethrow mounds. Our results indicate that both species exhibit an ability to modify their environment in favor of their own regeneration, but under current conditions, beech is more successful than spruce and can be expected to increase its dominance in the future.

Oak (Quercus petraea (Matt.) Liebl. and Quercus robur L. grouped), European beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.) are three major species of western and central European forests. When conditions are suitable for the three species, silvicultural management often favours oak because of its greater economic interest. Forest managers know that beech and hornbeam are strong competitors for oak during the regeneration phase, but the conditions that influence the relative success of the regeneration of the three species growing in mixture are still poorly characterised. The natural regeneration of the three species 20 years after canopy openings was studied based on 108 study sites established in 2001 in French forests impacted by the windstorms Lothar and Martin in 1999. In spring and summer 2018 and 2019, all saplings over 0.1 m in height were counted, species were identified and diameter at breast height (DBH) was measured for all saplings over 1.30 m. The height of the saplings with the highest and median DBH in each plot was recorded for each species. Mixed models were used to analyse the combined effects of former stand type, distance from the edge of the gap and soil conditions on species presence, sapling abundance, DBH and height. The modelling approach highlighted the preponderant role of the initial seed rain on the presence and sapling density of the three species compared to interspecific competition or distance from the edge. The two latter factors had a secondary effect on sapling DBH and height. Beech and hornbeam saplings were more abundant than oak saplings regardless of soil conditions (on average, 3097, 3063 and 344 saplings ha−1, respectively), suggesting a strong competitive ability of these two species. Oak was present on 22% (43% for hornbeam and 68% for beech) of the studied plots, at a low density but with a height and DBH similar to that of beech or hornbeam. This result highlights the high dissemination capacity of beech and hornbeam, which prevents the establishment of a stand dominated by oak. When seeking to obtain oak-dominated stands in the lowlands of Europe, the abundance of beech and hornbeam can be a limiting factor that could lead to the disappearance of oak from large areas if no silvicultural operations are performed to promote it.

Disturbances have been recognized as a key factor shaping the species composition, structure and dynamics of natural forest ecosystems. In Europe, where forests driven by spontaneous processes have survived in relic form, knowledge about natural disturbance regimes is still fragmentary. To expand this knowledge, we reconstructed stand-level growth and analyzed the spatio-temporal pattern of release signals in the increment chronologies of individual trees as indicators of disturbance events in the Western Carpathians (Central Europe). The study was carried out in five old-growth forests formed by Fagus sylvatica L., Abies alba Mill. and Picea abies (L.) H. Karst. Depending on the stand, the analyses included tree-ring series of 84–193 trees sampled over areas of 5.9–13.6 ha and aimed at determining (1) the spatio-temporal pattern of disturbance severity over the last two centuries, (2) whether disturbances have been synchronized in time across the study sites and (3) whether disturbances have induced pulsed dynamics of stand development manifested as fluctuations in radial tree increment at the level of entire stands. In the period 1850–2010, the percentage of decades with the proportion of released trees

Douglas fir (Pseudotsuga menziesii) has regenerated naturally in European forests since the middle of the 20th century. Some cases of an invasive character of the species have been reported under specific site conditions, but systematic data on the extent of natural regeneration and spread of Douglas fir across different forest communities are largely lacking. Due to its potential tolerance to increasing summer droughts, Douglas fir has been suggested as a sustainable future tree species for Central European forests. In this study, we investigated natural regeneration of Douglas fir in comparison to native tree species in 39 forest stands in Switzerland belonging to different forest communities. We analyzed the regeneration success of Douglas fir, Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica) with respect to ecological site conditions. The proportion of Douglas fir seedlings (

Lacking structural diversity in production forests has been evidenced to decrease epiphytic bryophytes and lichens. One approach to create structurally more diverse forests is retention forestry. Only a small number of studies focused on the effectiveness of retention measures in continuous-cover forestry. Most studies have been conducted in even-aged, clear-cut based management systems and applied different approaches, but they all have in common that the retained trees have been examined for epiphytes only after harvest. Thus, it remains unclear whether these trees or even a certain tree species could take the life-boat function for epiphytes on logged sites. Thus, prior to logging, we assessed epiphytic bryophytes and lichens on potential large living retention trees, here referred to as habitat trees (HT), of Abies alba and compared the diversity pattern to nearby average trees (AT; A. alba, Fagus sylvatica or Picea abies) of smaller sizes in selectively harvested continuous-cover forests. Selection of AT was based on the average stem diameter of all trees within the stand. We found that species richness and Simpson diversity of lichens were significantly higher on HT. For bryophytes, F. sylvatica AT showed significantly higher Simpson diversity. Mixed models revealed positive effects of F. sylvatica on bryophytes, whereas large stem diameters and elevation were the driving forces for lichens. Additionally, ordinations revealed clear patterns in species composition separating between conifers and broadleaved trees, and along increasing altitude and stem diameter. Concerning HT selection, we suggest to focus rather on the tree species diversity than on stem diameter, when aiming to protect epiphytic bryophytes and lichens.

Vertical gradients of habitats are a typical characteristic of forest ecosystems. Sun-exposed dead wood in the upper canopy, for instance, provides a habitat for saproxylic beetles distinct from that in the more shaded dead wood below the canopy. Canopy research, however, is challenging due to both the limited accessibility and potential confounding effects of temperature on trapping probability when activity traps are used. We studied saproxylic beetle assemblages along a complete vertical gradient without bias caused by temperature effects on activity. Using crane-like constructions attached to the top of large Silver Fir trees (Abies alba), we exposed bundles of freshly cut branches of European Beech (Fagus sylvatica), Silver Fir and Norway Spruce (Picea abies) in three different vertical strata (upper canopy, mid-canopy and near the ground). The bundles in the upper canopy were fully exposed to the sun and the bundles in the mid-canopy and near the ground were in the shade. We allowed beetles to colonize the bundles of branches for one growing period and then reared beetles from each bundle over three years. The species composition of saproxylic beetle assemblages differed between bundles in the upper canopy and near the ground; bundles in the mid-canopy had an intermediate assemblage composition. The abundance of saproxylic beetles was higher near the ground than in the upper canopy, whereas the number of species showed the opposite pattern. Overlapping confidence intervals of sample-based rarefaction and extrapolation curves for species diversity indicate that estimated gamma diversity per stratum is similar across the three strata. Our results support earlier studies that revealed the importance of habitat heterogeneity as a driver of the biodiversity of taxa associated with dead wood. As we controlled for wood diameter and tree species diversity, our study suggests that the microclimatic variability within dead wood – and thus habitat heterogeneity for saproxylic beetles – is higher in the upper canopy than near the ground. For biodiversity conservation in forests, our results support a strategy of enhancing the number of trees with microhabitats, particularly those with dead branches in the upper tree crown. Dead branches and standing dead trees should only be removed, e.g. for safety reasons, if no other option is available.

Aim The establishment of broadleaved - conifer mixtures has had positive effects on productivity. However, it is still not clear the degree to which belowground space occupation contributes to these effects and how root traits of the respective species differ between mixed and pure stands. Thus, the aim of this study was to examine how enrichment of beech forests with conifer species impacts fine root biomass and other root traits across variable site conditions. Methods We studied 20 mature pure and mixed stands of European beech (Fagus sylvatica), Norway spruce (Picea abies), and Douglas-fir (Pseudotsuga menziesii), and determined differences in biomass, spatial distribution, and morphology of fine roots (≤2 mm, to 60 cm soil depth) among beech – conifer mixtures and pure stands of the respective species in two regions with differing site conditions in Northern Germany. Results Site conditions had strong effects on fine root biomass (FRB) and fine root area index (RAI). Both FRB and RAI were significantly higher across all stand types on the sites with lower belowground resource availability. On the less favorable sites, FRB significantly increased with increasing beech proportion. In contrast to specific root area (SRA) and RAI, specific root length (SRL) was not affected by site conditions but differed significantly among species. No overyielding was observed when FRB was plotted against basal area and/or area potentially available (APA), which reflects the aboveground horizontal space configuration. Spatial fine root biomass patterns of all species in both monospecific and mixed stands changed along the vertical soil profile at both sites. FRB decreased with increasing soil depth, with the exception of beech in mixed stands. Conclusion Our data suggest that both amount and distribution of tree fine roots in pure and mixed stands are highly variable and depend primarily on-site conditions and secondarily on tree species identity. By disentangling soil and species identity effects, we conclude that beech has a remarkable potential for adjusting fine root biomass to cope with unfavorable conditions as compared to spruce and Douglas-fir.

The success of beech regeneration depends on resource availabilities, which are both heterogeneously distributed in forests and influenced by climate change impacts such as drought and heat waves. To ensure beech regeneration success in the future, it is therefore of great interest to understand the influences of different resource availabilities and their potentially interactive effects on beech seedling survival. In an experimental canopy gap study, we investigated the effects of direct (DIRSF) and diffuse (DIFFSF) solar radiation, soil fertility, groundwater influence, micro-site elevation, vegetation and root competition of overstorey trees on the survival of beech seedlings two years after planting in 2017. The inverse of fine root densities found for overstorey beech (BGRB) and oak (BGRO) was interpreted here as an approximation of the availability of below ground resources, mainly soil water. A logistic model demonstrated positive and interactive effects of DIFFSF, BGRB and soil fertility, emphasizing the complementary resource use pattern of beech seedlings. DIRSF showed a negative effect on survival that was enhanced on groundwater-dominated and higher elevated micro-sites and linked to intensified water limitation. The initial stature of seedlings, the presence and biomass of vegetation and BGRO had no significant effects on beech seedling survival. The unexpected extend to which DIFFSF affected beech seedling survival, the given significance of complementary effects of DIFFSF, BGRB and soil fertility, as well as found interactive effects of DIRSF are discussed in the context of the 2018/19 drought event. Our results suggest that silvicultural measures, such as the creation of larger gaps, can significantly improve resource availabilities, providing an opportunity to increase survival of beech seedlings in the face of climate change impacts.

European beech (Fagus sylvatica L.) is a common tree species in Central European forests but the fitness of this species under future climate conditions is still a matter of debate. Here, we study the response of transplanted beech saplings in terms of their chemical and morphological traits to different levels of soil drought in a mountainous, partially open, storm damaged Norway spruce forest. Throughfall was excluded by roof constructions in three consecutive growing seasons. Spatial soil drought gradients resulted from soil water consumption by heterogeneously distributed mature spruce trees. Individual drought stress dose (DSD) was assessed for each beech sapling using cumulative soil matric potential in the rooting zone. After three years of drought treatment, we analyzed biomass components, traits of leaves and fine roots of sixty beech saplings. In the third year, the classical permanent wilting point in the soil was exceeded for some beech saplings, however, all saplings survived the drought treatments. Several chemical plant traits responded to DSD sum of the last two years, while morphological traits and biomass components were mostly not or weakly correlated with DSD. Potassium concentration and associated C:K and N:K ratios in fine roots were most sensitive to drought stress. We assume that K and other nutrients were hardly available in the extremely dry forest floor and that the undersupply could not be compensated by nutrient uptake from the mineral soil. Increasing C concentration in leaves indicates an acclimation towards sclerophylly to maintain the hydraulic function of leaves. Increasing specific root length (SRL), specific root tip density (SRTD) and decreasing fine root diameter also indicate a morphological acclimation of saplings to increasing DSD. Weak correlations between morphological traits and DSD partly resulted from non-linear responses to increasing DSD. Maximum number of mycorrhizal root tips and maximum fine root biomass occurred at medium DSD. Our results suggest that the acclimation of chemical and morphological traits fortifies the resilience of beech saplings against soil drought in the years after transplantation. However, reduced uptake of soil nutrients caused by drought can only be partially compensated by redistribution within the sapling. An expansion of the rooting zone in the moist, nutrient-poor subsoil can improve the water uptake of beech saplings during drought periods, but this strategy hardly improves their nutrient supply.

Central Europe's temperate forests are heavily shaped by centuries of human activity. Their natural vegetation, mainly consisting of beech-dominated (Fagus sylvatica) deciduous forests, has been widely replaced by more profitable species grown outside of their natural ranges. This has strongly influenced forest-dwelling communities. Necessary adaptations to changing climatic conditions and the increasing demand for forest ecosystem multifunctionality are reversing these shifts in tree species composition. Integrative approaches that seek to balance production and conservation goals promote mixed forests of beech with spruce (Picea abies), pine (Pinus sylvestris), or oak (Quercus spp.). These mixed forests more closely resemble the natural vegetation and have reduced vulnerability to disturbances compared to coniferous monocultures, but higher commercial value compared to pure beech forests. However, our understanding of how different levels of admixture of commercially relevant tree species to beech forests affect multi-trophic diversity and community composition remains limited. We investigated herbaceous plants, fungi, oribatid mites, springtails, true bugs, beetles, birds and bats in 41 mature forest stands differing in tree species composition. We assessed the effects of admixtures on abundances and alpha and gamma diversity, i.e. the total number of species per forest type, and a measure of multidiversity by comparing reference beech stands with stands containing varying proportions of admixed species. At the plot level, the proportion of admixtures was especially important regarding oak and pine. Increasing shares of oak positively affected birds, true bugs and herbivorous beetles. Increasing shares of pine benefitted herbivorous true bugs and understory plants but negatively affected other true bugs, bats, and litter-decomposing fungi. Spruce admixture resulted in higher saproxylic beetle and bird diversity. At the landscape level, admixture significantly increased gamma diversity in plants, mycorrhizal and litter decomposing fungi and herbivorous and saproxylic beetles. Only springtail gamma diversity decreased in the presence of admixture. Admixture also significantly altered community composition for six out of 13 taxa. Indicator species were found for all forest types, and seven species groups included species significantly associated with pure beech stands. Our results indicate that forestry decisions determine forest biodiversity across trophic levels via tree species composition, combining habitat heterogeneity effects and tree species-specific associations. Even low shares of admixed species affect local abundances and diversity. By displacing some species while benefitting others, admixing also alters community composition. This study provides a basis for estimating how altering tree species composition in Central European forests changes the diversity and composition of forest communities.

Reliable characterizations of developmental condition can help elucidate disturbance regimes, characterize structural development, and identify and describe old-growth. However, current forest life cycle development phase classifications are based on inconsistent, incompatible, or unreliable a priori archetypal structures that fail to capture the natural dynamics of old-growth European beech (Fagus sylvatica L.) forests subject to a small-scale disturbance regime. We demonstrate an alternative protocol for capturing phases of biomass upgrade based solely on the proportion of live-tree volume in seven progressive tree size classes, with an optional deadwood-share cut-off (30%) to also identify deadwood-rich patches when desired. The proportions of a 10-ha primeval European beech forest in the Ukraine assigned in 156.25 m2 grid cells to each of the Dominant Biomass Strata phases were in keeping with previously reported estimates. Amid a matrix (>60%) of Overstory, Upper Overstory, and Emergent phases, roughly a tenth of the area was classified to the early Open/Seedling and Understory phases, the Lower and Upper Midstory phases, and the Lower Overstory phase, respectively. Further, 12% of grid cells—across all phases—were deadwood-rich. The biomass proxies of live volume, basal area, and mean tree size increased distinctly with each subsequent phase, and were lower in the deadwood-rich category, in accordance with the forest life cycle. Structural complexity proxies varied inversely with biomass when defined as the distribution of volume among canopy layers, but similarly to biomass when defined using metrics based on tree size differences. High volumes of large-diameter deadwood were observed in all phases, consistent with previous observations of acyclic transitions following mortality. In pure primeval European beech, the synchronous pattern of biomass and size-based structural complexity metrics (including the standard deviation of tree diameters, the Gini coefficient for basal area, the diameter differentiation index T, and the structural complexity index SCI) may provide a natural model for the simultaneous optimization of volume and small-scale complexity in managed forests. With local adaptation, the proposed Dominant Biomass Strata classification protocol could be applicable to any site or forest type and used to classify stand development phases in young forests following stand-initiation or to classify patch development phases in old-growth forests subject to maintenance dynamics.

Large herbivores play a key role in terrestrial ecosystems, and their populations alter the plant composition in many ecosystems. One example is deer, whose populations in the Northern Hemisphere have increased over the last decades. This has resulted in increased browsing pressure on saplings and, as a consequence, has hampered forest regeneration in some areas. Such herbivore-induced changes in the regeneration of forest stands have changed their composition and biodiversity. Although there is an established link between the deer population density and the level of damage caused by browsing, the question remains open: What is the effect of increasing deer density over years on the regeneration of palatable and less browsing-resistant tree species? In this study, we investigated the relationships between the regeneration dynamics of five tree species (European beech Fagus sylvatica, silver fir Abies alba, sycamore Acer pseudoplatanus, hornbeam Carpinus betulus, and oak Quercus spp.) and browsing pressure in two years with low and high red deer (Cervus elaphus) density and at similar roe deer (Capreolus capreolus) density. We set up experimental plots in Roztocze National Park (central-eastern Poland), a protected area where natural predators of deer are constantly present. In addition to deer density, we analysed parameters that may affect browsing intensity: height of saplings, forage availability (sapling density), sapling diversity and light intensity (canopy openness). We found that increasing red deer density significantly increased browsing on all tree species, with saplings taller than 50 cm being under the strongest pressure. Moreover, higher deer density altered deer forage selection – it increased their selection for unpalatable European beech and decreased for highly preferred sycamore. Additionally, more species-diverse patches and closed canopy attracted deer and increased the probability of browsing on saplings. Contrary to our predictions, sapling density decreased browsing intensity. The study confirms that high ungulate density has significant effects on tree recruitment and may alter tree species composition of the forest stand. We provide clear evidence that deer herbivory plays a crucial role in tree regeneration in top-down processes in natural ecosystems.

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Tree litter decomposition on disturbed post-mining sites has been mainly studied within successional gradients, whereas almost no results were shown from afforested spoil heaps. Litterfall and its decomposition rate are considered the most important ecological processes for soil restoration during stand development on such initial forest habitats. These processes allow development of a functional ecosystem and productive forest stands. Moreover, the pedogenesis process on such “soilless”’ habitats can be significantly improved and accelerated by tree species selection during afforestation. The main aim of the study was to determine litter decomposition rates of nine tree species used for afforestation of a lignite mine spoil heap. We assumed that leaf litter decomposition rates would differ among tree species studied and that the site conditions would significantly influence this process. Our study was conducted on the spoil heap of the lignite open cast mine in Belchatow, central Poland. We studied leaf litter decomposition of Alnus glutinosa, Betula pendula, Pinus sylvestris, Quercus robur, Q. rubra and Robinia pseudoacacia in pure stands of these species (home stands), and litter decomposition of Acer pseudoplatanus, A. glutinosa, Fagus sylvatica, Prunus serotina, Q. rubra, and R. pseudoacacia in Scots pine stands. We used the litterbag method. The experiments lasted for three years and the samples were collected every three months. Leaf litter decomposition calculated for home stands after three years of decomposition was 94.4% of the initial leaf mass for A. glutinosa, 70.9% for R. pseudoacacia, 70.1% for P. sylvestris, 68.3% for B. pendula, 66.9% for Q. rubra and 61.5% for Q. robur. In Scots pine stands, after three years of the experiment, 92.3% of the initial leaf mass decomposed for P. serotina, 85.7% for A. glutinosa, 83.5% for A. pseudoplatanus, 65.2% for R. pseudoacacia, 50.9% for Q. rubra and 40.1% for F. sylvatica. A. glutinosa, R. pseudoacacia and Q. rubra leaves decomposed significantly faster in home stands than in Scots pine stands. Site aspect significantly influenced litter decomposition of the species studied, with higher rates mostly on the western slope. Our study revealed that the decision on tree species used for afforestation might shorten the period needed for soil restoration and achievement of sustainability of novel ecosystems. Proper selection of main and admixture tree species for afforestation of the post-mining sites might reduce the renewal period of the soilless and newly created habitats, which may provide noticeable ecological and economical effects during stand management.

Deadwood plays a crucial role in forest ecosystems, yet its impact on soil properties and specifically soil organic matter (SOM) stabilization is hitherto not fully understood or studied. We hypothesized that downed deadwood would enhance the light, labile SOM fraction in forest topsoils, and that those changes would be enhanced by advanced decay and higher rates of soil bioturbation that would move deadwood fragments into mineral soil. To test our hypotheses, we took topsoil samples directly next to European beech ( Fagus sylvatica L.) downed deadwood and samples from paired reference points at eight stands in Southwest Germany. From those samples we separated SOM into three density fractions linked to physical and chemical SOM stabilization processes: the free light fraction, the aggregate-occluded light fraction and the mineral-adsorbed heavy fraction. On silicate bedrock, deadwood increased the free light fraction by 57% ( 6.0 ± 4.2 mg g −1 ) compared to reference points. In contrast on calcareous bedrock, deadwood decreased the free light fraction by 23% ( 9.0 ± 3.5 mg g −1 ) compared to reference points. Deadwood with advanced decay from all sites increased the aggregate-occluded light fraction by 40% ( 3.7 ± 1.1 mg g −1 ) as well as total soil organic carbon (SOC) stocks by 24% ( 12.8 ± 4.5 mg cm −3 ) as compared to reference points. In summary, the light fraction of SOM was affected by deadwood depending on site conditions and the more stable, aggregate-occluded fraction eventually increased near decayed deadwood through interactions between stimulated biological activity and both particulate and dissolved organic matter. Altogether these results indicate that deadwood increases SOC stocks at sites where SOM decomposition is slow enough to enable occlusion of particulate organic matter within aggregates.

In Europe, concerns regarding the provision of ecosystem services from forests, such as biodiversity, has led to a widespread conversion from even-aged to close-to-nature forest management. These concerns have also led to a demand for quantifying stand structure, dynamics, and species diversity in order to evaluate ecosystem status and devise management action. In this study, species distribution, species association, and size diversity in a semi-natural, unmanaged beech forest in Denmark were analyzed using spatial indices including uniform angle index, mingling index, and differentiation index and spatial functions including pair correlation function, bivariate pair correlation function, mark variogram, and the Wiegand scheme. To analyze the spatial patterns of tree species, two plots, one in a less disturbed part of the forest and the other in a more recently disturbed part, was selected. Based on the spatial functions, all species showed a clustered pattern as a result of forest dynamics. Fagus sylvatica L. was segregated from other species and was more likely to form pure groups. In contrast, Ulmus glabra L.-Fraxinus excelsior L. and Ulmus glabra L.-Acer psedoplatanous L. showed positive association. All species in the less disturbed part of the forest showed positive spatial correlation of tree diameters, probably as a result of gap-phase dynamics. However, a lack of spatial correlation of tree diameters was observed for beech and elm trees in the more recently disturbed part of the forest. Our results indicated that spatial functions using stem-mapped data provide more reliable results and additional insights into the stand structure than neighborhood based indices. The study findings can be used to align forest management practices with goals of protecting biodiversity in managed forest.

Beech forests are important for biodiversity conservation in Europe and studies to identify sustainable forest management practices are therefore required. The ground beetle Carabus olympiae Sella, 1855, is a large steno-endemic endangered alpine species with very restricted ranges. Its known range is only delimited in two beech forests in the western Italian Alps where beech wood is still harvested. Forty individuals were collected and radio-tracked in 2014–2015 in order to assess the effects of forest management on microclimatic conditions, microhabitat use and movements. Regarding microhabitat selection deadwood and tree bases were preferred, and were used as refuges during the daytime. Bare ground was not used. The length of the path travelled by individual insects was more variable and the tortuosity was lower in managed than in unmanaged stands, suggesting that management induced more constrained trajectories and variable distances. We concluded that logging may exert short-term negative effects on C. olympiae ground beetles. However, the preference for tree bases and deadwood suggests that forest management, concurrently, may also be beneficial, on the condition that: i) the coppice, which provides more suitable microhabitats, prevails over conversion to high forest, and ii) deadwood originating from cutting (branches and treetops) is properly accumulated.

Common gardens are suited for analysing the behaviour of different species in a common environment. We used a common garden experiment including 12 different tree species (Fagus sylvatica, Pseudotsuga menziesii, Abies grandis, Larix kaempferi, Chamaecyparis lawsoniana, Pinus contorta, Pinus mugo, Abies procera, Picea abies, Quercus robur, Abies alba, and Picea sitchensis) grown at 13 different sites, and representing almost 50 yrs of measurements, for answering the following questions: (i) how do the species differ in their average biomass production?, (ii) how does their performance vary in space, and (iii) how does their performance vary over time. The analyses showed that the North American conifers including A. grandis, and P. sitchensis had a significantly higher potential for biomass production than the other species. However, while P. sitchensis was relatively invariant to site conditions, the analysis indicated that, compared to the other species, A. grandis benefited more than the other species from a general improvement in growing conditions. The effectiveness of substituting fossil fuels and carbon intensive materials with woody bioenergy is highly dependent on plant growth rates. Our results may suggest a selection of species with superior biomass production and carbon sequestration.

The aim of this paper was to investigate the functional composition of the understory of Mediterranean beech forest stands that have been managed in two different ways, namely, coppicing and tree by tree harvesting. In particular, we used a trait-based approach to characterize old coppice and high forest stands, analyzing their differences and evaluating the status of old coppices by considering their conversion towards high forest stands. The study area was the Montagne della Duchessa massif in central Italy, which lies at the center of the Apennine chain. Sixty-six plots were laid out and their species abundance and structural parameters were recorded. Data on plant traits were collected using both European databases and the literature available. Redundancy analysis was performed to assess the relationship between trait states and management, and forward selection was used to identify the structural parameters with a significant effect on trait variability. A Wilcoxon Rank-Sum test was done to assess differences in trait states between the management types. High forests proved to be more related to traits typical of mature forest conditions, while old coppices seemed not to have a clear trait association, except for some trait states related to open habitats, and showed the same “mature forest” trait composition, even if with lower abundances. This indicates that, despite the higher initial disturbance pressure, once abandoned, old coppices tend over time to evolve naturally towards mature forest functional conditions.

Understanding long-term successional changes in old growth forests affected by stand-replacing disturbance is particularly important in the context of contemporary changes in climate and disturbance regimes. We analyzed seven decades of succession following a stand-replacing wind disturbance (in 1947) in Badinsky prales, one of the best preserved old-growth fir-beech forests in western Carpathians (Central Europe), and contrasted the post-disturbance development with changes that occurred in the adjacent undisturbed old-growth forest. Both the disturbed and undisturbed sections of the old-growth forest showed compositional and structural changes that differed in their starting point, magnitude, and ecological mechanisms, but forest composition, structure and light conditions appeared to be converging across the two disturbance histories. The windthrow was initially dominated by early-successional goat willow (Salix caprea L.) that declined in abundance, basal area, and growth over time as beech (Fagus sylvatica L.) gradually increased in both abundance and basal area to dominate all canopy layers by 2015. This increase in beech dominance over time within the windthrow mirrored increasing beech dominance in the undisturbed old-growth forest which was caused by the gradual decline of silver fir (Abies alba Mill.). The fact that old-growth forests originally co-dominated by fir and beech appear to be transitioning to forests dominated by beech regardless of the disturbance history suggests that beech expansion may be a robust process that should be considered in both old-growth conservation and forest management where timber harvest with low canopy retention may have similar effects on forest dynamics as a stand-replacing windthrow.

Research results on the structure of European OGF are often contradictory; while some researchers stress equilibrium structures, others suggest that this rarely happens due to biomass accumulation. If the former were the case, then there would be a fairly strong argument that OGF should serve as natural references for selection management. At the same time, mountain mixed selection forests are in many regions considered to be the most “natural” type of MF, and thus to a large extent similar to corresponding OGF. However, because there are few old-growth forests (OGF) left in Europe, comparisons between OGF and selection-managed forests (MF) are rare. Since nature-based silviculture should follow natural processes and not exclude any species from its natural range, in this study we compared two mixed OGF and neighboring MF ( Piceo-Abieti-Fagetum illyricum ) in the Dinaric Mountains of Bosnia and Herzegovina. The MF were managed by the single-tree selection system for almost a century. The results indicated that this management approach yielded a statistically significant difference in tree species composition and presence of large-diameter trees. The cumulative diameter distributions, however, were similar in OGF and MF as both exhibited the shapes that are considered to provide demographic equilibrium. On the species level, though, this was the case only for beech. Species occurrence matrices indicated significant dominance of young European beech ( Fagus sylvatica L.) trees over silver fir ( Abies alba Mill.) and Norway spruce ( Picea abies L. Karst) in OGF. Nevertheless, based on the results from MF, the study highlights the crucial role of silvicultural measures that may potentially provide targeted long-term coexistence of the studied broadleaved and coniferous tree species.

In the study of vegetation changes in European beech ( Fagus sylvatica L.) and Norway spruce ( Picea abies (L.) Karst.) forests in the Orlicke hory Mts. (the Sudetes range, Czech Republic), 34 research plots were surveyed in 1951–2011 using the seven-point Braun-Blanquet scale. The long-term research was motivated by studying the effects of the pollution disturbance in the mountains of the Sudetes system in the 1980s, but also by the understanding of autonomous development of vegetation differing in human interventions. On the studied plots, soil samples were collected periodically from particular soil horizons for physical and chemical analyses. The results document the fact that beech forests showed a slow and almost one-way succession change in 1951–2011 while in spruce stands more pronounced tendencies of cyclic development and much varied dynamics were evident at the level of particular sites. In recent 20 years, the populations of younger tree species have augmented both in beech and spruce forests. Especially during the air-pollution disturbance, the species diversity decreased moderately and almost returned to the original values at the end of observations. Moderately increasing continentality of the vegetation composition and retreat of warmth-requiring species are typical of beech forests while an increase in nutrient-demanding species and retreat of light-requiring and moisture-demanding species are characteristic of spruce forests. Undergrowth in beech forests is rather more conservative from the aspect of developmental stages than undergrowth in spruce forests. The effect of forest origin on the temporal development of vegetation and species diversity was not statistically significant in either of the forest types. The test of the effect of chemical properties of soil showed the most important role of available potassium and calcium content in humus horizon and magnesium content in B horizon in beech forests and the crucial role of nitrogen content and soil reaction in A horizon in spruce forests.

Light availability in forests is a strong driver for forest development and diversity. Tree species develop differently under varying levels of light. Understanding the reasons for the individual growth strategies of tree species is crucial to understand dynamics of forest communities. This study aims at further disentangling aboveground biomass allocation patterns and growth variables for saplings of the tree species sycamore maple (Acer pseudoplatanus L.), European beech (Fagus sylvatica L.), and European ash (Fraxinus excelsior L.). Plants were destructively sampled along a light gradient. European beech allocated more biomass to its branches and less to its stem, in comparison to the other two species. The relative growth rate (RGR) and leaf mass area (LMA) of all species increased towards an asymptote along the increasing light gradient, whereas the leaf are ratio (LAR) decreased. The rate of increase and decrease differed among the tree species. Net assimilation rate (NAR) and absolute growth rate (AGR) both also increased with light availability, but the distinction among the species was not as clear. This study showed varying reactions of all three species to light and allowed a quantitative distinction among the species regarding their shade tolerance (ash