Mixture Of Beech Research Articles

Local neighborhood affects stem rehydration under drought: evidence from mixtures of European beech with two different conifers.

Mixed-species forests are, for multiple reasons, promising options for forest management in Central Europe. However, the extent to which interspecific competition affects tree hydrological processes is not clear. High-resolution dendrometers capture sub-daily variations in stem diameter; they can simultaneously monitor stem growth (irreversible changes in diameter) and water status (reversible changes) of individual trees. Using the information on water status, we aimed to assess potential effects of tree species mixture, expressed as local neighborhood identity, on night-time rehydration and water stress. We deployed 112 sensors in pure and mixed forest stands of European beech, Norway spruce, and Douglas fir on four sites in north-western Germany, measuring stem diameter in 10-minute intervals for a period of four years (2019-2022). In a mixture distribution model, we used environmental variables, namely soil matric potential, atmospheric vapor pressure deficit, temperature, precipitation, and neighborhood identity to explain night-time rehydration, measured as the daily minimum tree water deficit (TWDmin). TWDmin was used as a daily indicator of water stress and the daily occurrence of sufficient water supply, allowing for stem growth (potential growth). We found that species and neighborhood identity affected night-time rehydration, but the impacts varied depending on soil water availability. While there was no effect at high water availability, increasing drought revealed species-specific patterns. Beech improved night-time rehydration in mixture with Douglas fir, but not in mixture with spruce. Douglas fir however, only improved rehydration at a smaller share of beech in the neighborhood, while beech dominance tended to reverse this effect. Spruce was adversely affected when mixed with beech. At species level and under dry conditions, we found that night-time rehydration was reduced in all species, but beech had a greater capacity to rehydrate under high to moderate soil water availability than the conifers, even under high atmospheric water demand. Our study gives new insights into neighborhood effects on tree water status and highlights the importance of species-specific characteristics for tree-water relations in mixed-species forests. It shows that drought stress of European beech can be reduced by admixing Douglas fir, which may point towards a strategy to adapt beech stands to climate change.

Tree species identity drives soil carbon and nitrogen stocks in nutrient-poor sites

The establishment of mixed forest stands is an option to enhance soil organic carbon stocks and to protect forest ecosystems from various impacts of climate change. Increasing temperatures and drought potentially affect the vitality of the native coniferous Norway spruce (Picea abies), often used in mixed forests. We investigated the effects of a replacement of Norway spruce by Douglas fir (Pseudotsuga menziesii) admixed to European beech (Fagus sylvatica) on carbon (C) and nitrogen (N) concentrations and stocks, as well as the vertical distribution and changes in forest floor and mineral soil (down to 30 cm depth). Two regions with different soil conditions (loamy vs sandy soils textures) were selected, considering four sites in each region. Each site included a quintet of neighboring forest stands (>85 yrs) of European beech, Douglas fir, and Norway spruce stands as well as mixtures of beech with either Douglas fir or spruce. Our results showed that the C stocks of the organic layer were significantly influenced by tree species, while the C stock of the mineral soil varied among soil types. Total soil organic C stocks demonstrated notable species-specific characteristics, primarily driven by the elevated C stocks in the organic layer. In sandy soils, conifers and mixed forests store 10 % more C and N in the organic layer compared to loamy soils, whereas the C and N stocks under beech remained unaffected, regardless of the site condition. The interaction between species and sites was significant only for Douglas fir and mixed Douglas fir/beech, indicating that the impact of species on C and N varied across sites and was notably pronounced in sandy soils. The higher potential for carbon and N storage in mixed-species forests compared to pure stands emphasizes the capacity of mixed forests to provide valuable ecosystem services, enhancing C sequestration in sandy soils.

Scientific opinion on the renewal of the authorisation of Scansmoke SEF7525 (SF-004) as a smoke flavouring Primary Product.

The EFSA Panel on Food Additives and Flavourings (FAF) was requested to evaluate the safety of the smoke flavouring Primary Product Scansmoke SEF7525 (SF-004), for which a renewal application was submitted in accordance with Article 12(1) of Regulation (EC) No 2065/2003. This opinion refers to the assessment of data submitted on chemical characterisation, dietary exposure and genotoxicity of the Primary Product. Scansmoke SEF7525 is obtained from a tar produced from a mixture of red oak, white oak, maple, beech and hickory. Based on the compositional data, the Panel noted that the identified and quantified proportion of the solvent-free fraction amounts to 32.6 weight (wt)%, thus the applied method does not meet the legal quality criterion that at least 50% of the solvent-free fraction shall be identified and quantified. At the maximum proposed use levels, dietary exposure estimates calculated with Food Additive Intake Model (FAIM) ranged from 0.6 to 3.8 mg/kg body weight (bw) per day at the mean and from 1.1 to 10.1 mg/kg bw per day at the 95th percentile. Based on the available information on genotoxicity on 44 identified components, the Panel concluded that two substances in the Primary Product, styrene and benzofuran, raise a potential concern for genotoxicity. In addition, a potential concern for genotoxicity was identified for the unidentified part of the mixture. Considering that the exposure estimates for styrene and benzofuran are above the threshold of toxicological concern (TTC) value of 0.0025 kg/kg bw per day for DNA-reactive mutagens and/or carcinogens and since further data are needed to clarify their potential genotoxicity, the Panel concluded that the potential safety concern for genotoxicity of the Primary Product cannot be ruled out.

Under storm risk, economic productivity of Norway spruce (Picea abies (L.) H. Karst) in monoculture shows sharper decline than in mixture with European beech (Fagus sylvatica L.)

Key messageBy calibrating and validating a forest growth model for seven species in Germany and coupling it with a wind damage simulator, we specifically estimated the impact of wind damage on the net present value of Norway spruce and European beech in mixture and monoculture. Under risk, the net present value of spruce managements saw the sharpest declines, although the highest end net present value was still obtained through a heavily thinned spruce monoculture.ContextWind damage is one of the most important risks to Central European forests, and adaptation measures are essential.AimAdaptive management strategies should simultaneously account for forest production and wind risk. We simulated the effect of adaptive measures on wind-risk in German forests.MethodsA process-based forest growth model, “3-PG Mix”, was recalibrated and coupled with the storm damage risk model “Lothar”. We investigated the effect of thinning regimes on wind risk in monoculture and mixed species stands. The net present value of the simulated regimes was calculated and compared (risk vs. no risk).ResultsSpruce regimes achieved the highest net present values when risk was not considered. Considering risk in spruce and beech mixtures and monoculture, all regimes reached values below 3000 € ha−1 by year 120. The exception was a heavily thinned spruce monoculture at 4507 € ha−1, being the most profitable regime under risk.ConclusionWe conclude, on the basis of this modelling study, that heavy thinning reduced storm risk and maintained a higher net present value in spruce. Species mixture of beech and spruce saw net present values levels remain more constant under risk, while beech monoculture increased.

Short-Term Effects of Anthropogenic Disturbances on Stand Structure, Soil Properties, and Vegetation Diversity in a Former Virgin Mixed Forest

Despite the sharply growing interest in the disturbances occurring in primary forests, little is known about the response of European virgin forests to anthropogenic disturbance. The present study investigated the effect of the first silvicultural interventions that took place nine years earlier in a former virgin forest (FVF). Changes in the stand structure, environmental characteristics, and diversity of ground vegetation were studied in comparison with a nearby virgin forest (VF), both consisting of a mixture of European beech and silver fir. While the tree density did not differ significantly between the two forests, the number of large trees, the basal area, and the stand volume were significantly reduced in the FVF. The deadwood volume was twice as great in the VF as in the FVF and was found in both forests, particularly from silver fir. Despite significantly better light conditions in the FVF, natural regeneration was not significantly higher than in the VF. However, a slight improvement in the proportion of silver fir and other tree species into total regeneration was reported. The soil temperature was significantly higher in the FVF, independent of the measurement season, while the soil moisture showed a higher value in the VF only in spring. The FVF is characterized by a greater soil CO2 emission, which is especially significant in summer and fall. The diversity of the ground vegetation did not yet react significantly to the silvicultural intervention. These preliminary findings are important in drawing suitable forest management practices that need to be applied in mixed beech–silver fir stands, especially in terms of maintaining species diversity. However, the short time frame since the intervention obliges further research on this VF–FVF pair over the next 10–20 years, at least regarding silver fir dynamics.

Non-native Douglas fir promotes epigeal spider density, but has a mixed effect on functional diversity

With climate change altering ecosystems worldwide, forest management in Europe is increasingly relying on more adaptable non-native tree species, such as Douglas fir (Pseudotsuga menziesii). However, the ecological consequences of the increased utilization of Douglas fir on arthropod diversity and ecosystem functioning are not fully known. Here we assessed how non-native Douglas fir as well as large- and small-scale differences in the environmental context, affect epigeal spider abundance, biomass, taxonomic and functional diversity, and community structure in Central European forests. Our study sites were divided into two regions with large differences in environmental conditions, with seven replicates of five stand types, including monocultures of native European beech (Fagus sylvatica), non-native Douglas fir and native Norway spruce (Picea abies), as well as two-species mixtures of European beech and each of the conifers. Contrary to our expectations, Douglas fir promoted small-scale spider diversity, and abundance and biomass (activity density). On the other hand, it decreased spider functional divergence and altered spider community structure. Microhabitat characteristics had opposing effects on spider diversity and activity density, with more open stands harboring a more diverse but less abundant spider community. Overall, our findings suggest that increasing Douglas fir utilization at the expense of Norway spruce does not necessarily decrease the diversity of epigeal arthropods and may even promote local spider diversity and activity density. However, care needs to be taken in terms of biodiversity conservation because typical forest spider species and their functional divergence were more strongly associated with native beech than with coniferous stands.

Drought Hardening of European Beech (Fagus sylvatica L.) and Silver Fir (Abies alba Mill.) Seedlings in Mixed Cultivation

To alleviate the enhanced frequency, duration, and intensity of drought as a consequence of global warming, admixing drought-sensitive European beech (Fagus sylvatica L.) with deep rooting silver fir (Abies alba Mill.) has been proposed. However, information on the performance of the admixtures of seedlings of these tree species at limited water availability has so far not been reported. In the present study, we investigated the significance of water deprivation in mixtures of beech and fir seedlings on the foliar relative water content (RWC), δ13C signature, total C and N contents, and C:N ratios of both species in a drought-rewetting cycle. Surprisingly, moderate drought triggered increased RWC in beech leaves and current year fir needles indicating drought hardening. The enhanced foliar RWC was preserved after rewatering in beech leaves, but not in current year fir needles. Drought did not significantly affect δ13C abundance in beech leaves, but enhanced the δ13C abundance (less negative values) in current and one-year old fir needles, indicating stomatal control in fir needles but not in beech leaves upon moderate drought. Total C contents of beech leaves were significantly increased upon drought and rewatering, but remained constant in fir needles. Foliar total N increased in both species upon drought and decreased upon rewatering. Accordingly, C:N ratios decreased in response to drought and recovered after rewatering. These results suggest that drought hardening may be achieved at least partially via osmotic adjustment by different compatible solutes in beech leaves and fir needles. No apparent effects of the number of neighbours were observed, although more fir neighbours tended to increase the RWC and total C contents of beech leaves. These results indicate that drought hardening in mixtures of beech and fir seedlings is largely independent of the number of interspecies neighbours.

Evaluation of a Restoration Approach After One Century – Effects of Admixed European Beech on the Natural Regeneration Potential and Humus Condition in Spruce Stands

About 100 years ago, groups of European beech were reintroduced into Norway spruce stands in some parts of Germany as a restoration approach. The aim of this approach was to maintain or rehabilitate the ecological function of soil fertility and the regeneration option of beech for the next generation. The effect of beech groups on surrounding spruce stands was studied in the Ore Mountains by recording natural regeneration of beech and humus layer thickness and form. Point pattern statistics were used to analyse the spread of beech regeneration and to determine factors influencing its establishment. It was found that the density of regeneration decreases with increasing distance from the beech group. However, beech regeneration was found up to distances of 69 m. Furthermore, it becomes evident that PAR radiation (maximum regeneration densities at PAR values of 35 W/m2) and fencing (3.41 times higher regeneration density compared to unfenced areas) against deer have a positive influence on beech regeneration density. Ordered categorical models were used to model humus form and non-linear models were used to model humus layer thickness. It could be proven that the most bioactive humus forms and lowest humus layer thicknesses were found within the beech group. With increasing distance to the beech group, the total humus layer thickness and the proportion of mormoder in the spruce stand increased. The positive influence of the beech group on the humus composition extends to about 40 m from the centre of the beech group. Due to the former arrangement of the beech groups in the terrain, the effects can also extend to the spruce stands in between. The hypotheses on the restoration approach of reintroducing groups of beech into spruce stands formulated by foresters 100 years ago can thus be confirmed. For future restoration approaches of spruce stands, groupwise mixtures of beech should be established with a distance of 40–50 m.

Intraspecific Relationships and Nest Mound Shape Are Affected by Habitat Features in Introduced Populations of the Red Wood Ant Formica paralugubris.

Simple SummaryRed wood ants (Formica rufa goup) are dominant ant species widespread in the Eurasian continent. These species have a strong ecological impact on the habitats they dwell in, being top-ranked predators. One of the most striking features of these ants is represented by the large nest mounds they build. In this study, we investigated how nest mound shape and colony organization of imported populations of Formica paralugubris varied in three different habitat types. We found that nest mounds differed in size, number and shape in the three habitats. In all the three sites, nests were connected by trails of workers, but the size of these nest-networks differed. We also investigated the pattern of intraspecific aggression among ants from different nests, and we showed that aggressiveness was higher within each population than between separate populations, a finding in line with a ‘nasty neighbor’ behavior.Ants belonging to the Formica rufa group build large nest mounds, which aid their survival during severe winters. We investigated whether different environmental features of the habitats affected the nest mound shape and the population structure. We assessed the shape of all the nest mounds and mapped inter-nest trails connecting mounds for three imported populations of Formica paralugubris in three forest habitats: fir-dominated, beech-dominated, and a mixture of fir and beech. Single-nest mounds were averagely smaller and flatter in the beech-dominated forest, probably because of lighter building materials. Nonetheless, by summing the volumes of all interconnected nests, the size was similar among all three sites. In fir- and beech-dominated forests, large nests were also central in the networks, suggesting a central place foraging model with these nests as reference. We finally performed aggression tests, and found that aggressiveness was significantly higher among nests belonging to the same population than between populations. The results highlight the plasticity of the species to adapt nest and colony structure to different environments. Additionally, it appears that none of these populations is unicolonial, as observed in various alpine sites, there and the observed patterns of aggression are coherent with the ‘nasty neighbor’ effect.

Tree species composition and soil properties in pure and mixed beech-conifer stands drive soil fungal communities

Soil fungi, especially the functional guilds of saprotrophs and symbiotrophs, play a central role in ecosystem processes such as decomposition and plant nutrient acquisition. Fungal communities are influenced by soil properties and management strategies such as tree species selection. Yet, the implications of the enrichment of temperate forests consisting of tree species in their native range with non-native tree species on soil fungal diversity and their functional groups are unknown. Here, we studied fungal communities in 40 plots (2500 m2 size per plot) located in two regions differing in site conditions (nutrient content, soil moisture and climate) in forests composed of European beech, spruce and Douglas-fir (non-native) and mixtures of beech with either spruce or Douglas-fir. We hypothesized that fungal community structures are driven by soil properties and tree species composition, generally resulting in higher fungal diversity in mixed than in mono-specific forests. We further hypothesized that Douglas-fir has a negative effect on ectomycorrhizal fungal species richness compared to native species, whereas saprotrophic fungal richness is unaffected. Fungal DNA barcoding and dissimilarity analyses showed significant separation of fungal communities between nutrient-rich and nutrient-poor regions and among forest types. Mycorrhizal species richness did not vary with forest type, but the relative abundance of mycorrhizal species was lower in Douglas-fir and mixed beech-Douglas-fir forests than in spruce or beech-spruce mixture forests. Conifer forests contained higher relative abundances of saprotrophic fungi than mono-specific beech forests. Among 16 abundant fungal orders in the soil, two containing saprotrophic fungi (Tremellales and Hymenochaetales) were enriched in conifer forests, regardless of site conditions and tree species mixture. The other fungal orders, including those dominated by mycorrhizal fungi (Russulales, Boletales, Atheliales and Cantharellales) showed variable patterns depending on site conditions and tree species. Our results show the impact of tree species composition and soil properties on soil fungi. The response of fungal guilds and taxa to forest types and soil properties can potentially influence nutrient fluxes.

Tree species mixing can increase stand productivity, density and growth efficiency and attenuate the trade-off between density and growth throughout the whole rotation.

Background and AimsMany recent studies emphasize that mixed species is a promising silvicultural option for sustainable ecosystem management under uncertain and risky future environmental conditions. However, compared with monocultures, knowledge of mixed stands is still rather fragmentary. This comprehensive study analysed the most common Central European tree species combinations to determine the extent to which mono-layered species mixing (1) can increase stand productivity and stem diameter growth, (2) increase stand density or growth efficiency, and (3) reduce competition and attenuate the relationship between stand density and stem diameter growth compared with mono-specific stands.MethodsThe study was based on 63 long-term experimental plots in Germany with repeated spatially explicit stand inventories. They covered mono-specific and mixed species stands of Norway spruce (Picea abies), silver fir (Abies alba), Scots pine (Pinus sylvestris), European beech (Fagus sylvatica), sessile oak (Quercus petraea), European ash (Fraxinus excelsior) and sycamore maple (Acer pseudoplatanus). Based on spatially explicit measurement, we quantified for each tree the intra- or inter-specific neighbourhood, local stand density and growth. We applied mixed models to analyse how inter-specific neighbourhoods modify stand productivity, stand density, growth efficiency, individual tree growth and the trade-off between individual tree growth and stand productivity.Key ResultsWe found stand productivity gains of 7–53 % of mixed versus mono-specific stands continuing over the entire rotation. All mixtures achieved a 3–36 % higher leaf area index until advanced stand age. Stem diameter growth increased by up to 31 % in mixed stands. The growth efficiency of the leaf area was up to 31 % higher, except in mixtures of sessile oak and European beech. The trade-off between stem diameter growth and stand productivity was attenuated by the mixture.ConclusionsThe increased productivity was mainly based on a density increase in the case of Norway spruce/silver fir/European beech and sessile oak/European beech and it was based on a more efficient resource use given the same stand density in the case of Scots pine/European beech and European ash/sycamore maple. In the other species assemblages the increased productivity was based on a combination of density and efficiency increase. We hypothesize that the density effect may be site-invariant and mainly depends on the structural species complementarity. The efficiency increase of growth may depend on the growth-limiting factor that is remedied by mixture and thus be co-determined by the site conditions. For forest management, the results indicate increased stand and tree size growth by species mixing. For the common mixtures examined in this study the results show that thinning for the acceleration of stem growth requires less density reduction and causes less stand growth losses than in monocultures. We discuss the consequences of our findings for silvicultural prescriptions for mixed-species stands.

Non-native Douglas fir (Pseudotsuga menziesii) promotes sentinel prey attack rates in Central European forests

The increased utilization of non-native tree species in monocultures or tree mixtures has repeatedly been shown to have negative consequences for the abundance and biomass of natural enemies. However, it is often unknown whether these effects translate into lower top-down control, and if so, whether these effects are driven by tree diversity and identity or by factors not strictly attributed to tree identity (e.g. light conditions or vegetation structure).Here, we used model caterpillars to study the effect of non-native Douglas fir (Pseudotsuga menziesii) on pest control in Central European forests. Model caterpillars were set at two strata (ground and herb layer) in 40 plots of five forest stand types. Monocultures of European beech (Fagus sylvatica), Douglas fir and Norway spruce (Picea abies) and two-species mixtures of European beech and each of the conifers were studied. We analyzed plot-level attack rates (total, arthropod, bird, and mammal attack rates) in relation to stand type, stand composition and microhabitat variability.Against expectations, stands with a higher proportion of Douglas fir had higher total and arthropod attack rates. However, this effect was lessened in stands with higher tree species diversity. Indirect effects of Douglas fir were stronger than direct tree identity and proportion effects, with both increased light availability and understory vegetation complexity promoting attack rates. Therefore, promoting vegetation complexity and light availability by thinning, or planting more open Douglas fir stands with a lower stem density could help to promote pest control in forest stands of non-native tree species.

Response of soil microbial communities to mixed beech-conifer forests varies with site conditions

Tree - soil interactions depend on environmental conditions. Planting trees may affect soil microbial communities and compromise their functioning, particularly in unfavorable environments. To understand the effects of tree species composition on soil microbial communities, we quantified structural and functional responses of soil microorganisms to tree species planted in various environments using substrate-induced respiration and phospholipid fatty acid analyses. Five forest types were studied including pure stands of native European beech (Fagus sylvatica), range expanding Norway spruce (Picea abies), and non-native Douglas-fir (Pseudotsuga menziesii), as well as the two conifer - beech mixtures. We found that microbial functioning depends strongly on soil nutrient concentrations in the studied forest sites. At nutrient-poor sites, soil microorganisms were more stressed in pure and mixed coniferous forests, especially in Douglas-fir, compared to beech forests. By contrast, microbial structure and functional indicators in beech forests varied little with site conditions, likely because beech provided ample amounts of root-derived resources for microbial growth. Since soil microbial communities are sensitive to Douglas-fir, planting Douglas-fir may compromise ecosystem functioning, especially at nutrient-poor sites. Overall, root-derived resources are important for determining the structure and functioning of soil microbial communities, so soil microbial responses to tree species will depend upon the provisioning of these resources as well as site-specific environmental conditions.

Mechanical and formaldehyde-related properties of medium density fiberboard with zeolite additive

Zeolite was investigated as a potential component in the production of medium-density fiberboard (MDF). A mixture of beech (40%), oak (30%), and pine (30%) wood chips was used for fiber production. Chips were cooked for 4 min in an Asplund defibrator with a vapor pressure of 8 bar, and a temperature of 180 °C. Chemicals were added on fibers in the blow line. The resins were added at 11 wt% based on oven-dried wood fibers. Ammonium sulphate was added at 0.72 wt% based on resins. Paraffin wax was added as 1.8 wt% based on resin. Zeolite was prepared in a separate tank for its use instead of lignocellulosic fibers in the production of 1 m³ MDF. The fibers were dried to 12% moisture. A temperature of approximately 190 °C and a pressure of approximately 32 kg.m-² were applied to the mixture for 280 s to make MDF panels (500 x 490 x 14 mm). Mechanical properties of MDF boards were significantly increased for bending (MOE) and elastic modulus (MOR), but a little negatively affected on internal bond (IB), physical properties were negatively increased thickness swelling (ThS) and water absorption (WA). Consequently, increasing zeolite minerals in MDF boards showed best results of formaldehyde emission properties of MDF.

Drought Resistance of Norway Spruce (Picea abies [L.] Karst) and European Beech (Fagus sylvatica [L.]) in Mixed vs. Monospecific Stands and on Dry vs. Wet Sites. From Evidence at the Tree Level to Relevance at the Stand Level

Frequency of drought years is expected to increase through climate warming. Mixed stands have often shown to be more productive than monospecific stands in terms of yield and of resistance against windthrows and bark beetle attacks. Mixture of beech and spruce is of particular interest. However, little is known about its growth reaction to drought. Therefore, we investigated the drought reaction of beech and spruce in mixed vs. monospecific stands along an ecological gradient. In particular, we sought evidence for mixture-related resilience on the individual tree level. Therefore, we quantified the response of tree ring width to drought. Moreover, we attempted to explain the relevance of individual tree response on the stand level by quantifying the stand level loss of volume growth after drought. At the individual tree level, beech was found to be more resilient and resistant in pure vs. mixed stands. Spruce, in contrast, was favored by mixture, and this was especially evident on drier sites. Along the gradient, growth losses at stand level increased in both mixed and pure stands in 2015, with growth gains on the drier sites observed in the same drought year, in accordance with the Stress Gradient Hypothesis. However, the stand level difference of growth loss between mixed and pure stands was not statistically significant. Mitigating mixture effects on the level of the individual tree thus did not become evident on the level of the whole stand.

Oak often needs to be promoted in mixed beech-oak stands - the structural processes behind competition and silvicultural management in mixed stands of European beech and sessile oak

Abstract: Forest ecosystems nowadays provide multiple ecosystem goods and services at a time and throughout all development phases. Species mixing is considered an effective measure to gain benefits beyond purely additive effects. However, the complex structural processes behind interspecific competition and temporal and spatial facilitative effects through mixing are still far from being understood and predictable. In particular the mixture of European beech (Fagus sylvatica L.) and sessile oak (Quercus petraea [Matt.] Liebl.) is gaining even more importance due to the fact that forests from these species are considered more tolerant to climatic effects and are expected to expand their natural range to the north due to global warming. The 30 long-term experimental plots analysed in this study reveal the structural processes in mixed beech-oak stands based on data at the tree and stand level. Using spatial and non-spatial structural indices, we can show an increasing dominance of beech over oak in unmanaged stands and the effectiveness of thinning operations to support oak. Those processes are representative for other light-demanding tree species in mixtures with shade-tolerant species. Improving the knowledge on the structural processes in mixed-species stands is particularly relevant when trying to modify forest structure in order to adapt forest management to shifting environmental conditions and the increasing demand for ecosystem services.

An original method for tree species classification using multitemporal multispectral and hyperspectral satellite data

This study proposes an original method for tree species classification by satellite remote sensing. The method uses multitemporal multispectral (Landsat OLI) and hyperspectral (Resurs-P) data acquired from determined vegetation periods. The method is based on an original database of spectral features taking into account seasonal variations of tree species spectra. Changes in the spectral signatures of forest classes are analyzed and new spectral–temporal features are created for the classification. Study sites are located in the Czech Republic and northwest (NW) Russia. The differences in spectral reflectance between tree species are shown as statistically significant in the sub-seasons of spring, first half of summer, and main autumn for both study sites. Most of the errors are related to the classification of deciduous species and misclassification of birch as pine (NW Russia site), pine as mixture of pine and spruce, and pine as mixture of spruce and beech (Czech site). Forest species are mapped with accuracy as high as 80% (NW Russia site) and 81% (Czech site). The classification using multitemporal multispectral data has a kappa coefficient 1.7 times higher than does that of classification using a single multispectral image and 1.3 times greater than that of the classification using single hyperspectral images. Potentially, classification accuracy can be improved by the method when applying multitemporal satellite hyperspectral data, such as in using new, near-future products EnMap and/or HyspIRI with high revisit time.

Density regulation of mixed and mono-specific forest stands as a continuum: a new concept based on species-specific coefficients for density equivalence and density modification

AbstractA wealth of recent research has improved our understanding of the structure, growth and yield of mixed-species stands. However, appropriate quantitative concepts for their silvicultural regulation remain scarce. Due to the species-specific stand densities, growing area requirements and potential over-density, the density and mixing regulation in mixed stands is much more intricate than in monospecific stands.Here, we introduce the species-specific coefficients: density equivalence coefficients (DEC), for density equivalence; and density modification coefficient (DMC), for density modification in mixed species stands. DEC is suitable for the conversion of the stand density and growing area requirement of one species into that of another species. DMC estimates the modification of maximum stand density by tree species mixing using as reference the maximum stand density of one of the species.First, we introduce the theoretical concept of these coefficients. Second, we derive the mean values of these coefficients based on long-term experiments using different mixtures of European beech. Third, we apply DEC and DMC for flexible regulation of the stand density and mixing proportion. Thus, silvicultural regulation of monospecific stands and mixed-species stands forms a continuum, where monospecific stands represent an extreme case of mixed-species stands.Lastly, we discuss the advantages and limitations of these concepts. Future directions comprise the inclusion of additional species, their integration in guidelines and simulation models, and their establishment for the quantitative regulation of experimental plots and the practical implementation in forest stands.

Benefits of Mixtures on Growth Performance of Silver Fir (Abies alba) and European Beech (Fagus sylvatica) Increase With Tree Size Without Reducing Drought Tolerance

To mitigate negative impacts of drought stress in the face of climate change, mixtures of tree species such as those between European beech (Fagus sylvatica) and silver fir (Abies alba) are assumed to lower risks in forest management. This study investigates the influence of mixing beech and fir on tree growth in general and in particular on tree species responses to the extreme drought event of 2003. For this purpose, we analyzed basal area increment series and carbon isotope composition (δ13C) in the wood of ~160 trees from three mixed-species sites in Germany and one site in Croatia. Overall growth performance for both fir and beech increased with proportions of the admixed species when accounting for the interactions with tree size and competition intensity. Mixing improved growth of large trees for both species irrespective of neighborhood density, whereas smaller trees benefitted only in denser neighborhoods. Positive mixing effects on radial growth were more pronounced in fir compared to beech, yet the latter benefitted by the admixture of fir with regard to growth recovery following drought. Both the resistance of radial growth against reduction during drought as well as the variation of isotopic composition throughout the drought period were not affected by mixing, indicating that water-use in these two species was not complementary under drought stress. Although trees from both species exhibited growth reductions during the drought, fir maintained higher absolute growth levels than beech during the drought. Both species benefited from growing in mixed neighborhoods but complementary effects depended on tree size and neighborhood density. Mixing fir and beech leads to positive or neutral effects on growth performance of trees, also in response to an extreme drought event. Since increasing tree species richness also spreads the risks associated with extreme events, mixtures of beech and fir can be recommended as a possible alternative for more drought-sensitive stands such as spruce monocultures.

ENSO and NAO affect long-term leaf litter dynamics and stoichiometry of Scots pine and European beech mixedwoods.

Litterfall dynamics (production, seasonality and nutrient composition) are key factors influencing nutrient cycling. Leaf litter characteristics are modified by species composition, site conditions and water availability. However, significant evidence on how large-scale, global circulation patterns affect ecophysiological processes at tree and ecosystem level remains scarce due to the difficulty in separating the combined influence of different factors on local climate and tree phenology. To fill this gap, we studied links between leaf litter dynamics with climate and other forest processes, such as tree-ring width (TRW) and intrinsic water-use efficiency (iWUE) in two mixtures of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) in the south-western Pyrenees. Temporal series (18years) of litterfall production and elemental chemical composition were decomposed following the ensemble empirical mode decomposition method and relationships with local climate, large-scale climatic indices, TRW and Scots pine's iWUE were assessed. Temporal trends in N:P ratios indicated increasing P limitation of soil microbes, thus affecting nutrient availability, as the ecological succession from a pine-dominated to a beech-dominated forest took place. A significant influence of large-scale patterns on tree-level ecophysiology was explained through the impact of the North Atlantic Oscillation (NAO) and El Niño-Southern Oscillation (ENSO) on water availability. Positive NAO and negative ENSO were related to dry conditions and, consequently, to early needle shedding and increased N:P ratio of both species. Autumn storm activity appears to be related to premature leaf abscission of European beech. Significant cascading effects from large-scale patterns on local weather influenced pine TRW and iWUE. These variables also responded to leaf stoichiometry fallen 3years prior to tree-ring formation. Our results provide evidence of the cascading effect that variability in global climate circulation patterns can have on ecophysiological processes and stand dynamics in mixed forests.