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Understanding the uncertainty in the parameterization of the two photosynthetic capacity parameters, leaf maximum carboxylation rate (Vcmax), and maximum electron transport rate (Jmax), is crucial for modeling and predicting carbon fluxes in terrestrial ecosystems. In gas exchange models, to date, Jmax is typically estimated from Vcmax based on a linear regression. However, recent studies have revealed that this relationship varies, dependent upon species, leaf groups, and time, so it is doubtful that the regression applies universally. Furthermore, far less is known regarding how other leaf traits affect the regression. In this study we analyzed the two key photosynthetic parameters and popularly measurable leaf traits, leaf chlorophyll concentration and leaf mass per area (LMA), of cool-temperate forest stands in Japan, aiming to construct a simple regression applicable to temperate deciduous forests, at least. The analysis was based on a long-term field dataset covering years of data for both sunlit and shaded leaves at different altitudes. Results showed that the best-fitted slope of the regression differed markedly from those previously reported, which were typically acquired from sunlit leaves. LMA had a significant effect on the regression, producing the lowest root mean square errors and the highest ratio of performance to deviation values (RPD = 2.017). Although more data are needed to validate in other ecosystems, our approach at least provides a promising way to substantially improve photosynthesis model predictions, by introducing leaf traits into the popular empirical regression of Jmax against Vcmax, and ultimately to better understand the functioning of the photosynthetic machinery.

The earliest appearance of elk/wapiti (Cervus canadensis) in eastern North America is not thoroughly documented due to the small number of directly dated remains. Until recently, no absolute dates on elk bone older than 10,000 14C yr BP (11,621 to 11,306 calibrated years (cal yr) BP) were known from this region. The partial skeleton of the Tope Elk was discovered in 2017 during commercial excavation of peat deposits from a small bog in southeastern Medina County, Ohio, United States. Subsequent examination of the remains revealed the individual to be a robust male approximately 8.5 years old at death. The large size of this individual is compared with late Holocene specimens and suggests diminution of elk since the late Pleistocene. Two accelerator mass spectrometry (AMS) radiocarbon assays on bone collagen samples taken from the scapula and metacarpal of this individual returned ages of 10,270 ± 30 14C yr BP (Beta-477478) (12,154 to 11,835 cal yr BP) and 10,260 ± 30 14C yr BP (Beta-521748) (12,144 to 11,830 cal yr BP), respectively. These results place Cervus canadensis in the terminal Pleistocene of the eastern woodlands and near the establishment of the mixed deciduous forest biome over much of the region. This early temporal placement also situates this early elk as closely following the last representatives of now-extinct megafauna such as the American mastodon (Mammut americanum) and contemporary with the Late Paleoindian inhabitants of the region.

Fossil charcoals from archaeological sites provide direct evidence for the relationship between environmental change and ancient peoples’ livelihoods in the past. Our identification of 5811 fossil charcoal fragments from 84 samples suggested temperate deciduous and mixed conifer-broadleaved forests as the dominant vegetation at the Erdaojingzi site in northeastern China ca. 3500 cal yr BP; the major representative taxa were Quercus, Pinus, and Ulmus. Four woody plants probably supplied humans with food resources at the Erdaojingzi site, including Quercus, Ulmus, Amygdalus/Armeniaca, and Ziziphus. The nuts of Quercus were utilized as staple foods because of their rich starch content. The leaves of Ulmus may have been used by humans because of their massive dietary fibre. Amygdalus/Armeniaca and Ziziphus probably provided fruits for humans. Based on the coexistence approach (CA) used on the fossil charcoals, we found that the MAT anomaly was 7.9 ± 5.9°C at ca. 3500 cal yr BP, which is almost the same as the modern one (7.8°C), while the MAP was halved from 772 ± 301 mm at ca. 3500 cal yr BP to 370 mm currently. The wet climate might have facilitated significant development of rain-fed agriculture, promoted the emergence of large settlements, and eventually facilitated the birth of civilization.

Excess N deposition has aroused concerns about its negative impacts on forest ecosystems. A two-year study was conducted to assess the responses of stomatal conductance (Gc) and carbon assimilation (Anet) of dominant tree species (Liquidambar formosana, Quercus acutissima and Quercus variabilis) to increased N deposition at a canopy and understory N additions experimental platform in a temperate deciduous broadleaved forest. Five treatments included N addition of 25 and 50 kg ha−1 y−1 onto either the canopy (C25 and C50) or the understory (U25 and U50), and a control treatment (CK, without N addition). Our results showed that neither canopy nor understory N addition had an impact on carboxylation capacity (Vcmax), the light saturated rate of electron transport (Jmax) and leaf-level net assimilation (AnL) of the studied tree species. Higher concentrations of N addition (U50 and C50 treatments) exerted negative impacts on Gc and Anet of L. formosana and Quercus acutissima under lower precipitation conditions, while lower concentrations of N addition (U25 and C25 treatments) had minimal impacts on overall ecophysiological function. The U50 treatment increased tree water use efficiency (WUE) of L. formosana in the second experimental year. Canopy and understory N addition generated differential effects on forest vegetation. The traditional approach with understory addition could not fully reflect the effects of increased N deposition on the canopy-associated assimilation processes.

Temperate deciduous forests dominated by oaks cover extensive areas in European lowlands. These ecosystems have been under intense anthropogenic use for millennia, thus their natural dynamics, and their regeneration in particular, is still not well understood. Previous studies found that pedunculate oak (Quercus robur), one of the most widespread and abundant species in European deciduous forests, regenerates in open habitats and forest edges, but not in closed forest interiors. However, these observations usually come from the core areas of the biome, and much less is known about such processes at its arid boundary, where limiting factors may be different, and climate change may first exert its effects.In a full factorial field experiment, we tested the effects of different habitats and increased growing season precipitation on the early regeneration of pedunculate oak in a forest-steppe ecosystem in Central Hungary, at the arid boundary of temperate deciduous forests. We planted acorns into three neighbouring habitats (grassland, forest edge, forest interior) and studied seedling emergence and plant performance under ambient weather and additional watering for four years.In the grassland habitat, seedling emergence was very low, and no seedlings survived by the fourth year. In contrast, seedling emergence was high and similar at forest edges and forest interiors, and was not affected by water addition. Most seedlings survived until the fourth year, with no difference between forest edge and forest interior habitats in numbers, and only minor or transient differences in size (leaf number, height).The lack of oak regeneration in the grassland contradicts previous reports on successful oak regeneration in open habitats, and may be related to a shift from light limitation to other limiting factors, such as moisture or microclimatic extremes, when moving away from the core of the deciduous forest biome towards its arid boundary. The similar number and performance of seedlings in forest edges and forest interiors may also be related to the decreasing importance of light limitation. The above-average precipitation in the year of seedling emergence (2016) might be a reason why watering had no effect on oak regeneration.Overall, our results highlight that oak regeneration and thus forest dynamics may be limited by different factors at a biome boundary compared to its core areas. Indeed, this very simple mechanism (inability of oak regeneration in grassland habitats) may contribute to the opening up of the closed forest biome, and the emergence of a biome transition zone.

Fagus sylvatica (beech) dominates the montane forests of the Apennines and builds old-growth high-conservation value stands. However, recent severe drought-induced diebacks raise concern on the future persistence of these forests and of Southern European mesophilous woodlands overall, growing at their dry edge. To explore the history of Apennine beech-dominated forests, we draw on the multiproxy paleoecological record from Lago Verdarolo, which includes a robust vegetation-independent temperature reconstruction. Numerical techniques are used to investigate the drivers of long-term Mediterranean mountain forest dynamics. Specifically, we focus on disentangling the ecological factors that caused the shift from high-diversity mixed forests to beech-dominated stands and on assessing the occurrence of legacy effects on present-day forests. Abrupt climate change largely drove vegetation dynamics during the Late Glacial and Early Holocene. Species-rich mixed Abies alba (silver fir) forests dominated about 10,500—5500 years ago, under rather dry and warmer-than-today conditions (+ 1—2 °C) and limited fire occurrence. Cooler and moister summers and increasing fire activity caused declines in several fire-sensitive temperate deciduous trees (for example, Ulmus, Tilia, Fraxinus) and favored the establishment of fir-beech forests around 5500 years ago. Further enhancement of fire activity and farming around 2000 years ago led to local Abies alba extinction and forest impoverishment. We conclude that the currently widespread monospecific Apennine beech forests are the result of multi-millennial land-use intensification superimposed on Late Holocene cooling and moistening. Given their higher drought-tolerance compared to beech stands, reviving ancient species-rich mixed fir forests represents a feasible and ‘tested’ possibility to adapt forests to climate change. Electronic supplementary material The online version of this article (10.1007/s10021-020-00587-4) contains supplementary material, which is available to authorized users.

Stocking and structural composition of a deciduous broad-leaved forest were determined to predict coarse woody debris quantity by quantifying the empirical relationships between these two attributes. The most ecologically significant families by stem density were Salicaceae, Betulaceae, Fagaceae, and Aceraceae. Populus davidiana was the most dominant species followed by Betula dahurica, Quercus mongolica, and Acer mono. The four species accounted for 69.5% of total stems. Numerous small-diameter species characterized the coarse woody debris showing a reversed J-shaped distribution. The coarse debris of P. davidiana, B. dahurica, and Q. mongolica mainly comprised the 10–20 cm size class, whereas A. mono debris was mainly in the 5–10 cm size class. The spatial patterns of different size classes of coarse woody debris were analyzed using the g-function to determine the size of the tree at its death. The results indicate that the spatial patterns at the 0–50 m scale shifted gradually from an aggregated to a random pattern. For some species, the larger coarse debris might change from an aggregated to a random distribution more easily. Given the importance of coarse woody debris in forest ecosystems, its composition and patterns can improve understanding of community structure and dynamics. The aggregation pattern might be due to density dependence and self-thinning effects, as well as by succession and mortality. The four dominant species across the different size classes showed distinct aggregated distribution features at different spatial scales. This suggests a correlation between the dominant species population, size class, and aggregated distribution of coarse woody debris.

Aims The soil microbial community plays a critical role in increasing phosphorus (P) availability in low-P, weathered soils by "mining" recalcitrant organic P through the production of phosphatase enzymes. However, there is a lack of data on the fungal and bacterial taxa which are directly involved in P mining, which could also serve as potential microbial bioindicators of low P availability. Methods and results Leveraging a 5-year P enrichment experiment on low-P forest soils, high-throughput sequencing was used to profile the microbial community to determine which taxa associate closely with P availability. We hypothesized that there would be a specialized group of soil micro-organisms that could access recalcitrant P and whose presence could serve as a bioindicator of P mining. Community profiling revealed several candidate bioindicators of P mining (Russulales, Acidobacteria Subgroup 2, Acidobacteriales, Obscuribacterales and Solibacterales), whose relative abundance declined with elevated P and had a significant, positive association with phosphatase production. In addition, we identified candidate bioindicators of high P availability (Mytilinidales, Sebacinales, Chitinophagales, Cytophagales, Saccharimonadales, Opitulales and Gemmatales). Conclusions This research provides evidence that mitigating P limitation in this ecosystem may be a specialized trait and is mediated by a few microbial taxa. Significance and impact of the study Here, we characterize Orders of soil microbes associated with manipulated phosphorus availability in forest soils to determine bioindicator candidates for phosphorus. Likewise, we provide evidence that the microbial trait to utilize recalcitrant organic forms of P (e.g. P mining) is likely a specialized trait and not common to all members of the soil microbial community. This work further elucidates the role that a complex microbial community plays in the cycling of P in low-P soils, and provides evidence for future studies on microbial linkages to human-induced ecosystem changes.

International audience; Hightlights:• Predictions of physiological process depends on climate model, species and region.• Predictions were improved after correction for the three models considered.• Processes simulated exhibited large variability at the plot scale.• This variability faded out at larger scales, owing to an aggregation effect.• Process predictions were more variable during the driest years.Abstract: Climate change affects various aspects of ecosystem functioning, especially photosynthesis, respiration and carbon storage. We need accurate modelling approaches (impact models) to simulate forest functioning and vitality in a warmer world so that forest models can estimate multiple changes in ecosystem service provisions (e. g., productivity and carbon storage) and test management strategies to promote forest resilience.Here, we aimed to quantify the bias in these models, addressing three questions: (1) Do the predictions of impact models vary when forcing them with different climate models, and how do the predictions differ under climate model vs. observational climate forcings? (2) Does the climate impact simulation variability caused by climate forcings fade out at large spatial scales? (3) How does using simulated climate data affect process-based model predictions in stressful drought events? To answer these questions, we present historical results for 1960-2010 from the CASTANEA ecophysiological forest model and use the data from three climate models. Our analysis focuses on monospecific stands of European beech (Fagus sylvatica), temperate deciduous oaks (Quercus robur and Q. petraea), Scots pine (Pinus sylvestris) and spruce (Picea abies) in French forests.We show that prediction of photosynthesis, respiration and wood growth highly depends on the climate model used and species and region considered. Predictions were improved after a monthly mean bias or monthly quantile mapping correction for the three models considered. The processes simulated by the impact model exhibited large variability under different climate forcings at the plot scale (i.e., a few hectares). This variability faded out at larger scales (i.e., an ecological region, 100 km(2)), owing to an aggregation effect. Moreover, process predictions obtained under different climate forcings were more variable during the driest years. These results highlight the necessity of quantifying the bias correction effect on process predictions before predicting flux dynamics with a process-based model.

Background and Aims Understorey species in temperate deciduous woodlands such as wild daffodil (Narcissus pseudonarcissus) and common snowdrop (Galanthus nivalis) have complex dormancy: seeds that are shed in late spring require warm summer temperatures for embryo elongation and dormancy alleviation, but then cooler temperatures for germination in autumn. As seasons warm and tree canopies alter, how will different seasonal temperature sequences affect these complex dormancy responses? Methods The effect of different sequences of warmer (+5 °C), current or cooler (–5 °C) seasons (summer to spring) on seed germination patterns over seven successive seasons were investigated, with all sequences combined factorially to determine the consequences of differential seasonal temperature change for the temporal pattern of germination (and so seedling recruitment). Key Results Little ( warmer > cooler); the majority of seeds that germinated over the whole study did so during the two autumns but also in year 2’s cooler summer after a warm spring. Conclusions Warmer autumns and winters delay first autumn germination of N. pseudonarcissus to winter but advance it in G. nivalis; overall, warming will deplete the soil seed bank of these species, making annual seed influx increasingly important for recruitment and persistence. This study provides a comprehensive account of the effects of temperature changes in different seasons on seed germination in these early spring-flowering geophytes and consequently informs how these and other temperate woodland species with complex seed dormancy may respond to future climate change.

Nitrogen deposition in the northeastern US changed N availability in the latter part of the twentieth century, with potential legacy effects. However, long-term N cycle measurements are scarce. N isotopes in tree rings have been used as an indicator of N availability through time, but there is little verification of whether species differ in the strength of this signal. Using long-term records at the Fernow Experimental Forest in West Virginia, we examined the relationship between soil conditions, including net nitrification rates, and wood δ15N in 2014, and tested the strength of correlation between tree ring δ15N of four species and stream water NO3− loss from 1971 to 2000. Higher soil NO3− was weakly associated with higher wood δ15N across species, and higher soil net nitrification rates were associated with higher δ15N for Quercus rubra only. The δ15N of Liriodendron tulipifera and Q. rubra, but neither Fagus grandifolia nor Prunus serotina, was correlated with stream water NO3−. L. tulipifera tree ring δ15N had a stronger association with stream water NO3− than Q. rubra. Overall, we found only limited evidence of a relationship between soil N cycling and tree ring δ15N, with a strong correlation between the wood δ15N and NO3− leaching loss through time for one of four species. Tree species differ in their ability to preserve legacies of N cycling in tree ring δ15N, and given the weak relationships between contemporary wood δ15N and soil N cycle measurements, caution is warranted when using wood δ15N to infer changes in the N cycle.

The predator satiation hypothesis (PSH) and the seed dispersal hypothesis (SDH) are widely adopted to predict the effects of masting on seed dispersal. However, the effects of masting composition on rodent-mediated seed dispersal interaction of sympatric tree species are largely overlooked in testing the two hypotheses. Here, masting in Quercus mongolica and Corylus mandshurica with contrasting seed traits was studied over two masting years and three non-masting years in a temperate deciduous forest in northeastern China, to investigate how masting composition regulates the indirect seed-seed interactions of sympatric tree species mediated by granivorous rodents. Our results showed that more seeds of Q. mongolica survived in seed stations and were less likely to be dispersed in masting years, well supporting the idea of PSH. However, seed dispersal of C. mandshurica was in congruence with the prediction of the SDH because of increased seed dispersal probability and dispersal distances in masting years. Rodents scatterhoarded more seeds of C. mandshurica not only in its own masting years but also in the masting years of another sympatric plant species, Q. mongolica, resulting in a positive relationship between seed caching and the sum of per capita seed availability. Moreover, masting of Q. mongolica or C. mandshurica decreased the proportion of seeds eaten by predators, benefiting each other’s seed survival. In addition, seeds of Q. mongolica were dispersed farther in the masting years of C. mandshurica despite rare seedling establishment. Our study using two sympatric masting tree species provided evidence that the effects of masting can be potentially influences by seed-seed interactions between sympatric tree species. We recommend that future work tests the PSH and SDH using long term data of several sympatric tree species, emphasizing the role of seed traits and seed-seed interactions in determining the effects of seed masting on tree regeneration.

Background and aims Deciduous angiosperm trees transport xylem sap through trunks and branches in vessels within annual growth rings. Utilizing previous growth rings for sap transport could increase vessel network size and redundancy but may expose new xylem to residual air embolisms in the network. Despite the important role of vessel networks in sap transport and drought resistance, our understanding of cross-ring connections within and between species is limited. Methods We studied cross-ring connections in four temperate deciduous trees using dye staining and X-ray microcomputed tomography (microCT) to detect xylem connectivity across growth rings and quantify their impact on hydraulic conductivity. Key results Acer rubrum and Fraxinus americana had cross-ring connections visible in microCT but only A. rubrum used previous growth rings for axial sap flow. Fagus grandifolia and Quercus rubra, however, did not have cross-ring connections. Accounting for the number of growth rings that function for axial transport improved hydraulic conductivity estimates. Conclusions These data suggest that the presence of cross-ring connections may help explain aspects of whole-tree xylem sap transport and should be considered for plant hydraulics measurements in these species and others with similar anatomy.

In this paper, we describe a new species Magnolia nanningensis sp. nov., based on exceptionally well‐preserved mummified fossil woods from the late Oligocene of the Nanning Basin, Guangxi, South China. The features of these woods indicate a close affinity to the section Michelia of the subgenus Yulania belonging to the genus Magnolia sensu lato (Magnoliaceae). Magnolia nanningensis is the first fossil record of the section Michelia from China, the modern diversity center of this group. These mummified woods provide fossil evidence supporting molecular dating that estimated an Oligocene age for divergence of the tropical evergreen section Michelia and the temperate deciduous section Yulania. Helical thickenings on vessel walls and a high degree of vessel grouping found in these fossil woods could be adaptive to temporary, possibly seasonal, droughts and, as suggested by other woods from the Nanning Basin, could be indicative of a monsoon‐influenced tropical climate in Guangxi during the late Oligocene. Helical thickenings have not been reported in magnoliaceous fossil woods prior to the Oligocene. The appearance of this trait was presumably a response to abrupt climate cooling near the Eocene–Oligocene boundary, followed by increase in climate seasonality. The associated increase of latitudinal zonation might be a possible trigger for divergence between the tropical evergreen sect. Michelia and the temperate deciduous sect. Yulania.

Conifers and deciduous trees greatly differ in regard to their phylogenetics and physiology as well as their influence on soil microclimate and chemical properties. Soil respiration (Rs) in forests can therefore differ depending on tree species composition, and assessments of the variation in Rs in various forest types will lead to a more thorough understanding of the carbon cycle and more robust long-term simulations of soil carbon. We measured Rs in 2019 and 2020 in stands of various species composition in a sugar maple forest near the northern range limit of temperate deciduous forests in Quebec, Canada. Seasonal variations in soil temperature had the largest influence on Rs, but conditions created by the stands also exerted a significant effect. Relative to the typical sugar maple-yellow birch forest (hardwoods), Rs in stands with >20% of basal area from balsam fir (mixedwoods) was increased by 21%. Whilst, when American beech contributed >20% of litterfall mass (hardwood-beech stands), Rs was decreased by 11 and 36% relative to hardwoods and mixedwoods, respectively. As a whole, Rs was significantly higher in mixedwoods than in other forest types, and Rs was significantly higher in hardwoods than in hardwood-beech stands. Sugar maple and American beech at the study site are near their northern range limit, whereas balsam fir is near its southern limit. Rs in mixedwoods was therefore higher than in hardwoods and hardwood-beech stands due to high root activity in the presence of fir, despite colder and drier soils. We estimated that root respiration in mixedwoods was more than threefold that in hardwoods and hardwood-beech stands. The lower Rs in hardwood-beech stands compared to hardwoods points to the lower soil temperature as well as the poor quality of beech litter (low decomposability) as indicated by a generally lower heterotrophic respiration. Other than soil temperature, regression models identified mixedwoods, soil water potential and Mg2+ activity in the soil solution as important predictor variables of Rs with about 90% of its variation explained. Our study shows the benefits of combining forest-specific properties to climatic data for more robust predictions of Rs.

Summary • Here we examine the effects of increased nitrogen (N) supply on the ectomycorrhizal fungal communities of a temperate oak savanna. • In a 16-yr N-addition experiment in which replicate 1000 m2 plots received 0, 5.4 or 17 g N m−2 yr−1, ectomycorrhizal sporocarp production was measured in the 14th, 15th and 16th year of fertilization. Ectomycorrhizal fungi (EMF) colonizing roots were examined by morphotyping-PCR-RFLP and sequence analysis in the 14th and 15th year of fertilization. • Total sporocarp richness was reduced by > 50% in both fertilization treatments in all 3 yrs, whereas Russula spp. produced approx. five times more sporocarps with 17 g N m−2 yr−1. Below-ground, treatment-scale species richness and species area curves were lower with 17 g N m−2 yr−1 but richness, diversity indices and evenness at smaller spatial scales were not. Dominant fungi colonizing roots included Cenococcum geophilum, common in all treatments, Cortinarius spp., dominant in unfertilized plots, and Russula spp., dominant with 17 g N m−2 yr−1. • Communities of EMF in this temperate deciduous ecosystem responded to N addition similarly to those of coniferous ecosystems in that increased N supply altered EMF diversity and community composition but differently in that dominance of Russula spp. increased.

Although the functional trait approach can facilitate the understanding of mechanisms that underline community responses to habitat alteration, only a few studies used this way on exploring the structure of insect assemblages compared to taxon-based analyses. We compared the descriptive power of medium-term effects (2014-2018) of forestry treatments in a temperate managed oak-dominated forest on taxon- vs. trait-based descriptors of ground beetle assemblages. The treatments included rotation forestry (partial preparation cutting, clear-cutting, retention-tree group, and mature closed forest as control) and continuous cover forestry (gap cutting) operations. The species composition was only slightly influenced by the treatments; on the ordination biplot, the control, retention tree group, and clear-cutting treatments formed relatively homogeneous groups, well separated from each other, while the others were scattered randomly in the ordination space. Over time, the species richness decreased in all treatments, but it was higher in the retention tree group treatment than in others in 2016 and 2017. The activity density also declined between years, but an immediate mass effect was revealed after the implementation of treatment types especially in the control, gap, and preparation cuts. We found that assemblages in the clear-cutting and retention-tree group had similar characteristics: high functional diversity; more open-habitat, generalist, and omnivore species and fewer carnivore species; while those in the control, gap, and preparation cutting groups had the opposite: lower functional diversity, more forest species, and more carnivorous species. Our findings will demonstrate that the simultaneous use of the two approaches will allow the most articulate understanding of the status of ground beetles assemblages in managed forests.

Climate warming is driving an advance of leaf unfolding date in temperate deciduous forests, promoting longer growing seasons and higher carbon gains. However, an earlier leaf phenology also increases the risk of late frost defoliation (LFD) events. Compiling the spatiotemporal patterns of defoliations caused by spring frost events is critical to unveil whether the balance between the current advance in leaf unfolding dates and the frequency of LFD occurrence is changing and represents a threaten for the future viability and persistence of deciduous forests. We combined satellite imagery with machine learning techniques to reconstruct the spatiotemporal patterns of LFD events for the 2003-2018 period in the Iberian range of European beech (Fagus sylvatica), at the drier distribution edge of the species. We used MODIS Vegetation Index Products to generate a Normalized Difference Vegetation Index (NDVI) time series for each 250 × 250 m pixel in a total area of 1,013 km2 (16,218 pixels). A semi-supervised approach was used to train a machine learning model, in which a binary classifier called Support Vector Machine with Global Alignment Kernel was used to differentiate between late frost and non-late frost pixels. We verified the obtained estimates with photointerpretation and existing beech tree-ring chronologies to iteratively improve the model. Then, we used the model output to identify topographical and climatic factors that determined the spatial incidence of LFD. During the study period, LFD was a low recurrence phenomenon that occurred every 15.2 yr on average and showed high spatiotemporal heterogeneity. Most LFD events were condensed in 5 yr and clustered in western forests (86.5% in one-fifth of the pixels) located at high elevation with lower than average precipitation. Elevation and longitude were the major LFD risk factors, followed by annual precipitation. The synergistic effects of increasing drought intensity and rising temperature combined with more frequent late frost events may determine the future performance and distribution of beech forests. This interaction might be critical at the beech drier range edge, where the concentration of LFD at high elevations could constrain beech altitudinal shifts and/or favor species with higher resistance to late frosts.

Aims: Traditional quantitative approaches to forest classification are based on differences in species abundance or incidence among communities. In these approaches, all species are regarded as biologically equidistant regardless of the biological heterogeneity. The objective of the study is to evaluate the potential of the “Discriminating Avalanche” approach, which integrates species abundance and biological heterogeneity, as a new basis for forest classification. Location: China, India, Iran, Ukraine, Germany, Italy, Mexico, Peru, and South Africa. Method: We illustrate our approach using a set of 35 large tree-mapped forest plots from various regions of the world. Our dissimilarity matrices, which integrate species abundance with biological heterogeneity, are compared with the standard Bray–Curtis and Whittaker dissimilarity indices, and provide the quantitative basis for a hierarchical cluster analysis. Results: Four distinct groups of forests were identified using the proposed forest dissimilarity matrix. Afro-montane forests from South Africa constitute a first group. A second group includes temperate deciduous broad-leaved forests dominated by oak (Quercus) and beech (Fagus) from Europe and China. Conifer-dominated forests constitute a third group. The remaining forests constitute the fourth group. Conclusion: Biological heterogeneity provides a practical basis for vegetation classification. The results of this study, based on a variety of temperate and tropical forests, suggest that a measure of biological dissimilarity based on evolutionary and morphological differences among species is more effective than the traditional species abundance-based approaches to classify an arbitrary set of plant communities. This approach promises greater refinement and consistency in ecological classification. In particular, it has advantage in classifying forests along large geographic scales in situations of high beta diversity and species turnover.

Despite the crucial role of the seed bank in forest conservation and dynamics, the effects of forest edge microclimate and climate warming on germination responses from the forest seed bank are still almost unknown. Here, we investigated edge effects on the realised seed bank and seedling community in two types of European temperate deciduous forest, one in the Oceanic and one in the Mediterranean climatic region. Responses in terms of seedling density, diversity, species composition and functional type of the seed bank at the forest edge and interior were examined along latitudinal, elevational and stand structural gradients by means of soil translocation experiments. Moreover, we translocated soil samples from high to low elevation forests in the two regions, thus performing a warming simulation. Density, species diversity and mortality of the seedlings varied with region and elevation. Seedling density also differed between forest edge and interior position, while seedling cover mainly depended on forest structure. Both the edge and interior forest seed bank contained a high proportion of generalist species. In Belgium, a more homogeneous seed bank was found at the forest edge and interior, while in Italy compositional and ecological differences were larger: at the forest edge, more light and less moisture demanding seedling communities developed, with a higher proportion of generalists compared to the interior. In both regions, the upland-to-lowland translocation experiment revealed effects of warming on forest seed banks with thermophilization of the realised communities. Moreover, edge conditions shifted the seedling composition towards more light-demanding communities. The establishment of more light and warm-adapted species from the seed bank could in the long term alter the aboveground vegetation composition, with communities becoming progressively richer in light-demanding generalists and poorer in forest specialists.

Severe droughts are expected to become more frequent and persistent. However, their effect on autumn leaf senescence, a key process for deciduous trees and ecosystem functioning, is currently unclear. We hypothesized that (I) severe drought advances the onset of autumn leaf senescence in temperate deciduous trees and (II) tree species show different dynamics of autumn leaf senescence under drought. We tested these hypotheses using a manipulative experiment on beech saplings and 3 years of monitoring mature beech, birch and oak trees in Belgium. The autumn leaf senescence was derived from the seasonal pattern of the chlorophyll content index and the loss of canopy greenness using generalized additive models and piecewise linear regressions. Drought and associated heat stress and increased atmospheric aridity did not affect the onset of autumn leaf senescence in both saplings and mature trees, even if the saplings showed a high mortality and the mature trees an advanced loss of canopy greenness. We did not observe major differences among species. To synthesize, the timing of autumn leaf senescence appears conservative across years and species and even independent of drought, heat and increased atmospheric aridity. Therefore, to study autumn senescence and avoid confusion among studies, seasonal chlorophyll dynamics and loss of canopy greenness should be considered separately.

Understanding how different taxa respond to global warming is essential for predicting future changes and elaborating strategies to buffer them. Tardigrades are well known for their ability to survive environmental stressors, such as drying and freezing, by undergoing cryptobiosis and rapidly recovering their metabolic function after stressors cease. Determining the extent to which animals that undergo cryptobiosis are affected by environmental warming will help to understand the real magnitude climate change will have on these organisms. Here, we report on the responses of tardigrades within a five‐year‐long, field‐based artificial warming experiment, which consisted of 12 open‐top chambers heated to simulate the projected effects of global warming (ranging from 0 to 5.5°C above ambient temperature) in a temperate deciduous forest of North Carolina (USA). To elucidate the effects of warming on the tardigrade community inhabiting the soil litter, three community diversity indices (abundance, species richness, and Shannon diversity) and the abundance of the three most abundant species (Diphascon pingue, Adropion scoticum, and Mesobiotus sp.) were determined. Their relationships with air temperature, soil moisture, and the interaction between air temperature and soil moisture were tested using Bayesian generalized linear mixed models. Despite observed negative effects of warming on other ground invertebrates in previous studies at this site, long‐term warming did not affect the abundance, richness, or diversity of tardigrades in this experiment. These results are in line with previous experimental studies, indicating that tardigrades may not be directly affected by ongoing global warming, possibly due to their thermotolerance and cryptobiotic abilities to avoid negative effects of stressful temperatures, and the buffering effect on temperature of the soil litter substrate., Tardigrades are well known for their ability to survive harsh environmental conditions; however, it is not known if they have the potential to survive global warming. We tested the ability of leaf litter tardigrades to resist future warming through a long‐term experimental warming approach. We failed to find any significant effect of warming on leaf litter tardigrades community, suggesting their potential to resist global warming.

We explored the timing of spring xylogenesis and its potential drivers in homogeneous mature forest stands in a temperate European region. Three species with contrasting leaf development dynamics and wood anatomy were studied: European beech, silver birch and pedunculate oak. Detailed phenological observations of xylogenesis and leaf phenology were performed from summer 2017 until spring 2018. Cambium reactivation (CR) occurred before the buds of oak and birch were swollen, whereas these two phenological phases were concurrent for beech. On the other hand, initial earlywood vessels were fully differentiated (FDIEV) after leaf unfolding for all three species. Timing of CR was correlated to average ring-width of the last 10 years (2008–17), tree diameter and, partially, with tree age. In addition, the timing of FDIEV was correlated to tree age and previous year’s autumn phenology, i.e., timing of wood growth cessation and onset of leaf senescence. Multivariate models could explain up to 68% of the variability of CR and 55% of the variability of FDIEV. In addition to the ‘species’ factor, the variability could be explained by ca 30% by tree characteristics and previous year’s autumn phenology for both CR and FDIEV. These findings are important to better identify which factors (other than environment) can be driving the onset of the growing season, and highlight the influence of tree growth characteristics and previous year’s phenology on spring wood phenology, wood formation and, potentially, forest production.

The coordination of plant leaf water potential (ΨL) regulation and xylem vulnerability to embolism is fundamental for understanding the tradeoffs between carbon uptake and risk of hydraulic damage. A legacy of observations in drylands suggests plants with vulnerable xylem more carefully regulate ΨL than plants with resistant xylem. We synthesized over 1600 ΨL observations, 122 xylem embolism curves, and xylem anatomical measurements of Quercus alba L., Liriodendron tulipifera L., and Acer saccharum Marsh. across ten contrasting forests to evaluate if the paradigm linking conservative ΨL regulation to vulnerable xylem applies to temperate deciduous trees. Additionally, we explored generalizable patterns of hydraulic trait acclimation in relation to forest age and climate. Contrary to the dryland paradigm, we found that the tree species with the most vulnerable xylem (e.g., Q. alba) regulated ΨL less strictly (anisohydric behavior) than the species with xylem more resistant to embolism (e.g., A. saccharum and L. tulipifera). This relationship was found across all sites, suggesting coordination among traits was largely unaffected spatio-temporal factors. Our findings indicate drought-response traits of temperate deciduous forest species are coordinated in fundamentally different ways than vegetation in arid climates.

The central-marginal hypothesis (CMH) predicts high genetic diversity at the species’ geographic centre and low genetic diversity at the species’ geographic margins. However, most studies examining the CMH have neglected potential effect of past climate. Here, we test six hypotheses, representing effects of past climate and contemporary range position, for their ability to explain the spatial patterns of genetic diversity in 37 populations of Betula albosinensis. Ecological niche modelling (ENM) revealed large and continuous suitable habitats in north, southwest and southeast China during the last glacial maximum (LGM) but a contraction of suitable habitats since the LGM. Pollen records further confirmed the existence of multiple refugia in north and south China. The spatial pattern of genetic diversity (i.e., expected heterozygosity, gene diversity and allele richness) were best explained by distance to the southern edge and distance to the range edge but also showed longitudinal and latitudinal gradients. Hypotheses accounting for the effects of climate (climatic suitability, climatic stability and climatic variability) had comparatively little support. Our findings show partial support for the CMH and illustrates that the existence of multiple LGM refugia, and suggests species abundance and past species movement play a role in shaping genetic diversity across species’ ranges.

Between-branch nitrogen competition is expected to be important during spring in temperate deciduous trees as nitrogen allocation would be higher in branches from earlier budburst than in those from later budburst. Such phenology-induced branch interaction would influence plant photosynthesis, but this has not been evaluated. Warming experiments were conducted on whole crowns (warmed trees; trunks and all branches of the same tree were warmed) or parts of the crowns (warmed branches with unwarmed control branches in the same tree), with unwarmed control trees, in saplings of the deciduous species Fraxinus lanuginosa. Spring leaf phenology and leaf photosynthetic traits were investigated to determine how the difference in temperature affects leaf phenology and photosynthetic traits. The timing of budburst was influenced by temperature—budburst was earlier in warmed trees and warmed branches than in control trees and control branches, but budburst timing did not differ between control trees and control branches or between warmed trees and warmed branches. In contrast, leaf traits were affected by the variation in phenology within crowns—nitrogen content and photosynthetic capacity were greater in the leaves of the warmed branches than in the control branches, but they did not differ between the leaves of warmed trees and control trees. Thus, branch warming altered the distribution of nitrogen between warmed and unwarmed branches as warmed branches developed faster, resulting in intracrown variation in leaf photosynthetic traits.

PREMISE Mosses are a major component of Arctic vegetation today, with >500 species known to date. However, the origins of the Arctic moss flora are poorly documented in the fossil record, especially prior to the Pliocene. Here, we present the first anatomically preserved pre-Cenozoic Arctic moss and discuss how the unique biology of bryophytes has facilitated their success in polar environments over geologic time. METHODS A permineralized fossil moss gametophyte within a block of Late Cretaceous terrestrial limestone, collected along the Colville River on the North Slope of Alaska, was studied in serial sections prepared using the cellulose acetate peel technique. RESULTS The moss gametophyte is branched and has leaves with a broad base, narrow blade, and excurrent costa. We describe this fossil as Cynodontium luthii sp. nov., an extinct species of a genus that is known from the High Arctic today. Cynodontium luthii is the oldest evidence of the family Rhabdoweisiaceae (by ≥18 Ma) and reveals that genera of haplolepideous mosses known in the extant Arctic flora also lived in high-latitude temperate deciduous forests during the Late Cretaceous. CONCLUSIONS The occurrence of C. luthii in Cretaceous sediments, together with a rich Pliocene-to-Holocene fossil record of extant moss genera in the High Arctic, suggests that some moss lineages have exploited their poikilohydric, cold- and desiccation-tolerant physiology to live in the region when it experienced both temperate and freezing climates.

Using the territory of the Orlovskoye Polesye National Park as a case study within the catchment basin of the Oka River (Mid-Russian Uplands, Oryol Region, Russia), we obtained palaeoecological data for studying response of forest landscapes within the forest-steppe ecotone to climate change and human impact through the Late Holocene. The paper presents reconstruction of environmental change on a local to regional scales based on plant macrofossil, spore-pollen and testate amoeba records from a peat core along with reconstruction of woodland coverage inferred from pollen data. Over the past 4000 years, the total woodland coverage has fluctuated insignificantly, ranging from 38 to 52%, while the structure of the forest has changed radically. Prior to 1500 cal. yr BP, both birch-pine and mixed temperate deciduous forests of oak, elm, ash and lime with Scots pine and well-developed shrub understory of hazel and alder grew in the region. The subsequent agricultural colonization of the territory led to a reduction of a broadleaved trees in forest stands since 1500 cal. yr BP. During the last few centuries, human activity largely associated with cutting/burning trees and farming favored the expansion of secondary forests dominated by birch.

RUSSIAN JOURNAL OF FOREST SCIENCE, 2019, No. 4, P. 294-303 THE EXPRESS-METHOD OF ESTIMATION OF EPIPHYTIC LICHENS DIVERSITY A. B. Ismailov 1 , J. Vondrak 2,3 , G. P. Urbanavichus 4 1 Mountain Botanical Garden, Dagestan Research Centre of the Russian Academy of Sciences Gadzhiev st. 45, Makhachkala, 367000 E-mail: i.aziz@mail.ru 2 Institute of Botany, Academy of Sciences of the Czech Republic Zamek, 1, Pruhonice, 25243 Czech Republic 3 Department of Botany, Faculty of Biological Sciences, University of South Bohemia Branisovska, 31, Ceske Budějovice, 37005, Czech Republic 4 Institute of Industrial Ecology Problems of the North, Kola Science Centre, Russian Academy of Sciences Fersmana st. 14a, Apatity, Murmansk Oblast, 184200, Russia Received 7 February 2018 Diversity of epiphytic lichens was studied for the first time by express-method on a 1-ha sampling plot in montane pine forest Pinetum kochianae herboso–caricosum on Gunib plateau in Dagestan mountains. We found 179 species from 77 genera and 36 families. Among them 33 species, 7 genera ( Dendriscocaulon , Gyalideopsis , Psoroglaena , Steinia , Tetramelas , Thelocarpon , Vezdaea ) and 3 families ( Gomphillaceae , Thelocarpaceae , Vezdaeaceae ) were found for the first time in Dagestan and 3 species ( Lecidella subviridis , Micarea hedlundii , Scoliciosporum sarothamnii ) were found for the first time in Caucasus. By means of this method we found twice as much epixylic and epiphytic lichens and non-lichenized fungi than previously were known for the whole area of 40 ha of the studied forest. Noted high proportion of microlichens (63%) evidences high. Ratio of number of species of micro- to macrolichens increased from 0.72 to 1.22. The genus coefficient indicators increased from 1.9 to 2.5. Number of the epiphytes and epixyles of pine increased by 38 species (by 46%) and by 8 generas (by 18%). Specific groups of lichens were found on decomposing deadwood and tree trunks. They indicate undisturbed communities and high conservation value of the pine forest. Keywords: pine forests, lichen flora, epiphytes, sampling plots, new findings, Gunib plateau, eastern Caucasus, Dagestan. Acknowledgements: This work was financially supported by the Russian Foundation for Basic Research (grant 15-29-02396). DOI: 10.1134/S0024114819030045 REFERENCES Abdurachmanova Z.I., Sadykova G.A., Tsenofloristicheskii analiz soobshchestv s dominirovaniem Pinus kochiana Klotsch ex K. Koch. Gunibskogo plato (Vnutrigornyi Dagestan) (The coenofloristical analysis of the communities with dominance of Pinus kochiana Klotsch. ex G. Koch. of the Gunib plateau (inland mountain Daghestan)), Fitoraznoobrazie Vostochnoi Evropy , 2015, Vol. 9, No. 2, pp. 112-122. Arup U., Ekman S., Lindblom L., Mattsson J.-E., High performance thin layer chromatography (HPTLC), an improved technique for screening lichen substances, The Lichenologist , 2007, Vol. 25, No. 1, pp. 61-71. Fritz O., Gustafsson L., Larsson K., Does forest continuity matter in conservation? – A study of epiphytic lichens and bryophytes in beech forests of southern Sweden, Biological Conservation , 2008, Vol. 141, No. 3, pp. 655-668. Fritz O., Heilmann-Clausen J., Rot holes create key microhabitats for epiphytic lichens and bryophytes on beech ( Fagus sylvatica ), Biological Conservation , 2010, Vol. 143, No. 4, pp. 1008-1016. Hafellner J., Turk R., Die lichenisierten Pilze Osterreichs - eine neue Checkliste der bisher nachgewiesenen Taxa mit Angaben zu Verbreitung und Substratokologie, Stapfia , 2016, Vol. 104, No. 1, pp. 1–216. 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Korchikov E.S., Lishainiki Samarskoi Luki i Krasnosamarskogo lesnogo massiva (Lichens of the Samara Bend and Krasnosamarskoe woodland), Samara: Samarskii universitet, 2011, 320 p. Lohmus A., Lohmus P., Vellak K., Substratum diversity explains landscape-scale co-variation in the species-richness of bryophytes and lichens, Biological Conservation , 2007, Vol. 135, No. 3, pp. 405-414. Murtazaliev R.A., Konspekt flory Dagestana. Euphorbiaceae - Dipsacaceae (Synopsis of the flora of Dagestana. Euphorbiaceae - Dipsacaceae ), Makhachkala: Epokha, 2009, Vol. 2, 247 p. Murtazaliev R.A., Konspekt flory Dagestana. Lycopodiaceae - Utricaceae (Synopsis of the flora of Dagestana. Lycopodiaceae – Utricaceae ), Makhachkala: Epokha, 2009, Vol. 1, 319 p. Murtazaliev R.A., Konspekt flory Dagestana. Melanthiaceae - Acoraceae (Synopsis of the flora of Dagestana. Melanthiaceae - Acoraceae ), Makhachkala: Epokha, 2009, Vol. 4, 231 p. 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Doctor's biol. sci. thesis), Petrozavodsk: BIN RAN, 2017, 467 p. Urbanavichene I.N., Urbanavichus G.P., Likhenoflora Mordovskogo zapovednika (annotirovannyi spisok vidov) (The lichen flora of the Mordovskii Reserve (an annotated species list)), Moscow: Komissiya RAN po sokhraneniyu biologicheskogo raznoobraziya, 2016, 41 p Vondrak J., Malicek J., Palice Z., Coppins B., Kukwa M., Czarnota P., Sanderson N., Acton A., Methods for obtaining more complete species lists in surveys of lichen biodiversity, Nordic Journal of Botany , 2016, Vol. 34, No. 5, pp. 619-626.

The effects of global warming are most pronounced in winter. A reduction in snow cover due to warmer atmospheric temperature in formerly cold ecosystems, however, could counteract an increase in soil temperature by reduction of insulation. Thus, soil freeze–thaw cycles (FTCs) might increase in frequency and magnitude with warming, potentially leading to a disturbance of the soil biota and release of nutrients. Here, we assessed how soil freeze–thaw magnitude and frequency affect short-term release of nutrients in temperate deciduous forest soils by conducting a three-factorial gradient experiment with ex situ soil samples in climate chambers. The fully crossed experiment included soils from forests dominated by Fagus sylvatica (European beech) that originate from different winter climate (mean coldest month temperature range ΔT>4 K), a range of FTC magnitudes from no (T=4.0 ∘C) to strong (T=-11.3 ∘C) soil frost, and a range of FTC frequencies (f=0–7). We hypothesized that higher FTC magnitude and frequency will increase the release of nutrients. Furthermore, soils from cold climates with historically stable winter soil temperatures due to deep snow cover will be more responsive to FTCs than soils from warmer, more fluctuating winter soil climates. FTC magnitude and, to a lesser extent, also FTC frequency resulted in increased nitrate, ammonium, and phosphate release almost exclusively in soils from cold, snow-rich sites. The hierarchical regression analyses of our three-factorial gradient experiment revealed that the effects of climatic origin (mean minimum winter temperature) followed a sigmoidal curve for all studied nutrients and was modulated either by FTC magnitude (phosphate) or by FTC magnitude and frequency (nitrate, ammonium) in complex twofold and, for all studied nutrients, in threefold interactions of the environmental drivers. Compared to initial concentrations, soluble nutrients were predicted to increase to 250 % for nitrate (up to 16 µg NO3-N kg−1DM), to 110 % for ammonium (up to 60 µg NH4-N kg−1DM), and to 400 % for phosphate (2.2 µg PO4-P kg−1DM) at the coldest site for the strongest magnitude and highest frequency. Soils from warmer sites showed little nutrient release and were largely unaffected by the FTC treatments except for above-average nitrate release at the warmest sites in response to extremely cold FTC magnitude. We suggest that currently warmer forest soils have historically already passed the point of high responsiveness to winter climate change, displaying some form of adaptation either in the soil biotic composition or in labile nutrient sources. Our data suggest that previously cold sites, which will lose their protective snow cover during climate change, are most vulnerable to increasing FTC frequency and magnitude, resulting in strong shifts in nitrogen and phosphorus release. In nutrient-poor European beech forests of the studied Pleistocene lowlands, nutrients released over winter may be leached out, inducing reduced plant growth rates in the following growing season.

Cessation of xylem formation or wood growth (CWG) and onset of foliar senescence (OFS) are key autumn phenological events in temperate deciduous trees. Their timing is fundamental for the development and survival of trees, ecosystem nutrient cycling and the seasonal exchange of matter and energy between the biosphere and atmosphere, and affects the impact and feedback of forests to global change. A large-scale experimental effort and improved observational methods have allowed us to compare the timing of CWG and OFS for different deciduous tree species in Western Europe, particularly in silver birch, a pioneer species, and European beech, a late-succession species, at stands of different latitudes, of different levels of site fertility, for 2 years with contrasting meteorological and drought conditions, i.e., the low moderately dry 2017 and the extremely dry 2018. Specifically, we tested whether foliar senescence started before, after or concurrently with CWG. Onset of foliar senescence and CWG occurred generally between late September and early November, with larger differences across species and sites for OFS. Foliar senescence started concurrently with CWG in most cases, except for the drier 2018 and, for beech, at the coldest site, where OFS occurred significantly later than CWG. The behavior of beech in Spain, the southern edge of its European distribution, was unclear, with no CWG, but very low wood growth at the time of OFS. Our study suggests that OFS is generally triggered by the same drivers of CWG or when wood growth decreases in late summer, indicating an overarching mechanism of sink limitation as a possible regulator of the timing of foliar senescence.

It is widely acknowledged that many plant species can keep stomata open during night. We examined how nocturnal stomatal conductance differs among potted saplings of nine temperate tree species from diverse native habitats in wet and dry soil conditions, and how it affects plant predawn water status. Nocturnal stomatal conductance in dry soil conditions was low in all the species (with a maximum value of 14.6 mmol m–2 s–1); in wet conditions, it was the highest in Populus tremula L., a fast-growing and anisohydric pioneer species, and the lowest in Quercus robur L., a late-successional and isohydric species. Relatively high nocturnal stomatal conductance in wet conditions in P. tremula compared with the other species resulted in the highest difference in water potential values between the leaves and soil at predawn. As drought progressed, different species tended to keep stomata almost closed at night, and the observed differences between anisohydric and isohydric species disappeared. At an ample soil water supply, nocturnal stomatal behaviour was species dependent and varied according to both the water-use and the life strategies of the species. Keeping that in mind, one should therefore be careful when using predawn leaf water potential as a proxy for soil water potential, sampling different species.

The effects of structural diversity on the carbon dioxide exchange (CO2) of forests has become an important area of research for improving the predictability of future CO2 budgets. We report the results of a paired eddy covariance tower study with 11 years of data on two forest sites of similar mean stand age, near-identical site conditions, and dominated by beech trees (Fagus sylvatica), but with a very different stand structure (incl. age, diameter distribution, stocks of dead wood and species composition) because of different management regimes. Here we address the question of how management and related structural diversity may affect CO2 fluxes, and tested the hypothesis that more structurally diverse stands are less sensitive to variations in abiotic and biotic drivers. Higher annual net ecosystem productivity (NEP) was observed in the managed, even-aged, and homogenous forest (585 ± 57.8 g C m−2 yr−1), than in the unmanaged, uneven-aged, and structurally diverse forest (487 ± 144 g C m−2 yr−1). About two-third of the difference in NEP between the sites was contributed by a higher annual gross primary productivity (GPP, 1627 ± 164 vs 1558 ± 118 g C m−2 yr−1) and one-third by a lower annual ecosystem respiration (Reco, 1042 ± 60 vs 1071 ± 96 g C m−2 yr−1) in the homogenous forest. Spring (April – May) and summer (June – July) were the two main seasons contributing to the overall annual differences between the sites, also, the sensitivities of seasonal NEP and GPP to environmental variables were stronger in the homogenous forest during those periods. Inter-annual variation of NEP was higher in the homogenous forest (coefficient of variation (CV) = 25%) compared to the heterogeneous forest (CV = 12%). At annual time scale, the higher variability of NEP in the homogenous forest is attributed to biotic factors such as fruit production and a time-dependent growth trend, outweighing differences in environmental sensitivities.

It has long been hypothesized that timing of leaf shedding is critical for plant fitness but there is little experimental evidence to support the hypothesis. According to an optimality theory, shedding of old leaves increases canopy photosynthesis despite some nitrogen (N) being lost as litterfall, when the ratio of daily photosynthesis to leaf N (N-use efficiency, ε) in old leaves, expressed as a fraction of ε in new leaves, becomes lower than the fraction of leaf N that is resorbed before shedding (RN). This was shown to be true for N-poor plants but not for N-rich plants in a pot experiment; however, the use of planting pots imposes a variety of physical, chemical and biological constraints that could change the experimental results. Here we conducted a 3-year field survey in a cool temperate deciduous forest to examine whether Alnus sieboldiana Matsum. (N2-fixing) and Carpinus tschonoskii Maxim. (non-N2-fixing) shed their leaves to increase canopy photosynthesis in accord with the above criterion. These species often grow sympatrically and were chosen as representatives of N-rich and N-poor plants, respectively. Overall, daily photosynthesis decreased with leaf age, accompanied by small changes in leaf N, resulting in a decrease in ε. In both species, ε of leaves at shedding expressed as a fraction of ε in new leaves was nearly equal to RN in all years, implying that the old leaves were shed to increase canopy photosynthesis. Our results, together with those of previous field surveys, suggested that the timing of leaf shedding is explained by N use in maximizing canopy photosynthesis across broad groups of species.

The Appalachian region of the United States is home to the largest temperate deciduous forest in the world, though surface mining has caused significant forest loss. Many former coal mines are now dominated by invasive plants, which often inhibit establishment of desirable species, especially slower-growing native trees. Autumn-olive (Elaeagnus umbellataThunb.) is a nonnative, nitrogen-fixing shrub that was historically planted on former coalfields, but now impedes reclamation. To better understand the influence ofE. umbellatamanagement practices on hardwood establishment, we evaluated two common management practices: cutting and cut stump herbicide treatment. Planted native tree species, including black cherry (Prunus serotinaEhrh.), pin oak (Quercus palustrisMünchh.), and red maple (Acer rubrumL.), were monitored for survival and performance over two growing seasons followingE. umbellataremoval. In each plot, we also measured plant-available nitrate (NO3−) and ammonium (NH4+) in soils using ionic exchange membranes. At the end of the first growing season, native tree survival was high, and the presence or absence ofE. umbellatahad little effect on tree survival or growth, despite the higher plant-available nitrate whereE. umbellatawas present. By the end of the second growing season, native tree survival dropped to 20% to 60% and varied amongE. umbellatatreatments. Survival was highest whenE. umbellatawas cut and treated with herbicide, though tree growth was similar across all treatments withoutE. umbellata. When establishing native trees to replaceE. umbellata, cutting and herbicide application treatment of the invader resulted in the highest overall efficacy (100% control), though the most cost-effective method may be to simply cut mature stands despite regrowth, as this resulted in equivalent native tree growth over 2 yr. While this allowedE. umbellataregeneration, it provided sufficient invader control to allow initial tree establishment. Cutting and herbicide application treatment resulted in lessE. umbellataregeneration and appears to provide greater assurance that established trees will persist over the long term.

The occurrence of terrestrial mosses in temperate deciduous forests is limited by abundant leaf litter that covers almost all of the soil, except along stream banks where mineral substrates are exposed by wind. However, stream banks are also subject to erosion that is a major disturbance for moss populations. Utilizing transplants and observations over a three period (2015–2017), we examined maintenance of current populations and establishment of new ones along the banks of two headwater streams, one in Virginia (Meadowood) and one in Illinois (Vishnu). Of the 224 plots, some with and some without mosses, that we monitored at the two stream study areas, 78 (35%) were lost to erosion or stochastic events. Areas with established moss populations had similar losses than areas without mosses (43% lost vs. 39% lost); however, losses at the two sites were very different—in Illinois, 41% of the original plots were lost, compared to 29% in Virginia. These differences in losses from erosion correspond to 32% greater number of high (>2 cm) and extreme (>4 cm) precipitation events at the Illinois site. In general, areas with mosses were lost at the same rate as those with leaf-covered bare soil. Leaf cover of moss plots, measured at height of the autumn leaf fall, averaged 12% at the Illinois site and 14% in Virginia, compared to plots without mosses that averaged 56–57% leaf cover, indicating that established moss populations are associated with exposed microsites, whereas microsites without mosses have high leaf cover. We examined the potential for colonization of new sites using transplants. Mosses transplanted onto bare soil successfully established 52% of the time, with unsuccessful ones mostly lost due to high leaf cover. Bare areas that did not receive transplants were colonized only 14% of the time, while bare areas within established moss populations were recolonized 48% of the time. We conclude that: 1) stream bank bryophyte populations are limited by leaf litter on the forest-side and erosion on the stream-side—the latter influenced by high precipitation events; 2) new potential habitats are often covered by leaf litter prohibiting establishment; 3) establishment of new populations in the local area appear to also be limited by availability (or dispersal) of diaspores; and 4) despite these limitations, losses from erosion appear to be counter-balanced by persistence and slow expansion of existing populations that remain largely litter free owing to slightly raised canopy surfaces and rapid recolonization of internally disturbed microsites.

Temperate forest productivity and functioning may be explained by complex interactions among tree canopy composition, topographic conditions, climate, morphogenetic identification and classification of humus forms. In this study, we report the main morphological feature of humus profiles classified according to both American (AHCM) and European (EHCM) classifications under the six most common forest stands in northern Iran, i.e., Alnus subcordata (AS), Acer velutinum (AV), Fagus orientalis-Carpinus betulus (FO-CB), Carpinus betulus (CB), Fagus orientalis (FO), and Fagus orientalis-Carpinus betulus-Parrotia persica (FO-CB-PP). Organic and organic-mineral layers samples were collected in 61 permanent plots (20 × 20 m) within a 30 × 30 cm metal frame, for identification. Our result showed that Mull was the dominant humus system according to both classifications, whereas Mor (AHCM) and Amphi (EHCM) were the less frequent humus systems in the study area. Mull and Amphi (EHCM) were dominant at the lowest slope and altitude under AS canopy cover; Moder was usually present at intermediate slope and altitude under FO-CB and FO-CB-PP; while Mor was the dominant form at intermediate slopes and highest altitudes under FO and FO-CB. Due to the temperature changes and litter decomposition, altitude seems to be the best predictor of humus type and litter thickness. Our findings also indicate that EHCM could be preferred in the identification and classification of humus forms in temperate deciduous forests in Iran.

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.

Quercus mongolica is a tree found in temperate deciduous forests in east Asia. In Japan, Q. mongolica var. crispula is commonly found; moreover, an oak whose morphology is similar to that of Q. mongolica var. mongolica of the Asian continent has been found in certain areas of Honshu and Hokkaido. Recently, the oak found in Honshu was described as Q. serrata subsp. mongolicoides (QSM). However, genetic comparison between this oak and Q. mongolica var. mongolica of the Asian continent has not been performed; the origin of QSM is thus unknown. Therefore, we aimed to determine the origin of QSM by conducting nuclear microsatellite (nSSR), chloroplast DNA (cpDNA) and leaf morphology analyses for the three taxa, as well as other congeners. The cpDNA variation overlapped among the three taxa, suggesting low discrimination ability for these taxa. Although morphological congruency was found between QSM and Q. mongolica var. mongolica, results of nSSR analyses showed that QSM contained a genetic admixture of Q. mongolica var. mongolica of the Asian continent and Q. mongolica var. crispula of Japan, bolstering an admixture hypothesis. The nSSR and cpDNA analyses suggested that Q. mongolica var. crispula can be the progenitor of Q. mongolica var. mongolica and harbors the ancestral cpDNA haplotypes. Therefore, we concluded that QSM might have been created by an admixture that likely occurred within Japan between Q. mongolica var. crispula and putative relict Q. mongolica var. mongolica, which might have diverged in or around Japan from Q. mongolica var. crispula during the late Pleistocene.

Dramatic increases in populations of large mammalian herbivores have become a major ecological issue, particularly in the northern hemisphere, due to their substantial impacts on both animal and plant communities through processes such as grazing, browsing, and trampling. However, little is known about the consequences of these population explosions on ecosystem functions. Here, we experimentally investigated how the population density of sika deer (Cervus nippon) in temperate deciduous forest areas in Japan affected the decomposition of mammal dung by dung beetles, which is a key process in forest ecosystems. We measured a range of environmental variables (e.g., vegetation cover, soil hardness) and the dung decomposition rate, measured as the amount of deer dung decomposed during one week, and sampled dung beetles at 16 study sites with three different deer densities (high/intermediate/low). We then used structural equation modeling to investigate the relationships between deer density, environmental variables, the biomass of dung beetles (classified into small or large species), and the dung decomposition rate. We found that the biomass of small species increased with increasing deer density, whereas that of large species was not related to deer density. Furthermore, the dung decomposition rate was positively related to the biomass of small species but unrelated to that of large species. Overall, our results showed that an increase in deer density affects the decomposition rate of mammal dung by changing the structure of dung beetle communities (i.e., increasing the number of small dung beetles). Such an understanding of how increases in large herbivore populations affect ecosystem functions is important for accurately evaluating the ecological consequences of their overabundance and ultimately managing their populations appropriately.

The structural dynamics of forest canopies involve complex interactions among the abiotic environment, stand structure, species composition and disturbance regimes. How the re-arrangement of tree canopies in space and time affects forest aboveground net primary productivity (ANPP) remains poorly understood, however. In this study, we analyzed a long-term dataset from a temperate deciduous forest in Northern Michigan, USA, to investigate two primary objectives: 1) what abiotic and biotic factors influence canopy complexity and its inter-annual variability, and 2) the direct and indirect effects that abiotic, biotic and canopy complexity variables have on ANPP. We hypothesized that inter-annual variability in canopy complexity would be lower in high complexity canopies and that temporal variability in complexity metrics would be inversely related to ANPP. We found that canopy complexity was highest in more taxonomically diverse stands with high variability in tree diameters and in stands dominated by Populus tremuloides and Populus grandidentata. Canopy complexity was lowest in stands dominated by Quercus rubra and Pinus strobus, which also had lower ANPP. Stands with a high stem density had lower inter-annual variation in canopy complexity, exhibited more height growth and an increase in canopy open space, which in turn enhanced ANPP. Our results provide novel empirical evidence linking temporal stability in canopy complexity to ANPP, and suggest that variability in canopy complexity over time, in addition to the overall mean canopy complexity, may be important when considering drivers of forest carbon uptake.

While both chronic white-tailed deer (Odocoileus virginianus Zimmermann) overbrowsing and invasive shrubs have been linked to native regeneration failure in temperate hardwood forests, little is known of their relative importance and possible synergistic effects. Therefore, we established three study areas in Connecticut to examine the interaction of three levels of invasive shrub control and absence or presence of deer herbivory on forest regeneration over 9 years. Five observations suggest that obtaining forest regeneration requires a comprehensive management strategy. First, competitive interference by invasive shrubs in intact thickets continued to impede forest regeneration, especially taller seedlings, after deer were excluded. Second, density of small seedlings increased following removal of the competitive interference by invasive shrubs. Third, deer browsing depressed growth of small seedlings into taller height classes. Fourth, preferential browsing reduced species richness, especially in taller seedling classes, by favoring growth of low palatability species such as beech. Lastly, if a disturbance (e.g., cutting) does not kill the root system of the invasive shrubs, the window of forest regeneration recruitment may be narrow because invasive shrubs can quickly recover. In stands with both established shrub thickets and high deer densities, invasive shrub control and multiyear reduction of deer densities are both recommended to obtain adequate forest regeneration.

Heavily disturbed post-mining sites are often difficult to restore to forestland due to chemical and physical soil limitations, as well as frequent animal herbivory of planted tree seedlings. Forest tree species differ in how they allocate resources to defensive compounds or growth in order to resist abiotic and biotic stresses after outplanting. However, the influences of plant nutrition and secondary metabolite production on browse susceptibility and recovery are not well understood within and among species, especially for temperate deciduous forest trees. We investigated foliar tannin and nutrient responses under fenced (to exclude white-tailed deer, Odocoileus virginianus) and non-fenced environments on an abandoned mine land in southwestern Indiana, USA. Using field fertilization (15N-9P-10K controlled-release fertilizer at 0, 30 g, and 60 g per seedling), we also created a gradient of nutrient availability for planted black cherry (Prunus serotina Ehrh.), bur oak (Quercus macrocarpa Michx.), northern red oak (Quercus rubra L.), and white oak (Quercus alba L.) seedlings. Fencing improved growth relative to non-fenced seedlings; fertilization improved growth for all species except northern red oak, but only when combined with fencing. Fertilization reduced foliar tannin concentrations for black cherry and white oak, but did not change browsing preference or browse recovery for any species. Without fencing, browsing selection was solely driven by tree species, whereby black cherry had a higher likelihood of being browsed compared to all oak species. This response was likely associated with differences among species in resource allocation patterns; black cherry prioritizes structural growth and recovery, while oaks allocate resources to both growth and secondary metabolite production. As fencing is often considered cost-prohibitive for mine reclamation and other restoration efforts, species selection is perhaps the most fundamental silvicultural tool to promote forest regeneration success under conditions of high animal browsing pressure.

A clear understanding of the relationship between two photosynthetic capacity parameters, maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax), is expected to reveal plant photosynthetic physiology strategies and is critical in determining the carbon and water cycle in the terrestrial biosphere. Increasing evidence in recent suggests the relationship is unstable in spatiotemporal contexts, casting a doubt on deriving Jmax solely from a single linear function of Vcmax as in most gas exchange models do. In this study, we have examined the instability of the relationship in terms of seasonal and interannual courses (from 2006 to 2014) as well as at different altitudes (550, 900, and 1500 m a.s.l.) and in different leaf types (sunlit and shaded) of the only dominant species of Fagus crenata Blume in typical cool temperate forests in Japan based on a long-term field dataset. Our results clearly indicated that there is not only remarkable seasonal variability in the two parameters themselves but also large variations in their ratios. The slope parameter of the best fitted single linear function for estimating Jmax from Vcmax varied also in different seasons and different years and different leaf types, as well as at different sites. Further exploration of the slope parameter with internal leaf traits and external climatic drivers revealed that the leaf chlorophyll content had a significant correlation with the slope parameter (R2 = 0.72, RMSE = 0.08, RPD = 2.00) but the impacts of climatic drivers were rather versatile. Our findings should hence advance understanding of the dynamics of photosynthetic capacity and the instability of the Jmax–Vcmax relationship, which should be considered explicitly in the future in order to substantially improve model predictions in terrestrial carbon cycle models.

Nothofagus antarctica (Antarctic beech) is one of the main woody plants in the temperate deciduous forests and anti-boreal forests of the southern hemisphere. Since colonization of the Andean-Patagonian region by European settlers, however, stands of this species have been severely affected by fires caused by human activities, considerably reducing their area. To restore these forests to their area occupied before the fires, it is necessary to use artificial regeneration, relying on production of transplants in forest nurseries. Due to the low capacity for seed propagation, we focus on possibilities of producing seedlings by vegetative propagation. In a trial, we collected cuttings during three sets of dates, and attempted to root them using three combinations of substrate and ten combinations of stimulators. Using the most favorable combination of collection period, substrate and stimulator tested resulted in rooting of 23% of the cuttings, which exceeds the documented germination rates for this species.

Non-structural carbohydrates (NSC) play important roles in metabolic processes of plants and represent important functional traits in plant adaptation to the external environment. However, there are few reports concerning intra-annual NSC distribution in temperate deciduous forests, especially for the purpose of comparison among different stand ages on China’s Loess Plateau. Here, NSC allocation dynamics with age ring-porous black locust tree was determined for the growing (May) and dormant (November) seasons over the period from sapling to dying trees—defined as a completely defoliated tree with dried branches in the growing season. It was noted that regardless of tree age, NSC concentration was highest in coarse roots [16.4 g per 100 g of dry mass (16.4% DM)] and stems (15.1% DM). At the tree level, NSC concentration was highest (14.3% DM) in a 30-year-old stand in November and lowest (4.1% DM) in dying stands in May. The pool of NSC at tree level was highest (25.2 kg DM per tree) in 30-year-old stands in November and lowest (0.13 kg DM per tree) in sapling stands in May. The concentration of NSC was significantly lower in May than in November for all tree ages, organs, and biochemical components. The results underscored the importance of NSC in plant growth on China’s Loess Plateau. It also provided a useful insight into the dynamics of NSC from sapling to dying broadleaved tree species.

Earthworm species with different feeding, burrowing, and/or casting behaviors can lead to distinct microbial communities through complex direct and indirect processes. European earthworm invasion into temperate deciduous forests in North America has been shown to alter microbial biomass in the soil and reduce the fungi-to-bacteria ratios. It is unclear how changes in earthworm species composition due to interspecific competition may alter this dynamics, especially under the ongoing invasion by Asian Amynthas and Metaphire species. Furthermore, it is also poorly understood how interspecific interactions involving different species may have species-dependent, non-additive effects on different groups of soil microorganisms. By conducting a two-year field experiment in a deciduous forest in the Mid-Atlantic, we examined how the Asian species Amynthas agrestis and Amynthas corticis , the European species Lumbricus rubellus and Octolasion lacteum , and their interactions affect soil microbial communities, and tested the hypotheses that the Asian species and the interaction between the two European species negatively affect bacterial biomass. We showed that while A. corticis generally had no effect on soil microorganisms, A. agrestis had a positive effect on microbial biomass, primarily by increasing the biomass of Gram-positive and Gram-negative bacteria. Consistent with our hypothesis, the interaction between L. rubellus and O. lacteum had a negative effect on bacteria biomass. We concluded that the ongoing invasion of the Asian earthworm A. agrestis in forest soils and potential displacement of L. rubellus due to interspecific competition may lead to increased bacterial biomass through increasing resource availability and disrupting the interaction between L. rubellus and O. lacteum , potentially causing increased carbon mineralization and reducing soil carbon storage.

Temperate deciduous forest ecosystems in northeastern North America are under increasing biotic and abiotic stresses that can have interactive effects on understory vegetation, and thus impact the next generation of forest canopy trees. We examined seedling responses of the common and increasingly dominant species Acer rubrum (red maple) to the combined effects of soil warming (+5 °C), chronic nitrogen fertilization (+50 kg N ha−1 yr−1), and invasion by the phytotoxic plant Alliaria petiolata (garlic mustard), and their interactions. We planted 296 first-year A. rubrum seedlings in a multifactorial field experiment to examine the effects of all combinations of the experimental treatments. Second-year Acer rubrum seedlings demonstrated higher aboveground growth under soil warming conditions. Further, soil warming positively influenced plant-soil feedbacks through higher arbuscular mycorrhizal colonization in fine roots. However, the positive growth responses and mycorrhizal colonization observed under soil warming were moderated by both N fertilization and A. petiolata invasion. Our results highlight the importance of developing management plans that consider how multiple environmental change factors affect tree seedling performance, particularly via the plant-soil interface.

The phenology of trees is highly susceptible to changing global temperatures. Leaf budburst advances with increasing spring temperatures, but can also be delayed when warmer winters reduce chilling exposure. Results from long-term observations show that increasing temperatures have triggered advanced budburst in the past decades, but some studies also show that budburst advance has slowed recently. Here, we conducted an experiment with five temperate deciduous tree species (Acer rubrum L., Larix laricina (Du Rois) K. Koch, Populus tremuloides Michx., Quercus ellipsoidalis E. j. Hill, Betula papyrifera Marsh.) and one invasive species (Rhamnus cathartica L.) in Minnesota, USA, to assess the impact of chilling on the timing of leaf budburst. We collected twigs over two winter seasons (2011/2012 and 2012/2013) on a biweekly basis and exposed them to spring-like temperatures of 21 °C/16 °C day and night, long day photoperiod (16 h). We found a significant relationship of advanced budbreak with increased chilling for all species tested (P < 0.001) and significant differences in the timing to budburst among all species (P < 0.001). Acer rubrum responded strongly to chilling, showing a very steep linear decline in days to budburst with increased exposure to chilling. On the other end of the spectrum, L. laricina responded least to increases in chilling. These results suggest that rising global temperatures will likely have diverse impacts on tree species with potential implications for species interactions such as competition.

Earthworm invasions are one of the most serious causes of ecological deterioration in the temperate deciduous forests of North America. Non-native earthworms impact understory vegetation, leaf litter layer, carbon dynamics, nutrient availability, and the associated food webs. Here we report a significant status change and confirm expansion of known range of Amynthas agrestis, one of the most serious invasive species in North America, and two of its close relatives, A. tokioensis and Metaphire hilgendorfi. The three species have never been confirmed to co-occur in North American ecosystems. We examined 1760 earthworms collected from 30 sites across northeastern USA, and identified them using a new morphological key. Our data show that sympatric occurrence of at least two, and often all three, species is more common than having only one species. In addition, A. tokioensis was dominant in many of these earthworm communities. The status change in species composition from only one species to two or three and the shift in dominance are most likely caused by previous incorrect species identification. Our results support expansion of known range of A. tokioensis and M. hilgendorfi northward and westward into states with colder winters. This range expansion may have taken place alongside that of A. agrestis in the last 10–20 years, but has long been overlooked. Altogether, results highlight an urgent need for correct species identification. The recognition of an expanding multi-species system represents a unique opportunity to further evaluate complex interactions among co-invading and resident species, and to investigate whether interspecific interactions have unexpected non-additive impacts on ecological processes.