Climate change mitigation and biodiversity conservation are key forest functions, but how to pursue them jointly in timber-managed forests is still unclear. We use a Europe-wide dataset of forest multi-taxon diversity and stand structure to (i) evaluate the importance of aboveground carbon stocks in determining species richness of six taxonomic groups; (ii) assess relationships between species richness and carbon stocks; (iii) discuss the potential to jointly enhance carbon and biodiversity and policy implications. Carbon-diversity relationships are positive for several groups, but mostly when deadwood pools are considered. Forest policies should consider the complex relationship between different carbon pools and taxonomic groups. Environmental policies emphasizing carbon sequestration in aboveground living biomass may conflict with biodiversity conservation by promoting homogeneous, fast-growing forests that fail to support species diversity of multiple groups. Sustainable forest management should acknowledge that deadwood carbon instead may translate into positive outcomes for both carbon storage and biodiversity conservation. Forests are essential for both climate change mitigation and biodiversity conservation, yet how to balance these goals in managed forests remains unclear. Here, using a Europe-wide dataset, the authors find that biodiversity increases with carbon stocks, but mostly when deadwood is included.

In 2023, more than half of olive harvests ( Olea europaea ) across Spain, Greece, and Türkiye were lost to drought. The same year late freeze destroyed 90% of the peach crop ( Prunus persica ) on the Georgia Piedmont and the apple crop ( Malus domestica ) in central New York, Vermont, and southern Quebec. Climate extremes now rank with the costliest threats to agriculture, but their role in forest recovery from diebacks that are happening globally is unknown for lack of tree fecundity estimates in forests. Tolerance of climate extremes could depend on past exposure but constrained by phylogenetic conservatism. We report a continental scale analysis of climate extremes and forest fecundity across North America and Europe showing that responses to late freeze and drought are happening now. Species differences are not explained by the traits typically included in ecological studies and they are weakly associated with phylogeny. Late freeze, that is, freezing temperatures that follow the onset of flower development in spring, is shown to be “normal” in North America, but not Europe, potentially explaining failed seed production due to delayed onset and the resultant shorter growing period by North American transplants dating back at least to the 18th century. Drought has thus far had the greatest impacts in dry forested regions, but here too, species differences are not explained by traditional trait values. If responses have been buffered from drought and late freeze by past exposure, acclimation and local adaptation prove inadequate as extremes intensify.

The transferability of single or joint species distribution models ((j)SDMs) depends on their ability to predict beyond the observed environmental range and to remain consistent despite shifts in biotic interactions. Transfer accuracy may be improved by recent advances in the application of deep learning that provide greater flexibility and potentially superior predictive accuracy than traditional approaches. We implemented jSDMs with deep and machine learning algorithms and measured the transfer accuracy from continental to regional areas in communities with different species composition. We ran jSDMs with deep neural networks (DNN), elastic net (EN), and stacked SDMs (sSDM) with random forests (RF). We used 134 689 occurrence records representing 1776 species of six taxonomic groups (beetles, birds, bryophytes, fungi, lichens and plants) from 2387 forest plots in Europe. We employed an agnostic modelling approach that covered most of the environmental conditions by including more than 100 satellite-derived variables and 98 climatic variables. The predictive power of the models within the training continental area was evaluated using AUC, whereas the transfer accuracy in the regional area was evaluated with the Boyce index calculated with independent presence records. We found that the DNN-jSDMs outperformed other models at continental scale, but model transfer from continental to regional extent was less accurate. We found that the accuracy of regional predictions was higher for taxonomic groups with better representation in the continental data, such as birds, bryophytes and plants. Depending on the algorithm and the taxonomic group, we achieved acceptable (Boyce > 0) to accurate (Boyce > 0.5) transferability for 32-78% of the species. Our findings underscored the need of considering trade-offs among hyperparameter tuning, spatial scales and model complexity. Our findings also suggest that the varying biotic interaction structures and, particularly, the different species compositions of the transfer areas, may affect model transferability more than previously considered.

To survive climate change, forest trees will have to shift seed production poleward. However, warming will not stimulate tree fecundity in the north if it is limited by other habitat variables. We evaluated the responses of tree fecundity to climate change for 292 tree species in North America and Europe, using response velocity, defined as (climate sensitivity) × (climate-change rate). The sensitivities to climate were estimated for each species and combined with rates of climate change to quantify how temperature, moisture deficits, and late freeze are influencing biogeographic shifts in tree reproduction. The results show that moisture deficit and late freeze, not annual temperature, drive changing seed production. Unlike annual temperature, which is increasing generally, change in these climate variables is not driving poleward shifts in seed production. These findings do not challenge the expectation that forests might eventually shift poleward. Rather, they show why current efforts offer divergent interpretations. The changes happening now are not consistent with annual temperature trends. As warming continues, fecundity changes can best be anticipated from temperature interactions with precipitation and extremes that impact flowering and fruiting in winter and spring.

Mast-seeding trees can vary seed output by orders of magnitude among years, but it remains unclear whether high seed production reduces per-seed investment, as predicted by fixed-budget allocation models. We quantified individual seed production with seed mass in European beech across 2792 trees and 123 populations spanning the species' range and quantified seed protein and lipid content in 35 populations. Seed mass increased with seed production, with seeds from high-seeding years being 14% heavier than those from low-seeding years, providing no evidence for a seed size-number trade-off and instead supporting variable reproductive allocation. By contrast, protein content decreased by 31% with increasing seed production, whereas lipid content increased (by 14%), indicating that nitrogen becomes constraining at high reproductive output while carbon-based provisioning is maintained. Climate further structured provisioning: seed mass and protein content were the lowest at climatic range margins, being 28% and 32% lower, respectively, than at the center of the climatic range. European beech can increase seed output without reducing per-seed biomass, but that nitrogen limitation and climatic constraints may strengthen regeneration bottlenecks at both trailing and leading margins, especially as climate warming intensifies.

A challenge in continuous cover forestry is converting even-aged stands to uneven-aged stands, which can be achieved by releasing advance regeneration through partial harvesting. Partial harvesting increases light and reduces competition, but its effects on oak seedling growth depend on harvesting intensity, direction, understory vegetation, and browsing pressure. Here, we conducted a three-year experiment (2016-2019) in central France, applying partial harvesting with varying intensities (7-30% of the initial basal area) within an 18 m radius around 217 naturally regenerated sessile oak (Quercus petraea (Matt.) Liebl.) seedlings in fenced and unfenced plots. We monitored seedling height growth, understory vegetation, and browsing impacts. Results showed that south-side harvesting uniquely influenced seedling growth, with positive effects only above a threshold of understory vegetation cover and for taller seedlings. Browsing exclusion further enhanced growth. Understory vegetation cover remained unaffected by partial harvesting, possibly due to drought conditions. These findings suggest that targeted south-side harvesting, combined with assessing seedling height and understory competition, can improve oak regeneration. Still forest managers should consider climatic conditions and may need complementary understory interventions to optimize outcomes.

We studied the effects of tree species and tree density on the capacity of a forest to buffer understory temperatures during the summer period. We dissociated tree-species and light effects by integrating incident solar irradiance and its proportion intercepted by the canopy into our analyses. We measured solar radiation and air temperature over three consecutive years (2018, 2019 and 2020) in 16 plots in Central France composed of mature stands of sessile oak and Scots pine with three types of composition: monospecific oak, monospecific pine and oak-pine mixture, and two levels of tree density. Air temperature and solar radiation were recorded simultaneously in the experimental plots and in a reference plot without forest cover.Our results show that the higher the incident irradiance the greater the difference in minimum temperature, and that the higher the intercepted irradiance the greater the difference in maximum temperature between below-canopy and open conditions. We found that tree species had a significant effect on the buffering capacity even when the light factor was taken into account. For a given incident irradiance and a given proportion of intercepted irradiance, the pine plots buffered understory temperatures less than the oak plots. Our results also show that higher maximum temperatures occurred in the understory than in open conditions for low values of intercepted irradiance and high values of incident irradiance, especially in the plots where Scots pine was present. The two species differ in leaf albedo and in their ability to regulate transpiration during droughts and these two characteristics may explain our results. Our study shows that Scots pine is less able to buffer summer temperatures than sessile oak. These results are of interest to forest managers since reducing stand density and mixing tree species are considered to be silvicultural strategies that can help cope with climate change.

The species richness of vascular plants in forests can have contrasting effects on the occurrence of non‐native insects. The establishment of non‐native insect populations may be facilitated by low plant species richness, which reflects the availability of few but easily accessible resources, or hampered by high plant species richness due to spatial dilution of resources or biotic resistance (i.e., resistance against biological invasions). The relationship between the species richness of plants and non‐native insects is likely influenced by disturbance regimes, which, in European forests, mostly consists of timber harvesting. We investigated this relationship considering two major forest attributes: (i) species richness of non‐native vascular plants and (ii) forest management. From 1101 forest plots in Europe, we gathered occurrences of 1212 vascular plant species, including 160 non‐native species, and of 2404 beetle species, including 29 non‐native species. We tested the relationship between the species richness of non‐native beetles and plants using non‐linear quantile regressions. We disentangled the effect of non‐native plant species richness from that of management on the species richness of non‐native beetles, while accounting for forest structural variables, using structural equation models. We found clear evidence of a hump‐shaped relationship between non‐native beetle and plant species richness. The general shape of the relationship persisted when considering only woody or non‐woody plants, as well as only non‐native plants. The relationship was also similar between managed and unmanaged forests. However, the proportion of non‐native beetles in managed forests was higher than in unmanaged forests at the same plant species richness. Management had a direct negative effect on non‐native beetle species richness, whereas non‐native plant species richness had a direct positive effect. When considering all direct and indirect effects, management facilitated the occurrence of non‐native beetles indirectly via non‐native plants rather than directly. Synthesis and applications . Species richness of native and non‐native vascular plants modulates the species richness of non‐native beetles through relationships with opposite signs. The interplay with management regimes and forest structures determines whether non‐native beetles are promoted. Forest management aimed at reducing the intensity of disturbance while encouraging native plant species richness could promote the dominance of dilution effects and biotic resistance and could moderate the establishment of non‐native insects.

The constraint caused by wild ungulates on forest regeneration is increasing worldwide. Hypotheses for plant association effects predict that species susceptible to herbivory can gain protection from other neighbouring plant species. In theory, such interactions could help limit the impact of browsing on the regeneration of specific tree species. However, the presence of neighbouring species can also result in increasing competition for resources between species. The resultant effects on forest regeneration of these interactions, both positive (protection against herbivores) and negative (inter-specific competition) are still unclear. To gain insight, we coupled models of browsing by roe deer (Capreolus capreolus) and of forest dynamics to simulate trajectories of oak (Quercus petraea (Matt.) Liebl.) regeneration admixed with species of contrasted palatability and growth rate under different scenarios of browsing pressure and initial sapling density. We also investigated how releasing oak saplings from all or specific neighbours during the simulation affect regeneration. We found that admixed species composition had a relatively weak effect on the density of oak recruits, but a strong effect on the duration of the regeneration phase. Oak regenerated faster when admixed with species of intermediate growth and low palatability (Fagus sylvatica) than with species of fast growth and high palatability (Carpinus betulus L.), except at intermediate sapling density and high browsing pressure where we found the opposite. Releasing oak from all competitors was most effective in promoting oak regeneration when admixed with both species together, although the benefit of competition release was much weaker at high browsing pressure. Lastly, we found that at low initial sapling density (i.e., 10 saplings/m2), oak regeneration was driven only by browsing and the effect of admixing species became negligible. Our study showed that admixing oak with palatable neighbours impedes rather than improves oak regeneration due to increased competition for resources. As such, we suggest that the benefits of herbivore diversion can be off-set by increased inter-specific competition.

Understanding and predicting responses of plant community diversity and ecosystem functioning to disturbance is essential to achieving forest conservation and management goals. In recent decades, the abundance and geographic distribution of wild ungulates have expanded in many parts of Europe due to, among other factors, land-use changes, hunting regulations and lack of predators. The study aims to explore the effects of deer browsing and grazing intensity, estimated through a browsing index on woody and semi-woody plants, on understorey vegetation composition, analysing both taxonomic and functional diversity. Specifically, we aim to test the intermediate disturbance hypothesis (IDH), which states that plant biodiversity peaks at intermediate levels of browsing intensity regarding plant species richness and functional groups. We also aim to identify species revealing different levels of browsing intensity, accounting for plant functional traits. Our results revealed that intermediate levels of browsing intensity, through species replacement, strongly and positively affected total species richness. This result is consistent with the IDH prediction, but distinct patterns varied across plant functional types. Moreover, increasing browsing intensity favoured disturbance-tolerant species by replacing functional traits. These species were characterised by ruderal traits, including high specific leaf area, low leaf dry matter content, small height and seed mass, annual and short lifespans. However, although browsing intensity increased functional richness and decreased functional redundancy, indicator species analysis revealed that high browsing intensity favoured highly competitive, browsing-tolerant perennial species. These results suggest that annual species may fail to colonise the understorey even if they are favoured by deer browsing, thereby affecting the functioning and the stability of ecosystem, with a potential homogenisation of understorey vegetation. Although confounding effects cannot be ruled out (e.g., local vegetation structure and diversity), our study highlights the need to consider functional diversity when assessing deer effects on vegetation to draw a complete picture of plant-large herbivore interactions.

Climate change causes far-reaching disruption in nature, where tolerance thresholds already have been exceeded for some plants and animals. In the short term, deer may respond to climate through individual physiological and behavioral responses. Over time, individual responses can aggregate to the population level and ultimately lead to evolutionary adaptations. We systematically reviewed the literature (published 2000-2022) to summarize the effect of temperature, rainfall, snow, combined measures (e.g., the North Atlantic Oscillation), and extreme events, on deer species inhabiting boreal and temperate forests in terms of their physiology, spatial use, and population dynamics. We targeted deer species that inhabit relevant biomes in North America, Europe, and Asia: moose, roe deer, wapiti, red deer, sika deer, fallow deer, white-tailed deer, mule deer, caribou, and reindeer. Our review (218 papers) shows that many deer populations will likely benefit in part from warmer winters, but hotter and drier summers may exceed their physiological tolerances. We found support for deer expressing both morphological, physiological, and behavioral plasticity in response to climate variability. For example, some deer species can limit the effects of harsh weather conditions by modifying habitat use and daily activity patterns, while the physiological responses of female deer can lead to long-lasting effects on population dynamics. We identified 20 patterns, among which some illustrate antagonistic pathways, suggesting that detrimental effects will cancel out some of the benefits of climate change. Our findings highlight the influence of local variables (e.g., population density and predation) on how deer will respond to climatic conditions. We identified several knowledge gaps, such as studies regarding the potential impact on these animals of extreme weather events, snow type, and wetter autumns. The patterns we have identified in this literature review should help managers understand how populations of deer may be affected by regionally projected futures regarding temperature, rainfall, and snow.

Les grands herbivores façonnent les communautés végétales, mais l’évaluation de leur influence sur le long terme à différentes échelles spatiales pose plusieurs défis méthodologiques. Les principales hypothèses pour les périodes pléistocène et holocène et leurs conséquences en termes d’impacts actuels sont évoquées. La place des grands herbivores dans les opérations de ré-ensauvagement est finalement discutée.

Aim: Climate is a major driver of large-scale variability in biodiversity, as a likely result of more intense biotic interactions under warmer conditions. This idea fuelled decades of research on plant-herbivore interactions, but much less is known about higher-level trophic interactions. We addressed this research gap by characterizing both bird diversity and avian predation along a climatic gradient at the European scale. Location: Europe. Taxon: Insectivorous birds and pedunculate oaks. Methods: We deployed plasticine caterpillars in 138 oak trees in 47 sites along a 19 degrees latitudinal gradient in Europe to quantify bird insectivory through predation attempts. In addition, we used passive acoustic monitoring to (i) characterize the acoustic diversity of surrounding soundscapes; (ii) approximate bird abundance and activity through passive acoustic recordings; and (iii) infer both taxonomic and functional diversity of insectivorous birds from recordings. Results: The functional diversity of insectivorous birds increased with warmer climates. Bird predation increased with forest cover and bird acoustic activity but decreased with mean annual temperature and functional richness of insectivorous birds. Contrary to our predictions, climatic clines in bird predation attempts were not directly mediated by changes in insectivorous bird diversity or acoustic activity, but climate and habitat still had independent effects on predation attempts. Main Conclusions: Our study supports the hypothesis of an increase in the diversity of insectivorous birds towards warmer climates but refutes the idea that an increase in diversity would lead to more predation and advocates for better accounting for activity and abundance of insectivorous birds when studying the large-scale variation in insect-tree interactions.

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

Managing forests to sustain their diversity and functioning is a major challenge in a changing world. Despite the key role of understory vegetation in driving forest biodiversity, regeneration and functioning, few studies address the functional dimensions of understory vegetation response to silvicultural management. We assessed the influence of the silvicultural regimes on the functional diversity and redundancy of European forest understory. We gathered vascular plant abundance data from more than 2000 plots in European forests, each associated with one out of the five most widespread silvicultural regimes. We used generalized linear mixed models to assess the effect of different silvicultural regimes on understory functional diversity (Rao's quadratic entropy) and functional redundancy, while accounting for climate and soil conditions, and explored the reciprocal relationship between three diversity components (functional diversity, redundancy and dominance) across silvicultural regimes through a ternary diversity diagram. Intensive silvicultural regimes are associated with a decrease in functional diversity and an increase in functional redundancy, compared with unmanaged conditions. This means that although intensive management may buffer communities' functions against species or functional losses, it also limits the range of understory response to environmental changes. Policy implications. Different silvicultural regimes influence different facets of understory functional features. While unmanaged forests can be used as a reference to design silvicultural practices in compliance with biodiversity conservation targets, different silvicultural options should be balanced at landscape scale to sustain the multiple forest functions that human societies are increasingly demanding. Different silvicultural regimes influence different facets of understory functional features. While unmanaged forests can be used as a reference to design silvicultural practices in compliance with biodiversity conservation targets, different silvicultural options should be balanced at landscape scale to sustain the multiple forest functions that human societies are increasingly demanding.image

Forest biodiversity studies conducted across Europe use a multitude of forestry terms,often inconsistently.This hinders the comparability across studies and makes the assessment of the impacts of forest management on biodiversity highly context-dependent.Recent attempts to standardize forestry and stand description terminology mostly used a top-down approach that did not account for the perspectives and approaches of forest biodiversity experts.This work aims to establish common standards for silvicultural and vegetation definitions,creating a shared conceptual framework for a consistent study on the effects of forest management on biodiversity.We have identified both strengths and weaknesses of the silvicultural and vegetation information provided in forest biodiversity studies.While quantitative data on forest biomass and dominant tree species are frequently included,information on silvicultural activities and vegetation composition is often lacking,shallow,or based on broad and heterogeneous classifications.We discuss the existing classifications and their use in European forest biodiversity studies through a novel bottom-up and top-driven review process,and ultimately propose a common framework.This will enhance the comparability of forest biodiversity studies in Europe,and puts the basis for effective implementation and monitoring of sustainable forest management policies.The standards here proposed are potentially adaptable and applicable to other geographical areas and could be extended to other forest interventions.

The European biodiversity and forest strategies rely on forest sustainable management (SFM) to conserve forest biodiversity. However, current sustainability assessments hardly account for direct biodiversity indicators. We focused on forest multi-taxon biodiversity to: i) gather and map the existing information; ii) identify knowledge and research gaps; iii) discuss its research potential. We established a research network to fit data on species, standing trees, lying deadwood and sampling unit description from 34 local datasets across 3591 sampling units. A total of 8724 species were represented, with the share of common and rare species varying across taxonomic classes: some included many species with several rare ones (e.g., Insecta); others (e.g., Bryopsida) were repre-sented by few common species. Tree-related structural attributes were sampled in a subset of sampling units (2889; 2356; 2309 and 1388 respectively for diameter, height, deadwood and microhabitats). Overall, multi-taxon studies are biased towards mature forests and may underrepresent the species related to other develop-mental phases. European forest compositional categories were all represented, but beech forests were over-represented as compared to thermophilous and boreal forests. Most sampling units (94%) were referred to a habitat type of conservation concern. Existing information may support European conservation and SFM stra-tegies in: (i) methodological harmonization and coordinated monitoring; (ii) definition and testing of SFM in-dicators and thresholds; (iii) data-driven assessment of the effects of environmental and management drivers on multi-taxon forest biological and functional diversity, (iv) multi-scale forest monitoring integrating in-situ and remotely sensed information.

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands. A new method to quantify three masting components from individual tree-years has revealed that globally, masting is uncommon in tree species that depend on mutualist dispersers, with its distribution further mediated by climate and nutrient availability.

Most European forests are used for timber production. Given the limited extent of unmanaged (and especially primary) forests, it is essential to include commercial forests in the conservation of forest biodiversity. In order to develop ecologically sustainable forest management practices, it is important to understand the management impacts on forest-dwelling organisms. Experiments allow testing the effects of alternative management strategies, and monitoring of multiple taxa informs us on the response range across forest-dwelling organisms. To provide a representative picture of the currently available information, metadata on 28 multi-taxa forest management experiments were collected from 14 European countries. We demonstrate the potential of compiling these experiments in a single network to upscale results from the local to continental level and indicate directions for future research. Among the different forest types, temperate deciduous beech and oak-dominated forests are the best represented in the multi-taxa management experiments. Of all the experimental treatments, innovative ways of traditional management techniques (e.g., gap cutting and thinning) and conservation-oriented interventions (e.g., microhabitat enrichment) provide the best opportunity for large-scale analyses. Regarding the organism groups, woody regeneration, herbs, fungi, beetles, bryophytes, birds and lichens offer the largest potential for addressing management–biodiversity relationships at the European level. We identified knowledge gaps regarding boreal, hemiboreal and broadleaved evergreen forests, the treatments of large herbivore exclusion, prescribed burning and forest floor or water manipulations, and the monitoring of soil-dwelling organisms and some vertebrate classes, e.g., amphibians, reptiles and mammals. To improve multi-site comparisons, design of future experiments should be fitted to the set-up of the ongoing projects and standardised biodiversity sampling is suggested. However, the network described here opens the way to learn lessons on the impact on forest biodiversity of different management techniques at the continental level, and thus, supports biodiversity conservation in managed forests.