Competitive releases of understorey trees are an important pathway to canopy recruitment in unmanaged, closed-canopy forests, with significant consequences for resilience of these ecosystems. As climate and disturbance regimes progressively shift, the dynamics of canopy accession are expected to change. However, the response norms of subcanopy trees to competitive release and other developmental drivers have been understudied. To investigate the aggregate effects of multiple factors (i.e., disturbance severity, climate, ontogeny, topography, and calendar year) on growth rates and duration of growth releases, we examined growth patterns of more than 17100 tree cores of European beech and Norway spruce collected on permanent research plots located across primary forest remnants in the Carpathian Mountains. The percentage of canopy removed on the plot was the dominant extrinsic driver of growth during release events for both species, with beech exhibiting a more pronounced positive response than spruce. For both species, growth response was significantly affected by ontogeny-related factors: beech growth primarily increased with diameter at release onset, whereas spruce responded primarily negatively to age at release onset. Size at release onset also emerged as the primary predictor of release duration for both species. Additionally, both species exhibited increases in released growth rates throughout the past century, indicating a relative increase in canopy accession rates. However, it remains uncertain whether this trend will persist under a potential further intensification of disturbance regimes and shifting climatic constraints, particularly as trees on warmer and drier southern slopes already display weaker growth responses to canopy release compared to individuals on less sun-exposed sites.

Old-growth forests uniquely support biodiversity while serving as some of the planet's most important carbon stocks. The influence of tree and stand age on carbon flux dynamics remains debated-an urgent question as climate-driven disturbances may reshape forest age structures and in situ carbon storage. To clarify these relationships in Fagus sylvatica, systems, we examined a unique dataset of 3,503 tree ring series from 190 plots across some of the best preserved old-growth forests from five southern European countries. By employing a dendrochronological approach and integrating key environmental variables, including elevation, slope, temperature, and the presence of large-diameter trees (>= 60 cm), we analyzed the complex relationships between tree/stand age within a plot (represented by plot-level mean values, hereafter "stand age") and aboveground carbon stock across live, standing, and lying deadwood pools. The average stand age was 220 years, with 230 tC & sdot;ha-1 of carbon stored in aboveground biomass and necromass. We found a positive correlation between age and carbon storage at both the individual tree and plot levels. Notably, the presence of large-diameter trees was the strongest indicator of carbon stock, with carbon accumulation peaking at about 30% large-tree stems proportion before stabilising, while younger beech trees (below 100 years old) had a smaller contribution to carbon storage. We found no evidence of a decline in carbon stock with advancing stand age across the studied sites. Despite the ecological importance of old-growth forests, many of them remain unprotected and are disappearing across Europe. Our findings highlight the importance of preserving old-growth forests to maximize their role as long-term ecosystem carbon reservoirs.

Disturbances are key drivers of forest structure and function, creating spatial and temporal heterogeneity across landscapes. Evidence shows that disturbance regimes are shifting with climate change, yet it remains unclear how historical disturbances continue to shape present-day forest structure, composition, and mortality. We combined dendrochronological reconstructions of disturbance over the past two centuries with repeated inventories from 133 permanent 0.1-ha plots in primary mixed-Fagus sylvatica forests in the Dinaric Mountains to investigate how the legacy of disturbance timing, severity, and frequency shapes contemporary forest structure and average annual basal area mortality. Our results showed that quadratic mean diameter increased with time since disturbance, peaking at similar to 150-175 years. Canopy layer diversity, although remaining relatively high (>0.8), declined with increasing time since disturbance. Disturbance severity modestly reduced horizontal size variability. Neither beech nor fir dominance responded to disturbance history. Structural equation modeling revealed that time since disturbance and its interaction with severity continued to directly affect mortality. Disturbance effects explained 13.5% of the total deviance. Historical disturbances had persistent legacy effects on mortality, with the highest rates in recently disturbed (<50 years) and long-undisturbed (>150 years) plots. The time-severity interaction identified a peak in mortality following recent very high-severity events, with average annual basal area mortality reaching approximately 9%. Mortality increased with larger quadratic mean diameter, declined with greater beech dominance, and rose under drier recent conditions. Together, these findings demonstrate that disturbance legacies shape forest structure and modulate contemporary mortality for centuries after disturbance, remaining detectable even amid emerging climate stress.

An improved understanding of how forest trees may respond individually and differentially to climate across broad environmental gradients, due to adaptation or physiological acclimation, may facilitate more robust forecasts of forest resilience under climate change. We present a framework for modeling stem diameter growth in adult canopy trees that accounts for responses to climate that may be unique for individuals in different ecological settings. We used data from > 10,000 tree cores from 888 forest inventory plots distributed across wide climatic gradients in two mountain ranges in Europe. We formulated a suite of nonlinear models for each of the four species to understand factors regulating annual radial growth. The models accounted for the effects of tree ontogeny, competition, nitrogen deposition (Nd), temperature, and precipitation. We compared two approaches to evaluate evidence for adaptation or acclimation in the growth–climate relations of trees. One method tested whether growth responses diverged for individual trees associated with distinct climate regimes. An alternate method fitted climate response functions with the deviation of climate in a given year from the prevailing average conditions at a tree location. We also tested whether the peak height of this function, representing the maximum growth capacity of a tree, depended on local average climate. For all taxa, models that incorporated within-species variation received stronger support relative to simpler models that assumed a consistent species-average growth response to climate. Growth in all but one species was best predicted by models fitted with climate deviations. Trees differed markedly in terms of their peak growth potential and climate optima, and in some cases, occupied suboptimal environments. Growth responses to nitrogen (N) inputs were also modulated by climate. Our framework offers a flexible approach for integrating individual-level climate sensitivity into tree demography models, which may allow for more rigorous investigations of forest dynamics, the outcomes of which may inform adaptive management strategies for mitigating climate change impacts.

Abstract Despite significant stochasticity, the occurrence of disturbance events is co‐determined by general ecological rules, such as temperature gradient with increasing altitude or stronger wind loads on slopes. A detailed understanding of past disturbance dynamics and their driving forces forms a crucial foundation for ensuring the sustainability of forest ecosystems. This is particularly important in the context of shifting disturbance regimes under accelerating climate change. The exceptionally well‐preserved Bohemian Forest Ecosystem, the largest contiguous forested area in Central Europe, provides a unique archive for studying past disturbance dynamics. Here, our objective is to clarify the ecological nature of disturbance phenomena to improve our understanding of forest ecosystem development. Using an extensive dendrochronological dataset of more than 7600 tree‐ring series distributed across diverse ecological gradients, we developed a unique transboundary disturbance chronology extending back to the early 17th century. Generalized linear mixed‐effects models were applied to assess relationships between environmental factors and disturbance regimes. Our results provide evidence of a slow but persistent acceleration of disturbance processes over the past 400 years. Elevation emerged as the strongest predictor of disturbance frequency. The likelihood of forest stand disturbance generally rises as altitude decreases, reflecting interspecific differences in morphological traits and elevation‐dependent tree‐growth potential. Forest type and aspect further modulated this effect, emphasizing the influence of local topography on the susceptibility to disturbances. Natural disturbance dynamics vary across the forest types rather than occurring in synchrony, thus promoting high disturbance complexity and forest landscape heterogeneity, particularly in primary forests. Synthesis . Under climate change and the underlying shift in the tree species composition, a higher probability of disturbances can be anticipated in mixed forests at lower elevations. However, our findings highlight the importance of maintaining the diversity of natural processes in supporting the resilience of forest communities to extreme and unpredictable disturbance events, thereby contributing to climate change mitigation.

Intensifying droughts and heatwaves are increasing hydraulic constraints on European beech (Fagus sylvatica L.) and driving recent tree vitality losses at its warmer and drier range margins. Network-wide growth models predict widespread beech growth declines under future warming, yet these models rarely account for intraspecific demographic variability, potentially underestimating the adaptive capacity of natural beech forests. We leveraged a network of 530 plots and ~11,000 trees from primary beech forests covering a broad environmental gradient in central and southeastern Europe to assess how demographic variability in growth dynamics modulates forest productivity. We explored demographic differences in temporal and spatial variation in radial growth patterns and growth sensitivity to climate warming. Previous summer maximum temperatures and climatic water balance were the dominant climatic constraints of radial growth in xeric regions, whereas growth in mesic regions was more closely associated with current spring and summer conditions. Large trees exhibited stronger sensitivity to prior-summer heat stress, while small trees had stronger associations with spring and summer moisture availability. Severe summer droughts caused pronounced multi-year growth legacies across the demographic strata only in xeric regions. Long-term growth trend analysis revealed substantial regional heterogeneity, with growth declines in mid-sized and large trees contrasted by gains in small and mid-sized young (mesic regions) and old trees (xeric regions). Recent growth declines were linked to rising summer temperatures and declining water balance across the forest strata. Overall, productivity losses outweighed gains across the study network under climate warming. Stand structural complexity and demographic variability in growth dynamics were key drivers of ecosystem productivity, but their positive effects diminished under severe climatic stress. Our findings highlight the critical role of demographic and structural heterogeneity in shaping beech growth dynamics under climate warming, and caution against inferring future ecosystem productivity trajectories without explicitly accounting for demographic variability.

The radial growth of temperate forests responds to climate change with remarkable variation across space and between species. However, there is limited understanding of how growing season extension and increasing drought stress contribute to long-term growth trends. Here, we calibrate the VS-Lite growth model using 2013 tree-ring chronologies from ten broadleaved and five coniferous genera in Central-Southeast Europe to predict intra-annual wood formation under four SSP climate scenarios through the 21st century. Results show that forecasted summer drought stress will be temporarily offset by an extended growing season, leading to stable or positive trends in tree-ring widths until a tipping point in the 2040s-2050s. During the second half of the 21st century, high-emission scenarios lead to growth acceleration in humid coniferous forests due to growing season extension and enhanced growth rate. In contrast, forecasted extension of the growing season is insufficient to compensate for declining summer growth rates at drier sites, resulting in significant growth reduction for all genera, particularly during dry years. Our results demonstrate that adjusting intra-annual wood formation to seasonal moisture availability may become crucial for tree survival in warmer climates. Furthermore, we highlight that only low-emission scenarios support non-declining stem growth in dry forests with current species composition.

Anthropogenic activities have significantly contributed to the loss and fragmentation of primary forests across the globe, which has accelerated biodiversity decline, particularly among highly specialised species dependent on unique forest structures. Nevertheless, comparative studies between primary and managed forests are scarce, despite their importance for effective monitoring and conservation planning. To address this knowledge gap, we conducted a comparative study using a unique dataset of permanent study plots established across some of the best-preserved, mixed-beech primary forests and their adjacent managed counterparts in the Western Carpathian Mountains. We assessed the effects of forest structure and tree age—determined through extensive dendrochronological reconstructions—on contemporary lichen communities. Lichen species richness and the richness of red-listed species were 26% and 50% higher in primary forests than in managed forests, respectively, highlighting the outstanding conservation importance of primary forests. Generalised least squares (GLS) modelling demonstrated that in managed forests, lichen species richness was strongly associated with structural attributes: It increased with maximum tree age and the diameter of standing deadwood, and decreased with higher basal area (BA) of living trees, likely due to reduced understory light. In contrast, no structural variables significantly explained richness in primary forests, likely due to structural saturation and widespread microhabitat availability. Elevation emerged as the sole variable with significant explanatory strength.These findings underscore the critical role of structural complexity in supporting lichen diversity under different management regimes and provide a robust evidence base for promoting elements such as old trees, deadwood—especially large standing deadwood—and reduced canopy density. At the same time, they reaffirm the irreplaceable value of primary forests as biodiversity refuges and highlight the need for landscape-level conservation strategies that integrate both intact primary and structurally enriched managed forests.

Extreme disturbance activity is a signature of anthropogenic environmental change. Empirical information describing the historical normative limits of disturbance regimes provides baseline data that facilitates the detection of contemporary trends in both disturbances and community-level responses. Quantifying the attributes of historical disturbances is challenging due to their transient episodic nature, with decades-to centurieslong intervals between recurrences. Unmanaged primary forests that support centuries-old trees therefore serve as unique reference systems for quantifying past disturbance regimes. We surveyed relict stands of primary beech-dominated forests over wide environmental gradients in the Carpathian Mountains of Europe. We collected core samples from 3,026 trees in 208 field survey plots distributed across 13 forest stands in two countries. We used dendrochronological methods to analyze time-series of annually-resolved ring-width variation and to identify anomalous growth patterns diagnostic of past forest canopy removal. A 180-year record (1810-1990) of spatially and temporally explicit disturbance events (n = 333) was compiled and used to derive statistical attributes of the disturbance regime. We quantified disturbance severity (canopy area lost), patch size, and return intervals. Our analyses describe a complex regime where a background of relatively frequent, smallscale, low-to intermediate-severity disturbance was punctuated by episodic large-scale high-severity events. Even the most severe events were non-catastrophic at a stand level, leaving significant residual tree cover that supported a continuity of ecological function. We did not detect evidence for an expected climate-induced intensification of disturbance with time, but methodological limitations precluded an assessment of disturbance activity in the decades since 1990.

Ongoing climate change is having profound impacts on the growth and distribution of trees worldwide. However, there remain substantial gaps in our understanding of how environmental factors influence tree-growth responses to climate at larger scales, which is critical for identifying regions susceptible to the impacts of climate change. In this study, we aimed to reveal the main environmental factors that determine the spatial heterogeneity of tree-growth sensitivity to temperature, precipitation, and drought across temperate forests in Northeast Asia (30-45 degrees N, 124-146 degrees E). Utilising an extensive tree-ring network of 101 chronologies of 22 tree species, across 79 sites, we found that local climate, and especially climate water deficit, plays a dominant role in shaping the spatial heterogeneity of tree-growth sensitivity, while geospatial variables were less important. Our analysis revealed a pervasive pattern of increased tree susceptibility to drought across Northeast Asian forests. Specifically, at sites experiencing high climate water deficit, tree growth was consistently reduced across both broadleaved and coniferous species under conditions of low precipitation, elevated temperatures, and increased dryness during the growing season. Our findings suggest that ongoing climate warming may further negatively affect tree-growth performance, especially at drier sites, across Northeast Asian forests.

Increasing forest CO2 absorption is ensured by enhanced gross primary production (GPP) which exhibited increasing trends as documented by CO2 flux measurements or by global vegetation models. Considering the simultaneous increase in ecosystem respiration, it is, however, uncertain how the growing GPP imprints in tree stem biomass increase. There is still a certain discrepancy between estimates of forest biomass trends derived from standardized tree-ring series, information acquired from repeated re-measurements of stem biomass at permanent plots, and information derived from vegetation models or flux-tower measurements. Standardization procedures of tree-ring series related to age/size trend removal make this data source unique for the assessment of climate-growth relationships and for climatic reconstruction, however it also increases uncertainty of this data source for biomass trends assessment. Here, we present an approach mimicking repeated data collection at permanent plots based on an extensive data set of tree-ring sites. In this way, we connected two strong benefits of above-mentioned data – reliable age-independent estimates of stem biomass by repeated measurements at permanent plots and a dense network of highly replicated data covering wide environmental gradients provided by tree-ring time series. Our tree-ring network captures core parts of distribution ranges of five main European temperate tree species. Density of tree-ring network is roughly 1 site per 25 km2 of forested area in Central Europe namely Czech Republic (area of 78 000 km2) making this tree-ring network probably densest in the world. We first manipulated original tree-ring data sets by their truncation in 1990 (data set mimicking sample collection in 1990) and then adapt the original data set so that it has similar age structure as the 1990 data set mainly by excluding old age classes (data set 2015) assuring age independency of our data. For both data sets and all sites included, we calculated mean stem diameter at breast height (DBH) of average 100-year old tree based on basal area increments. We then tested for differences in DBH between 1990 and 2015. We found that all species except Pinus sylvestris showed a significant increase in stem dimension as indicated by DBH between 1990 and 2015. The highest DBH increase exhibited Abies alba (+13.5%), followed by Fagus sylvatica (+5.5%), Quercus sp.(+5.2%) and Picea abies (+4.7%). Differences in DBH between 2015 and 1990 were relatively homogenous across environmental gradients suggesting prevailing influence of large-scale factors independent on local conditions. Picea abies and Fagus sylvatica exhibited lesser increase in stem dimensions in colder areas. Furthermore, Picea abies and Quercus sp. showed a significant enhancement of growth at productive sites with fast growing individuals. Quercus also significantly enlarged DBH at locations with more positive trends in SPEI, i.e. those experiencing a trend towards wetter climate. Our results corroborate the pervasive growth acceleration in core region of European temperate forests leading to presence of larger canopy-level trees in current forests than in the past. Increasing stem size makes trees more sensitive to disturbances and potentially leads to their shorter life spans as reported in other studies.

Natural disturbances such as windthrows and bark beetle outbreaks are essential in the formation of natural forest ecosystem structures in Central Europe. Therefore, evaluating disturbances' spatial and temporal extent and synchronicity is critical for understanding of forest dynamics. This study aimed to evaluate the long-term natural disturbance history of primary mixed-beech forests and investigate the species composition-temporal synchronisation relationship. We collected a unique dataset of > 6,000 tree cores across 14 forest stands on 174 study plots, and using dendroecological methods we reconstructed 200-year-long plot-level disturbance histories and evaluated synchronicity within the stands. Subsequently, we used GLMs to evaluate the tree species diversity-synchronicity relationship. The results showed substantial temporal variability of natural disturbances and a prevalence of low and moderate severity disturbances. Disturbance synchronisation was higher in the Western than in the Eastern Carpathian forests, which have a lower proportion of admixture tree species. Moreover, the GLMs showed a strong positive dependence of synchronicity on tree species richness. The results contradict the general assumption that mixed-species forests have higher resilience to disturbances than monospecific forests. The reason behind these findings can be attributed to the substantial admixture of Norway spruce, and its vulnerability to disturbances such as windthrow and bark beetle outbreaks.

An observed acceleration of tree mortality rates in European forests has been attributed to the impacts of climate change and extreme disturbances. Ecosystem recovery depends on regeneration success, but the recruitment of juveniles has been recognized as bottleneck in the development of forests. We investigated the potential importance of biotic (canopy tree abundance, ungulate herbivory) and abiotic (light, soil nutrients) factors in the limitation of regeneration in montane primary forests in central Europe. We used widely distributed forest inventory data (n = 348 plots) for two forest types, multiple tree taxa, and two life stages (seedlings and saplings). Seedling densities were promoted by more abundant parent trees, but saplings were either negatively influenced or unaffected by the number of conspecific adults. Browsing intensity (per capita defoliation severity) strongly limited the density of seedlings, but not saplings, at a community level. Low understory light levels were positively associated with seedling densities, but either did not affect or depressed sapling abundance A tolerance of shading was enhanced by nitrogen availability in some taxa. Our findings reflect highly complex, context-specific regeneration processes that vary by species and life stage within species.

With ongoing global warming, increasing water deficits promote physiological stress on forest ecosystems with negative impacts on tree growth, vitality, and survival. How individual tree species will react to increased drought stress is therefore a key research question to address for carbon accounting and the development of climate change mitigation strategies. Recent tree-ring studies have shown that trees at higher latitudes will benefit from warmer temperatures, yet this is likely highly species-dependent and less well-known for more temperate tree species. Using a unique pan-European tree-ring network of 26,430 European beech (Fagus sylvatica L.) trees from 2118 sites, we applied a linear mixed-effects modeling framework to (i) explain variation in climate-dependent growth and (ii) project growth for the near future (2021-2050) across the entire distribution of beech. We modeled the spatial pattern of radial growth responses to annually varying climate as a function of mean climate conditions (mean annual temperature, mean annual climatic water balance, and continentality). Over the calibration period (1952-2011), the model yielded high regional explanatory power (R2 = 0.38-0.72). Considering a moderate climate change scenario (CMIP6 SSP2-4.5), beech growth is projected to decrease in the future across most of its distribution range. In particular, projected growth decreases by 12%-18% (interquartile range) in northwestern Central Europe and by 11%-21% in the Mediterranean region. In contrast, climate-driven growth increases are limited to around 13% of the current occurrence, where the historical mean annual temperature was below ~6°C. More specifically, the model predicts a 3%-24% growth increase in the high-elevation clusters of the Alps and Carpathian Arc. Notably, we find little potential for future growth increases (-10 to +2%) at the poleward leading edge in southern Scandinavia. Because in this region beech growth is found to be primarily water-limited, a northward shift in its distributional range will be constrained by water availability.

Basic ecological theory suggests that a tradeoff between competitiveness and stress tolerance dictates species range limits at regional extents. However, empirical support for this key theory remains deficient because the necessary spatial and temporal coverage and scalability of field observations has rarely been achieved. We harnessed an extensive dendroecological network (> 22 000 tree‐ring samples from 816 forest inventory plots) to disentangle competition‐limited from climate‐limited growth in both overstory and understory trees. Growth synchrony among trees thereby served as an integral metric of climate sensitivity, an approach that we justify in supplementary analyses of growth responses to temperature, precipitation, and the standardized precipitation‐evapotranspiration index. Sampling plots were arranged along elevational climate and vegetation gradients throughout the Carpathian Mountains, ranging from mixed‐species lowland forests to coniferous forests at high elevations. With mixed‐effect modelling, we also identified non‐climatic factors (stand characteristics, species diversity, and disturbance history) that modulate spatial patterns in the growth rate and synchrony of European beech Fagus sylvatica and Norway spruce Picea abies. Beech exhibited reduced growth and increased climate sensitivity towards higher elevations but performed better when species diversity was higher. The growth of spruce increased towards its lower range boundary, but understory cohorts grew poorly under interspecific competition. Overall, climate sensitivity was lower in more productive stands with benign climatic conditions and in recently disturbed sites with reduced stand density. These contrasting performances at mid‐elevations where the two species overlap (900–1300 m a.s.l.) reflect their evolutionary history, which enables them to be competitive (beech) or cold‐stress tolerant (spruce). This history will affect interactions between the two species under climate warming and shape macroecological patterns in the Carpathian ecoregion and likely other parts of Europe. Our findings point to a growing advantage of competitively stronger species in montane and subalpine vegetation zones.

In recent decades, extreme droughts have affected Central Europe, altering forest structure and function with significant socioeconomic consequences. Most Central European forests are used for timber production and provide various ecosystem services and habitats for forest-dwelling species. The extent to which recent weather extremes have impacted these forests was poorly quantified. Furthermore, the drivers of drought resistance remain uncertain, potentially misleading predictions of future forest development. In this study, we analyzed the impacts of recent droughts on the growth of managed forests in the Czech Republic based on tree-ring width of five common and commercially important tree species, European beech (Fagus sylvatica), Norway spruce (Picea abies), Scots pine (Pinus sylvestris), sessile oak (Quercus petraea), and pedunculate oak (Quercus robur). We assessed the 2015-2019 "dry period", which contains two extreme droughts. We also examined the drivers of growth reductions during three major drought events (2003, 2015, 2018) between 1995 and 2019, including the effects of tree age, size, elevation, and drought intensity. We identified drought-induced growth reductions for all five species during the "dry period" compared with the 2005-2009 "reference period", and Scots pine exhibited the highest resistance to drought (-13% growth) whereas Norway spruce showed the highest drought sensitivity (-30% growth). However, for the two recent droughts, the resistance of the three broadleaved species was higher than the two coniferous species. The effects of age and elevation on drought resistance varied with drought intensity. And European beech trees at lower elevations were significantly more negatively affected by droughts than trees at higher elevations. Our results indicate that a highly variable growth response to drought across species can be expected as climate changes. Under warmer and drier conditions, growth reductions could be more pronounced for drought-sensitive species at lower elevations, potentially threatening timber supply sustainability and other services.

In this era of biodiversity loss and climate change, quantifying the impacts of natural disturbance on forest communities is imperative to improve biodiversity conservation efforts. Epiphytic and epixylic lichens are effective forest quality bioindicators, as they are generally long-lived organisms supported by continuity of specific forest structures and their associated microclimatic features. However, how lichen communities respond to the effects of fluctuating historical disturbances remains unclear. Using a dendrochronological approach, this study investigates how natural disturbance dynamics indirectly influence various lichen community metrics in some of Europe’s best-preserved primary mixed-beech forests. Mixed modelling revealed that natural historical disturbance processes have decades-long effects on forest structural attributes, which had both congruent and divergent impacts on lichen community richness and composition. Total species richness indirectly benefited from both historical and recent higher-severity disturbances via increased standing dead tree basal area and canopy openness respectively - likely through the presence of both pioneer and late-successional species associated with these conditions. Red-listed species richness showed a dependence on habitat continuity (old trees), and increased with disturbance-related structures (standing dead trees) whilst simultaneously benefiting from periods without severe disturbance events (old trees and reduced deadwood volume). However, if the disturbance occurred over a century in the past, no substantial effect on forest structure was detected. Therefore, while disturbance-mediated forest structures can promote overall richness, threatened species appear vulnerable to more severe disturbance events – a concern, as disturbances are predicted to intensify with climate change. Additionally, the high number of threatened species found reinforce the critical role of primary forest structural attributes for biodiversity maintenance. Hence, we recommend a landscape-scale conservation approach encompassing forest patches in different successional stages to support diverse lichen communities, and the consideration of long-term disturbance dynamics in forest conservation efforts, as they provide critical insights for safeguarding biodiversity in our changing world.

The future performance of the widely abundant European beech (Fagus sylvatica L.) across its ecological amplitude is uncertain. Although beech is considered drought-sensitive and thus negatively affected by drought events, scientific evidence indicating increasing drought vulnerability under climate change on a cross-regional scale remains elusive. While evaluating changes in climate sensitivity of secondary growth offers a promising avenue, studies from productive, closed-canopy forests suffer from knowledge gaps, especially regarding the natural variability of climate sensitivity and how it relates to radial growth as an indicator of tree vitality. Since beech is sensitive to drought, we in this study use a drought index as a climate variable to account for the combined effects of temperature and water availability and explore how the drought sensitivity of secondary growth varies temporally in dependence on growth variability, growth trends, and climatic water availability across the species' ecological amplitude.Our results show that drought sensitivity is highly variable and non-stationary, though consistently higher at dry sites compared to moist sites. Increasing drought sensitivity can largely be explained by increasing climatic aridity, especially as it is exacerbated by climate change and trees' rank progression within forest communities, as (co-)dominant trees are more sensitive to extra-canopy climatic conditions than trees embedded in understories. However, during the driest periods of the 20th century, growth showed clear signs of being decoupled from climate. This may indicate fundamental changes in system behavior and be early-warning signals of decreasing drought tolerance. The multiple significant interaction terms in our model elucidate the complexity of European beech's drought sensitivity, which needs to be taken into consideration when assessing this species' response to climate change.

Primary forests are spatially diverse terrestrial ecosystems with unique characteristics, being naturally regenerative and heterogeneous, which supports the stability of their carbon storage through the accumulation of live and dead biomass. Yet, little is known about the interactions between biomass stocks, tree genus diversity and structure across a temperate montane primary forest. Here, we investigated the relationship between tree structure (variability in basal area and tree size), genus-level diversity (abundance, tree diversity) and biomass stocks in temperate primary mountain forests across Central and Eastern Europe. We used inventory data from 726 permanent sample plots from mixed beech and spruce across the Carpathian Mountains. We used nonlinear regression to analyse the spatial variability in forest biomass, structure, and genus-level diversity and how they interact with plot-level tree age, disturbances, temperature and altitude. We found that the combined effects of genus and structural indices were important for addressing the variability in biomass across different spatial scales. Local processes in disturbance regimes and uneven tree age support forest heterogeneity and the accumulation of live and dead biomass through the natural regeneration, growth and decay of the forest ecosystem. Structural complexities in basal area index, supported by genus-level abundance, positively influence total biomass stocks, which was modulated by tree age and disturbances. Spruce forests showed higher tree density and basal area than mixed beech forests, though mixed beech still contributes significantly to biomass across landscapes. Forest heterogeneity was strongly influenced by complexities in forest composition (tree genus diversity, structure). We addressed the importance of primary forests as stable carbon stores, achieved through structure and diversity. Safeguarding such ecosystems is critical for ensuring the stability of the primary forest, carbon store and biodiversity into the future.