Nitrogen deposition is a key global change driver that can alter soil processes and ecosystem functioning in forest ecosystems. Biochar is widely used as a soil amendment to improve soil properties and ecosystem functioning, yet how biochar regulates soil multifunctionality (SMF) across different nitrogen deposition levels remains poorly understood, particularly in plantation forests. Here, we conducted a field experiment in mature Larix kaempferi plantations to examine how biochar addition influences SMF across simulated nitrogen deposition levels and to explore the microbial mechanisms underlying these responses. The effects of biochar on SMF were strongly dependent on nitrogen addition levels. Biochar increased SMF under both ambient and high nitrogen additions, but reduced SMF under low nitrogen addition when applied at high biochar rates, indicating context-dependent responses of SMF to biochar under varying nitrogen deposition conditions. SMF was more strongly associated with fungal richness and community composition, whereas bacterial community properties and microbial network attributes showed only weak associations with SMF. Structural equation modeling revealed that fungal community composition directly influenced SMF and acted as a major pathway through which biochar application affected SMF. Although biochar significantly altered microbial network structure, these changes were not strongly associated with variation in SMF. Overall, our results indicate that biochar regulates SMF under different nitrogen deposition levels primarily through shifts in fungal community rather than through changes in bacterial community and microbial interaction networks. These findings highlight the importance of accounting for nitrogen deposition context when applying biochar in subtropical plantation forests.

There are still unexplored connections between tree growth and remotely sensed time-series are waiting to be discovered. Research results that combine dendrochronological data (tree-ring widths) and remotely sensed image time-series are generally scarce. We provide new findings that relate to the radial growth of different tree species (pedunculate and Turkey oak, European beech and Scots pine) and MODIS Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and Land Surface Temperatures (LST) daytime and night-time time-series. Significant correlations between MODIS observations (from 2000 to 2013, averaged to monthly and annual values) and radial growth of the trees have been found. All four tree species were statistically related to each of the four indices for some specific months within the growing season. LSTd annual values were significantly related to the radial growth of three species (Turkey oak, beech and pine) and annual EVI and LSTn to a single species (pine and beech, respectively). NDVI did not statistically correlate (p<0.05) with any of the tree-ring width chronologies. Values of EVI were statistically negatively related to Scots pine growth patterns (coefficient-0.546). LSTd was statistically related to the growth of Turkey oak (coefficient-0.571), European beech (coefficient-0.538) and Scots pine (coefficient-0.569), while LSTn had a high negative correlation with European beech (coefficient-0.674).

Structural adaptations of wood to environmental conditions play a crucial role in shaping its mechanical and hydraulic properties, which are vital for the performance and survival of fir and beech. In this study, we investigated how site-specific climatic conditions influence tree-ring widths and wood-anatomical traits of fir and beech in the Carpathians. Increment cores were collected from three forest stands across the Carpathians, each characterized by distinct climate regimes. We developed chronologies for mean tree-ring width (MRW), mean lumen area of vessels/tracheids (MLA), cell density (CD), relative conductive tissue area (RCTA), and, for fir, mean tangential cell wall thickness (CWTTAN), covering the period from 1980 to 2016. By comparing MRW and wood-anatomical traits with climatic variables—daily minimum and maximum temperatures and daily precipitation sums from E-OBS climate data—we identified clear differences among the three sites. The relationships between tree-ring widths and wood-anatomical traits varied between fir and beech, reflecting species-specific responses to local climate conditions. Notably, beech appeared more sensitive to warm summer temperatures, while fir was comparatively less affected. Evaluating the variability in radial growth and wood anatomy is essential for understanding the plasticity of fir and beech under diverse environmental conditions, and represents a first step toward predicting their responses to future climate scenarios.

Understanding competition between trees is essential for sustainable forest management as interactions between trees in uneven-aged mixed forests play a key role in growth dynamics. This study investigated nine competition indices (CIs) for their suitability to model the effects of neighboring trees on silver fir (Abies alba) growth in Dinaric silver fir-European beech (Fagus sylvatica) forests. Although numerous competition indices have been developed, there is still limited consensus on their applicability in different forest types, especially in mature, structurally complex forest stands. The indices were evaluated using the adjusted coefficient of determination in a linear model wherein the volume growth of the last five years for 60 dominant silver fir trees was modeled as a function of tree volume and competition index. The results demonstrated that distance-dependent indices (e.g., the Hegyi height-distance competition and Rouvinen-Kuuluvainen diameter-distance competition indices), which consider the distance to competitors and their size, perform better than distance-independent indices. Using the optimization procedure in calculating the competition indices, only neighboring trees at a distance of up to 26-fold the diameter at breast height (DBH) of the selected tree (optimal search radius) and with a DBH of at least 20% of that of the target tree (optimal DBH) were considered competitors. Therefore, competition significantly influences the growth of dominant silver firs even in older age classes. The model based solely on tree volume explained 32.5% of the variability in volume growth, while the model that accounted for competition explained 64%. Optimizing the optimal search radius had a greater impact on model performance than optimizing the DBH threshold. This emphasizes the importance of balancing stand density and competition in silvicultural practice.

Changing temperature and precipitation patterns are shaping tree climate-growth limitations. The influence of climate change affects individual tree species differently, and can also differ across extensive geographical regions. The Carpathians, a vast mountainous area of Europe, host significant numbers of silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.), both of which exhibit distinct climate-growth responses despite sharing similar ecological niches. Our study aims to discern the effects of climate change across Carpathians and forecast the future growth trajectories of silver fir and European beech within this area. We selected eight sites along the Carpathian arc at similar elevations and edaphic conditions, dendrochronologically sampled and measured 15 mature canopy trees of both species. Using the Vaganov-Shashkin process-based model, we simulated radial growth and computed growing season variables as well as temperature and moisture limitations. Model calibration covered the period from 1985 to 2015. E-OBS data were then used to simulate the period between 1985 and 2022, while the bias-corrected prediction of the RCP 4.5 scenario was utilized for predictions from 2023 to 2050. Our research revealed three distinct regions in the Carpathians, each with varying climate-growth limitations: the northern, south-western, and south-eastern areas. Northern sites primarily experienced limitations due to cold temperatures, while southern sites were predominantly constrained by insufficient moisture, intensifying eastward. Silver fir in northern sites exhibited significant low-temperature limitations and showed a higher response to climate conditions compared to European beech. Conversely, European beech consistently showed higher moisture-driven growth limitations than silver fir, indicating a better adaptability of silver fir to dryer conditions. Differences between recent and future periods were non-significant in most cases. However, there was a gradual convergence of northern sites to climatically limited growth in south-western sites.

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.

Key message Provenance controls conductive area of stem secondary xylem, leaf area, and stable isotope (C, N, and O) ratios of beech leaves, while no significant effects were observed for ectomycorrhizal community composition. Abstract Beyond growth parameters and drought tolerance, comparatively little is known about the functioning of different beech ( Fagus sylvatica L.) provenances. We investigated properties of leaves, stem secondary xylem, and ectomycorrhiza (ECM), and explored their interdependencies to identify the best performing beech provenance in optimal growth conditions. The study was conducted on 23-year-old trees in a provenance trial. The investigated provenances originated from Atlantic (Belgium—BE), Alpine (Italy—IT, Slovenia—SI), and continental climates (the Czech Republic—CZ). A significant effect of provenance was observed for stem vessel diameters and conductive area, as well as for foliar %C, δ 13 C, δ 15 N, and δ 18 O. δ 13 C as a proxy of intrinsic water use efficiency (iWUE) showed that the highest iWUE was achieved in BE provenance. Individuals with a better iWUE had wider growth rings regardless of provenance. Better iWUE was associated with lower specific leaf area (SLA). ECM community composition and diversity indices did not differ significantly among the provenances. Specific ECM taxa were associated with individuals with high SLA, δ 13 C, δ 15 N, and δ 18 O. In optimal growth conditions with no stress events, BE is a promising provenance due to an efficient water conducting system with high vessel diameters and conductive area, and high iWUE, while Alpine provenances showed an adaptation of their water conducting system to freezing conditions at their original locations. Integrating findings from different compartments improves our understanding of functioning of different beech provenances.

The Slovenian climate has undergone significant fluctuations, and an understanding of the past climate is necessary to improve models and recognise long-term patterns. The cryosphere environment, such as ice core samples, provides valuable palaeoclimate data. Palynology and dendroclimatology are also effective ways to study long-term changes in vegetation and reconstruct past climates using pollen and tree proxies. Sediment cores from various locations in Slovenia have been studied to understand past environmental changes. Borehole temperature profiles as well as historical records were also used to reconstruct past climate conditions. Studies have shown specific periods when climatic changes likely played a major role, but a complete timeline of the Slovenian climate throughout the Holocene has not yet been fully developed.

European forests are becoming increasingly threatened by climate change and more frequent droughts. The likely responses of species to climate change will vary, affecting their competitiveness, their existence, and consequently, forest management decisions and measures. We determined the influence of climate on the radial growth of European beech and silver fir along the Carpathians to find similarities between the two species and the main differences. Along the Carpathian Mountains, seven sites with mature fir–beech stands above 800 m above sea level were selected and analyzed. Our study confirmed different responses depending on species and location. A more pronounced response of tree growth to climate was observed on the eastern side of the Carpathians, while it was less expressed or even absent on the southern sites. Both beech and fir show better radial growth with higher precipitation in July and slower growth with higher average and maximum temperatures in June of the current year. Fir demonstrates a positive correlation between radial growth and temperature in winter, while beech demonstrates a negative correlation between radial growth and temperature in summer. In the 1951–1960 decade, the average tree ring widths in fir and beech were largest at the southern sites compared to the other sites, but since 2011, the southern sites have had the lowest increase while northern sites have had the largest. Both species respond differently to climate and are likely to follow different competitive paths in the future.

The grains of three barley varieties were milled and sieved to obtain respective milling fractions with a content of beta-glucans (b-G) from 1.4 to 10.7%. The enriched fraction obtained by the extraction and precipitation contained 24.7% of b-G. The differences between the ratio of stable C carbon isotopes were established. Milling fractions with coarse particles had more beta-glucans and a more negative ratio of δ13C isotope in comparison to the respective intact barley grain. However, the enriched fraction had a less negative isotope ratio. So, it is not expected that the deviation from the stable isotope ratio of grain in milling fractions is the result of the content of b-G, but it depends on other barley grain constituents. In different parts of barley grain, there are substances with different stable isotope ratios, and by milling and sieving, they are assorted to the same milling fraction with most of the b-G. The method for determining the ratio of a stable carbon isotope in diverse barley grain fractions, applied in this investigation, is potentially opening the possibility for an additional method of screening the concentration of bioactive constituents in barley grain.

To enhance our understanding of forest carbon sequestration, climate change mitigation and drought impact on forest ecosystems, the availability of high-resolution annual forest growth maps based on tree-ring width (TRW) would provide a significant advancement to the field. Site-specific characteristics, which can be approximated by high-resolution Earth observation by satellites (EOS), emerge as crucial drivers of forest growth, influencing how climate translates into tree growth. EOS provides information on surface reflectance related to forest characteristics and thus can potentially improve the accuracy of forest growth models based on TRW. Through the modelling of TRW using EOS, climate and topography data, we showed that species-specific models can explain up to 52 % of model variance (Quercus petraea), while combining different species results in relatively poor model performance (R2 = 13 %). The integration of EOS into models based solely on climate and elevation data improved the explained variance by 6 % on average. Leveraging these insights, we successfully generated a map of annual TRW for the year 2021. We employed the area of applicability (AOA) approach to delineate the range in which our models are deemed valid. The calculated AOA for the established forest-type models was 73 % of the study region, indicating robust spatial applicability. Notably, unreliable predictions predominantly occurred in the climate margins of our dataset. In conclusion, our large-scale assessment underscores the efficacy of combining climate, EOS and topographic data to develop robust models for mapping annual TRW. This research not only fills a critical void in the current understanding of forest growth dynamics but also highlights the potential of integrated data sources for comprehensive ecosystem assessments.

Natural regeneration of tree species is sensitive to silvicultural interventions. This study aimed to investigate the effects of different cutting intensities and local topographic and soil conditions on the composition of stable carbon (delta C-13) and oxygen (delta O-18) isotopes in wood of young beech (Fagus sylvatica L.) trees. Beech saplings in the regeneration layer were sampled in summer 2018 at three study sites in Dinaric fir-beech forests in the karst area of Slovenia. Three different cutting intensities were performed in 2012: i) no cutting (control), ii) 50% cutting of the stand's growing stock creating thinned stands, and iii) 100% cutting of the stand's growing stock creating 0.4 ha canopy gaps. We show that delta C-13 increased along the gradient of cutting intensity. On average, delta C-13 values in the tree rings were similar to 2 parts per thousand increased in trees from canopy gaps than from closed control stands. Furthermore, delta C-13 was higher on south-facing slopes characterized by higher air temperatures and lower relative humidity compared to north-facing slopes of karst sinkholes. Additionally, the results suggest a dependence of delta O-18 on interannual and cross-site climatic variations, particularly in the case of summer precipitation amount. delta O-18 also responded to soil depth, with beech individuals exhibiting lower values on deeper soils, presumably characterized by higher soil water availability compared to shallow soils. The results are discussed in the context of future climate change, as many beech-dominated forests on karst terrain in the Dinaric Mountains are particularly affected by climate warming and drying due to prolonged and reoccurring summer droughts, intensified large-scale disturbances, and often shallow soils with low water storage capacity.

The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe’s largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands. The atmosphere has dried across most regions of Europe in recent decades, a trend that can be attributed primarily to human impacts, according to tree ring records spanning 400 years and Earth system model simulations.

European beech (Fagus sylvatica L.) is an important component of forests in the alpine and continental biogeographical regions of Croatia. This study aimed to (1) analyze the long-term response of beech to climate, (2) identify potentially critical climatic conditions that could negatively affect the radial increment (RI) and vitality of beech, and (3) evaluate differences in the response of beech between the two biogeographical regions in Croatia. We used the 16 × 16 km Croatian ICP Forests Level 1 network. On a total of 25 plots, we cored between 5 and 24 trees for dendrochronological analysis. Tree-ring widths (TRW) were measured and standardized using cubic spline. TRW chronologies for the two regions were calculated and correlated to the temperature and precipitation data and Standardized Precipitation and Evapotranspiration Index (SPEI) using bootstrapped correlations. Continental region precipitation from April to August and alpine region precipitation from June to August were significantly important for RI. Temperature was less important for RI than precipitation in both regions, but the importance of the negative impact of above-average temperatures in the continental region and the positive impact of above-average precipitation in the alpine region has increased over the last two decades. A comparison with the 3-month SPEI confirmed the significant influence of high temperatures and the lack of precipitation in August on the RI of beech trees in both regions.

Climate anomalies significantly shape forests around the World. Intensive climate changes (global warming and drought) that have occurred since 20th century have caused more extreme climate events and boosted forest mortality. Different drought resistance in the Quercus sp. was observed among species and tree populations up to the genotype level. Species-specific responses to drought further complicate the understanding of the drought-induced changes in forests. We selected 20 radial growth and six stable carbon isotope ratio (δ13C) chronologies of Quercus cerris and Q. robur from Serbia. Since both δ13C and radial growth chronologies are influenced by surrounding stressors, including nonlinear climate trends, a more flexible approach to their modeling was required, and we, therefore, chose a generalized additive mixed model (GAMM) for data processing. A total of 20 climate and environmental variables were included in models to better understand their relationship and climate predictions/reconstruction. In the GAMM, a better fit was obtained for δ13C and more xeric Q. cerris (adj. R2 0.646) than for radial growth and Q. robur GAMMs performances. The potential for predicting radial growth and δ13C based on 20 different climate and environmental variables was tested with GAMM. Chronologies were split into two subsets for GAMM calibration and validation. GAMM predictions were calibrated using the first 25 years (1961-1985), while the second subset (1986-2010) was used for model validation. Both oak species showed higher similarity between measured and predicted δ13C, opposite of radial growth. A xeric oak species (Q. cerris) showed higher sensitivity to climatic and environmental factors, reflected in better GAMM prediction potential. Species-specific differences in radial growth and δ13C were observed. The results presented in this study suggest that xeric oak species such as Q. cerris are more sensitive to environmental factors in both δ13C and radial growth. According to the GAMM results, the more climate-sensitive Q. cerris showed better relationships with the analyzed factors than Q. robur. It was concluded that δ13C responds more strongly and quickly to climatic anomalies than TRW and that the analyzed climatic and environmental factors can be a reliable indicator of cambial productivity and stress periods of both oak species. Keywords: Dendrochronology, Dendrochemistry, Stable carbon isotope, Tree ring, Quercus, Drought, GAMM. Acknowledgments: This research was supported by the Science Fund of the Republic of Serbia, PROMIS, #6066697, TreeVita. TL acknowledge the financial support from the Slovenian Research Agency - research core funding No. P4-0107 Program research group “Forest Biology, Ecology and Technology” and research grant J4-8216 “Mortality of lowland oak forests - consequence of lowering underground water or climate change?” Note: This contribution is a summary of a study by Kostić S, Levanič T, Orlović S, Matović B, Stojanović DB. Xeric Turkey oak (Quercus cerris L.) is a more reliable climate indicator than hydric pedunculate oak (Q. robur L.) in the same stand conditions: Stable carbon isotope ratio (δ13C) and radial growth approaches (In press)

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is a non-native tree species in Slovenia with the potential to partially replace Norway spruce in our native forests. Compared to spruce, it has several advantages in terms of volume growth, wood quality and tolerance to drought. This is important given the changing climate in which spruce is confronted with serious problems caused by increasing temperatures and drought stress. At three sites (one on non-carbonate bedrock and deep soils, and two on limestone with soil layers of varying depths), 20 Douglas-fir and 20 spruce per site were sampled in order to compare their radial growth response to climate and drought events. The radial growth of Douglas-fir exceeds that of spruce by about 20% on comparable sites. It is more responsive to climate than spruce. Above-average temperatures in February and March have a significant positive effect on the radial growth of Douglas-fir. In recent decades, above-average summer precipitation has also had a positive influence on the radial growth of Douglas-fir. Compared to spruce, Douglas-fir is less sensitive to extreme drought events. Our results indicate that Douglas-fir may be a good substitute for spruce in semi-natural managed forest stands in Slovenia. The planting of Douglas-fir should be allowed in Slovenian forests, but the proportion of it in forest stands should be kept lower than is the case with spruce today.

The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions.

344 European beech tree-ring width chronologies

Sessile oak (Quercus petraea [Matt.] Liebl.) and Turkey oak (Quercus cerris L.) dominated mixed forests are common in low montane and hilly regions in Hungary. Here, we aimed to describe the long-term pattern and climatic responses of the radial growth of Q. petraea and Q. cerris in a xeric low-elevation forest, using retrospective tree-ring analysis for the period 1910–2019. We performed separate analyses with time series of full tree-ring (TRW), earlywood (EW) and latewood (LW) widths. Our results showed that the radial growth of the two species was largely synchronous over time, but became transiently divergent for a 20-year period after a drought in 1968, due to the greater-than-expected growth of Q. cerris and the supressed growth of Q. petraea. Precipitation was the major growth-limiting factor for both species, with a strong positive influence on LW particularly during the current early growing season (March-June), on EW in the previous late summer (August-September) and in the current early spring (March), and on all tree-ring traits in the previous December. The radial growth of both species was negatively related to temperature in the spring (May) and late summer (August) of both current and previous years. The climate-growth relationships showed general instability over time: the most striking temporal change was a gradual shift of positive correlations with precipitation and SPEI during the growing season from spring (March-May) to summer (June-August) since the 1980s over the analysed period. The two species had similarly low growth resistance to droughts in four studied pointer years (1968, 1993, 2002 and 2012), but Q. cerris exhibited a greater capacity to recover over the four post-drought years, and thus higher growth resilience, particularly after the drought of 1968. Our results contribute to the better understanding of the role of climate variability and droughts in the growth of the two co-existing species in transitional locations between closed forests and forest-steppes.