PD Dr. Georg von Arx

In Europe, oak tree-ring chronologies spanning millennia offer considerable potential for dendroclimatology. However, site conditions might influence the climate-growth relationships, particularly for species such as lowland European oak (Quercus robur/petraea) that grow under a range of soil moisture conditions. The inclusion of sub-fossil or archaeological samples in chronologies often introduces uncertainty regarding the soil moisture regime in which the trees grew, potentially impacting the contained signal and the suitability of millennia-long oak chronologies as paleoclimate proxies. Here, we present a rare example of a multi-parameter study on the quantitative wood anatomy of oak. We analysed the climate-growth relationships of earlywood vessel sizes, earlywood width and latewood width in trees from five nearby stands situated on wet and dry soils in north-eastern Switzerland that experienced the same atmospheric conditions. We observed a large variety of climate-growth relationships. And we observed both signal plasticity (variability of climate growth relationships between site categories) and classical signal instability over time. In fact, the only stable relationships are between earlywood vessel sizes in trees on wet soils and winter/early spring temperatures. The relationship between late spring/early summer precipitation and latewood width on dry soils is probably stable as well but less reliable. In both cases, the correlation coefficient reaches values as high as r = 0.6. We suggest that signal instability needs to be explored with further and larger datasets before oak can be reliably used as a paleoclimate proxy.

Ring-density parameters, such as maximum latewood density (MXD), blue intensity (BI), and quantitative wood anatomy (QWA), can be highly sensitive to summer temperatures. While MXD is traditionally obtained through resource-intensive X-ray densitometry, advancements in high-resolution image processing offer alternative methods for measuring density metrics. This study evaluates latewood BI (LWBI) chronologies developed from two image resolutions (Epson: 2400 dpi and Skippy: 6700 dpi) against QWA-derived MXD (aMXD) for whitebark pine (Pinus albicaulis, PIAL) in the Greater Yellowstone Ecoregion, USA. LWBI metrics exhibited robust linear relationships with June–August (JJA) maximum temperatures (i.e., R² = 0.27 for Epson and R² = 0.31 for Skippy; p < 0.01), but differences between image resolutions were not statistically significant. Spatial relationships were robust for LWBI, though the relationships with Epson and Skippy were similar. Additionally, Skippy may have captured a longer growing season signal (June–September) compared with Epson, while Epson improved with selections of a larger fraction of darkest pixels (e.g., 30–50 %). Our findings also indicate that% darkest pixel selections affect outcomes differently when measuring LWBI from Epson and Skippy images. This pilot study highlights the potential of LWBI as a faster alternative to QWA, with both metrics demonstrating significant climate sensitivity in PIAL. By successfully capturing strong temperature signals from PIAL, an understudied and ecologically critical species, this research supports the fusion of dendroclimatological applications to produce a more robust climate signal, as well as the development of millennial-length climate reconstructions in high-elevation ecosystems of North America.

Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotope compositions of tree-ring compounds preserve information about environmental waters; however, our understanding of their isotopic relationships is hampered by the lack of long-term data sets. We investigated correlations using unique 17-year (2006–2022) δ¹⁸O and δ²H time series of bi-weekly measured soil solution, modelled precipitation and xylem water, along with those of tree-ring α-cellulose and lignin methoxy groups from Norway spruce (Picea abies) across three Swiss forest sites. We show that tree-ring cellulose δ¹⁸O preserves water source information more effectively than δ²H, making it better suited for ecohydrological reconstructions. We propose δ²H of tree-ring lignin methoxy groups as an alternative proxy for soil water sources, supported by strong correlations where cellulose failed to track soil water isotopes. Significant linear isotopic relationships within and across sites enable the development of transfer functions that link tree-ring to water sources, particularly precipitation and xylem water. We exemplify how these transfer functions can be used to estimate the seasonal origin of water sourced by trees during the growth period. Our findings enhance the interpretation of environmental water isotope signals in tree rings and promote the use of tree-ring isotope-based tools for retrospective retrieval of forest water dynamics.

Southwestern North America has experienced significant temperature increases over the last century, leading to intensified droughts that significantly affect montane forests. Although tree-ring data have provided long-term context for this recent drought severity, the varying physiological responses of trees to climate variability make it challenging to disentangle the combined influence of temperature and soil moisture. Here we investigate complex climate-growth relationships in Rocky Mountain bristlecone pine (Pinus aristata) at a low-elevation and a high-elevation site using quantitative wood anatomy (QWA). Significant correlations with climate were found for low-elevation tree-ring width (TRW) and earlywood chronologies, including positive correlations with spring and early summer precipitation and drought indices and negative correlations with spring and early summer maximum temperatures. At high elevations, TRW and earlywood chronologies show positive responses to summer moisture, whereas latewood chronologies correlate positively with August and September maximum temperatures and negatively with August precipitation. We leverage this differing seasonality of moisture and temperature signals and compare the QWA data to known droughts. The earlywood lumen area is found to be highly responsive to drought because of its physiological reliance on water availability for maintaining turgor pressure during cell enlargement. We also observed a decline in temperature sensitivity at the high elevation site, suggesting shifts in the dominance of limiting factors. Integrating QWA with traditional dendrochronology improves interpretations of tree-ring data for use in climate reconstruction, offering detailed insights into tree physiological responses and the mix of environmental and developmental controls on cell growth.

Quantitative wood anatomy (QWA), which involves measuring wood cell anatomical characteristics commonly on dated tree rings, is becoming increasingly important within plant sciences and ecology. This approach is particularly valuable for studies that require processing a large number of samples, such as those aimed at millennial-long climatic reconstructions. However, the field faces significant challenges, including the absence of a publicly available comprehensive protocol for efficiently and uniformly producing high-quality wood thin sections for QWA along dated tree-ring series. This issue is especially critical for more brittle subfossil wood, in addition to fresh material from living trees. Our manuscript addresses these challenges by providing a detailed protocol for producing thin anatomical sections of wood and digital images, specifically tailored for long chronologies of tree-ring anatomy with an emphasis on conifer wood. The protocol includes step-by-step procedures for sample preparation, sectioning, and imaging, ensuring consistent and high-quality results. By offering this well-tried-and-tested protocol, we aim to facilitate reproducibility and accuracy in wood anatomical studies, ultimately advancing research in this field. It aims to serve as a reference for researchers and laboratories engaged in similar work, promoting standardized practices and enhancing the reliability of QWA data.

Interactions between biotic and abiotic stressors reduce forest health, particularly in high-elevation forests. Because trees are expected to resist biotic and abiotic stressors in unique ways, it remains unknown how specific processes, such as growth and defense, relate to tree survival in a compound disturbance environment. Comparing trees that either died or survived mountain pine beetle (MPB) provides a natural experiment to test how multiple stressors jointly mediate susceptibility to MPB. We cored whitebark pine in the Greater Yellowstone Ecosystem to measure growth, resin ducts, and xylem anatomy using standard quantitative wood anatomy techniques. Overall, anatomical measurements increased model accuracy by 7.1 % compared to ring widths alone. We found growth-defense tradeoffs for all trees; for resistant trees, however, resin duct density varied negatively with the pore space fraction (lumen) of tree rings – not the structural carbon fraction (tracheid walls). Despite showing less structural carbon and total growth at the time of the outbreak, susceptible trees displayed anatomical resistance in their early lives. Over time, susceptible trees had less positive growth responses during years of high snowpack, and more negative responses of lumen area and theoretical hydraulic conductivity during years of high temperatures and drought. Susceptible tree decline was catalyzed during the decade 1940, which coincides with first reports of the invasive white pine blister rust (WPBR) in the region. Together, our findings provide support that differential responses of whitebark to temperature and drought contributed to reduced structural carbon storage that, likely exacerbated by WPBR, predisposed trees to MPB mortality.

Central European forests experienced high rates of air pollution in the second half of the 20th century, especially along the borders of Czechia, Germany and Poland. Consequently, tree-growth declines were detected in heavily polluted forests. However, information about how pollution has influenced growth-climate responses beyond tree-ring width (RW) in pollution-affected forests remains sparse. In this study, we investigated the impact of high-level pollution during 1960s-1980s in Central Europe on the climatic signals of various tree-ring parameters of Norway spruce, including RW, latewood Blue Intensity (LWBI), and maximum cell wall thickness (CWT), to understand how tree growth and climatic sensitivity were affected. Tree-ring cores were collected from six temperature-limited high-elevation sites within four pollution-affected regions in Czechia and northern Slovakia. RW and LWBI were measured for all samples and CWT was produced from two sites with contrasting pollution impacts. Distinct pollution-related RW growth suppression was detected in 1970s to 1980s at several sites. LWBI and CWT chronologies were highly correlated (r _LWBI = 0.52–0.75; r _CWT = 0.63–0.68) with growing season (April-September) temperature and did not exhibit clear signs of distortion by pollution compared to RW (r _RW = 0.28–0.58). Pollution stress seemed to reduce tree growth by decreasing cell numbers and made RW less sensitive to climate. This study reveals that impacts of pollution on different tree-ring parameters varied which can further influence their climatic sensitivities. It provides valuable insight in improving the utility of pollution-affected tree-ring chronologies by choosing appropriate parameters, which can ultimately contribute to substantially improving the calibration of climate reconstructions from heavily polluted regions.

Quantitative wood anatomy is a crucial field increasingly used in dendrochronology due to its high intra-ring resolution and close link to ecophysiological processes. However, earlywood vessel chronologies in ringporous species often show low statistical quality, such as weak common signal strength and low expressed population signal (EPS). This raises questions about whether these limitations are inherent to the wood type or if methodological refinements could improve chronology robustness. This study evaluates how the amount of measured wood per ring (tangential width) and tree replication impacts the statistical quality and reliability of climate-growth relationships. Therefore, we conducted a systematic analysis using a highly replicated dataset (21 trees per site, 45 mm tangential width per tree) from Fraxinus excelsior and Quercus robur as a robust benchmark. We employed advanced image analysis, resampling, and data simulation  techniques. Our analyses show that the spread (uncertainty) of obtained climate correlation values increases with lower replication and common signal strength, with replication as the most influential factor, followed by within-tree accuracy linked to the tangential width. We recommend collecting at least two 5-mm cores (8–10 mm TW) per tree and sampling a minimum of 20 trees in environments without a strong limiting factor (low common signal strength). In contrast to common practice, we promote subsampling based on surface quality rather than high correlation with the tree-ring width master chronology and target an EPS ≥ 0.85 for earlywood vessel chronologies. Finally, careful screening within the array of earlywood vessel variables (first row, mean size, different quantiles, etc.) enables to maximize the signal strength. We believe that our approach, results, and recommendations can contribute to improving the robustness of quantitative wood anatomy chronologies in ring-porous species, but likely also in other wood types.

Introduction: Quantitative wood anatomy (QWA) along a time series of tree rings (known as tree-ring anatomy or dendroanatomy) has proven to be very valuable for reconstructing climate and for investigating the responses of trees and shrubs to environmental influences. A major obstacle to a wider use of QWA is the time- consuming data production, which also requires specialized equipment and expertise. This is why the research community has been striving to reduce these limitations by defining and improving tools and protocols along the entire data production chain. One of the remaining bottlenecks is the analysis of anatomical images, which broadly consists of cell and ring segmentation, followed by manual editing, measurements, and output. While dedicated software such as ROXAS can perform these tasks, its accuracy and efficiency are limited by its reliance on classical image analysis techniques. However, the reliability and accuracy of automatic cell and ring detection are key to efficient QWA data production.
Methods: In this paper, we target automatic ring segmentation and deliberately focus on the most challenging case, circular ring structures in arctic angiosperm shrubs with partly very narrow and wedging rings. This shape requires high precision combined with a large global context, which is a challenging combination for instance segmentation approaches. We present a new iterative regression-based method for more precise and reliable segmentation of tree rings.
Results and discussion: We show a performance increase in mean average recall of up to 18.7 percentage points compared to previously published results on the publicly available MiSCS (Microscopic Shrub Cross Sections) dataset. The newly added uncertainty estimation of our method allows for faster and more targeted validation of our results, saving a large amount of human labor. Furthermore, we show that panoptic quality performance on unseen species is more than doubled using multi-species training compared to single-species training. This will be another key step toward an AI-based version of the currently available ROXAS implementation.

Tree rings are crucial for reconstructing past climates, with maximum latewood density (MXD) as a key metric. However, wood integrity is critical for accurate MXD-based reconstructions, raising concerns when using potentially degraded relict wood. Quantitative wood anatomy (QWA) provides a morphometric alternative. We compared X-ray and QWA-derived density measurements from recent and five-millennia-old relict wood from Siberia's Yamal region. We measured bulk density and holo-cellulose-to-wood ratio and employed spectroscopic analyses to identify chemical factors affecting density loss. The findings indicate likely abiotic degradation in relict wood, evidenced by significantly lower bulk density, holo-cellulose content, and MXD than recent samples, while anatomical density and maximum radial cell wall thickness appeared unchanged. MXD-based estimates suggested 1.7°C colder June-August (JJA) temperatures 4,700 years ago, while QWA-based estimates indicated 0.4°C warmer JJA temperatures than the 20th-century mean. For relict wood with potential mass loss due to degradation, QWA is recommended over traditional MXD methods.

Increasing aridity is a major threat to forests worldwide. Understanding tree functional constraints under drought and their impacts on resilience and mortality among species is crucial to assess the impacts of global change on forests. We analyzed the long-term drought and atmospheric CO₂ responses in three Mediterranean co-occurring species with differing drought tolerances (Pinus pinaster < Pinus pinea < Juniperus oxycedrus). In this mixed forest, P. pinaster exhibited widespread mortality and mistletoe infection, P. pinea showed scattered mortality, and J. oxycedrus showed no decline. Using tree-ring data (1978–2016), we compared intrinsic water-use efficiency (iWUE) and xylem hydraulic traits in healthy and non-healthy individuals of both pine species and healthy junipers. Healthy P. pinaster trees produced a more hydraulically efficient xylem, with wider lumen tracheids, than non-healthy trees, whereas P. pinea showed no anatomical differences between health statuses. Healthy P. pinaster displayed greater anatomical plasticity, adjusting hydraulic conductivity and cell-wall thickness to water availability. Despite small differences in average iWUE, the response of iWUE to rising CO₂ and drought differed between species and health statuses. J. oxycedrus and P. pinea showed steady iWUE increases, but P. pinea experienced periods of stagnation following an extreme drought, later recovering regardless of health status. In contrast, iWUE in P. pinaster plateaued for over 20 years after a decline-inducing drought, particularly in non-healthy, mistletoe-infected trees. Differences in iWUE response to CO₂ and anatomical plasticity to drought may explain the contrasting mortality patterns among these coniferous species. Our results suggest a long-term decline spiral in P. pinaster induced by low hydraulic efficiency in drought-induced defoliated trees and limited physiological responses to rising CO₂ and drought. Increasing drought stress makes pine recovery increasingly unlikely.

Introduction: Quantitative wood anatomy is critical for establishing climate reconstruction proxies, understanding tree hydraulics, and quantifying carbon allocation. Its accuracy depends upon the image acquisition methods, which allows for the identification of the number and dimensions of vessels, fibres, and tracheids within a tree ring. Angiosperm wood is analysed with a variety of different image acquisition methods, including surface pictures, wood anatomical micro-sections, or X-ray computed micro-tomography. Despite known advantages and disadvantages, the quantitative impact of method selection on wood anatomical parameters is not well understood.

Methods: In this study, we present a systematic uncertainty analysis of the impact of the image acquisition method on commonly used anatomical parameters. We analysed four wood samples, representing a range of wood porosity, using surface pictures, micro-CT scans, and wood anatomical micro-sections. Inter-annual patterns were analysed and compared between methods from the five most frequently used parameters, namely mean lumen area (MLA), vessel density (VD), number of vessels (VN), mean hydraulic diameter (D_h), and relative conductive area (RCA). A novel sectorial approach was applied on the wood samples to obtain intra-annual profiles of the lumen area (A_l), specific theoretical hydraulic conductivity (K_s), and wood density (ρ).

Results: Our quantitative vessel mapping revealed that values obtained for hydraulic wood anatomical parameters are comparable across different methods, supporting the use of easily applicable surface picture methods for ring-porous and specific diffuse-porous tree species. While intra-annual variability is well captured by the different methods across species, wood density (ρ) is overestimated due to the lack of fibre lumen area detection.

Discussion: Our study highlights the potential and limitations of different image acquisition methods for extracting wood anatomical parameters. Moreover, we present a standardized workflow for assessing radial tree ring profiles. These findings encourage the compilation of all studies using wood anatomical parameters and further research to refine these methods, ultimately enhancing the accuracy, replication, and spatial representation of wood anatomical studies.

Robust, high-resolution proxy information on hydroclimate is critical for understanding the recent European drying in the context of natural variability. This is particularly true for Fennoscandia and the surrounding northern high latitude regions, where such records are scarce, and little is known about the physical drivers of these rare events. Recently, the potential of tree-ring Blue Intensity (BI) of Pinus sylvestris L. from cool drought-prone sites has emerged as a source of high-resolution hydroclimate information. Limitations to these proxies may however be linked to the analytical measurement resolution of the technique as well as potential color-related biases caused by the heartwood-sapwood transition and decay-associated discoloration of the tree-ring samples. These proxy uncertainties need to be addressed before the methodology can be used more systematically in the context of hydroclimate reconstructions. Here, we evaluate the reliability of BI tree-ring parameters, specifically regarding their ability to accurately track both low-frequency variations as well as hydroclimate extremes. This is accomplished by benchmarking these parameters against newly developed quantitative wood anatomical (QWA) data from Pinus sylvestris trees in southeast of Sweden. The ΔBI parameter shows a high similarity to its QWA analogue across scales ranging from interannual to centennial, suggesting that the Δ conversion efficiently overcomes the long-term trend biases seen in the raw BI data. The earlywood and latewood BI parameters record largely the same strong spring-summer precipitation signal, together explaining over 50 % of the variance in May-July precipitation, as do their QWA counterparts. However, both BI and QWA show a pronounced asymmetric response to precipitation extremes such that dry extremes are captured better than the wet extremes. This dry-biased extreme value capture needs careful consideration in future reconstruction efforts. We conclude that tree-ring BI holds significant potential for contributing to regional reconstructions, especially given the untapped opportunities to utilize the region’s extensive collection of historical pine material for paleoclimate research.

Key message: Local hydroclimatic conditions influenced black spruce xylem anatomy in boreal treed fens. Earlywood cells were sensitive to early summer temperature, indicating that future warmer climates could negatively impact the xylem structure. Abstract: Black spruce (Picea mariana) growing in treed boreal fens in North America face significant challenges due to anticipated warming and moisture deficits. To assess site and climate influence on black spruce xylem anatomy, we investigated two treed fens at different elevations (740 m and 320 m a.s.l.) in Alberta, Canada. We examined key xylem traits – cell number, cell lumen area, and cell wall thickness – comparing the two sites to assess the effects of local conditions. Additionally, we correlated these anatomical features with long-term temperature, precipitation, and vapor pressure deficit (VPD) data to evaluate the impact of inter-annual climate variability. We observed larger cell lumens and thinner cell walls in trees at the lower-elevation fen. Xylem climate responses were clearer at the higher-elevation fen, characterized by a more stable water table. Here, previous year summer temperatures were negatively associated with cell number. High temperatures and VPD during the current year late spring and early summer reduced earlywood lumen size. Precipitation showed marginal associations at both sites. This study demonstrates the utility of quantitative wood anatomy in understanding environmental influences on tree xylem anatomy in treed fens. Differences in climatic responses between nearby sites highlight the importance of local hydroclimatic conditions in shaping xylem structure. Notably, observed sensitivity of cell lumen area to spring and early summer temperature and VPD suggests that climate warming could significantly impact the xylem structure and water transport efficiency of black spruce in treed boreal fens.

The xylem anatomy of diffuse-porous tree species in temperate forests affects their water transport efficiency and drought resistance, thereby affecting their growth and survival. However, it remains unclear how xylem anatomical traits of different diffuse-porous species respond and adapt to warming and drying climate. Here, we assessed the main climate factors driving xylem anatomy of four dominant diffuse-porous tree species (Acer mono, Betula platyphylla, Populus davidiana, and Tilia amurensis) in the temperate forests of northeastern China. We identified distinct vessel patterns among the four species: A. mono and B. platyphylla exhibited larger, sparse vessels, whereas P. davidiana and T. amurensis displayed more small vessels. All xylem anatomical traits were categorized into three distinct clusters largely representing vessel number, vessel size and vessel density. Drought, caused by rising temperatures and declining precipitation, affected xylem formation, while the growth of the four species did not benefit from warming despite the rather low annual mean temperature of 3.0 °C. A. mono is mostly influenced by prior-year climate, and B. platyphylla has low climate sensitivity, while P. davidiana and T. amurensis respond promptly to current-year drought. Under continuously increasing warming conditions, A. mono and B. platyphylla adopted a more "conservative strategy" of reducing the vessel number, size, and density. Populus davidiana showed increased hydraulic safety at the expense of efficiency, while T. amurensis prioritized hydraulic efficiency. Our findings suggest that the ability of these species to persist under future climate scenarios will largely depend on their hydraulic strategies and the balance between growth and water use. Our results contribute to developing forest management practices dealing with preserving ecosystem stability and species diversity of temperate forests in the face of future climate change.

Forests are under pressure and going through rapid changes. However, current inventorying and monitoring (IM) programs are often either disjointed, too narrow in their scope and/or do not operate at fine enough temporal resolutions, which may hinder scientific understanding, the timely supply of information, fast decision making, and may result in the sub-optimal use of resources. For these reasons, there is an urgent need for Advanced Forest Inventorying and Monitoring (AIM) programs to (i) achieve expanded relevance (by augmenting data/information across ecosystem properties and trophic levels), (ii) have increased temporal resolution (by tailored data collection frequency), and (iii) make use of technological advances (by incorporating novel tools and technologies). The Advanced Inventorying and Monitoring for Swiss Forests (SwissAIM) initiative was launched in 2020 to address these needs. SwissAIM builds upon the foundation offered by the existing programs (e.g., national forest inventory, long-term forest ecosystem research, biodiversity monitoring). It aims to offer a collaborative and adaptive framework to enable integrated data collection, evaluation, interpretation, analysis, and modeling. Ideally, it will result in a more responsive system with respect to current and predicted biotic/abiotic stressors that will challenge Swiss forests. Developing such a system implies identifying the information needs of different stakeholders (e.g., science, policy, practice), related technical requirements, and governance frameworks. Here, we present (i) the main features of the SwissAIM initiative (vision, scientific questions and variables, governance and engagement), (ii) the main outcomes of the participatory design process (measurements, sampling, and plot design), (iii) the potential transferability of AIM initiatives outside Switzerland (timing, relevance, practicability), and (iv) the key messages that emerged (i.e., need for advancement, integration and transdisciplinarity, statistical underpinning). Since similar needs related to forest inventorying and monitoring are emerging throughout Europe and elsewhere, the objective of this opinion paper is to share our experience and promote a dialog with those interested in developing AIM initiatives in other countries and regions.

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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.

Tree cores are a highly valuable scientific resource. Annual growth ring data can, for example, improve our understanding of climate change impacts and effects of environmental pollution, allow for better annual estimations of tree growth patterns and carbon storage, and help quantify dynamics and changes in forest ecosystems. The value of coring trees for research has been weighted against concerns around the potential harm coring might cause to trees. To date, there is indeed limited research accurately quantifying the potential effects of coring on tree growth and only a handful of studies assessing its influence on mortality. Consequently, many European long-term forest inventorying and monitoring programs are concerned that tree coring might bias the repeated tree measurements in permanent plots, which they rely on for assessments of states and changes of forests. In this study, we assessed the effects of tree coring on the growth and mortality of three widespread European tree species approximately 10 years after they were cored. We used repeated tree measurements from permanent research sites in Switzerland and Ukraine. In Switzerland, we assessed 35 cored and 159 uncored Norway spruce (Picea abies) trees as well as 147 cored and 332 uncored silver fir (Abies alba) trees. In Ukraine, we assessed 348 cored and 6'611 uncored European beech (Fagus sylvatica) trees. We found no statistical evidence that coring negatively affected the growth or mortality of the three tree species assessed. Although we cannot rule out subtle effects on tree health and wood quality, our findings do not provide any evidence that coring affects or biases repeated measurements (such as DBH measures and recording of mortality) performed on the investigated tree species. Tree coring could therefore be considered more often for routine incorporation, particularly in long-term forest inventorying and monitoring programs and initiatives.

Widespread shrubification across the Arctic has been generally attributed to increasing air temperatures, but responses vary across species and sites. Wood structures related to the plant hydraulic architecture may respond to local environmental conditions and potentially impact shrub growth, but these relationships remain understudied. Using methods of dendroanatomy, we analysed shrub ring width (RW) and xylem anatomical traits of 80 individuals of Salix glauca L. and Betula nana L. at a snow manipulation experiment in Western Greenland. We assessed how their responses differed between treatments (increased versus ambient snow depth) and soil moisture regimes (wet and dry). Despite an increase in snow depth due to snow fences (28–39 %), neither RW nor anatomical traits in either species showed significant responses to this increase. In contrast, irrespective of the snow treatment, the xylem specific hydraulic conductivity (Ks) and earlywood vessel size (LA95) for the study period were larger in S. glauca (p < 0.1, p < 0.01) and B. nana (p < 0.01, p < 0.001) at the wet than the dry site, while both species had larger vessel groups at the dry than the wet site (p < 0.01). RW of B. nana was higher at the wet site (p < 0.01), but no differences were observed for S. glauca. Additionally, B. nana Ks and LA95 showed different trends over the study period, with decreases observed at the dry site (p < 0.001), while for other responses no difference was observed. Our results indicate that, taking into account ontogenetic and allometric trends, hydraulic related xylem traits of both species, along with B. nana growth, were influenced by soil moisture. These findings suggest that soil moisture regime, but not snow cover, may determine xylem responses to future climate change and thus add to the heterogeneity of Arctic shrub dynamics, though more long-term species- and site- specific studies are needed.