Understanding how the hydrological cycle of tropical regions has responded to recent climate change is critical for assessing ecosystem resilience, carbon cycling, and the risk of large-scale forest transitions. However, long-term observational records of precipitation remain sparse across much of the tropics, and existing datasets often disagree on both the magnitude and direction of rainfall trends. In particular, whether recent changes reflect general drying, wetting, or an amplification of rainfall seasonality remains unresolved.

This talk examines how stable oxygen isotope ratios (δ¹⁸O) preserved in annually resolved tree rings can provide large-scale, seasonally resolved insights into hydroclimate change. The analysis draws on an Amazon study based on oxygen isotope chronologies from two tree species with contrasting growth phenologies and hydrological settings: Cedrela odorata from terra firme forests, which forms annual rings during the wet season, and Macrolobium acaciifolium from seasonally flooded forests, which grows during the terrestrial phase coinciding with the Amazon dry season. Although sampled from sites separated by approximately 1000 km, large-scale atmospheric moisture transport and Rayleigh distillation processes impart a coherent basin-scale climatic signal to both records, allowing wet- and dry-season trends to be evaluated independently.

The two δ¹⁸O chronologies exhibit opposing long-term trends since around 1980, with increasing δ¹⁸O values in the dry-season record and decreasing values in the wet-season record, consistent with an intensification of rainfall seasonality. The talk highlights the specific ecohydrological and phenological conditions that make this type of inference possible, and discusses the distinct sources of uncertainty that can affect interpretation across different records. Key conditions relating to growth seasonality, moisture sourcing, and signal integration must be met in order to draw comparable conclusions from other tree-ring isotope datasets. The talk therefore outlines the potential and common pitfalls associated with applying tree-ring isotope approaches to assess large-scale changes in climate seasonality.

How to cite: Barcante Ladvocat Cintra, B., Gloor, E., C. A. Baker, J., Boom, A., Schöngart, J., Clerici, S., Pattnayak, K., and Brienen, R.: Intensification of the Amazon hydrological cycle inferred from tree-ring stable isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12811, https://doi.org/10.5194/egusphere-egu26-12811, 2026.

Tropical dendrochronology presents many challenges. Few tree species develop reliable annual growth rings that can be accurately dated to the calendar year. Accessing primary forests and old-growth trees requires significant labor and investment. Researchers have difficulty finding the trees, resulting in limited sample size, one of the key factors for the development of successful tropical tree-ring chronologies. Skepticism exists regarding whether Douglas's method should be the sole approach for dating tropical trees. However, cross-dating—finding a common growth pattern across a large area—remains the only way to accurately assign calendar years to growth rings. This method is essential for developing centuries-long tree-ring chronologies. Our studies demonstrate that Douglas's method works in tropical dendrochronology. Once trees are correctly dated, other methods can be applied, such as quantitative wood anatomy, isotopes, wood density, and radiocarbon dating. This study describes a nearly 10-year effort to construct a network of tropical tree-ring chronologies in eastern Amazonia. It includes the key challenges that prevented dating trees at some of the tropical sites visited. Samples of 342 trees of the species Cedrela odorata, distributed across seven locations, were collected from living and legally harvested trees in forests of eastern Amazonia. Three tree-ring width chronologies have been successfully dated, including a new tree-ring width chronology from Cedrela, in the Altamira National Forest, dated from 1885 to 2016. Provisional chronologies of tree-rings from Cedrela are presented here: (1) a 190-year record from Inupuku and a (2) 328-year chronology from Mukuru. Both sites are located in the Jari River valley, home to the tallest trees ever discovered in the Amazon basin. A third 113-year record from the Monte Alegre site, located in the Rio Paru State Forest. Our results demonstrate the influence of local physical and topographical soil attributes, in terms of their moisture retention capacity, on the successful development of tree-ring chronologies in some locations. Stand and gap dynamics, as well as sample size, also play an important role in whether trees can be dated or not. Despite these challenges, our efforts show that crossdating is possible in primary tropical forests, and the advantage of having precisely dated trees is the ability to learn about climate variability over the past centuries in the vast and largely unknown Amazonian territory.

How to cite: Granato, D., Borges de Lima, R., Armando Silva da Silva, D., Peter, B., Bastos Gorgens, E., Jose da Silva, J., da Costa Pereira, M., and Viana Brito, R.: Crossdating and the challenges in tropical dendrochronology: perspectives from a 10-year effort and seven site collections in eastern Amazonia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-89, https://doi.org/10.5194/egusphere-egu26-89, 2026.

Climate warming is increasing atmospheric moisture demand globally, intensifying hydroclimatic variability and ecosystem stress, particularly in climate-sensitive mountain regions. The Himalayan climate system, particularly Northewestern Himalayas (NWH), is shaped by moisture driven through Indian Summer Monsoon and Western Disturbances interacting with complex orography, resulting in highly dynamic climatic conditions. Recent increases in global temperatures have altered this circulation system, leading to enhanced climatic variability. However, long-term, region-specific climate records remain sparse across the NWH, limiting our understanding of these changes. Tree rings serve as high-resolution natural archives of past climate variability, and offer critical insights into the region's climatic history and its driving forces. The present study develops tree-ring chronologies from a dense network of five sites in the Baspa Basin, NWH, using 275 increment cores (89 from Cedrus deodara and 186 from Pinus wallichiana). Individual ring-width series were detrended using age-dependent splines, and chronologies were developed employing ‘Signal-free’ method. Composite regional chronologies were generated for both species through averaging same species ring widths as having high inter-site correlation and species-specific growth–climate relationships were assessed. The analyses identified vapour pressure deficit (VPD) as the dominant limiting factor of radial growth with spring VPD (February–April; FA-VPD) strongly constraining Cedrus deodara growth (r = −0.77) and summer VPD (June–July; JJ-VPD) limiting Pinus wallichiana growth (r = −0.63). VPD integrates the combined effects of temperature and humidity, influencing stomatal conductance and carbon assimilation, and thus exerting primary control on tree growth. While temperature shows a negative relationship and precipitation a comparatively weaker positive influence. Based on these relationships, we developed basin-scale, multi-season tree-ring reconstructions of FA-VPD (1771–2023 CE) and JJ-VPD (1834–2023 CE) using Cedrus deodara and Pinus wallichiana, respectively. These reconstructions explain approximately ~59% and ~40% of the variance in FA-VPD and JJ-VPD, respectively, during the calibration period. The FA-VPD reconstruction reveals a long-term increasing trend, characterized by two phases (1771–1917 and 1918–2023), with 1917 identified as a significant change-point year. In contrast, JJ-VPD shows a decreasing trend since the early twentieth century, consistent with enhanced monsoonal moisture availability in the basin. These divergent seasonal moisture trends imply future shifts in forest composition, with increasingly favourable conditions for Pinus wallichiana and heightened vulnerability of Cedrus deodara. Phase-wise teleconnection analyses indicate a weakening influence of El Nino Southern Oscillation and Interdecadal Pacific Oscillation, alongside an increasing role of the Indian Ocean Dipole, a pattern further supported by sea surface temperature spatial correlation analyses. Our findings highlight the critical role of large-scale climate drivers in shaping local hydroclimatic stress in the NWH. The seasonally resolved VPD reconstructions offer actionable baseline information for climate adaptation strategies, including forest management, species selection, drought preparedness, and risk reduction planning for climate-sensitive Himalayan communities.

How to cite: Lal, D., Shekhar, M., Dhyani, R., Singh, S., Sharma, A., and Chand, P.: Multi-Species Tree-Ring Networks reveals seasonal shifts in Vapour Pressure Deficit trends and evolving Ocean-atmospheric Teleconnections in the Baspa basin, Northwestern Himalayas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6980, https://doi.org/10.5194/egusphere-egu26-6980, 2026.

Living and relict Qilian juniper (Juniperus przewalskii Kom.) trees from the northeastern Tibetan Plateau provide a unique paleoclimate archive spanning centuries to millennia. Various climate signals reflected by Qilian Juniper tree-ring records from different elevations inspire us to investigate the temperature and precipitation covariance along the altitude. Here, we analyses temperature and precipitation measurements from 60 meteorological stations between 1139 and 3663 m asl on the northeastern Tibetan Plateau. We find that summer temperature and precipitation are positively correlated at higher elevations, while they show an inverse relationship at lower elevations. We also observe that anthropogenic warming has led to wetter (drier) conditions at higher (lower) elevations. Not captured by gridded climate data, our results suggest that tree ring-based hydroclimate reconstructions from arid Asian mountain systems are localised representations. We argue that warming-induced convective precipitation is altering the hydrological cycle of Asian ‘Water Towers’ through changes in plant growth, vegetation composition, snow cover, glacier extent, and river runoff.

How to cite: Gao, L., Bebchuk, T., Gou, X., and Büntgen, U.: Observational confirmation and dendrochronological implication of increasing temperature and precipitation covariance on the northeastern Tibetan Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8597, https://doi.org/10.5194/egusphere-egu26-8597, 2026.

Since the late 20th century, a newly emerging atmospheric teleconnection—the trans-Eurasian heatwave-drought train—has intensified remarkably during summer, driving concurrent heatwave-drought events from Eastern Europe to East Asia. Three centuries of tree-ring records confirm that the recent intensity of this pattern is unprecedented. Meanwhile, the circumglobal teleconnection, which historically dominated continental-scale Eurasian heatwaves, shows no discernible trend under global warming—signaling a fundamental shift in Eurasian summer climate dynamics. The mechanism involves Rossby wave propagation linked to warming sea surface temperatures in the Northwestern Atlantic and enhanced Sahel precipitation, both amplified by the combined effects of anthropogenic warming and natural variability. Land-atmosphere feedbacks through soil moisture deficits further intensify the pattern regionally. Climate projections indicate that anthropogenic forcing will continue to strengthen this pattern throughout the 21st century.

How to cite: Kim, M.-S., Jeong, J.-H., Yoon, J.-H., Kim, H., Wang, S.-Y. S., Woo, S.-H., and Linderholm, H. W.: Emerging trans-Eurasian heatwave-drought train in a warming climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8763, https://doi.org/10.5194/egusphere-egu26-8763, 2026.

Most current knowledge of past hydroclimatic variability over the last millennium in Western Europe is derived from tree-ring records. However, only a limited number of these archives span the entire millennium, which limits our ability both to place recent climate change within a long-term perspective and to characterize past climatic periods with sufficient resolution. Consequently, climatic conditions during the Medieval Climate Anomaly (MCA; ~900–1250 CE), generally considered relatively warm, as well as the transition toward the cooler conditions of the Little Ice Age (LIA; ~1350–1850 CE), remain poorly constrained, in terms of their temporal and spatial heterogeneity across Europe. In France, a quasi-millennial tree-ring δ¹⁸O chronology for the Paris basin (δ¹⁸O_PB), spanning the periods from 1046 to 1240 CE and from 1306 to 2007 CE, has been developed. However, data remain lacking for the transitional interval between the MCA and the LIA, a period that may have been critical for past societies and for understanding the dynamics of long-term climate variability.

In this study, we use oak tree-ring cellulose δ¹⁸O, a robust proxy for hydroclimatic conditions in lowland regions. Five site-specific δ¹⁸O chronologies were developed: one based on living trees and four derived from oak beams from medieval buildings, all located in central-western France. Correlations with δ¹⁸O_PB over overlapping periods range from 0.52 to 0.72, allowing the central France chronologies to be merged with δ¹⁸O_PB to produce a continuous millennial δ¹⁸O record spanning 1046–2023 CE. The strongest relationships with instrumental climate data over 1901–2023 CE were observed for June–August SPEI (r = −0.71), maximum temperature (r = 0.65), and May–August precipitation (r = −0.57). The final reconstruction was calibrated against June–August SPEI, which showed the highest predictive skill (r² = 0.50) and the greatest temporal stability across the calibration/verification split periods.

Hydroclimatic conditions are characterized in terms of long-term trends, regime shifts, and extremes, with particular emphasis on the transition between MCA and LIA. The results provide new insights into past summer drought variability in the region, revealing that the most extreme events occurred toward the end of the MCA (e.g. 1222, 1252, 1287, and 1331 CE). In contrast, drought conditions in the last decade (2014–2023 CE) are unprecedented over the past millennium and occur within a broader, statistically significant drying trend that has developed over the past century.

How to cite: Hureau, C., Daux, V., Penchenat, T., Le Digol, Y., Couturier, Y., Régnier, E., and Gautier, E.: Tree-ring δ18O illuminates hydroclimatic context during the Medieval Climate Anomaly–Little Ice Age transition in central-western France, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18133, https://doi.org/10.5194/egusphere-egu26-18133, 2026.

Stomatal conductance (g_s) regulates CO₂ and water fluxes of plants. Although experiments have shown that g_s decreases with elevated CO₂, it is unclear how g_s is responding in situ to long-term exposures to rising CO₂ and a changing climate. Tree ring isotope analysis provides a unique method to assess tree ecophysiological responses to long-term exposures of slowly changing environmental conditions. In particular, it has been suggested that changes in g_s can potentially be inferred from tree ring stable oxygen isotope ratios (δ¹⁸O_trc). Several studies have indeed used δ¹⁸O_trc trends to conclude that g_s has not significantly changed from pre-industrial values. However, it remains unclear whether δ¹⁸O_trc is sufficiently sensitive to detect the magnitude of change in g_s expected due to CO₂ increases and climatic changes. Here, we evaluate the sensitivity of δ¹⁸O_trc trends to CO₂ and climate induced changes in g_s, and to VPD and temperature increases since the beginning of the 20th century, using current theoretical models. We find that temporal changes in g_s only significantly affect δ¹⁸O_trc trends when the Péclet effect is present, and then only in dry climates. In contrast to the weak effects of g_s on δ¹⁸O_trc trends, we find that temporal increases in VPD and temperature, independent of changes in g_s, have far greater contributions to δ¹⁸O_trc trends. Thus, this increasingly popular method should be used with caution, because it is highly challenging to unambiguously attribute trends in δ¹⁸O_trc to changes in g_s. Despite current limitations, we recommend how future studies can address these challenges in efforts to detect long-term g_s trends from tree ring records.

How to cite: Carter, I., Brienen, R., and Gloor, E.: Can oxygen isotopes in tree rings be used to detect stomatal responses to global change?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5090, https://doi.org/10.5194/egusphere-egu26-5090, 2026.

Forests are central to climate-change mitigation but are increasingly threatened by global change components, such as more frequent extreme weather and climate events (particularly drought and heatwaves) and increasing nitrogen deposition, resulting in great uncertainties for the future of the essential ecosystem services they provide. Drought and heatwaves impair physiological mechanisms underpinning tree growth and forest productivity, and they may trigger tree mortality, thus constraining the forest carbon sink. On the one hand, nitrogen deposition stimulates tree growth in nitrogen-limited forests, but when exceeding the empirical nitrogen critical load could cause forest dieback, through soil acidification and nutrient imbalances, but also by making trees more vulnerable to drought. Many questions remain: How do global change components interact and affect forest functioning? Which tree ecophysiological mechanisms are involved?  Are those mechanisms synchronized at tree and ecosystem scales (in terms of temporal trends and intra-annual seasonal changes)? Does nitrogen deposition affect tree and forest responses to climate extremes under a CO₂ richer world? The NEXTRES project aims at addressing these questions by applying a multi-scale approach combining tree-based measurements (including long-term growth and stable carbon, oxygen and nitrogen isotopes together with intra-annual scale carbon isotope analyses) to ecosystem responses (Gross Primary Production and Evapotranspiration). We studied eleven forest sites along climatic and nitrogen deposition gradients (3–42 kg N ha⁻¹ yr⁻¹) across Europe, within the ICOS and ICP Forests networks, focusing on four widespread tree species (Fagus sylvatica, Quercus spp., Picea abies, Pinus sylvestris). Across sites, basal area increment generally declined during recent climate extremes (e.g. the 2018 drought), with a stronger response in the case of broadleaf vs. conifer species, followed by recovery in subsequent years at most of the sites. Preliminary isotope results for Fagus sylvatica at two sites show contrasting responses: intrinsic water-use efficiency (iWUE) increased during the 2018 drought at Sorø (Denmark), coinciding with reduced growth, whereas a severe late frost at Collelongo (Italy) reduced growth without a clear iWUE response, suggesting different plant strategies in terms of leaf gas exchanges and carbon allocation. Preliminary intra-annual δ¹³C analyses from Picea abies trees in Davos (Switzerland) reveal higher and more variable δ¹³C values during the extreme year in 2018, with elevated values in latewood compared to earlywood, highlighting strong seasonal modulation of drought responses. The coupling between tree-level and ecosystem responses will be assessed at the multidecadal and intra-seasonal scale, as well as the contribution of nitrogen deposition in modulating forest vulnerability and resilience to climate extremes.

Acknowledgments. Project funded by the European Union - NextGenerationEU under the National Recovery and Resilience Plan (PNRR) - Mission 4 Education and research - Component 2 From research to business - Investment 1.1 Notice Prin 2022 - DD N. 104 del 2/2/2022, title “Effects of nitrogen deposition and climate extremes on European forests: combining stable isotopes in tree rings and ecosystem fluxes (NEXTRES)”, proposal code 202299J927 - CUP J53D23002640006. We thank all collaborators at the forest sites for assistance in the field.

How to cite: Guerrieri, R., Montedoro, M., Berlanda, S., Arcidiaco, L., Rossi, M., Mazzenga, F., Rinne-Garmston, K., and Matteucci, G. and the ICOS and ICP Forests collaborators: Forest responses to nitrogen deposition and climate extremes as assessed by combining stable isotopes in tree rings and ecosystem fluxes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12479, https://doi.org/10.5194/egusphere-egu26-12479, 2026.

Stem radial growth is driven by the interaction between environmental conditions and tree physiological processes. As a result, tree rings serve as valuable natural archives, recording environmental information over time. In tropical forests, data on past climate variability and historical canopy greenness—an important indicator of forest health—are often limited in duration. Studying tree rings can thus provide essential insights into historical climate dynamics and canopy condition, helping us better predict the responses of tropical forests to global environmental changes. Here we present the first ring-width index chronologies (RWI) and canopy greenness (NDVI) time series of Zanthoxylum rhetsa (Roxb.) DC. from three moist forest sites in Bangladesh aligned along a gradient of increasing human disturbance. We compared historical annual radial growth rates with monthly, seasonal and annual climate data and NDVI values derived from high resolution Landsat images. Our analyses showed that the growth of Z. rhetsa is primarily influenced by pre-monsoon temperatures and monsoon precipitation, with pre-monsoon climate signals becoming stronger in recent decades. The signal strength of the RWI chronologies, however, varied across study sites along the disturbance gradient, with stronger signals in the sites with low disturbance intensity. At the ecosystem level, canopy greenness (NDVI) was highly correlated with tree growth rates over the past two decades. NDVI showed high sensitivity to drought, particularly at drier sites. Global warming and drought are detrimental to forest health and thus limiting the carbon sequestration potential of moist tropical forests. By taking Zanthoxylum rhetsa as a model tree species in three Bangladeshi moist tropical forests we demonstrate how tree-ring analysis can be combined with remote sensing to reconstruct canopy dynamics for periods preceding the availability of satellite imagery for NDVI calculations that could be replicable to other tropical forests.

How to cite: Bhattacharjee, K., Islam, M., Braeuning, A., Gebrekirstos, A., Khan, M. A. S. A. K., Khan, F. N., Hassan, B., Hasan, H., and Rahman, M.: Coupled dynamics of tree-ring growth and canopy greenness (NDVI) along a disturbance gradient in South Asian moist tropical forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1816, https://doi.org/10.5194/egusphere-egu26-1816, 2026.

Intrinsic water use efficiency (iWUE) quantifies the trade-off between carbon gain and water loss providing an indicator of stomatal regulation in response to environmental change. iWUE can be estimated for different temporal and spatial scales, from sub-daily to annual and from leaf to ecosystem scale. Tree-level iWUE estimates are commonly derived from stable carbon isotope compositions (δ¹³C) in tree rings. Laser ablation technology facilitates the analysis of δ¹³C at fine intra-ring resolution, providing insights to intraseasonal iWUE variations. Despite the promise of intraseasonal iWUE derived from tree-ring archives, links and discrepancies between iWUE estimates representing different scales are poorly understood.

This study investigates intraseasonal iWUE over 2002–2019 in a Scots pine dominated stand (Hyytiälä, southern Finland) at three spatial scales: shoot, tree and ecosystem scale. Empirical iWUE estimates are derived from shoot gas exchange, tree-ring δ¹³C and eddy covariance (EC). iWUE estimates were integrated to temporal resolution corresponding to tree-ring subsections using growth modeling and assimilation-based weighting. To understand differences in these iWUE estimates, we apply a multi-layer, multi-species, soil-plant-atmosphere-transfer model (pyAPES).

The level differences between shoot-, tree- and ecosystem-scale iWUE estimates were in line between measurement- and model-based estimates. Both showed that ecosystem-scale iWUE was 40% lower than shoot- or tree-scale iWUE. Model results suggested half of this difference was explained by the presence of other species in the stand and understory. Most of the remaining difference was attributed to neglecting the difference between leaf and air temperature in the calculation of ecosystem-scale iWUE.

δ¹³C-based iWUE correlated moderately with EC-based iWUE at inter- and intra-annual resolutions (r=0.58). δ¹³C-based iWUE correlated more strongly with modelled iWUE (ecosystem, tree, shoot) at both inter- and intra-annual resolutions (r=0.74–0.87), suggesting modelled iWUE may be more robust over multi-decadal timeframes than EC-based iWUE. Clearest miss-matches between intraseasonal δ¹³C-based iWUE and EC-based iWUE (or modelled iWUE) were during the two dryest years of the study period. This may be caused by remobilization of reserves, or other drought related processes affecting isotopic fractionation or, alternatively, uncertainties in dating wood formation processes during drought. Plausibly this indicates that tree-ring δ¹³C is not a robust indicator of iWUE during severe drought but rather provides means to pinpoint periods of such conditions.

How to cite: Leppä, K., Launiainen, S., Tikkasalo, O.-P., Sahlstedt, E., Young, G. H. F., Schiestl-Aalto, P., Kolari, P., Tang, Y., and Rinne-Garmston, K. T.: Can leaf-to-ecosystem-scale process modeling resolve differences in multi-scale intrinsic water use efficiency estimates?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7032, https://doi.org/10.5194/egusphere-egu26-7032, 2026.

Competition is a key ecological process for forest stands, as it directly regulates resource availability and thereby tree growth and mortality, ultimately shaping stand structure and composition.

In this study, we field-collected competition measurements and dendrochronological analyses to examine how individual tree characteristics (age and size) and competitive status (Hegyi index) interact to modulate growth, drought-resilience components (resilience, recovery and resistance), and climate sensitivity (quantified via climate–growth correlations) of Norway spruce (Picea abies), silver fir (Abies alba) and Scots pine (Pinus sylvestris), sampled at 11, 8 and 6 sites, respectively, across Central and Eastern Europe. 

Building on ecological theory, we expect competition to have a stronger effect on tree radial growth during non-disturbance periods and to lose importance when disturbance events occur. Specifically, we expect drought resistance and recovery to vary nonlinearly with competitive pressure: at low competition, reduced demand and a more favourable microclimate may buffer drought impacts, whereas at intermediate–high competition, resource limitation should dominate and reduce performance. We further hypothesize that canopy-dominant trees recover faster after drought due to better access to resources.

Preliminary results show that competitive status strongly affects radial tree growth rates while climate sensitivity and resilience appear to be driven primarily by local site conditions and species-specific traits and only secondly by competitive status. Trees under higher competitive pressure generally exhibited higher resistance and longer recovery periods and showed weaker sensitivity to climatic conditions translating into generally lower resilience; however, responses vary widely among the three species.

Our study provides new insights into how competition, individual tree characteristics, and climate interact to shape growth rates, climate sensitivity, and drought tolerance. Our findings clarify how competition and stand density shape growth and drought responses across climates. This can guide climate-specific density targets (e.g., thinning intensity) to reduce drought impacts and improve resilience, and can support evidence-based forest policy and adaptive management.

How to cite: Partemi, R., Castagneri, D., Popa, A., Popa, I., Klisz, M., Jeleń, J., Koszelak, A., Svoboda, M., Bošeľa, M., Poltak, D., Levanič, T., Dieni, R., Buras, A., and Jevšenak, J.: The effect of competition on radial growth, drought resilience and climate sensitivity of three conifer species across Central and Eastern Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6590, https://doi.org/10.5194/egusphere-egu26-6590, 2026.

Climate change is expected to increase both the frequency and the intensity of climate extremes, such as drought events in mountain ecosystems. Thus, in a climate change perspective, the resilience of Alpine forests is directly linked to their capacity to adapt to extreme events and cope with water scarcity and high temperatures. Investigating the response of different tree species is essential to understand the complexity of forest ecosystem adaptation, resistance and resilience to severe drought periods and the role of forests in mountainous areas. Besides, in high-altitude forests, plant species growing in wetter terrains have a smaller safety hydraulic margin and are possibly less resistant than plant species raising in dry environments because of their differences in physiological responses and evapotranspiration processes.

Therefore, it is interesting to focus on a comparative study between two areas differing in terms of climate and ecology, a dry and a wet site, in order to analyse which environment is more capable to cope with extreme conditions. In the context of the Agile Arvier project, supported by funding from the European Union’s economic recovery plan, we carried out dendrochronological analyses by assessing climate-growth relationships and applying drought ‘resilience indices’ (RRR) based on tree-ring width. The drought severity was defined by the Standardised Precipitation Evapotranspiration Index (SPEI).

In this survey, the monitoring sites are located in the western Alps, (Italy, Aosta Valley region). One site, situated in Torgnon is characterized by dry conditions while the other site, located in Champorcher displays wet conditions. In both sites, two tree species, Larix decidua Mill. and Picea abies (L.) H.Karst., were sampled for tree-ring analyses at four different altitudes: 1500, 1800, 2000 and 2200 m a.s.l.

Our results highlight the contrasting water use strategies between larch and spruce and show differences in physiological and anatomical responses to drought stress. Specifically, we show that species responses vary with elevation and site conditions (dry versus wet), and that these differences become particularly evident during specific anomalous years. However, analyses across different altitudes introduce some uncertainties, making it difficult to draw a definitive conclusion about which species exhibits a more efficient recovery from extreme heat and drought events.

Furthermore, these changes are occurring rapidly in the Alps, with important consequences for tree species adapted to strong climate seasonality and short growing season, altering the role of Alpine European larch and Norway spruce forests in carbon sequestration and mitigation of climate change.

How to cite: Guarnieri, C., Oggioni, S. D., Oddi, L., Koliopoulos, S., Ferraris, D., Filippa, G., Grosso, F., Morra di Cella, U., Pogliotti, P., and Galvagno, M.: Heat and drought in the Alps: comparative tree-ring study between European larch and Norway spruce growing in dry and wet conditions , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12161, https://doi.org/10.5194/egusphere-egu26-12161, 2026.

Tree-ring studies commonly rely on stand-level chronologies derived from ten or more trees and interpret growth responses at the annual scale. While this approach has been highly successful for detecting broad climate signals, it obscures individual-level variability and collapses intra-annual processes that regulate tree growth and water relations. Yet key physiological responses to forest density—particularly those related to water stress—operate at the scale of individual trees and days to weeks rather than years. Providing physiological context to annual tree-ring records may therefore be essential for assessing whether intermediate density reductions translate into greater tree hydraulic safety. 

Here, we investigate how forest density affects tree growth and water relations by combining annual tree-ring data with intra-annual and spatially explicit structural measurements in a forest density experiment established in 2019 on nutrient-poor sandy soils in the Netherlands. The experiment comprises four density treatments (control, high thinning ~20% removal, shelterwood ~80% removal, and clearcut) across three temperate tree species (Fagus sylvatica, Pseudotsuga menziesii, and Pinus sylvestris). Our structural measurements (as captured by terrestrial laser scanning) reveal that local tree density varies strongly within treatments, with intra-treatment variability reaching up to 50%. This heterogeneity allows us to construct a continuous density gradient at the individual-tree level rather than relying solely on treatment- or stand-level averages, which commonly mask divergent individual responses in aggregated tree-ring chronologies. 

Tree-ring analyses show a consistent increase in annual growth with decreasing stand density. However, high-frequency dendrometer measurements indicate that this enhanced growth is not necessarily accompanied by improved tree water status, suggesting that reduced competition does not automatically translate into greater hydraulic safety. We propose that this decoupling arises from compensating mechanisms such as increased evaporative demand under more open canopies and higher water uptake by understory vegetation. Overall, our results demonstrate that integrating annual tree-ring records with intra-annual physiological measurements and high-resolution forest structural data provides essential context for interpreting growth responses to forest density. They further indicate that tree water and density relations are more complex than commonly assumed, with multiple compensating processes potentially masking density effects. This multi-scale perspective enables a shift from purely correlative inference toward a more process-oriented understanding of how forest density shapes tree growth under increasing drought stress.

How to cite: Meijers, E., de Vries, J., Nabuurs, G.-J., and Sterck, F.: Tree rings in context: linking annual growth, intra-annual water relations, and forest structure in a density experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17435, https://doi.org/10.5194/egusphere-egu26-17435, 2026.

Reconstructing masting, the variable and synchronized seed production by a plant population, is key to assessing trees species resilience to past climate variability and predict fecundity of forest ecosystems under global warming. Masting has shifted in recent decades, linked to climate warming, with consequences for seed production and forest reproduction, and wider cascading effects on forest food webs. Nevertheless, we have little understanding of natural long-term variability in masting, and no method to reconstruct masting in the absence of annual seed-crops observations.

Here, we investigated tree-ring width and a wide range of wood anatomical traits to disentangle the effect of masting and drought on wood anatomy, using individual times series (1980-2022) from Fagus sylvatica (L.) cores sampled in Woodbury (UK). Results showed that tree-ring width and the majority of wood anatomical traits were correlated with current-year May temperature, precipitation, and SPEI drought index, while stronger correlations were observed with previous-year summer conditions. In contrast, masting, quantified as seed production, mainly correlated with summer conditions two years prior. This complex multi-year pattern, supported by literature, is further reinforced by the evident one-year lag between the TRW chronology and the seed production time series.

These results set the premises for the implementation of a structural equation model that incorporates the underlying connections between biotic and abiotic variables. This approach will establish the possibility of disentangling of drought and masting effects on wood anatomy, and provide the basis for masting reconstructions using wood anatomy. The reconstruction of past masting events beyond current limitations is of extreme ecological relevance under ongoing climate condition and highlights the potential offered by wood anatomy in this framework.

How to cite: Resente, G., Lehejček, J., Hacket Pain, A., and Ascoli, D.: Unveiling secrets from the past: wood anatomy to disentangle masting and drought, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18490, https://doi.org/10.5194/egusphere-egu26-18490, 2026.

Antiquity was a formative era for Europe with a lasting cultural impact on the continent. In the densely forested regions north of the Alps, material culture was characterised by the use of wood as a primary raw material. For over half a millennium (ca. 1st century BCE–5th century CE) the Romans dominated large parts of western and central Europe. They introduced numerous innovations and new species like wine (Vitis vinifera), sweet chestnut (Castanea sativa), walnut (Juglans regia) into their north-western provinces. But above all, the Roman presence meant an anthropogenic influence on natural landscapes on an unprecedented scale. In the light of current discussions about limited growth, scarcity of resources and modern concepts of sustainability, the question arises as to how an ancient state apparatus managed to satisfy the increasing demand for the fundamental resource of wood over the course of its several hundred years of existence - and at what price.

In contrast to prehistory, Antiquity is the earliest period for which we have written sources for the areas north of the Alps. However, from the historical record the drivers behind the Roman timber economy and its impact on woodland exploitation and forest dynamics remain poorly understood. To address this, we collected empirical evidence spanning a full millennium (300 BCE–700 CE) to study forest exploitation in Antiquity. Our unique dataset of 20.397 dendrochronologically dated archaeological woods reflects decades of dendroarchaeological work from ca. 30 laboratories in France, Germany, Switzerland, Austria, Belgium and the Netherlands. Our investigations reveal significant increases in woodland exploitation during Roman occupation, with regional differences in onset, intensity, and duration. With improved infrastructure, and organization Roman logging increasingly extended into primary forests. The 3rd century CE marks a tipping point, with sharp declines in wood use and long-distance transport, alongside evidence of overexploitation of old-grown forests. Late Antiquity is characterized by an overall decline in felling activities during the 4th and 5th centuries and a reestablishment of old-grown forests. These findings demonstrate how Roman imperial expansion fundamentally reshaped woodlands north of the Alps and contribute to the environmental and economic history of European Antiquity.

How to cite: Seim, A., Muigg, B., and Haneca, K. and the interdisciplinary dendroarchaeology team: Woodlands of Antiquity: Roman forest exploitation and timber economy between the Alps and the Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9314, https://doi.org/10.5194/egusphere-egu26-9314, 2026.

Germany has one of the most extensive railway networks in Europe. Due to the effects of climate change and the increasing frequency of extreme weather events, there is a growing risk to railway infrastructure posed by poor vitality of trees along rail tracks. Due to the forest edge effect, these trackside trees are exposed to greater variation in temperature and humidity, and are more strongly affected by weather extremes than their equivalents within a forest stand.

The project RailVitaliTree (Tree vitality monitoring and modelling of drought-related risks along railroads with remote sensing and dendroecology) has a multidisciplinary approach, using remote sensing, dendroecological, and hydroclimatic analyses, to study tree vitality and microclimatic conditions along the German railway network. For this, increment cores of Quercus robur and Pinus sylvestris were extracted at four sites per species, where each site consists of a subsite along the railway and a corresponding reference in the forest.

Our results show that trees along the railway had higher radial growth than reference trees in the forest. In fact, although mean series produced by pooling all trackside and all reference trees display that the growth trend of trackside and reference trees is highly synchronous (Q. robur GLK = 0.87; r = 0.83 and P. sylvestris GLK = 0.82; r = 0.60), the mean ring width and basal area increment of trackside trees were higher than that of the reference trees. So why do these trees seemingly grow better along railway tracks?

Despite more radial growth, trackside trees of either species did not show a notably stronger response to climate parameters than the reference. However, there was a greater relative decrease in ring width and basal area increment of trackside trees in both species during known drought years. In order to investigate this difference in sensitivity and growth of trackside trees during drought events we use a high-resolution, species-specific drought-stress index developed by the German Meteorological Service, identifying when plant-available soil water is below drought thresholds. Through this work, we aim for a deeper understanding of this special type of forest edge, so to better assess its possible impacts on the railway system.

How to cite: Häusser, M., Hannak, N., Billig, L., Kurtz, W., Schmidt-Walter, P., and Bräuning, A.: How do oak and pine cope with edge effects along railway tracks?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18852, https://doi.org/10.5194/egusphere-egu26-18852, 2026.

Climate-driven changes in high-elevation forest distribution and reductions in snow and ice cover have major implications for ecosystems and global water security. In the Greater Yellowstone Ecosystem of the Rocky Mountains (United States), recent melting of a high-elevation (3,091 m asl) ice patch exposed a mature stand of whitebark pine (Pinus albicaulis) trees, located ~180 m in elevation above modern treeline, that date to the mid-Holocene (c. 5,950 to 5,440 cal y BP). Here, we used this subfossil wood record to develop tree-ring-based temperature estimates for the upper-elevation climate conditions that resulted in ancient forest establishment and growth and the subsequent regional ice-patch growth and downslope shift of treeline. Results suggest that mid-Holocene forest establishment and growth occurred under warm-season (May-Oct) mean temperatures of 6.2 °C (±0.2 °C), until a multicentury cooling anomaly suppressed temperatures below 5.8 °C, resulting in stand mortality by c. 5,440 y BP. Transient climate model simulations indicate that regional cooling was driven by changes in summer insolation and Northern Hemisphere volcanism. The initial cooling event was followed centuries later (c. 5,100 y BP) by sustained Icelandic volcanic eruptions that forced a centennial-scale 1.0 °C summer cooling anomaly and led to rapid ice-patch growth and preservation of the trees. With recent warming (c. 2000–2020 CE), warm-season temperatures now equal and will soon exceed those of the mid-Holocene period of high treeline. It is likely that perennial ice cover will again disappear from the region, and treeline may expand upslope so long as plant-available moisture and disturbance are not limiting.

How to cite: McWethy, D., Pederson, G., Chellman, N., Toohey, M., Jungclaus, J., Lee, C., Stahle, D., Martin, J., Alt, M., Kichas, N., Whitlock, C., and McConnell, J.: Dynamic treeline and cryosphere response to pronounced mid-Holocene climatic variability in the US Rocky Mountains, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13123, https://doi.org/10.5194/egusphere-egu26-13123, 2026.

Tree‑line shifts are a key response of forest ecosystems to global warming, especially in high‑mountain ranges where climatic gradients are steep. While rising temperatures would suggest upward migration, actual tree‑line dynamics are also modulated by water availability and historic land‑use intensity. We examined tree‑line changes in the Lesser Caucasus over the past 25 years using a combination of dendrochronological data from 15 high‑elevation sites and remote‑sensing images spanning the region’s diverse climates from humid subtropical conditions near the Black Sea to semi‑arid regimes in the southeast. The land-cover classification with Landsat 5, 8 and 9 imagery (30x30m spatial resolution) from the years 1998 and 2023 shows a general upward trend of tree-lines but with strong spatial variations: the humid northwestern part experienced advances of up to 2.2m/year, whereas the more arid southeastern sector recorded retreats of up to 1.2m/year. Tree‑ring width chronologies reveal a weak, positive relationship with winter and summer temperatures, indicating improved growth under a warming climate. Water limitation in tree-ring width is slightly stronger in the drier northeast of the Lesser Caucasus than in the more humid northwest. But the signal is generally weak, there is no clear hydroclimatic trend and the spatial differences may only reflect the uneven distribution of species across the sampling network. Interpretation of these findings suggests warmer summers under rather constant moisture regimes have permitted tree growth beyond current tree-lines. However, at mid‑ and low‑latitudes, tree-lines on south‑facing slopes are usually situated lower than on north‑facing slopes because water limitation - not thermal limitation - dominates on the sun‑exposed aspect. In our study area, we also observe lower tree-lines on south‑facing slopes, yet those same slopes exhibit the strongest upward shifts over the last three decades. Hence, tree-line dynamics cannot be explained by temperature or drought alone. The most plausible additional drivers include snow dynamics and the recent reduction of anthropogenic pressure (e.g., reduced grazing and illegal logging) that has enabled upslope forest expansion, especially on south‑facing slopes. Further monitoring of tree growth dynamics across the Caucasus region, and particularly in the southern Lesser Caucasus, where tree-ring data are currently lacking, would be essential to resolve the observed tree-line shifts and anticipate potential future changes.

How to cite: Schneider, L., Weber, A., Martin-Benito, D., Dhyani, R., Seim, A., Gavashelishvili, A., Kvaratskhelia, R., and Profe, J.: Climatic and anthropogenic drivers of tree-line shifts in the Lesser Caucasus over the past 25 years revealed by tree-rings and remote sensing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17131, https://doi.org/10.5194/egusphere-egu26-17131, 2026.

Dendrochemistry is used to understand the temporal dynamics of changes in elemental concentrations in the environment, including those associated with environmental pollution. However, fundamental questions remain about the mechanisms of elemental uptake, distribution of elements within annual growth rings, and the potential for translocation throughout sapwood. Many quantitative techniques used in dendrochemistry to assess where and which elements are present are destructive, time-consuming, and expensive to measure at an annual resolution. Synchrotron X-Ray Fluorescence (SXRF) imaging offers an innovative, non-destructive method for identifying which elements are present, where they are located within the sample, and their relative concentrations. In this presentation, we showcase novel dendrochemistry techniques using SXRF to document how elemental patterns change across the lateral and vertical dimensions of trees. Preliminary results show non-uniform elemental uptake and distribution throughout both mature uncontaminated trees and young saplings spiked with heavy metals. SXRF images of cross-sectional tree disk samples indicate hot spots of elemental concentrations associated with active growth areas (e.g., bark and branches) and wounds within the tree-rings rather than uniform elemental distribution. These results indicate a need for more robust sampling and analysis of dendrochemistry samples, and SXRF techniques are one method to help achieve this. 

How to cite: Canning, C., Laroque, C., and Muir, D.: Synchrotron X-Ray Fluorescence Imaging Sheds Light on The Uniformity of Elements Across Annual Growth Rings.  , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5537, https://doi.org/10.5194/egusphere-egu26-5537, 2026.

Stable isotope analysis of tree rings provides critical insight into past environmental and climatic conditions. Traditionally, the elemental analyzer has been the benchmark sample introduction peripheral for isotope ratio mass spectrometers (EA IRMS) for spatially resolved δ¹³C measurements in wood and cellulose. However, recent developments in using laser ablation as sample introduction peripheral for both the IRMS (LA-IRMS) and cavity ring-down spectroscopes (LA-CRDS) introduce promising alternatives that combine cost efficient, rapid analysis with high spatial resolution and simplified sample handling.

In this study, we present a comparative evaluation of LA-CRDS and LA-IRMS for δ¹³C measurements relevant to tree ring research. We examine figures of merit for LA-CRDS and LA-IRMS using pulsed nanosecond solid-state lasers at 213 nm wavelength (Teledyne Photon Machines) coupled via a dedicated ablation chamber (Terra Analitic) to a Picarro CO2 isotope analyzer (G2201-i) and Sercon HS2022 IRMS. Key performance indicators such as accuracy, precision, and spatial resolution are assessed to determine the suitability of both techniques for high-resolution tree-ring analysis.

Our findings highlight scenarios where each of these techniques offer advantages, such as faster throughput and reduced infrastructure requirements, while maintaining analytical rigor. These results underscore the growing potential of LA-IRMS and LA-CRDS as innovative tools for the tree-ring research community and broader environmental studies.

This advancement opens new opportunities for high-resolution dendrological studies, enabling a broader adoption of isotope-based research, including climate reconstructions, past and present environmental studies, and tracing anthropic activity.

How to cite: Stremtan, C., Puscas, C., Sahlstedt, E., Wožniak, J., Hoffman, M., and Rinne-Garmston, K.: Advancing Tree-Ring Isotope Analysis: A Comparative Assessment of LA-CRDS and LA-IRMS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16456, https://doi.org/10.5194/egusphere-egu26-16456, 2026.