Orals: Wed, 6 May, 14:00–17:55 | Room 0.49/50
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 (δ18OPB), 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 δ18OPB over overlapping periods range from 0.52 to 0.72, allowing the central France chronologies to be merged with δ18OPB 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 (gs) regulates CO2 and water fluxes of plants. Although experiments have shown that gs decreases with elevated CO2, it is unclear how gs 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 gs can potentially be inferred from tree ring stable oxygen isotope ratios (δ18Otrc). Several studies have indeed used δ18Otrc trends to conclude that gs has not significantly changed from pre-industrial values. However, it remains unclear whether δ18Otrc is sufficiently sensitive to detect the magnitude of change in gs expected due to CO2 increases and climatic changes. Here, we evaluate the sensitivity of δ18Otrc trends to CO2 and climate induced changes in gs, and to VPD and temperature increases since the beginning of the 20th century, using current theoretical models. We find that temporal changes in gs only significantly affect δ18Otrc trends when the Péclet effect is present, and then only in dry climates. In contrast to the weak effects of gs on δ18Otrc trends, we find that temporal increases in VPD and temperature, independent of changes in gs, have far greater contributions to δ18Otrc trends. Thus, this increasingly popular method should be used with caution, because it is highly challenging to unambiguously attribute trends in δ18Otrc to changes in gs. Despite current limitations, we recommend how future studies can address these challenges in efforts to detect long-term gs 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.
Posters on site: Wed, 6 May, 10:45–12:30 | Hall X5
Wildfire is a fundamental Earth system process that has shaped terrestrial ecosystems, biogeochemical cycles, and human societies for millions of years. The Mediterranean Basin is one of the world’s major fire hotspots, where climatic extremes interact with dense human populations and long-standing land-use legacies, frequently resulting in severe wildfire activity. Nevertheless, the knowledge on the long-term history of Mediterranean fires has remained poor, and existing information is often difficult to access and reuse, with governmental documents, independent research groups, and numerous unpublished or inaccessible datasets. This lack of integration has limited our ability to detect wide-scale retrospective regional patterns, understand the drivers of fire occurrence, and place recent wildfire extremes within their historical context. Here, we present the Mediterranean Fire History Database (MedFireAtlas), the first openly accessible, standardised, region-wide compilation of long-term Mediterranean fire history data, designed to address this critical knowledge gap.
The MedFireAtlas database integrates two types of data, covering different temporal resolutions and spanning both southern Europe and the North African regions of the Mediterranean Basin. The first type of data includes 43 site-level tree-ring-based fire history reconstructions spanning from the 13th century onward, mainly from forests characterised by surface-fire regimes. These datasets offer annually resolved and multi-century long information for surface-fire-adapted species, primarily Pinus nigra, as well as Cedrus atlantica and Pinus pinaster. The second type of data includes governmental documentary fire records, primarily covering the mid-20th century to recent decades, available through open or authorised sources. It contains over 1.8 million documentary records from a total of ten countries. All entries were harmonised under a common metadata structure, including location, date, cause (when available), burned area, and data type. End-to-end data architecture, workflows, quality-control procedures, and metadata guidelines within the database ensure consistency and reliability. The MedFireAtlas links detailed recent fire occurrences with multi-century historical reconstructions, enabling spatiotemporal analyses of fire regimes and regional patterns that are not possible using either data source alone.
The key feature of MedFireAtlas is an interactive web interface built by R Shiny that enables users to visualise, filter and download fire data through a spatial interface. The platform provides full capabilities to investigate long-term temporal trends, country-level and regional patterns, and comparisons among multiple datasets, supporting scientific research and applied uses, providing valuable multi-century benchmarks for fire regime modelling and long-term ecological and climate research. The MedFireAtlas is designed as a living, community-driven resource: researchers and fire management agencies across the Mediterranean are encouraged to contribute their new or historical datasets. Overall, the MedFireAtlas establishes the first comprehensive database initiative for regional fire regime representing a critical step toward integrated, science-based fire management in one of the world’s most fire-prone and climate-vulnerable regions.
How to cite: Şahan, E. A., Arianoutsou, M., Ascoli, D., Barčić, D., Carcaillet, C., Christopoulou, A., Fulé, P., Gutiérrez, E., Ivanović, A., Jevšenak, J., Kherchouche, D., Köse, N., Moris, J. V., Ogris, N., Rožić, R., Slimani, S., Touchan, R., and Martínez-Sancho, E.: The MedFireAtlas: A regional historical fire database for the Mediterranean Basin , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7197, https://doi.org/10.5194/egusphere-egu26-7197, 2026.
Wood formation (xylogenesis) represents the mechanistic link between short-term physiological processes and long-term tree-ring patterns and thus provides a key entry point to connect processes, patterns, and predictions in tree growth research. Although numerous xylogenesis datasets already exist worldwide, their real strength emerges when they are considered together, enabling large-scale syntheses of growth phenology, cell production dynamics, and climate sensitivity across species and biomes. FAIRWood builds on this opportunity as an international initiative that is developing an open database to harmonize, connect, and increase the scientific value of xylogenesis data. This presentation introduces the FAIRWood project, its objectives, and the scope and description of the database.
FAIRWood brings together observations from intra-annual wood formation monitoring, including data on cambial activity and successive cell differentiation phases, collected across multiple sites, climates, and taxa. Each record is accompanied by metadata that describes the sampling design, protocols, temporal resolution, and sampling-, tree- and stand-level characteristics, ensuring data preservation, harmonization, reuse, and cross-study comparability according to the FAIR principles. The database aims to host data on both xylem and phloem formation of stems, branches and coarse roots for gymnosperms and angiosperms and integrate automated tools for data visualization, exploration and basic processing, with the aim of increasing the visibility and accessibility of past and ongoing monitoring efforts.
By unifying observations, metadata, and analytical tools within a single framework, FAIRWood aims to foster international collaboration while also acting as a shared platform to enhance the visibility of datasets and projects produced by research groups. This integrated approach enables large-scale analyses across space, time, and taxa, supports comparative studies, and strengthens the development and evaluation of vegetation models as well as forest responses to global environmental change.
How to cite: Fonti, P., Cabon, A., Flores, O., Hughes, M., Nabais, C., Larysch, E., Marchand, L., Morino, K., Nägelin, M., Li, X., Prislan, P., Sergent, A. S., Silvestro, R., Stangler, D., Wang, W., and Rathgeber, C.: FAIRWood: An open database for global xylogenesis research, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16957, https://doi.org/10.5194/egusphere-egu26-16957, 2026.
Understanding drought-induced changes in tree carbon dynamics is crucial, as forests play a significant role in regulating the global carbon cycle. Tree-rings can serve as detailed archives of intra-seasonal environmental changes, such as intrinsic water-use efficiency (iWUE) in their stable carbon isotope composition (δ13CRing). However, it remains unclear how multiple, simultaneous physiological responses to drought affect these records. We traced drought and recovery-associated physiological responses from leaves to phloem, roots, and tree-rings in seven-year-old Pinus sylvestris using δ13C analysis of sucrose, high-resolution δ13CRing analysis by laser ablation and leaf gas exchange. Although sucrose captured leaf-level processes, intra-annual δ13CRing was intermittently uncoupled from leaf-level processes over time. When scaled to the conventional approach in δ13CRing research—analysing whole annual rings or distinguishing between earlywood and latewood sections—the drought event was not detectable. This study emphasises the need for cautious interpretation when using conventional δ13CRing analysis to study plant stress responses, while demonstrating the potential of high-resolution intra-annual δ13CRing for uncovering tree adaptation mechanisms in the context of climate change.
How to cite: Rinne-Garmston, K., Leppä, K., Tang, Y., Salmon, Y., Saurer, M., Angove, C., Adamczyk, B., Jyske, T., and Sahlstedt, E.: Drought adaptation and recovery in Scots pine: δ13C evidence from laser ablation and CSIA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5475, https://doi.org/10.5194/egusphere-egu26-5475, 2026.
The combination of tree-ring radiocarbon (14C) and stable isotope ratios of carbon, oxygen, and hydrogen has been proposed as a valuable approach to solve dating uncertainties in this period and is therefore a helpful tool for reconstructing Late Glacial climate conditions. However, sample throughput at annual to sub-annual resolution remains limited by current wood pretreatment methods, as no established protocol exists that is suitable for both 14C and stable isotope analyses, given their distinct requirements (i.e., ultra-clean cellulose for 14C analysis, preservation of original isotopic signatures and cellulose homogeneity for stable isotope analysis). Additionally, Late Glacial subfossil wood often suffers from degradation, resulting in lower cellulose content compared to modern wood. Here, we introduce a novel cellulose extraction method suitable for both 14C and stable isotope measurements, thereby reducing labor intensity and substantially increasing analytical throughput of multiproxy analyses. The new method was systematically evaluated using both modern and Late Glacial subfossil wood and benchmarked against established reference protocols optimized specifically for either 14C or stable isotope analyses. Two major modifications were introduced: (1) the addition of a strong base step to isolate the alpha cellulose fraction, and (2) modified reaction times for both base and bleaching steps. We present preliminary results with a special focus on preservation of isotopic (14C, 13C, and 18O) signatures and cellulose yield. The feasibility of the new cellulose extraction method for multiproxy analysis is discussed, along with remaining challenges and directions for further optimization.
How to cite: Ando, K., Staub, S., Guidobaldi, G., Nievergelt, D., Saurer, M., Schneider, L., Verstege, A., Friedrich, M., Fonti, P., Reinig, F., Wacker, L., and Treydte, K.: Combined wood cellulose extraction method for radiocarbon and stable isotope analysis , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20447, https://doi.org/10.5194/egusphere-egu26-20447, 2026.
In the 1950s and 1960s, atmospheric nuclear bomb tests caused a significant and rapid increase of the atmospheric radiocarbon content, almost doubling it in 1963 (Hua et al. 2022). Known as the 14C bomb pulse, this provides a clear timestamp for materials formed during this period and afterwards. It has proven invaluable in tracking carbon cycle dynamics and environmental changes (Levin & Hesshaimer 2000). It can be used in any process which exchanges carbon with the atmosphere or incorporates carbon from the atmosphere such as plants.
Here we present a study using the rapid atmospheric radiocarbon fluctuations of the 1950s & 1960s to assess the tree-ring growth pattern and growing season length of five Scots pine trees from five Norwegian sites, from 63°15’ to 69°24’ N, over a period of 15 years (6 years using direct measurements and 9 years using indirect measurements). For each tree, rings within the period 1950-1965 were sliced into the largest practical number of subannual sections (up to 10), depending on the width of the ring in the sample. After cellulose extraction, the 14C content of each increment was measured to a high precision.
Cumulative wood formation usually follows a sigmoid shape, with slower growth during spring and early summer, faster growth in midsummer, and decreasing activity towards the end of the vegetation period (e.g. Schmitt et al. 2004). In European and North American conifers of cold environments, the onset of cambial activity can vary from the beginning of May to early June, depending on intra-annual weather-, snow-depth- and soil conditions (Vaganov et al. 1999; Deslauriers et al. 2003; Rossi et al. 2007; Hettonen et al. 2009). Despite these variations, maximum tree-ring growth rate seems to be limited to a short period, which in most European and North American conifer species is about the time of maximum day length (Rossi et al. 2006).
By adapting the sigmoid growth curves to match the 14C results of the cellulose increments to the atmospheric signal, we obtain a growth curve and growing season length which are independent from other assumptions. Comparison to the presumed growing season parameters (start, end, and length) derived from meteorological data, then, provides a valuable source of information to understand the connection between tree growth and environmental parameters. The 14C bomb pulse, acting as a magnifying lens, this research will help to understand the connection between atmospheric CO2 isotopic values and that of the tree-rings formed under these conditions
How to cite: Nadeau, M.-J., Svarva, H., Grootes, P. M., Seiler, M., Khumalo, W., and Philippsen, B.: Estimating tree-ring growth using the radiocarbon bomb pulse, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14315, https://doi.org/10.5194/egusphere-egu26-14315, 2026.
Seasonal variations in moisture sources are found in many regions, and tree ring isotopic records from such regions are known to respond to variations in these moisture sources. However, how the relative strengths of the distinct moisture sources influence tree ring isotopic records is not well understood.
The Western Himalayas (WH), a hydro-climatically sensitive region, has two distinct moisture sources: westerlies, which provide snow during winter, and the South-west monsoon, bringing rain during summer. To understand how these moisture sources leave their imprint in the tree ring, isotopic characterization of precipitation, xylem and leaf water was carried out for two years (2023-2024). Forty trees, of species commonly employed in dendroclimatic research, from two climatologically distinct locations in the WH, Manali and Keylong, were studied. Precipitation samples were collected throughout the sampling interval, while xylem and leaf samples were collected immediately before (June) and after (October) the monsoon. The isotopic composition of xylem and leaf water collected during June and October is expected to reflect the isotopic signature of snow and rain, respectively. Cryogenic vacuum extraction was employed to extract water from xylem and leaf samples. Stable isotopic analysis (δ18O, δ2H) of all samples was performed using an IRMS (Delta V Plus, Thermo Scientific).
The results indicated winter precipitation was enriched in 2H and 18O compared to monsoon rain. The d-excess of winter precipitation was higher than that of the monsoon, suggesting source of moisture was from a comparatively drier region. Precipitation at Keylong showed a signal depleted in 2H and 18O for all seasons compared to that at Manali. The isotopic composition of xylem water mimicked seasonal isotopic variability in precipitation, suggesting that trees in the WH indeed sample water from snow and rain sequentially during the growing season. The leaf water exhibited higher enrichment in 18O than in 2H (higher than that predicted by equilibrium fractionation) over the xylem isotopic composition. This suggested δ2H of leaf water was better at reflecting the isotopic composition of precipitation than δ18O, especially when the relative humidity is lower. Our results suggested intra-annual isotopic characterization of tree rings from the WH has the potential to reveal past variations in the strengths of westerlies and monsoon.
How to cite: Puthiyandi, S., Managave, S., Padhya, V., and Deshpande, R.: Tracing signatures of dual moisture sources in tree-rings: insights from xylem and leaf water isotopic study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1150, https://doi.org/10.5194/egusphere-egu26-1150, 2026.
The oxygen isotope composition (δ18O) of precipitation is strongly linked to climate and becomes integrated into tree-ring archives. However, this climatic information is only partly preserved in tree rings, as it is modified by hydrological processes prior to root water uptake and by physiological processes before cellulose synthesis. This complicates tree-ring isotope-based climate reconstructions. Nevertheless, direct links between δ18O in precipitation (δ18OP) and tree-ring cellulose (δ18OC) have been rarely tested, largely due to the lack of long-term precipitation δ18O records. Over the past two to three decades, numerous δ18OC chronologies have been established, and they can now be combined with δ18OP data from AI-supported models with high spatiotemporal resolution. This provides a unique opportunity to systematically evaluate the linkage between δ18OP and δ18OC.
In this study, we used a network of 45 annually resolved δ18OC chronologies across Europe starting in 1950 and compared them with monthly time series of Piso.AI modelled δ18OP for the corresponding locations. Our main research questions were: (1) which seasonal δ18OP signals are recorded in δ18OC? (2) Is the relationship between δ18OP and δ18OC stable over recent decades? (3) Which factors (species, geography, climate) control the strength of this relationship across the network?
We found that correlations between δ18OC and monthly δ18OP were strongest for June, July and August of the current year at most sites. Significant correlations were also observed for other months, including months from the previous year in some cases, but without a consistent pattern across the network. To further examine these relationships, we calculated seasonal and annual mean δ18OP values. Compared with unweighted δ18OP mean values, precipitation-amount weighting reduced correlations with spring, early summer and annual means, thereby narrowing the dominant signal window to the summer period (May–August mean δ18OP). We found that the δ18OP–δ18OC relationship was stable across sites over recent decades, with no systematic change in correlation strength over time. Ongoing analyses use (1) the correlation coefficients (r values) between δ18OC and δ18OP and (2) the δ18O offset between cellulose and precipitation, both considering annual and June-July-August δ18OP values. These metrics are used to investigate the role of species, geography, climate in controlling the observed δ18OP–δ18OC linkage. Our findings improve the understanding of site- and species-specific isotope signal transfer from water sources to tree rings and help identify spatial and temporal climate signals reflected in tree-ring δ18O.
How to cite: Diao, H., Saurer, M., Nelson, D. B., and Lehmann, M. M.: The link between δ18O in precipitation and tree-ring cellulose across time, space and species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3764, https://doi.org/10.5194/egusphere-egu26-3764, 2026.
Understanding the impact of volcanic eruptions on climate over the last two millennia is essential to place current anthropogenic climate change into a long-term context. High-resolution proxy archives are crucial for this purpose, yet their availability decreases rapidly back in time. Besides ice cores, speleothems and corals, tree rings represent a uniquely valuable archive, providing records with annual resolution of past-climate change. Volcanic eruptions are among the most impactful natural forcings on Earth’s climate, through the injection of gaseous plumes into the atmosphere that can induce warming or cooling of the planet surface. While some of these impacts are well-known and studied, there are many older volcanic events whose details are unknown or uncertain, due to the lack of direct historical evidence.
Volcanic plumes transport volatile elements (e.g., S, Fe, Zn, Cu, Hg) that can be absorbed by trees and recorded in the yearly tree-ring layers. So far, dendrochemistry has been widely applied to assess anthropogenic pollution, but our research explores its potential as a novel proxy: by identifying chemical spikes of these elements in tree rings of known age, it may be possible to correlate them with known volcanic eruptions or identify previously unrecognized volcanic events. Here we present data obtained at Diamond synchrotron on tree rings from juniper (Juniperus communis) samples from Kevo, Finland, whose dendrochronological records extend back to the early Middle Ages. These measurements revealed distinct peaks in metal elements such as Zn and Cu, which are typically enriched in volcanic plumes and can be hosted in the wood as semi-nutrients. Some concentration peaks detected in the tree rings correspond to the ages of major Icelandic eruption from the lower Middle Ages.
These preliminary results suggest that dendrochemical analyses may provide a new archive of past volcanic activity. If validated, this approach could significantly improve reconstructions of volcanic eruptions of the past and corresponding climate variability over the last two millennia.
How to cite: Beghini, E. L., Marzoli, A., Carrer, M., Dibona, R., Baker, D., Newton, R., Geraki, K., and Callegaro, S.: Tracing volcanic events in tree rings, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7658, https://doi.org/10.5194/egusphere-egu26-7658, 2026.
Climate change projections for the equatorial Ecuadorian Andes are contradictory due to topographic diversity and interplay of multiple climatic influences. Intensifying droughts and increasing precipitation variability impact the livelihood of local populations which depend on agriculture and hydroelectric energy sources and thus are highly vulnerable to long- and short-term climatic changes. Overall, the hydroclimate of the northern tropical Andes is influenced by multiple climate systems such as the Intertropical Convergence Zone (ITCZ), the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO) (Dominguez-Castro et al., 2017). The interaction of these large-scale climate systems across the complex Andean topography results in strong variability of local climate conditions. As a result, the available instrumental climate data is spatially and temporally limited. Tree-rings and stable isotopes can be used as high-resolution climate proxy to complement and extend instrumental records and investigate local climate impacts.
This study focuses on exploring the potential of multiple tropical Ecuadorian tree species, beyond the Polylepis-focused approaches common in Andean dendroclimatology. For a feasibility study, five tree species of the western cordillera located about 30 km north of Quito were selected. Dendrocores were retrieved at an elevation of 2000 – 3000 m a.s.l in the protected Cambugán primary forest, a primary and secondary forest in the Piganta river catchment (Atahualpa) and a private agroforest area. Although uncertain seasonality in the Andean tropics complicates the use of standard dendrochronological applications, preliminary observations suggest that growth patterns and potential annual tree-rings may be influenced by local precipitation patterns characterized by a dry season. Other potential growth-limiting factors appear largely persistent across the research area. Overall, the identification and description of growth-ring boundaries across multiple tropical tree species will provide the foundation for robust chronologies and future dendroclimatological analyses using stable isotopes. This could enable further investigation in the reconstruction of local precipitation and drought patterns in relation to large-scale climate influences (ENSO, ITCZ, PDO).
How to cite: Meyer, L., Helle, G., Mariscal Chavez, A., and Dietze, E.: Exploring the potential of multiple tropical tree species for dendroclimatology in the Ecuadorian Andes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12930, https://doi.org/10.5194/egusphere-egu26-12930, 2026.
Climate change is profoundly altering forest ecosystems worldwide by affecting tree growth, mortality and regeneration through rising temperatures, shifting precipitation regimes and more frequent extreme events. Provenance trials provide a powerful framework to assess how tree populations from different climatic origins perform under changing environmental conditions. Here, we analysed tree-ring data from 25 common gardens and 176 provenances spanning a broad gradient from the Mediterranean to Scandinavia. These trials encompassed four climatic clusters (Northern, Central, Southwestern and High elevation) and six widespread European tree species (Quercus robur, Quercus petraea, Picea abies, Pinus sylvestris, Pinus pinaster and Larix decidua). More than 5,500 increment cores were collected and measured using standard dendrochronological methods. Provenances were classified as originating from climates that were warmer or colder, drier or wetter, or locally similar relative to conditions at the trial sites. For each trial and provenance class, we quantified radial growth patterns, climate–growth relationships and resilience components (resistance, recovery, resilience) to past warming and drying events. Our results indicate strongly species- and region-specific responses. The clearest patterns emerged for Quercus robur from the Northern cluster, where provenances originating from warmer regions showed enhanced heat vulnerability and reduced radial growth, indicating a smaller thermal safety margin under additional warming, whereas provenances from cooler regions responded more positively to increased spring temperatures. In contrast, the opposite pattern emerged for Larix decidua and Pinus pinaster from the Southwestern cluster, where provenances from warmer origins exhibited higher heat tolerance than those from cooler parts of the native range. Overall, our findings demonstrate that provenance choice can substantially modify tree growth and resilience to extreme weather events, and that these effects are strongly region- and species-specific.
How to cite: Jevšenak, J. and Krajnc, L. and the OptForests: Species- and region-specific climate sensitivities of European tree provenances across a continental gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15820, https://doi.org/10.5194/egusphere-egu26-15820, 2026.
Recent extreme climate events have severely impacted forests worldwide. Deciduous forests, in general, and oak-dominated forests, in particular, are more frequently and severely affected by repeated and intensified drought events than other biomes. In this context, updated insights into oak responses to drought events are needed to understand their resilience and adaptability capacity in order to promote forest management practices that mitigate the adverse effects of climate change. To analyze the response of pedunculate oak (Quercus robur L.) to droughts, we used an extensive tree-ring network comprising more than 2100 trees from 90 sites across Romania and the Republic of Moldova. Given evidence that the Carpathian Mts. significantly influence regional climate patterns, we split our network into three clusters based on sites’ positions relative to the Carpathians: western, eastern, and southern sites. We used resilience indices, following Lloret et al. (2011), to quantify oak responses to droughts, while multinomial logistic models were used to assess the occurrence probability of positive or negative pointer years in growth rates in relation to the Standardised Precipitation-Evapotranspiration Index. Regarding the resilience index, we found no significant differences between the clusters; however, eastern sites exhibited lower resistance and higher recovery rates. By contrast, the western sites exhibited the highest resistance and the lowest recovery rate. Multinomial logistic models indicated that, at southern sites, there is a higher probability of negative pointer years during winter droughts, whereas spring droughts are associated with a higher probability at eastern sites. Overall, our findings highlight spatial differences in growth plasticity and drought adaptability of pedunculate oak in Southeastern Europe in relation to the Carpathian Mts.
How to cite: Popa, A., Ionita, M., Popa, I., Nagavciuc, V., and Roibu, C.-C.: Oaks and extremes: Contrasting responses of Quercus robur to drought in Southeastern Europe, shaped by the Carpathians, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8178, https://doi.org/10.5194/egusphere-egu26-8178, 2026.
The archives of Holy Mount Athos, Greece, an UNESCO World Heritage Site, constitute an invaluable treasure trove of Byzantine and post-Byzantine documents and manuscripts that offer unique evidence for reconstructing past climate, resulting from the long-term human presence in the area through monasticism. This study combines references to climatic events from the archives of the Holy Monastery of Vatopedi with the study of annual growth rings using the dendrochronology method on samples of Aleppo pine, with the aim of identifying and cross-validating historical climate extremes.
Research in the Historical Archive of the Holy Monastery of Vatopedi focused on extreme phenomena, searching manuscripts mainly for keywords such as floods, frost, storms, famine, and periods of drought, yielding references stretching back several years. To this end, approximately 150 letters from monks in the wider Vatopedi area were studied and 28 references to climatic events were recorded, focusing on the mid-18th to the mid-19th century. At the same time, samples were collected from 20 different trees in three clusters of Aleppo pine within the forest area of the Holy Monastery of Vatopedi using Haglöf Sweden increment borer. The implementation of a Lignostation system for high-resolution ring-width and density measurements resulted in ring timeseries associated with extreme precipitation and ambient temperature in the region’s climate.
The initial samples processed reveal significant correlations between years with “narrow rings” and recorded episodes of drought or flooding, reinforcing the reliability of both types of data. These findings reconstruct climate extremes on Mount Athos before the era of measuring instruments, providing baseline data for assessing long-term variability and informing contemporary climate change adaptation strategies in Mediterranean landscapes.
How to cite: Karadimitris, A., Pantazis, C., Koutsanitis, D., and Nastos, P.: Reconstructing past climate variability on Holy Mount Athos, Greece using monastic archives and dendrochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5882, https://doi.org/10.5194/egusphere-egu26-5882, 2026.
Global afforestation and forest expansion have substantially altered forest age structures, leading to an increasing dominance of younger stands. Ecological theories such as size‐asymmetric competition and growth–defense trade‐offs suggest that age‐related shifts in resource allocation and size may influence drought responses, yet empirical evidence remains limited. Here, we use tree-ring records from 1,089 sites across China to examine age-dependent patterns of drought resilience, quantified in terms of resistance and recovery. Our results show that recovery capacity generally increases with tree age, whereas resistance displays a non-linear relationship, declining at younger ages before increasing beyond an age threshold. These findings highlight systematic age-related differences in drought resilience across climatic gradients and suggest that forest age structure may play an important role in mediating forest responses to increasing drought stress. Our results provide observational evidence relevant for understanding forest vulnerability and resilience under ongoing climate change.
How to cite: Liu, J., Li, Z., Chen, S., Liu, Y., Fu, B., and Feng, X.: Evidence and Theoretic Basis for Enhancing Forest Drought Resilience through the Protection of Old Trees, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7130, https://doi.org/10.5194/egusphere-egu26-7130, 2026.
Green alder (Alnus alnobetula) is a tall, deciduous shrub widespread across the treeline ecotone in the Central European Alps. This study evaluated the impact of growing-season cold stress on radial stem growth (RG) under field conditions and in a controlled environment. RG was recorded by dendrometers on mature shoots (c. 20 yr old; n=18) at the treeline (2140–2150 m asl) on Mt. Patscherkofel during 2023, when several short-term cold spells occurred during the growing season (minimum air temperature (Tair): –1.2°C). In addition, 3–4 yr old saplings (n=5) were exposed to a 2-day cold spell in a climate chamber (minimum Tair: –2.3°C). We hypothesized that a slight frost during the growing season would transiently suppress RG, potentially resulting in a bimodal growth pattern. Contrary to this expectation, two-thirds of mature shoots in the field ceased RG after a mid-season cold spell (day of the year (DOY) 219), and one-third ceased after a late-season cold spell (DOY 241). In contrast, young shoots exposed to an experimental cold spell showed a decline–but no halt–in RG, resulting in significantly lower RG than in controls (P<0.05). The results of this study revealed that (i) mature shoots of Alnus alnobetula can exhibit divergent RG responses to growing season cold spells, ranging from short-term suppression to complete cessation, and (ii) age-specific responses exist, as RG in young shoots did not cease after an experimental frost. The findings suggest that individual- and age-specific sensitivities of RG to growing season cold stress ensure persistence and facilitate establishment of Alnus alnobetula in the harsh and highly variable alpine treeline environment.
This research was funded in whole by the Austrian Science Fund (FWF; grant-DOI: 10.55776/P34706).
How to cite: Oberhuber, W., Wieser, G., and Gruber, A.: Differential radial stem growth responses of Alnus alnobetula to short-term cold stress, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2545, https://doi.org/10.5194/egusphere-egu26-2545, 2026.
