In recent decades, Europe has experienced more frequent flood and drought events. However, little is known about the long-term, spatiotemporal hydroloclimatic changes across Europe. We show the first climate field reconstruction spanning the entire European continent based on tree-ring stable isotopes. A pronounced seasonal consistency in climate response across Europe leads to a unique, well-verified spatial field reconstruction of European summer hydroclimate back to 1600. We find distinct phases of European hydroclimate variability as possible fingerprints of solar activity (coinciding with the Maunder Minimum and the end of the Little Ice Age), pronounced decadal variability and a long-term drying trend from the mid 20th century. The recent European summer conditions are highly unusual in a multi-century context and unprecedented for large parts of central and western Europe.

How to cite: Freund, M., Helle, G., Balting, D., Ballis, N., Schleser, G., and Cubasch, U.: European hydroclimate variability of the past 400 years based on tree-ring isotopes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14680, https://doi.org/10.5194/egusphere-egu23-14680, 2023.

It has recently been argued that tree-ring stable isotopes (TRSI) can reveal persistent long-term hydroclimate trends that are usually not captured by more traditional dendroclimatic studies using tree-ring width or density (Büntgen 2022). Since the putative long-term discrepancy between ‘growth-dependent’ ring width and density versus ‘growth-independent’ TRSI proxies is likely unrelated to biases from age-trend removal (Büntgen et al. 2021; Yang et al. 2021), we propose a re-evaluation of the predictive power of various tree-ring parameters for reconstructing climate variability at interannual to multimillennial timescales. We analyse 7800 high-resolution δ¹⁸O, δ¹³C, δD measurements from about 200 high-elevation conifers of the Alpine Holocene Triple Tree Ring Isotope Record (AHTTRIR; Arosio et al. 2022) to assess ultra-long climate trends well beyond the segment length of individual tree-ring samples. Despite the spatiotemporal data heterogeneity, and associated signal complexity of AHTTRIR, we show that δ¹⁸O values contain a reasonable level of coherency with summer hydroclimate variability. In line with two independent TRSI studies from central Europe and monsoon Asia (Büntgen et al. 2021; Yang et al. 2021), our new δ¹⁸O Alpine chronology reveals a significant long-term drying trend over the past 6000 years. We interpret this multimillennial hydroclimate trajectory as a response to long-term negative orbital forcing (i.e., insolation changes due to the Earth’s axial precession). Our findings advise caution when applying corrections to TRSI data in order to preserve Holocene long trends. Considering the unique paleoclimatic values of TRSI, more such records are needed from a wide range of species and regions in both hemispheres.

Arosio Tito, Malin Ziehmer, Kurt Nicolussi, Christian Schluechter, Andrea Thurner, Andreas Österreicher, Peter Nyfeler, and Markus Christian Leuenberger,. 2022. “Alpine Holocene Triple Tree Ring Isotope Record.” PANGAEA, 2022. https://doi.pangaea.de/10.1594/PANGAEA.941604.

Büntgen Ulf. 2022. “Scrutinizing Tree-Ring Parameters for Holocene Climate Reconstructions.” Wiley Interdisciplinary Reviews: Climate Change, e778.

Yang Bao, Chun Qin, Achim Bräuning, Timothy J. Osborn, Valerie Trouet, Fredrik Charpentier Ljungqvist, Jan Esper, Lea Schneider, Jussi Grießinger, and Ulf Büntgen. 2021. “Long-Term Decrease in Asian Monsoon Rainfall and Abrupt Climate Change Events over the Past 6,700 Years.” Proceedings of the National Academy of Sciences 118 (30): e2102007118.

How to cite: Arosio, T., Nicolussi, K., Leuenberger, M., Krusic, P. J., Esper, J., and Büntgen, U.: Holocene-long climate signals in tree-ring stable isotopes from the European Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8180, https://doi.org/10.5194/egusphere-egu23-8180, 2023.

Tree-rings are a valuable proxy for reconstructing past environmental conditions such as climate at annual or intra-annual resolutions. Tree-ring dating has an enormous potential for better understanding climate dynamics under a changing climate. In Alpine regions, changes in climate may well lead to switches between temperature-limitation and precipitation-limitation. However, such changes cannot be separated from local environmental influences such as altitude and aspect. In this study, we applied the standard statistical approaches of dendrochronology to understand climate-growth relationships as a function of elevational gradients to understand how altitude conditions the impacts of climate change impacts on tree growth. For the growth of European Larch (Larix decidua) trees in the Turtmann river basin (2000 m a.m.s.l.), a glacier-fed river basin in the Swiss Alps, located in south-western Switzerland, we find that climate warming is leading to some switching from temperature limitation to precipitation limitation and vice-versa according to altitude. The climate-growth relationship further reveals that the growth of Larix decidua in this river basin is positively correlated with the October and November temperature of the previous year (r= 0.46, α=0.01). Comparing these changes with other tree-ring chronologies from the international tree-ring data bank (ITRDB) for the same species at much lower elevation transects  (e.g. 1500 m and 900 m a.m.s.l) show that the tree growth switches from temperature limitation to precipitation limitation. The growth of Larix decidua for these lower elevation trees correlates positively with the current year June-July precipitation (r= 0.40, α=0.01). A number of factors including differences in micro-climate and the effects of aspect (i.e. north versus south facing) across the elevational gradient are most likely to be responsible for these differences. Therefore, in the context of Swiss Alps where the temperature is rising at more than twice the global average, there is likely a breakpoint where the signal changes from temperature-limitation to precipitation-limitation across the elevational gradient and that climate change is causing this breakpoint to rise with altitude through time.

Keywords: Tree-rings, Larix decidua, Climate change, Turtmann river, Swiss Alps 

How to cite: Islam, N., Lane, S., Vennemann, T., and Meko, D.: Identification of an elevational breakpoint where climatic signal changes for the growth of Larix decidua tree rings in a glacier-fed river basin in the Swiss Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8493, https://doi.org/10.5194/egusphere-egu23-8493, 2023.

Tropical forests and woodlands are key components of global carbon and water cycles and due to their importance we need to better understand present and future tropical tree growth responses to climatic variation. Tree-ring analyses provide long-term datasets from which such responses can be derived. A substantial number of tropical tree-ring chronologies exist with hundreds of topical tree species showing potential for tree-ring analyses. Despite this large potential, a quantitative analysis of the distribution and characteristics of tropical tree-ring chronologies is missing. We compiled a network of >490 tropical ring-width chronologies to assess their geographic and climatic distribution, and the gaps therein. To evaluate the potential for climate reconstructions we assessed the timespan covered by these chronologies, the strength of their common growth signal (rbar), where the strongest climate-growth correlations are found, and how these chronology attributes correlate with mean climatic conditions per site. Finally, we used species-distribution modelling to identify regions with high potential for building long chronologies. We answer these questions at pantropical level and address important differences between continents and between angiosperms and gymnosperms. Tropical chronologies have been built in all continents and tropical climate types but chronology building is biased towards high-elevation locations and gymnosperms, with clear gaps in warmer and wetter climates, on the African continent and for angiosperm species. Chronology length correlated negatively with mean annual temperature (MAT), while the common growth signal decreases with increasing mean annual precipitation (MAP) and MAT. Drier sites have the most responsive chronologies: the strength of the precipitation-growth correlations decreases with increasing MAP, but showed no correlation with MAT. Tropical dendrochronological studies already cover a substantial part of the tropics and most areas are expected to have 5 to 15 species with potential to generate centennial chronologies. This study wil provide an important basis to select species and areas to expand dendrochronological studies to underrepresented areas and improve our understanding of the climatic drivers of tropical forest tree growth. 

How to cite: Groenendijk, P., Babst, F., Granato Souza, D., Locosselli, G., Mokria, M., Pumijumnong, N., Trouet, V., Panthi, S., Zexin, F., and Zuidema, P. and the Tropical Tree-ring Network: The potential of tree-ring chronologies to global-change studies in the tropics: a quantitative review, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10257, https://doi.org/10.5194/egusphere-egu23-10257, 2023.

Global warming has considerably advanced the start of the growing season of temperate trees. However, the rate of this phenological change does not necessarily track the changes in the date of the last spring frost, also induced by climate change, which may result in a higher risk of false spring. When a late spring frost (LSF) occurs during tree leaf emergence, it can lead to complete tree defoliation. Although the impacts of LSFs are rarely fatal for a tree, they may play a decisive role in combination with extreme droughts in determining species distribution limits in the near future.

Here we aimed at assessing the impact of LSFs on tree growth of a frost-sensitive species, European beech (Fagus sylvatica L.), and retrospectively quantify the LSF regime in two sites of the Swiss Jura mountains. We collected increment cores of beech and a more freezing tolerant species, Norway spruce (Picea abies (L.) Karst) from a site where LSF damage was observed in May 2020 located at 1,365 m asl and in a second site where no frost damage was observed in 2020 at 1,065 m asl. Climate-growth relationships were established at both sites and for two different periods (1953–1986 and 1987–2020) to identify species-specific climatic drivers and potential temporal shifts. To further distinguish years with LSF impacts on beech radial growth, climatic signals not related to LSF recorded in the spruce series were removed from the beech chronologies.

Our preliminary analyses indicated that tree growth was dominated by different climatic factors in the two study sites: tree growth was limited by cold temperatures during both study periods in the higher elevation site whereas drought signals were apparent in tree growth during the second study period in the lower elevation site. Interestingly, beech growth was initially negatively and then positively related to spring minimum temperature at the higher elevation site. At the lower elevation site, warm temperatures in spring promoted tree growth of both species only during the second period (1987–2020). By subtracting the climatic signals of spruce on beech chronologies, we identified five and two years potentially affected by LSF during the last 30 years at the upper and lower sites, respectively. We are currently calibrating phenological models to climatically identify the years with potential frost damage and verify if these years are consistent with the ones identified with the previous dendrochronological analyses.

We further hypothesized that a damaging spring frost followed by a severe drought during summer may have a much larger impact than drought alone. Further investigations should be conducted on this aspect as the frequency and severity of extreme droughts are expected to increase while spring onset will continue to advance under a warmer climate, potentially increasing the risk of frost damage. 

How to cite: Vitasse, Y., Baumgarten, F., Reim, J., Gessler, A., and Martinez-Sancho, E.: Late spring frost impacts on radial growth of European beech near its upper elevational limit, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14702, https://doi.org/10.5194/egusphere-egu23-14702, 2023.

Primary beech-dominated forests are rare in Central Europe, while the knowledge of natural processes of these ecosystems is crucial for understanding the forest dynamics providing complex of ecosystem services. In order to understand these ecosystems better, which were one of the most widespread in this region, we decided to study their disturbance regimes and their long-term and recent trends driven mostly by natural disturbances.

The study was conducted within the region of Carpathian Mountains including 14 stands and 210 permanent study plots. All living and dead trees were inventoried on these plots, while selected trees were cored. Disturbances were reconstructed by examining individual tree growth patterns: (1) rapid juvenile growth rate (open canopy recruitment), and (2) abrupt, sustained increases in radial growth (release). From these disturbance patterns we reconstructed other disturbance parameters as disturbance severities, patch sizes and plot proportions of disturbed plots on the stand scale characterizing disturbance regime. Further, generalized linear mixed effect models were used to asses long-term and recent trends in these disturbance parameters.

Studied ecosystems were driven by mixed severity disturbance regime. The disturbance events revealed continuous gradient from low-severity, small-scale events to higher-severity, larger-scale events, and this gradient was progressively increasing with the rotation period. The low severity class was the most frequent, but it had similar canopy area disturbed (23.9 %) as moderate and high severity class (34.4 %, 27.1 %), respectively. The very high severity class had the longest rotation period and it affected only 14.7 % of overall canopy area disturbed. Long-term and recent trends in disturbance severities and patch areas were not detected. Plot proportions of disturbed plots on the stand scale had slightly declining trend in time over last two centuries, but the recent trend was not detected.

Analysis of the recent trends in disturbance characteristics have not shown increasing trend, as it was reversely observed in Europe proving the value and stability of these ecosystems under pressure of climate changes. Based on our findings we highly recommend to localize and protect primary and old-growth forests for their high conservation values, high and stable carbon stock, and provision of other ecosystem services. For enhancement of the managed forests´ stability we could recommend to support natural species composition and nature-based forest management mimicking natural disturbance regimes as retention silvicultural system combining irregular shelterwood and selection systems with occasional clear cuts.

The study and its authors were supported by the Czech Science Foundation (project No. 21‐27454S). We thank all staff involved in the data collection and their processing.

How to cite: Janda, P., Svitok, M., Vostárek, O., Mikoláš, M., Bače, R., Čada, V., Pavlin, J., Nagel, T., Begović, K., Fodor, E., Ujházy, K., Frankovič, M., Synek, M., Dušátko, M., Kníř, T., Kozák, D., Kameniar, O., Buechling, A., and Svoboda, M.: The mixed severity disturbance regime of primary beech-dominated forests and its trends of 200 years development, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3377, https://doi.org/10.5194/egusphere-egu23-3377, 2023.

Wildfire is a dynamic natural phenomenon the causes and consequences have changed for millions of years. We previously found out and discussed the fire history of Western Anatolia to understand the drivers of fires over 600 years. In that study, we find out that simultaneous fires occurred in multiple sites and this period overlapped with the longest and most severe drought period of the past 550 years and the fire frequency decline after 1934 coincided with the period of the first forest protection law in 1937. Dry, as well as prior wet conditions were the main drivers of fires in the black pine forests in western Anatolia. On the other hand, to highlight the direct human influence in a high-risk fire region, we sampled one additional site from Antalya (Türkiye) and collected fire-scarred wood samples from both living trees and remnant woods. In this study, we developed a 519-year-long site-level composite chronology using dendrochronological methods with low frequency and no significant relationship was found between dry and major fire years. The recorded fire years for each individual showed that a fire in one tree did not spread and grow to other neighbouring trees. Despite the high risk of fire, fires occurred less frequently can be interpreted as an intense human influence in the area, also observed axe marks in the catface formations and the nomadic tents right next to the site highlight the human influence. These forests were used extensively by the Turkish tribes also called “Yörüks”, who led a nomadic life in the Taurus Mountains for centuries. Although this area is under a high fire risk, the low fire frequency may be due to the reduced amount of combustible materials by goat grazing. Since goats feed not only on grass but also on fresh sprouts, helps to reduce the frequency of fires by consuming both the combustible material under the forest and the branches of the trees closer to the forest ground. Due to the grazing, shoots close to the ground decrease that also decreases the probability of the shift in fire regime from surface to crown fire. We believe that protecting and promoting the culture of Yörüks in the Taurus Mountains will be an important way to protect not only the culture but also the forests.

This research was funded by the Scientific and Technological Research Council of Turkey (TÜBİTAK) (Project number: 118O306). 

How to cite: Şahan, E. A., Gürçay, B., and Güner, H. T.: The History of Fire, Human Influence and Climate in Black Pine Forests, Western Anatolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13879, https://doi.org/10.5194/egusphere-egu23-13879, 2023.

While numerous correlational studies on the impact of climatic variation on tree ring formation consider plant functional traits, masting cycles and stochastic disturbances, the role of soil properties is frequently neglected due to insufficient data availability. Using a homogenous dataset of increment cores collected in mature stands at 1562 different forest sites with detailed plot specific climate, stand and soil information in the province of Styria in Austria we are focusing on the role of soil water storage (plant available water capacity – AWC) and soil nutrient status on tree ring formation. The study area covers a wide altitudinal and climate gradient with mean annual temperatures ranging from 2.1°C to 10.2°C and mean annual precipitation ranging from 695 mm to 2024 mm. Generalized Additive Mixed Models (GAMM) for annual tree ring width over 38 years (1980 to 2018) were fitted for six tree species (Abies alba, Fagus Sylvatica, Larix decidua, Picea abies, Pinus sylvestris, Quercus robur/petrea). Individual tree characteristics, stand attributes, general site characteristics (terrain information calculated from high resolution ALS), downscaled climate information in high temporal resolution, and soil information were used as independent variables. Soil data was derived from a morphological description of 80 cm soil pits dug on each corresponding forest site. Via pedo-transfer-functions (using functions available from the literature as well as derived from laboratory analyses of approximately 25% of the pits), soil characteristics such as AWC and soil nutrient status were calculated.

In a two-step procedure, we first developed a general tree growth model, including solely tree and stand attributes (e.g. age, competition) and general site specific information available in high spatial resolution (e.g. slope, aspect, irradiance, mean annual temperature, precipitation). Subsequently, we added soil attributes to the model and checked for their effect on model parameters. AWC and soil nutrient status do have significant influence on tree ring formation when added to the tree ring model. However, this effect varies amongst tree species. The results are consistent with tree species specific traits as available from literature: E.g. deep rooting species like Quercus benefit more from high water storage capacity than shallow rooting Picea abies; the effect of soil nutrient status is most pronounced for Fagus sylvatica, which has high nutritional requirements and more negligible for Pinus sylvestris, with low nutritional requirements. As soil formation itself depends upon geological substrate, landform and climate, the improvement of model quality when adding additional soil information is moderate.

How to cite: Gadermaier, J., Wächter, E., Grabner, M., Vospernik, S., and Katzensteiner, K.: On the role of soil water storage capacity and soil nutrients on tree growth of selected tree species in Central Europe., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11606, https://doi.org/10.5194/egusphere-egu23-11606, 2023.

Tropical forests have been least studied for dendrochronology following the general perception that tropical trees do not form growth rings, exacerbated by the limited number of scientists focusing on tropical trees. This has created a gap in global dendrochronological studies. Through the two successful Africa Dendrochronological Fieldschools that were conducted in 2021 and 2022 in Zambia, we identified 32 tree species in 3,200m² area of plots from the wet Miombo woodlands. 72% of these species demonstrated good potential for annual ring formation. Julbernardia and Brachystegia species where the oldest and dominant tree species. We developed chronologies from Julbernardia paniculata (140 years), Brachystegia longifolia (series Intercorrelation = 0.42, oldest tree = 160 years), and Brachystegia boehmii (series Intercorrelation = 0.49, oldest tree = 140 years). We also developed a strong multi-species chronology with thirteen wet Miombo woodland species (series Intercorrelation = 0.41, chronology length = 143 years). We found the average monthly precipitation of September to May and the maximum temperature of March to be the main climate variables driving tree growth. Through the two field schools, we trained 48 people from 10 countries (Belgium, Brazil, Cameroon, Colombia, DRC, Ghana, Namibia, South Africa, USA, and Zambia) of four continents (Africa, Europe, North America, and South America).

How to cite: Ngoma, J. and the Justine Ngoma: Tree-Ring Formation of Zambia’s Wet Tropical Miombo Woodlands- Exploratory Research Through African Dendrochronology Fieldschools, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3917, https://doi.org/10.5194/egusphere-egu23-3917, 2023.

Our understanding of wood formation is poor. Key anatomical properties in conifer and ring-porous tree species that have not been explained include the overall anatomy of growth rings (with consistent transitions from low-density earlywood to high density latewood), strong relationships between latewood density and temperature (used for historical temperature reconstructions), the regulation of cell size, and overall growth-temperature relationships. We have developed a theoretical framework based on observations on Pinus sylvestris L. in northern Sweden. These observed anatomical properties emerge from our framework as a consequence of interactions in time and space between the production of new cells, the dynamics of developmental zones, and the distribution of carbohydrates across the developing wood. Here we find that the diffusion of carbohydrates is critical in determining the final ring anatomy, potentially overturning current understanding of how tree growth responds to environmental variability and transforming our interpretation of tree rings as proxies of past climates.

How to cite: Friend, A., Eckes-Shephard, A., and Tupker, Q.: Latewood density and overall ring anatomy responses to temperature in Scots pine explained by carbohydrate diffusion and cellular kinetics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3515, https://doi.org/10.5194/egusphere-egu23-3515, 2023.

Tree ring growth is strictly bound to annual environmental conditions. Therefore, dendrochronology represents a solid tool for investigating the relationship between the whole plant growth and climate at high temporal resolution, especially in the context of ongoing climate change.

The temperature increase in the Alpine and Arctic ecosystems has been proven to enhance shrub growth contributing to the Arctic/Alpine greening, while the effects of the interaction between temperature and other climatic variables (e.g. precipitation/snowfall regime) on the shrub growth have often been neglected.

With the aim of parsing the relationships between the annual growth of Vaccinium myrtillus L., a key species in the Alpine tundra, temperature, precipitation, snowfall regime (i.e., in terms of temperature-based snowfall, known as snow water equivalent) and their interaction, we analyzed the xylem rings of 100 cross sections of underground bilberry stem, collected along a 500 meters altitude gradient above the tree line and corresponding over a period of 20 years (1995-2015). Furthermore, aiming at linking different ecological scales, we have adopted an ecological upscaling approach. With reference to the area and the period considered, we calculated NDVI using satellite images, and we studied the relationships between this vegetation index, climate, and the anatomical parameters.

Our results showed that both number (i.e. ramet age) and mean width of the rings were negatively affected by altitude. The mean annual temperature and snowfall showed significant interaction effects on mean ring width and xylem mean lumen area. Cold years (i.e. low mean annual temperature) and abundant snowfall led to a reduction in the mean ring width, while the snowfall regime did not affect annual ring width in warm years. Xylem mean lumen area was affected by precipitation only in cold years. The mean growth season NDVI increased significantly in the time span considered and showed a positive relationship with the average age of the bilberry community. The interaction between rainfall and average temperature of the vegetative season influenced the NDVI: a negative relationship between vegetation index and rainfall was observed in cooler vegetative seasons, while the relationship was specular in the case of higher temperatures.

These results suggest that future scenarios should not overlook the precipitation regime effect by virtue of its possible role in snowpack permanence and drought during the growth season. In this light the shrub expansion could also be curbed by the change of precipitation regime and the increased frequency of extreme climate events (e.g., shift of snowfall regime and intensification of heat waves). Moreover, our findings confirmed the potential use of the remote sensing tool for the understanding of the response of dwarf shrub communities to climate change also for long-term monitoring of these plant communities.

How to cite: Vuerich, M., Trotta, G., Braidot, E., Elisa, P., Casolo, V., Alberti, G., and Boscutti, F.: From wood anatomy to satellites: new frontiers for the upscaling of climate change in the Alpine tundra, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4413, https://doi.org/10.5194/egusphere-egu23-4413, 2023.

Carbon dioxide [CO₂] has reached almost 420 ppm in 2022 (Friedlingstein et al. 2022) and may increase to 600 ppm by the year 2100. Understanding plant responses to increasing CO₂ is essential for predictions of plant productivity and of future climate (Ehlers et al. 2015). The hydrogen isotopes protium (¹H) and deuterium (²H or D) exhibit the largest isotope effects, and D is fractionated by both physical and biochemical processes. Thus, hydrogen isotope compositions of plant compounds have a remarkable potential to further our knowledge about plant physiological and environmental processes. However, whole-molecule δD depends on the δD of the plant’s water source, fractionation by transpiration, and enzyme isotope effects. To disentangle these influences, isotopomer analysis is required since enzyme isotope effects influence stable isotope abundance in specific intramolecular positions (Ehlers et al. 2015), called isotopomers. As CO₂ increases over decades, plant responses to T and CO₂ over decades are important. For forests, opposing effects of CO₂ and T determine if forests will in the future be a sink or source of CO₂ (Van der Sleen et al. 2015; Sperry et al. 2019). Furthermore, a mechanistic understanding of physiological responses is essential to be able to estimate future C assimilation using ecosystem models. Photorespiration is a side reaction of photosynthesis that reduces C assimilation in most vegetation, and photorespiration is reduced by increasing CO₂ yet exacerbated by rising T (Van der Sleen et al. 2015; Sperry et al. 2019). Therefore, we aim to unravel how photorespiration will develop under scenarios of rising CO₂ and climate change.

Tree rings help us understand interactions of plants and environmental drivers over decades-millennia. Variables that can be measured on tree rings fall into two groups. Variables like ring width are valuable for integrating effects of several environmental drivers on tree growth. In contrast, isotopomers depend on individual biochemical events and are therefore better for mechanistic studies.

We use an NMR (nuclear magnetic resonance) method to analyze isotopomers of the glucose units of tree-ring cellulose, to elucidate physiological changes in trees during past decades of increasing CO₂. In this contribution, we will report results of two kinds of experiments to investigate long-term tree responses.

First, in manipulation experiments we calibrate isotopomer responses to environmental drivers, in particular CO₂ and T. Second, we analyse tree-ring series over previous decades of rising CO₂, and use the calibrations from the manipulation experiments to deduce shifts in photosynthetic metabolism over decades. For selected tree species, we will present combined results from both kind of experiments, conclusions on physiological changes of these trees over past decades, and implications for future C assimilation by broadleaved trees.   

References

Ehlers et al., 2015. https://doi.org/10.1073/pnas.1504493112.

Friedlingstein et al., 2022. https://doi.org/10.5194/essd-14-1917-2022.

Sleen et al., 2015.  https://doi.org/10.1038/ngeo2313.

Sperry et al., 2019. https://doi.org/10.1073/pnas.1913072116.

How to cite: Haddad, L., Zuidema, P., Smith, B., Marshall, J., and Schleucher, J.: Isotopomers as tools to unravel forest carbon balance over decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-871, https://doi.org/10.5194/egusphere-egu23-871, 2023.

The analysis of a Europe-wide network of tree-ring stable isotopes has shown that the climatic signal of δ²H in tree-ring cellulose (C₆H₁₀O₅), is far weaker compared to those recorded in carbon (δ¹³C) and oxygen (δ¹⁸O)isotopes. Furthermore, the δ²H and δ¹⁸O relationships were shown to be site dependent and significantly deviated from the Global Meteoric Water Line. These results suggest that non-climatic effects are modifying the hydrological signature of δ²H. Recent experiments have underlined the potential of δ²H in tree-ring cellulose as a physiological indicator of shifts in autotrophic versus heterotrophic processes. However, the impact of these processes has not yet been quantified under natural conditions.

Defoliating insect outbreaks can disrupt photosynthetic production and carbon allocation, stimulating the remobilization of stored carbohydrates. Such disturbance events, therefore, provide unique opportunities to evaluate the impact of changes in the use of fresh versus stored non-structural carbohydrates, i.e., of non-climatic signals stored in δ²H. By exploring a 700-year tree-ring record from Switzerland, we assess the impact of 79 larch budmoth (LBM, Zeiraphera griseana) outbreaks on the growth of its Larix decidua host trees.

LBM outbreaks significantly altered the tree-ring isotopic signature, creating a ²H-enrichment and a depletion in ¹⁸O ¹³C. Changes in tree physiology during outbreak years are shown by the decoupling of δ²H and δ¹⁸O (O–H relationship), in contrast to the positive correlation in non-outbreak years. The O–H relationship in outbreak years was not significantly affected by temperature, indicating that non-climatic physiological processes dominate over climate in determining δ²H variations. We conclude that the combination of these isotopic parameters may serve as a metric for assessing changes in physiological mechanisms over time and that hydrogen isotopes can be considered as a proxy for non-climatic disturbance signals in dendrochronological research.

How to cite: Vitali, V., Peters, R., Lehmann, M., Leuenberger, M., Treydte, K., Büntgen, U., Schuler, P., and Saurer, M.: Exploring the climatic and non-climatic fingerprints of the hydrogen isotope signals in tree rings., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4254, https://doi.org/10.5194/egusphere-egu23-4254, 2023.

Under elevated CO₂, photosynthetic carbon isotope discrimination is expected to increase in response to photosynthesis stimulation driven by the growth of atmospheric CO₂. While this response is widely documented in laboratory, field experiments and short-term observations, long-term proxies indicate that such response is not universally observed in forested ecosystems. We investigated historical trends of  photosynthetic carbon isotope discrimination derived from carbon isotope measurements of tree rings (Δ¹³C) from a large set of chronologies across a variety of climate regions and biomes. We first predicted Δ¹³C response to CO₂ as reconstructed from a recent meta-analysis of paleo and elevated CO₂ data to detect and quantify the magnitude of Δ¹³C change-if any driven solely by increases in atmospheric CO₂. In a second step we assessed the deviation of observed tree-ring Δ¹³C from the that predicted in response to CO2 only. We found that the majority of tree-ring chronologies (~80%) exhibited a negative deviations from the expected Δ¹³C if driven by a CO₂ stimulation of photosynthesis (A). Chronologies with negative deviations were negatively correlated with vapor pressure deficit (VPD), and correspond to sites with a  maximum of 30% increase in VPD over the period of record. The widespread negative Δ¹³C deviations are consistent with a reduction of stomatal conductance (gs) or A having not increased as much as expected for a given CO₂-driven stimulation of A.

How to cite: Belmecheri, S., Szejner, P., Frank, D., Voelker, S., Lavergne, A., and Guerrieri, R.: Environmental drivers of observed photosynthetic carbon isotope discrimination in trees, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10684, https://doi.org/10.5194/egusphere-egu23-10684, 2023.

Forest productivity projections remain highly uncertain, notably because underpinning physiological controls are delicate to disentangle. Whereas photosynthesis (carbon source) has been commonly assumed to drive tree growth, growing evidence show that direct limitations to cambial activity (sink limitation) represent a substantial control of tree growth. It nevertheless remains unclear to which extent source and sink limitations interact to determine tree growth because these processes mostly respond to the same environmental cues. Radiation is a notable exception, but its annual variations are typically small and covary with multiples cofactors in natural settings. Large volcanic eruptions, which have been suggested to enhance forest photosynthesis globally through diffuse light fertilization, provide a unique opportunity to retrospectively isolate source and sink activities. Here, we use a multi-proxy dataset of tree-ring records distributed over the extra-tropical Northern Hemisphere to investigate the effect of eruptions on tree photosynthesis and growth. Dual tree-ring isotope records (¹³C and ¹⁸O) denoted a widespread 2–4 years increase of photosynthesis following eruptions, likely as a result of diffuse light fertilization. We found evidence that enhanced photosynthesis transiently drove ring width, but the latter further exhibited an independent decadal anomaly. Our results provide empirical evidence of essentially decoupled photosynthesis and tree growth response to large volcanic eruptions, hence suggesting widespread sink limitation to tree growth over the Northern Hemisphere.

How to cite: Cabon, A. and Anderegg, W. R. L.: Large volcanic eruptions elucidate source vs sink limitations to tree growth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4392, https://doi.org/10.5194/egusphere-egu23-4392, 2023.

Variation in life-history and ecophysiological traits has key ecological significance in plants, in which environmental changes play a central role throughout their life cycles. Stone pine (Pinus pinea L.) is one of the most characteristic species of the Mediterranean basin that is able to grow under harsh, limiting conditions and is typically defined as a masting species. Considering the high economical value associated with edible nut production, the masting habit of stone pine has been a main concern for forest management of the species. Here, we investigate the masting mechanism through characterization of temporal changes in tree ring-width (TRW), ecophysiological (cellulose Δ¹³C and δ¹⁸O) and cone yield patterns for five monospecific stands in north-central Spain. The regional positive (r = 0.41, SE = 0.25) and negative (r = –0.89, SE = 0.49) relationships involving tree growth vs. Δ¹³C and δ¹⁸O, respectively, suggest drought impairing carbon uptake via stomatal regulation for water saving occurring in the area during the period of 1960–2016. Increasingly positive relationships between TRW and Δ¹³C indicate intensifying impacts of drought on tree performance over time. By analyzing Δ¹³C–yield interannual dynamics, we found variable coupling of cone production with leaf-level gas exchange during the 4-year reproductive cycle of the stone pine. Particularly, the strongly positive relationships between Δ¹³C and yield with a 3-year lag, corresponding to strobili development and pollination, vanished and became non-significant in the recent decades. Thus, weather conditions during conelet emergence are not driving anymore cone production, which initially was sink-limited. In contrast, the relationships between Δ¹³C and a 1-year lagged yield, i.e. when cone enlargement and seed maturation occur, largely increased over the study period running from nearly zero (1960–1989 period) to above 0.50 (1987–2016 period) indicating a recent source limitation of reproduction driven by a harsher climate. Our results provide evidence that, although cone yield does not impose a penalty on aboveground biomass increments, it is becoming progressively limited by warming-induced effects of drought on tree ecophysiological performance.

How to cite: Shestakova, T. A., Sin, E., and Voltas, J.: Long-term physiological insights of cone production as related to carbon isotope fractionation in stone pine forests of northern Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11894, https://doi.org/10.5194/egusphere-egu23-11894, 2023.

Studies on physiological response of suppressed trees to selection harvest are scarce. Understanding how trees respond to changes in environmental factors following harvest is needed for continuous cover forestry that aims to optimize both environmental impacts and economical gain. The physiological response of the trees can be understood by measuring stable carbon isotope composition (δ¹³C) which records the changes in photosynthesis and water use of the tree. The processes that determine the response can be further elaborated by comparing the measured isotopic signal to process-level model simulations.

We studied the response of Norway spruce (Picea abies) trees to selection harvesting on a fertile drained peatland forest located in southern Finland. The studied area consisted of a control plot which was left intact and of harvested plot which was thinned in March 2016. We measured intra-annual δ¹³C from tree-rings covering the period from 2010 to 2020 at the Stable Isotope Laboratory of Luke (SILL) (Lehtonen et al., accepted). The measured δ¹³C was compared to modelled ¹³C discrimination (Δ¹³C) simulated with a vertically resolved ecosystem model describing tree photosynthesis (Launiainen et al., 2015).

The δ¹³C measurements showed that after the harvest Δ¹³C decreased already on the following growing season. The overall decrease was ca. 3.3 ‰ on average between pre- and post-harvest periods. The decrease was caused by both changes in CO₂ assimilation of the spruce trees and differences in meteorological conditions between pre- and post-harvest years. We simulated Δ¹³C with three different models with increasing number of fractionation processes considered. All three models predicted that as a response to harvest the Δ¹³C would decrease, however, none of the models could replicate the observed 3.3‰ drop in Δ¹³C. The most complex Δ¹³C model that included ¹³C fractionation in mitochondrial and photorespiration as well as transport of CO₂ from stomata to mesophyll was the closest to the measurements.

The vertically resolved model allowed us to estimate that the changes in photosynthetically active radiation, relative humidity and needle temperature following the harvest contributed the most to the observed decrease in Δ¹³C. Further, model sensitivity analysis showed that the modelled Δ¹³C is the most sensitive to g₁ parameter and mesophyll conductance. The g₁ parameter is related to calculation of stomatal conductance (Launiainen et al., 2015; Medlyn et al., 2011). By tuning the g₁ parameter and mesophyll conductance we were able to bring the modelled Δ¹³C closer to the observations.

References

Launiainen et al., Ecological Modelling, 312, 385-405, 2015.
Lehtonen et al., Forest Ecology and Management, accepted.
Medlyn et. al., Global Change Biology 17, 2134–2144, 2011

How to cite: Tikkasalo, O.-P., Leppä, K., Launiainen, S., Peltoniemi, M., Mäkipää, R., Rinne-Garmston, K., Sahlstedt, E., Young, G., Bokareva, A., Lohila, A., Korkiakoski, M., Schiestl-Aalto, P., and Lehtonen, A.: Modelling the change in tree ring 13C discrimination as a response to selection harvest in a drained peatland forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7502, https://doi.org/10.5194/egusphere-egu23-7502, 2023.

Accelerated development of energy resources around the world has significantly increased forest change associated with oil and gas activities, leading to both carbon dioxide and methane emissions. The impacts of these anthropogenic indirect greenhouse gases play a significant role on forest ecosystems at the regional and global scales.

In this study we aim to reveal site-specific differences in stable carbon isotope (δ¹³С) variability of pine trees (Pinus sylvestris) growing on the territory of (i) oil and gas reservoirs located in Almetyevsk and Leninogorsk regions (Tatarstan Republic, Russian Federation) classified as “disturbed”; and (ii) in a remote “undisturbed” site in Raifa, which is located ca. 250 km away from the oil and gas deposits.

Tree cores were sampled from the south- and north-facing sides of each of the nine trees for both study sites using a Pressler increment borer. The state-of-the-art classical dendrochronological method was applied for the tree-ring width measurements and cross-dating. Each annual ring was split using a sharp BA-170P NT blade under the Leica M50 microscope. Stable carbon isotope measurements were performed for each year separately using a Delta V Plus isotope mass spectrometer (Thermo Fisher Scientific, Germany) via a Flash HT Plus in constant flow mode. Based on the nine individual trees stable carbon isotope chronologies were developed from 1930 to 2022. Tree-ring δ¹³C in wood chronologies were corrected according to δ¹³C atmospheric CO₂ for both study sites.

Results of our study indicate significant differences between carbon isotope variability in tree rings from “disturbed” the oil and gas deposits site, which is rapidly developed over the recent decades compared to the “undisturbed” natural forest site.

This work was funded by the Kazan Federal University Strategic Academic Leadership Program (PRIORITY-2030).

How to cite: Churakova (Sidorova), O., Batalin, G., Gareev, B., Mingazov, G., Terekhin, A., Tishin, D., Kuzina, D., and Nurgaliev, D.: Impact of gas emissions from oil and gas reservoirs on stable carbon isotope variability in tree rings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9286, https://doi.org/10.5194/egusphere-egu23-9286, 2023.