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Interdisciplinary Tree-Ring Research

Tree rings are one of nature’s most versatile archives, providing insight into past environmental conditions at annual and intra-annual resolution and from local to global scales. Besides being valued proxies for historical climate, tree rings are also important indicators of plant physiological responses to changing environments and of long-term ecological processes. In this broad context we welcome contributions using one or more of the following approaches to either study the impact of environmental change on the growth and physiology of trees and forest ecosystems, or to assess and reconstruct past environmental change: (i) dendrochronological methods including studies based on tree-ring width, MXD or Blue Intensity, (ii) stable isotopes in tree rings and related plant compounds, (iii) dendrochemistry, (iv) quantitative wood anatomy, (v) ecophysiological data analyses, and (vi) mechanistic modelling, all across temporal and spatial scales.

Co-organized by BG3
Convener: Kerstin Treydte | Co-conveners: Elisabet Martinez-SanchoECSECS, Flurin Babst, Jernej Jevšenak
| Mon, 23 May, 13:20–14:48 (CEST), 15:10–16:38 (CEST)
Room 0.14

Mon, 23 May, 13:20–14:50

Chairpersons: Kerstin Treydte, Elisabet Martinez-Sancho

Kristina Anderson-Teixeira and the ForestGEO dendrochronology team

Tree rings provide an invaluable long-term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree-ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree's growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3-month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3-month seasonal windows), with concave-down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible.

How to cite: Anderson-Teixeira, K. and the ForestGEO dendrochronology team: Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3077, https://doi.org/10.5194/egusphere-egu22-3077, 2022.

Stefan Klesse et al.

Drought legacy effects in radial tree growth have been extensively studied over the last decade and are found to critically influence carbon sequestration in woody biomass. Typically quantified as a deviation from “normal” growth, drought legacy magnitude and statistical significance depend on the definition of expected vs. unexpected growth variability under average conditions – a definition that has received insufficient theoretical validation.

Here, we revisit popular legacy effect analyses using the International Tree-Ring Data Bank (ITRDB) and employ a synthetic data simulation to disentangle four key variables influencing the magnitude of legacy effects. We show that legacy effects i) are mainly influenced by the overall auto-correlation of radial growth time series, ii) depend on climate-growth cross-correlation, iii) are directly proportional to the year-to-year variability of the growth time series, and iv) scale with the chosen extreme event threshold. Our analysis revealed that legacy effects are a direct outcome of the omnipresent biological memory.

We further found that the interpretation of legacy effects following individual drought events at specific sites is challenged by high stochasticity, and show that the commonly perceived stronger legacy effects for conifers are the result of higher auto-correlation compared to deciduous broadleaves. Given that the existing literature has not sufficiently addressed biological memory, we present two pathways to improve future assessment and interpretation of legacy effects. First, we provide a simulation algorithm to a posteriori account for auto-correlated residuals of the initial regression model between growth and climate, i.e. a corrected Null model to determine statistical significance, thereby retrospectively adjusting expectations for “normal” growth variability. The second pathway is to a priori include lagged climate parameters in the regression model. This substantially reduces the magnitude of observed legacy effects and thus challenges us to revisit estimates of drought-induced growth deviations by considering the full spectrum of expected growth behavior. 

How to cite: Klesse, S., Babst, F., Evans, M. E. K., Hurley, A., Pappas, C., and Peters, R. L.: Drought legacy effects in radial tree growth are rarely significant under heightened statistical scrutiny, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3881, https://doi.org/10.5194/egusphere-egu22-3881, 2022.

Florian Schnabel et al.

Intensifying climate change is successively increasing the frequency and intensity of extreme climate events such as droughts. In 2018–2019, Central European forests were hit by two consecutive hotter drought years that were unprecedented in their severity at least in the last 250 years. Such hotter droughts, where drought coincides with a heat wave, may have severe detrimental impacts on forest ecosystems as highlighted by reports of widespread tree defoliation and mortality across Central Europe in 2018–2019. Here, we examine the effect of this unprecedented event on tree growth and physiological stress responses (measured as increase in wood carbon isotope composition, Δδ13C) in a Central European floodplain forest ecosystem. We used tree rings of the dominant tree species Quercus robur, Acer pseudoplatanus and Fraxinus excelsior to compare growth responses, Δδ13C and drought legacy effects during the consecutive drought years 2018–2019 with effects observed in former single drought years (2003, 2006, 2015). We found that tree growth was, except for F. excelsior, not reduced in 2018 and that drought responses in 2018 were comparable to responses in former single drought years. This indicates that water availability in floodplain forests can partly buffer drought effects and meteorological water deficits. Nonetheless, the 2018 drought – which was the hottest and driest year since the start of records – induced drought legacies in tree growth while former drought years did not. Consistent with this observation, all tree species showed strong decreases in growth and increases in Δδ13C in the second hotter drought year 2019. The observed stress responses in 2019 were stronger than in any other examined drought year. We posit that the cumulative effect of two consecutive hotter drought years likely caused this unprecedented stress response across all species. Drought responses were consistent for both drought-stress indicators (growth response and Δδ13C), but the timing and magnitude of responses were species-specific: Q. robur exhibited the overall smallest response, followed by A. pseudoplatanus with the strongest response in F. excelsior. We discuss these species-specific differences in light of the species’ stomatal control (inferred from high-resolution sap flow measurements during drought at our site) and species’ resistance to xylem cavitation. Overall, our findings highlight that consecutive hotter droughts constitute a novel threat to forests, even in floodplain forests with comparably high levels of water supply. These results and similar research may contribute towards understanding and forecasting tree species responses to more frequent hotter droughts under intensifying climate change.

How to cite: Schnabel, F., Purrucker, S., Schmitt, L., Engelmann, R. A., Kahl, A., Richter, R., Seele-Dilbat, C., Skiadaresis, G., and Wirth, C.: Impacts of the 2018-2019 drought: cumulative growth and stress responses in a floodplain forest ecosystem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6271, https://doi.org/10.5194/egusphere-egu22-6271, 2022.

Jeanne Rezsöhazy et al.

Tree-ring widths represent the most commonly used proxy to reconstruct the climate of the last millennium at high resolution, thanks to their large-scale availability. The approach often relies on a relationship between tree-ring width series and climate estimated on the basis of a linear regression. The underlying linearity and stationarity assumptions may be inadequate. Dendroclimatic process-based models, such as MAIDEN (Modeling and Analysis In DENdroecology), may be able to overcome some of the limitations of the statistical approach. MAIDEN is a mechanistic ecophysiological model that simulates tree-ring growth starting from surface air temperature, precipitation and CO2 concentration daily inputs. In this study, we successfully include the MAIDEN model into a data assimilation procedure as a proxy system model to robustly compare the outputs of an Earth system model with tree-ring width observations and provide a spatially-gridded reconstruction of continental temperature, precipitation and winds in the mid to high latitudes of the Southern Hemisphere over the past centuries. More specifically, we evaluate the benefits of using process-based tree-growth models such as MAIDEN for reconstructing past climate with data assimilation compared to the commonly used linear regression. The comparison of the reconstructions with instrumental data indicates an equivalent skill of both the regression- and process-based proxy system models in the data assimilation framework. Nevertheless, the MAIDEN model still brings important advantages that could result in more robust reconstructions beyond the instrumental era. Moreover, improvements continuously made in such models or in their calibration procedure also offer encouraging perspectives. Important steps have thus been made to demonstrate that using a process-based model like MAIDEN as a proxy system model is a promising way to improve the large-scale climate reconstructions with data assimilation.

How to cite: Rezsöhazy, J., Dalaiden, Q., Klein, F., Goosse, H., and Guiot, J.: Using a process-based dendroclimatic proxy system model in a data assimilation framework: a test case in the Southern Hemisphere over the past centuries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4552, https://doi.org/10.5194/egusphere-egu22-4552, 2022.

Jacinda O'Connor et al.

High-resolution palaeoclimate proxies are fundamental to our understanding of the diverse climatic history of the Australian mainland, particularly given the deficiency in instrumental datasets spanning greater than a century. Annually resolved, tree-ring based proxies play a unique role in addressing limitations in our knowledge of interannual to multi-decadal temperature and hydroclimatic variability prior to the instrumental period. Here we present cross-dated ring-width (RW) and minimum blue-intensity (BI) chronologies spanning 70 years (1929 – 1998) for Podocarpus lawrencei Hook.f., the Australian mainland's only alpine conifer, based on nine full-disk cross-sections from Mount Loch in the Victorian Alps. Correlations with climate variables from observation stations and gridded data reveal a significant positive relationship between RW and mean monthly maximum temperatures in winter throughout central Victoria (r = 0.62, p < 0.001), and a significant negative correlation to winter precipitation (r = -0.51, p < 0.001). We also found significant negative correlations between RW and monthly snow depth data from Spencer Creek in New South Wales (r = -0.60, p < 0.001). Of the assessed BI parameters, delta blue-intensity (ΔBI; the difference between early- and late-wood BI) displayed the greatest sensitivity to climate, with robust spatial correlations with mean October to December maximum and minimum monthly temperatures (r = -0.43, p < 0.001; r = -0.51, p < 0.001) and July precipitation (r = 0.44, p < 0.001), across large areas of northern Victoria. These promising findings highlight the utility of this species for future work. With the very limited availability of suitable long-lived and cross-datable species on the Australian mainland, these results have implications for the significant advancement of palaeoclimate records in southeastern Australia and the potential for improvement in our understanding of past climate in the region.

How to cite: O'Connor, J., Henley, B., Brookhouse, M., and Allen, K.: Piloting novel multi-centennial palaeoclimate records from mainland southeast Australia., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6899, https://doi.org/10.5194/egusphere-egu22-6899, 2022.

Nasrin Salehnia and Jinho Ahn

Trees are one of the best sources of high-resolution proxy data to understand the past climate. By analyzing Tree Ring Width (TRW) data with climate variables and indicators, we can find main clues, which can help us to encode paleoclimate signals. Nowadays, scientists try to model TRW data with various climate data versus reconstructing the mentioned data for an extended period through different statistical methods. One of the newest methods is AI (Artificial Intelligence). This study aimed to model TRW data with the most effective climate variables by comparing the statistical methods vs. the AI method. First, seven climate variables were gathered from the nearest synoptic station (Sokcho) to the TRW site (Whachae Peak-Sorak), in northeast South Korea, during 1901–1998. The climate variables include maximum temperature (Tmax), minimum temperature (Tmin), mean temperature (Tm), diurnal temperature range (DTR = Tmax – Tmin) (°C), precipitation (Pr) (mm), and vapor pressure (VP) (hPa). The in-situ data were applied to correct the Climate Reach Unit (CRU, Version 4.03). Moreover, we have checked two meteorological drought indices, namely the Palmer drought index (PDSI) and standardized precipitation index (SPI). We applied two regression methods (namely multiple linear regression (MLR) and stepwise regression (SR)) and one AI (Nonlinear autoregressive with exogenous input (NARX)) method. In the first step of analyzing data, we did not see any specific significant results for the relationship between drought effects and TRW data in the case study. Then in the second step, modeling continued with the climate variables. Finally, the results demonstrated that among the three used methods, the NARX method achieved the best outcomes, as MLR with r = 0.44 (p < 0.003); SR with r = 0.27 in p < 0.001; and the NARX model was the best outcomes with r = 0.78. This study revealed that regression methods were not strong enough to reconstruct TRW data. Whereas, by noticeable results, the AI method has obtained the best performance.    

How to cite: Salehnia, N. and Ahn, J.: Applying artificial intelligence in modeling the relationship of tree ring growth index with different climate variables, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2212, https://doi.org/10.5194/egusphere-egu22-2212, 2022.

Liliana Siekacz et al.

'Blue Rings' (BRs) are distinct wood anatomical anomalies recently discovered in several tree species. Studies connect their occurrence to lower than normal temperatures during the cell wall lignification phase of xylogenesis which usually continue after radial growth is completed, following the growth season. BRs are also potentially more sensitive to temperature than frost rings which require freezing temperatures (linked with the forcing of volcanic eruptions) to form. Therefore, systematic analysis of blue rings can add another level of time resolution and/or sensitivity to dendroclimatic studies.  North American bristlecone pine is an invaluable resource for paleoclimatological reconstruction due to its extreme longevity (its specimens are reported to commonly exceed the age of 4000 years), high durability and favourable environmental conditions which hamper decay, enabling the construction of chronologies spanning more than 8000 years. Preliminary results for the last 1000 years reveal that BRs in bristlecone pine coincide significantly with major volcanic eruptions. Detailed analysis of recorded temperature conditions in the years of BRs formation can therefore provide additional information on the impact of volcanic eruptions on climate in periods where meteorological observations are unavailable. To establish baselines for this, we present the climatic context of BR occurrence in bristlecone pine for the period since 1895 where modelled surface mean monthly temperatures are available for the grid cell pertaining to the study area location (4km spatial resolution, from PRISM Climate Group, Oregon State University). A group of 83 cores of bristlecone pine (originating from the vicinity of the Sheep Mountain/Patriarch Grove area of the Ancient Bristlecone Pine Forest in the White Mountains of California, 37.5 W 118.2 N) was thin sectioned on a GSL 1 microtome and further prepared following Gärtner & Schweingruber (2013) safranine and astrablue staining procedures to reveal lignified cell walls in red and underlignified cell walls in blue. Scanned and digitized thin-sections were measured and cross-dated noting years of BR occurrence.  A generalized linear mixed-effects model (GLMM) was fit with mean monthly temperatures and distance from treeline (DTL) as independent variables, and a binary response variable representing the absence (0) or presence (1) of a BR in a particular year, in a particular sample. Results indicate that BRs positively correlate with mean monthly temperatures of February and October and negatively with April, June, August, September and DTL. BR formation most strongly correlates with September temperatures, and interestingly, also lacks correlation with July temperatures.

How to cite: Siekacz, L., Pearson, C., Salzer, M., and Koprowski, M.: Climatic context of blue ring formation in high elevation bristlecone pine (Pinus longaeva D.K. Bailey)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6713, https://doi.org/10.5194/egusphere-egu22-6713, 2022.

Ionel Popa et al.

A composite Silver fir tree ring width chronology from seven mountain sites in the Eastern Carpathian Mountains (Europe) was established for AD 1588-2021, with SSS>0.8 and EPS>0.85 for AD 1750-2012. The bootstrap correlation analysis of the tree ring index with monthly climate parameters (temperature and precipitation) shows a positive and relatively time constant response to mean winter-spring temperature (November to March). The correlation between Silver fir tree ring proxy and winter-spring temperature is high and statistically significant (0.556 at p<0.05). The reconstruction statistics (R2, RE, CE and DW) indicate a good skill of the regression model between proxy data and winter temperature back to 1901. RE and CE statistics range between 0.32 and 0.39, and DW has values between 2.05 and 2.18. These results show good reliability of the model, and for the entire period, the reconstruction explains ~ 30% of winter temperature variability. The temperature reconstruction from AD 1750 shows inter-decadal fluctuation induced by low frequencies sinusoids (waves). The reconstructed mean winter temperatures for the 1750-2012 period was -2.93°C with -0.31°C colder than the 1961-2009 reference period. The longest period with high frequencies of years with low temperatures was recorded in 1740-1800, coinciding with the end of the Little Ice Age. After this coldest winter period, a six-year period with extreme warm winters was identified. The warming trend was more distinguishable science AD 1880 to the present, especially through the high frequency of mild winters. The coldest reconstructed winters for entire period were find in 2003 (anomalies= -1,56), 2012 (anomalies = -1,32) and 1965 (anomalies = -1,24). The warmest winters were recorded in 2001 (anomalies = +1,71), 1998 (anomalies = +1,48) and 2007 (anomalies = +1,37). The pattern of spatial correlation between proxy data and winter-spring temperature releases a wide extend of high correlation (>0.5), covering the North-Western Carpathians, continues with the Eastern chain of the Carpathian Mountains and finishes with the extreme South-East of Romania. Correlation with the Central Europe gridded temperatures is significant (>0.4), and with the Alpine Arc grid, temperatures are quite low (0.3). This result provides a regional scale of the winter-spring temperature reconstruction, suggesting a possible west-east gradient across Europe, potentially influenced by the interplay between the eastward expansion of Atlantic influence and the westward expansion of the West Asian influence.

How to cite: Popa, I., Roibu, C., Perșoiu, A., Kern, Z., and Sidor, C.: Silver fir tree ring width: a proxy for winter temperature variability in the Carpathians?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8154, https://doi.org/10.5194/egusphere-egu22-8154, 2022.

Juliana Nogueira et al.

Instrumental data derived from meteorological stations provide a fairly reliable record of climate variability for at least the last century for most parts of Europe. Proxy-based climate reconstructions have been extensively developed throughout the continent over recent decades to extend these records further back in time. However, to date, parts of central and eastern Europe remain underrepresented, leading to gaps in high-resolution climatic information even in recent centuries. This issue is predominantly linked to large uncertainties in existing records and limitations in data quality associated with a generally weak climatic sensitivity of available proxy records. The REPLICATE project, presented here, aims to address this deficiency by utilizing various tree-ring parameters from temperature-sensitive Norway spruce (Picea abies). The samples, collected from treeline or near-treeline environments, will be used to develop a set of temperature reconstructions across four sub-regions of the Carpathian Mountains. By doing so, we aim to contribute to filling in the spatial paleoclimatic and data quality gap in central-eastern Europe. To improve the climatic signal, we utilized a combination of tree ring width (TRW) corrected for non-climatic (disturbance) trends and blue intensity (BI) series derived from scanned images as a surrogate for maximum latewood density. We also developed a novel tree-ring parameter similar to BI based on high-resolution reflected light microscope images of the tree sample surface – termed surface intensity (SI) – which accounts for resolution and color bias limitations commonly encountered in BI datasets. Additionally, traditional thin section-based quantitative wood anatomy (QWA) parameters and their reflected light surface imaging-based counterparts (sQWA) were also included. Integrating this range of tree-ring parameters in a complementary fashion helps isolate, optimize and extract stronger climatic signals by accounting for and minimizing a range of parameter-specific limitations and biases, yielding improved calibration with a more accurate representation of low-frequency climatic trends and high-frequency extremes. From these multi-parameter tree-ring chronologies, annually resolved, robust, high-quality summer temperature reconstructions, extending to the early to mid-17th century, are under development for four Carpathian locations (i.e., northern Slovakia, western Ukraine, northern and central Romania). Initial results indicate that the reconstructions based on such a multi-parameter approach can produce paleoclimatic records with reduced uncertainty that explain between 50% and 60% of the regional temperature variability. These reconstructions will contribute to a more highly resolved temperature dataset in a part of Europe with considerable research potential, resulting in an improved spatial representation of past European temperature fluctuations. Also, by providing a reliable historical context to evaluate return periods and magnitudes of temperature extremes, they will contribute to assessing potential future socioeconomic impacts of climate change (e.g., on agriculture) and developing possible mitigation solutions.

How to cite: Nogueira, J., Rydval, M., Begović, K., Lexa, M., Schurman, J., Jiang, Y., von Arx, G., Björklund, J., Seftigen, K., and Tumajer, J.: Multi-parameter reconstruction of the past 400 years of Carpathian temperatures from tree rings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6541, https://doi.org/10.5194/egusphere-egu22-6541, 2022.

Miloš Rydval et al.

Climate change is a global-scale issue of societal, economic, and political importance and so understanding the climate of the present within the context of past climate variability is of vital importance. Dendroclimatic reconstructions play a key role in contextualizing recent climate change by improving our understanding of historical climate conditions. The climatically-sensitive blue intensity (BI) tree-ring parameter is gaining prominence as a more affordable and accessible alternative to traditional X-ray densitometry. Yet the accurate representation of low-frequency trends and high-frequency extremes using scanner-based BI remains a challenge due to color-related biases and resolution limitations. As part of the REPLICATE project, which aims to develop a set of robust multi-parameter temperature reconstructions from Carpathian Norway spruce (Picea abies) tree rings, methodological advances in sample surface preparation, imaging and measurement techniques have produced series analogous to BI from ultra-high resolution (~74 700 true dpi) images. Series from these microscope-based reflected light images of the tree-ring sample surface, termed surface intensity (SI), represent the binary (black-white) segmentation of wood anatomical structure, which approximates anatomical density. By eliminating color altogether and using a high-resolution system, the most substantial drawbacks of scanner BI (i.e., discoloration and resolution biases) are bypassed and hence climate signal optimization is achieved by more accurately representing low-frequency climatic trends and high-frequency extremes. A comparison of SI chronologies with a multi-parameter tree-ring dataset from a large-scale parameter assessment study by Björklund et al. (2019) showed that this novel SI parameter can outperform its BI couterpart in terms of common signal (interseries correlation) and climate signal strength, and that it is on par with the best-performing X-ray densitometric chronologies. However, existing programs are not currently designed to effectively capture SI measurements and so additional development of measurement software is required to unlock the full potential of this new parameter. Continued improvement of high-resolution imaging techniques will aid the attainment of unbiased long tree-ring chronologies by overcoming color biases and resolution issues, but also holds promise for the development of surface quantitative wood anatomy (sQWA) datasets from reflected light images of samples. These improvements will therefore not only lead to more accurate dendrochronological paleoclimatic records and climate reconstructions but will also find future application in a broad range of dendrochronological contexts.

How to cite: Rydval, M., Björklund, J., von Arx, G., Begović, K., Lexa, M., Nogueira, J., Schurman, J., and Jiang, Y.: High-resolution wood surface imaging for dendrochronology: towards the development of unbiased reflected light timeseries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10771, https://doi.org/10.5194/egusphere-egu22-10771, 2022.

Vladimir Shishov et al.

More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic activity of the cambium. Despite this importance, there are still few attempts to quantitatively describe cambium dynamics.

In this study, we present a state-of-the-art Band Model of Cambium Development, based on the hypothesis of the kinetic heterogeneity of the cambial zone and the connectivity of the cell structure as the forming water-conducting tissue of the coniferous tree.

The new model significantly simplifies the assessment of seasonal cell production for individual trees of studied forest stand based on the same climate signal. It allows the entire range of individual absolute variability in the forming rings of any tree in the stand to be quantified.

Due to the simplicity new approach can be applied for the most of conifer forests where the climate plays a role of limiting growth factor.

How to cite: Shishov, V., Tychkov, I., and Zelenov, G.: A Band Model of Cambium Development as a new tool of xylogenesis development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-174, https://doi.org/10.5194/egusphere-egu22-174, 2022.

Mikhail Zharkov et al.
Margarita Popkova et al.
Daria Belousova and Vladimir Shishov

Mon, 23 May, 15:10–16:40

Chairpersons: Elisabet Martinez-Sancho, Kerstin Treydte

Roel BRienen et al.

The Amazon is the largest catchment in the world, discharging ca. 17% of global freshwater, and plays an important role in the global water and carbon cycles. Recent decades have seen an increase in floods of the Amazon river, but also increases in dry season severity and length. Instrumental long-term climate data to assess the magnitude of these changes are relatively scarce. Tree-ring based climate reconstructions may help improving past climate records from this vast region and put these changes in historical perspective.

While standard tree ring widths chronologies in the tropics are generally weakly related to climate, tree ring d18O records from Cedrela odorata in Bolivia are a proven proxy for Amazon basin-wide rainfall, and thus Amazon river discharge. However, these “terra firme” trees grow during the wet season and thus do not provide information on the dry season. Here we present a new proxy for dry season precipitation from Amazonian floodplain trees of Macrolobium acaciifolium from the western Amazon. As this species grows during the non-flooded period, the dry season, their tree ring d18O records should pertain variation of dry season precipitation d18O. A comparions of tree ring d18O from floodplain and terra firme trees show opposing trends since the 1970s, indicating increases in wet season precipitation and decreases in dry season precipitation. These records are consistent with recent trends in peaks and troughs of Amazon river levels, and provide support of a recent intensification of the Amazon hydrological cycle. We conclude that tree-ring d18O records are an important tool for tropical climate reconstructions, and even allow climate reconstructions with seasonal resolution. In addition, as signals arise from variation in (meteorological) precipitation d18O, tree ring d18O chronologies do not need detrending, and show highly synchronized patterns even over very large scales, allowing rigorous cross-dating between species and sites, and facilitating further development in this vast region

How to cite: BRienen, R., Cintra, B., Baker, J., Gloor, E., Schöngart, J., Boom, A., Helle, G., and Leng, M.: Oxygen isotopes in Amazon tree rings as indicators of change in the hydrological cycle , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5358, https://doi.org/10.5194/egusphere-egu22-5358, 2022.

Olga V. Churakova (Sidorova) et al.

Rapid temperature and vapor pressure deficit (VPD) increase along with precipitation decrease over the past decades lead to massive wildfires and permafrost degradation in boreal forests. Conifer trees growing in subarctic regions are highly sensitive to these climatic changes due to their location at the high latitudes, where air temperature is the limiting factor, but also water relations have a strong impact on tree growth.

In this study, we aimed (i) to assess the usability of local vs. gridded climate data; (ii) to reveal how conifer trees capture temperature and moisture signals based on the local weather station data vs. gridded data from the two Siberian sites in northeastern Yakutia and eastern Taimyr, and one site from northwestern Canada in Mackenzie Delta; (iii) to perform trend analysis of climatic data and δ18O in tree-ring cellulose; and (iv) to carry out spatial correlation analysis of oxygen isotope patterns and determine the distribution of climatic signal over broad geographical scales in the Siberian and Canadian subarctic.

Comparative analysis of the local and gridded climatic data (air temperature, precipitation and VPD) for the three study sites showed that mainly temperatures are highly correlated between each other. Subarctic trees grow in a temperature-limited environment; therefore, the large spatial coherence of temperature signals is not surprising. Conversely, insignificant correlations between local and gridded for precipitation and rather low correlations for VPD is attributed to the more heterogeneous nature of moisture variables at larger spatial scales. Therefore, analyzing moisture changes in the subarctic using local weather station data is advantageous compared to gridded data.

Trend analysis of the climate data showed that drastic changes in climate variability occurred from the 1980s in the investigated subarctic regions and were even more pronounced from 2000 to 2021. Recent warming and development of drought conditions were stronger in the Canadian subarctic than the Siberian subarctic sites. Drastic precipitation changes, temperature and VPD increase mainly occurred during winter, spring and autumn in the studied subarctic regions. New updated stable isotope chronologies from remote subarctic regions allowed us to accurately reconstruct moisture changes using precipitation and VPD data from the local weather stations while reconstructing air temperature using gridded data.

This research was funded by the Russian Science Foundation (RSF) grant number 21-17-00006.

How to cite: Churakova (Sidorova), O. V., Zharkov, M. S., Fonti, M. V., Trushkina, T. V., Barinov, V. V., Taynik, A. V., Porter, T. J., Kirdyanov, A. V., Arzac, A., and Saurer, M.: Tree-ring oxygen isotope patterns from Siberian and Canadian subarctic to test usability of local versus gridded climate data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8756, https://doi.org/10.5194/egusphere-egu22-8756, 2022.

Nazimul Islam et al.

Stable isotope analyses (δ18O, δ2H) combined with the tree-ring dating have enormous potential for tracing freshwater resource availability under changing climate and in the context of the impacts of other human activities. This study focusses on the isotopic composition of tree-rings in combination with an anatomical analysis of the European Larch (Larix Decidua) species from different upstream and downstream sites along the Turtmänna river in south-western Switzerland. The results show distinctive patterns of year-to-year tree-ring growth from their constructed chronology dated back to 1851 (i.e. a 170-year record). A trend of a decreasing growth was noted over the last two decades. Decreasing growth was correlated (r = 0.50) with a decrease in precipitation and an increase in temperature (r = 0.30) during the growing season (between June and October) of previous and current years. The isotopic analysis shows a depletion in 18O in the trees fed by glacial meltwater close to the river as compared to the trees fed by precipitation distal to the river. Given the changes in climate, trees closer to the river are becoming more dependent on river-derived water, which in turn is sourced from melting glaciers. This hence has important consequences for the hydropower generation and water availability.

How to cite: Islam, N., Vennemann, T., and Lane, S. N.: Use of stable isotope signals from tree rings as proxy for tracing the combined effects of climate change and hydropower on glacier-derived water resources in the Turtmänna river catchment, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5873, https://doi.org/10.5194/egusphere-egu22-5873, 2022.

Javier del Hoyo Gibaja et al.

Within the field of dendrochronology, different sub-disciplines arise using the information stored in the wood for a variety of purposes. In this study, we use dendroprovenance to develop a methodology that allows us to infer the source area of instream large wood (LW) at the river basin scale applying fingerprinting techniques.

LW is mainly supplied to fluvial ecosystems by riparian vegetation and nearby areas, and the presence of wood in a river determines its geomorphology and ecology; but also, it is associated with an increase in danger and risk to infrastructures and population. For this reason, research on the origin of LW is essential to better understand LW processes and to facilitate decision-making in the management of the forest and the river.

The tracers we have used so far are the stable isotopes coming from the water molecule: hydrogen (D/H) and oxygen (18O/16O). These isotopes show spatial variations depending on evaporation-precipitation processes and resulting isotopic fractionation. Subsequently, the water absorbed by a tree growing in a particular place stores this isotopic signal, and when that tree (or a piece of it) falls and becomes part of the river ecosystem, we can use this isotopic signal to infer the origin of the wood.

Our study site is a 50 km reach of the Rhone River between Lake Geneva and Genissiat dam (3000 km2 of catchment) in France, where all arriving wood is stored upstream from the dam. The goal is to differentiate the wood coming from the two main tributaries, the Arve and Valserine rivers (located in different mountain systems) since they are the main wood suppliers at Genissiat.  

Preliminary results show clear differences in the isotopic composition when comparing samples from one tributary and the other, with the most notable differences in the most recent tree rings.

Lastly, we plan to analyze other tracers such as minor and trace elements that are linked to the geology and combine them with the isotopic ratios in a multivariate analysis to determine the origin of the wood in a more accurate manner. Consequently, we will have developed a new dendroprovenance method that can be extrapolated to other fields, taking a step forward in the application of our knowledge about tree rings.

How to cite: del Hoyo Gibaja, J., Vennemann, T., Vauridel, M., and Ruiz-Villanueva, V.: Dendroprovenancing instream wood at the watershed scale applying fingerprinting techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7719, https://doi.org/10.5194/egusphere-egu22-7719, 2022.

Elisabet Martínez-Sancho et al.

Oxygen isotopes (δ18O) in tree rings carry a strong potential to retrospectively evaluate tree water uptake and physiological response to climate. Their interpretation can, however, be challenging due to the complexity of the isotopic fractionations along the soil-tree-atmosphere continuum. Indeed, several processes play a role in defining the final tree-ring isotopic signal: source water variations, evaporative processes at the soil surface and leaf level, and mixing of xylem water that might exchange with new assimilates associated with phloem transport and synthesis of wood constituents. Disentangling these influences along the growing season and how climate conditions modify them are remaining challenges to exploit the full potential of δ18O tree-ring records as a climate proxy.

In this study, we aim at identifying the contribution of leaf water enrichment and source water on the tree-ring δ18O signature by assessing intra-annual variations of δ18O along the soil-leaf-tree ring pathway of larch (Larix decidua Mill.). We focus on two sites with contrasting water availability in the Lötschental valley (Swiss Alps) and three consecutive growing seasons (2011-2013). Our approach takes into consideration specific timing of the involved processes with a high spatio-temporal resolution: environmental conditions, diurnal sapflow-derived transpiration rates, δ18O analysis of xylem and leaf water, and intra-annual tree-ring δ18O measurements coupled with wood formation kinetics. Structural equation models (SEM) were applied to statistically assess the relations among δ18O values of the different pathway components. Furthermore, we calibrated mechanistic models of leaf-water and tree-ring cellulose δ18O to explore site-specific contributions of the fractionation processes (e.g., Péclet effect and the proportion of xylem-cellulose synthesis exchange [Pex]) and investigated their climatic drivers.

Our results showed that intra-annual xylem water δ18O and transpiration rates differed between sites and years whereas needle water δ18O did not differ significantly between sites (but between years). However, tree-ring cellulose δ18O values were higher at the dry site resembling those differences observed in xylem water δ18O. SEMs reinforced these results since xylem water δ18O contributed more to cellulose δ18O in comparison to needle water δ18O, and this effect was more prominent at the dry site. Vapor pressure deficit (VPD) had strong control on the overall leaf water-related 18O-fractionations. However, mechanistic leaf-water δ18O models did not indicate a relevant role of the Péclet effect in our study. Most importantly, mechanistic models of cellulose δ18O revealed that Pex was variable along the growing season and its variability was significantly associated with variations in VPD.

Our study suggests that the imprint of the source water signal on the δ18O signature in tree rings is highly dominant, particularly during episodes of high VPD, potentially overwriting signals coming from leaf fractionation processes.

How to cite: Martínez-Sancho, E., Fonti, P., Gregori, A., Gessler, A., Lehmann, M., Saurer, M., and Treydte, K.: Vapor pressure deficit governs the relative contribution of leaf and source water to intra-annual δ18O variations of tree rings , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7577, https://doi.org/10.5194/egusphere-egu22-7577, 2022.

Philipp Schuler et al.

While carbon (δ13C) and oxygen (δ18O) isotopes in tree-ring cellulose are widely used as climatic and physiological proxy in dendro sciences, the processes that are affecting the fractionation of non-exchangeable hydrogen (δ2H) isotopes and shaping the tree-ring δ2H profile are barely understood and thus not widely applied yet.

To establish a first comprehensive comparison of the photosynthetic and post-photosynthetic 2H-fractionation of northern-hemisphere trees, we sampled leaves and twigs of 152 trees representing 73 species, 48 genus, 19 families and 12 orders containing both evergreen and deciduous angio- and gymnosperms in a common garden, as well as diurnal cycles (6 species from 6 families) of leaf sugar. We extracted leaf water and sugar, as well as twig water and the current year twig xylem cellulose for δ2H analysis. Leaf sugar and twig cellulose were measured with a newly established hot water vapour equilibration method.

Our findings show a wide variation in 2H-fractionation between species growing at a common site. The measured δ2H values ranged from -63.5 to –33.4‰ for xylem water, between -22.3 and +28.5‰ for leaf water, between -160.9 and +12.6‰ for leaf sugar and between -79.1 and +6.9‰ for twig cellulose. The biological fractionation between leaf water and leaf sugar ranged between -169.6 and +24.2‰ and between leaf sugar and current year twig cellulose from -34.6 to +116.8‰. In general, sugar and cellulose of gymnosperms were significantly more 2H depleted than those of angiosperm species, with no impact of the leaf shedding behaviour to the measured δ2H values. We observed significant differences in the δ2H values between different orders and families, but not between genus and species within a family or genus, respectively. This pattern indicates that the photosynthetic and post-photosynthetic 2H-fractionation are based on conservative metabolic reactions with a generally low mutation rate.

Additionally, the results from our diurnal sampling of leaf sugar are showing first evidence for a dynamic and species-specific nature of the photosynthetic 2H-fractionation, which is in contrast to current models, which are assuming the same constant 2H-fractionation processes for all plant species.

We conclude that the here presented results will help to improve our understanding of the mechanisms influencing the δ2H values of leaf sugar and tree-ring cellulose and thus enabling the scientific community to use δ2H in tree-ring cellulose as the third isotope-proxy for dendrochronological studies.

How to cite: Schuler, P., Vitali, V., Saurer, M., Gessler, A., Buchmann, N., and Lehmann, M.: The phylogenetic impact on photosynthetic and post-photosynthetic hydrogen isotope fractionation in 73 tree species, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5772, https://doi.org/10.5194/egusphere-egu22-5772, 2022.

Anna Wieland et al.

Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ13CLM and δ2HLM values) have been shown to be reliable proxies of past temperature variability. Recent studies revealed δ2HLM values even work in temperate environments where classical tree-ring width and maximum latewood density data are less skilful. In this presentation, we report 100 years of annually resolved δ13CLM values of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany. The series are compared with regional to continental scale climate observations to assess their potential for paleoclimate reconstruction. The δ13CLM values were corrected for both the Suess effect to mitigate the effect of decreasing δ13C in atmospheric CO2 and the physiological tree response to increasing atmospheric CO2 concentrations using different factors for possible changes in discrimination. The calibration of δ13CLM chronologies against regional instrumental data reveals highest temperature sensitivity with mean summer, annual, and previous-year September to current-year August temperatures.

We additionally compared the new δ13CLM chronology with the previously produced δ2HLM series of the same trees to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. The δ2HLM values predominantly reflect large-scale temperatures since highest correlations were found with western European temperatures. Weak and mainly non-significant correlations were found between precipitation and both isotopic chronologies (δ13CLM and δ2HLM values). Our findings described for the first time the great potential of using δ13CLM values from temperate, low elevation environments as a proxy for local temperatures, whereas the combination of both proxies supports the reconstruction of temperature variations at different spatial and temporal scales.

How to cite: Wieland, A., Greule, M., Roemer, P., Esper, J., and Keppler, F.: Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups: assessing the potential for temperature reconstructions at different spatial and temporal scales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3369, https://doi.org/10.5194/egusphere-egu22-3369, 2022.

Valentina Vitali et al.

Stable carbon (δ13Cc) and oxygen (δ18Oc)isotopes measured in tree-ring cellulose, together with tree-ring width (TRW), have been used extensively to investigate the effects of past climatic conditions on tree growth. By contrast, the information recorded by the third major chemical component of tree-ring cellulose, the non-exchangeable carbon-bound hydrogen, has been explored far less due to methodological drawbacks and lack of understanding of 2H-specific fractionations. In this first Europe-wide assessment we investigate the signals stored in the hydrogen isotope ratios in tree-ring cellulose (δ2Hc), from a unique collection of 100-years records, from two major genera (Pinus and Quercus) across 17 sites (36°N to 68°N).

The climate correlation analyses showed weak climate signals in the δ2Hc high-frequency chronologies, compared to those recorded by δ13Cc and δ18Oc, but similar to the TRW ones. The δ2Hc climate signal strength varied across the continent and was stronger and more consistent for Pinus than for Quercus. The δ2Hc inter-annual variability was strongly site-specific. Focusing on the effect of extreme climatic conditions during years with extremely dry summers, we observed a significant 2H-enrichment in tree-ring cellulose for both genera. Our findings clearly indicate that δ2Hc registers information about hydrology and climate, but it also records non-climatic signals such as physiological mechanisms associated with carbohydrates storage remobilization 2H-specific fractionations and growth.

To disentangle the climatic and non-climatic signals in δ2Hc, we investigated its relationships with δ18Oc and TRW. We found significant relationships negative between δ2Hc and TRW at 7 sites and positive between δ2Hc and δ18Oc at 10 sites, while the rest of the sites did not show any significant relationships. The agreement with the TRW chronologies confirms the relationship between growth and δ2Hc, while the divergencefrom δ18O suggests a loss of the hydrological signal in δ2Hc. These highlights, once again,a stronger physiological component in the δ2H signature independent from climate. Advancements in the understanding of 2H-fractionations and their relationships with climate, physiology, and species-specific traits are therefore needed to improve the mechanistic modeling and interpretation accuracy of δ2Hc in plant physiology and paleoclimatology. Such advancements could lead to new insights into trees’ carbon allocation mechanisms, and responses to abiotic and biotic stressors.

How to cite: Vitali, V., Martínez-Sancho, E., Treydte, K., Andreu-Hayles, L., Dorado-Liñán, I., Gutiérrez, E., Helle, G., Leuenberger, M., Loader, N. J., Rinne-Garmston, T. K., Schleser, G., Allen, S., Waterhouse, J., Saurer, M., and Lehmann, M.: The unknown third - exploring the climatic and non-climatic signals of hydrogen isotopes in tree-ring cellulose across Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-673, https://doi.org/10.5194/egusphere-egu22-673, 2022.

Vaclav Treml et al.

Climate controls forest biomass production through direct effects on cambial activity and indirectly through interactions with CO2, air pollution, and nutrients availability. Atmospheric concentration of CO2 and sulfur or nitrogen deposition could exert a robust indirect control on wood formation, since they influence the stomatal regulation of transpiration and carbon uptake, that is, intrinsic water use efficiency (iWUE). Here we provide 120-year long time series of iWUE, tree growth, climatic and sulfur and nitrogen(SN) deposition trends for two widespread tree species, Pinus sylvestris (PISY) and Picea abies (PCAB), at their lower and upper distribution margins in Central Europe. The main goals were to explain iWUE trends using theoretical scenarios and climatic and SN deposition data and to assess the contribution of climate and iWUE to the observed growth trends. Our results show that after a notable increase in iWUE between the 1950s and 1980s, the positive trend slowed down. Substantial rise of iWUE since the 1950s resulted from a combination of an accelerated increase in atmospheric CO2 (Ca) and a stable level of leaf CO2 (Ci). The offset of observed iWUE values from the trajectory of iWUE growth proportional to increase in Ca (constant Ci/Ca scenario) was explained by trends in SN deposition (all sites) together with the variation of drought conditions (low-elevation sites only). Increasing iWUE over the 20th and 21st century improved tree growth at low-elevation drought-limited sites. In contrast to low-elevation sites, recent warming was the main reason for the growth increase at high-elevation PCAB. We propose that SN pollution should be considered to explain the steep increases in iWUE of conifers in the 20th century in a broader area of Central Europe and in other regions with a significant SN deposition history.

How to cite: Treml, V., Tumajer, J., Jandova, K., Oulehle, F., Rydval, M., Cada, V., Treydte, K., Masek, J., Vondrovicova, L., Lhotakova, Z., and Svoboda, M.: Increasing water-use efficiency mediates effects of atmospheric carbon, sulfur, and nitrogen on growth variability of central European conifers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6826, https://doi.org/10.5194/egusphere-egu22-6826, 2022.

Arivoara Rabarijaona et al.


As a widespread species, sessile oak (Quercus petraea) populations occupy a wide range of ecological conditions with different local selection pressures, especially different drought exposure, which would have favoured different locally adapted populations. Water-use efficiency (WUE), which is defined at the tree level as the ratio between the biomass produced and the quantity of water transpired during the same period of time, is an interesting candidate trait for adaptation to drought. Six hundred trees from sixteen different provenances planted in 1993 in a common garden in the North-Eastern of France were harvested during the 2014-2015 winter. Intrinsic WUE (WUEi), estimated from carbon isotope composition (δ13C) measurements of tree-rings, was compared among and within provenances for three contrasted years: (i) 2000, a wet year; (ii) 2003, a severely dry year; (iii) and 2005, a moderately dry year. The main purpose was to assess the drought-adaptive character of WUEi for sessile oak trees. For this, (i) the adaptive character of WUEi was evaluated by relating population mean WUEi to the mean pedoclimatic conditions of their provenance sites. (ii) The phenotypic plasticity of WUEi to drought was evaluated by comparing  the values observed in 2003 and 2005 to those of  2000 ; this plasticity was also related to the mean pedoclimatic conditions of their provenance sites. (iii) The contribution of WUEi to tree and population fitness was assessed from the relationship between WUEi and tree growth. Significant differences in δ13C (thus WUEi) were found among populations. However, no linear relationship was established between mean population δ13C and the mean pedoclimatic conditions of the provenance sites. Based on these results observed on juvenile sessile oak trees in the relatively wet conditions of the common garden, no local adaptation in terms of WUEi was detected. An increase in drought intensity resulted in an increase in population WUEi and all provenances displayed a similar plasticity of WUEi to drought, suggesting no among population diversity for drought responses. A significant correlation between WUEi and tree growth was detected only during the wet year, when populations with a higher WUEi also had a higher growth index. Moreover, a much larger variability in WUEi was demonstrated within populations (2–4‰) than among-population (0.6‰).

Key words : Climate change, assisted migration, local adaptation, water-use efficiency, fitness, diversity

How to cite: Rabarijaona, A., Ponton, S., Bert, D., Ducousso, A., Richard, B., Levillain, J., and Brendel, O.: Among-provenance diversity and phenotypic plasticity of water-use efficiency in sessile oak populations growing in a mesic common garden., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7275, https://doi.org/10.5194/egusphere-egu22-7275, 2022.

Christian Mohr et al.

Large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water-limited environments. Here, we quantify growth and photosynthetic responses of Pinus radiata plantations to the Maule Mw 8.8 earthquake in geometrically simple headwater catchments of Chile's Coastal Range. To this end, we combine high-resolution wood anatomic (lumen area) and biogeochemical (δ13C of wood cellulose) proxies of daily to weekly tree growth sampled from trees on valley bottoms and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree trees on the valley floor had enlarged lumen area and lowered δ13C, while trees along the hillslope ridge had a reverse trend. Our findings favor a control of soil water on this response, largely consistent with models that predict how enhanced postseismic vertical soil permeability causes groundwater levels to rise on valley floors, but fall along the ridges. Statistical analysis with non-parametric boosted regression trees reveals that streamflow discharge gained importance for photosynthetic activity on the ridges, but lost importance on the valley floor after the earthquake. We conclude that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short-lived signals that we identified, however, imply that such responses are only valid under water-limited, rather than energy-limited tree, growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality.

How to cite: Mohr, C., Manga, M., Helle, G., Heinrich, I., Giese, L., and Korup, O.: Trees Talk Tremor—Wood Anatomy and δ13C Content Reveal Contrasting Tree-Growth Responses to Earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2223, https://doi.org/10.5194/egusphere-egu22-2223, 2022.

Renata Feher et al.

Information regarding the Spatio-temporal behavior of extreme natural phenomena, such as avalanches, has become necessary due to the increase in human casualties and property damage in recent decades. Thus, the prevention of geomorphological risks associated with high mountain areas requires knowledge of the characteristics of geomorphological processes that occur here. Avalanches occupy a central place among these phenomena with the greatest destructive capacity (Voiculescu, 2000).

The aim of this study is to 1) reconstruct the past activity of snow avalanches in the Tarcu Mountains and to fill a gap in knowledge due to the lack of such studies in the studied area and 2) to point out the synchronicity of major events with those reconstructed in other mountain areas in the Southern Carpathians: Bucegi, Făgăraş, Piatra Craiului, Parâng Mountains. The morphology of the investigated area determines the formation of constrained avalanches. For events reconstruction, we used semi-quantitative Shored index (Shroeder, 1980). We identified 51 events in a 101-year chronology in Picea abies: 12 events with Ibetween 10-20% and 6 events with Ibetween 20-40%. The relatively young age of the trees is a good indicator of the disturbances caused by past events. We based our reconstruction on dating growth disturbances such as reaction wood, traumatic resin ducts, and scars. Reaction wood, very present in our case, highlighted the intensity of avalanche activity and the expansion of events. Resin ducts and scars are a good indicator of avalanches that brought us important information in the dating of events and helped us to delimit the affected areas (the 2005 synchronous event with other 9 couloirs). The return period values are higher than those obtained by Corona et al. (2010) in the French Alps (2.5-12 years), smaller than those obtained by Corona et al. (2007) in the Swiss Alps (slightly over 20 years) and similar to those obtained by Decaulne et al. (2012) in Northern Iceland (15-20 years). 11 events synchronous with events of another 11 couloir (1985, 1987, 1988, 1998, 2000, 2005, 2006, 2007, 2008, 2010, 2016).

In the future we want to highlight the type of avalanche by relating the activity of avalanches to cold season temperatures by using the Standardized Winter Index (IIS) (Micu, 2009; Voiculescu, Onaca, 2014) and climate scenarios, cf. Germain et al. (2009). Our study can be the basis for the elaboration of hazard and risk maps, in the perspective of tourist investments in the Tarcu Mountains or in the development of tourist activities in safe conditions.

How to cite: Feher, R., Chiroiu, P., and Voiculescu, M.: Snow avalanche activity in the Țarcu Mountains, Southern Carpathians. Comparative analysis based on tree ring studies., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8925, https://doi.org/10.5194/egusphere-egu22-8925, 2022.

Luka Krajnc et al.

Radial growth, wood density and climate-growth relationship of four Douglas fir provenances were analysed separately for the juvenile and the adult phase. Two pairs of provenances were selected from an existing IUFRO provenance trial planted in 1971 based on their diameter at breast height and vitality. Increment cores were extracted from individual trees, on which we measured tree-ring widths (RW), earlywood widths (EWW) and latewood widths (LWW). Wood density was assessed in standing trees using resistance drilling. The climate-growth correlations were calculated between provenance chronologies of RW, EWW, LWW and latewood share, and day-wise aggregated Standardised Precipitation-Evapotranspiration Index (SPEI). We calculated the accumulated drought effects by aggregating climatic water deficits into a log-logistic probability distribution to obtain the SPEI index series of different seasons, starting from three weeks to nine months, including the effect of previous growing season. In all provenances, RW, and consequently EWW and LWW, were wider in juvenile period than in adult period. Share of latewood was in all cases higher in juvenile wood then in mature wood. All four provenances have similar wood density in both analysed growth phases. The general effect of wet conditions in current growing season was positive, indicating that Douglass fir’s radial growth was favoured in moist years, and reduced in dry years. The significant positive effect of SPEI on LW was observed also at the beginning of previous growing season. Our analysis showed that when selecting the most promising provenance for planting, it needs to be considered that growth rate may change from juvenile to adult period. Only by combining climate-growth analysis with measurements of external tree features we can compare and assess the suitability of certain provenances for planting in current and future climate.

How to cite: Krajnc, L., Hafner, P., Jevšenak, J., Gričar, J., and Brus, R.: Tree rings, wood density and climate-growth relationships of four Douglas fir provenances in sub-Mediterranean Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9627, https://doi.org/10.5194/egusphere-egu22-9627, 2022.