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.

'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.

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.

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.

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.

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.

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.

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.

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 [P_ex]) 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 P_ex 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.

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.

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 (C_a) and a stable level of leaf CO₂ (C_i). The offset of observed iWUE values from the trajectory of iWUE growth proportional to increase in C_a (constant C_i/C_a 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 20^th 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.

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 I_t  between 10-20% and 6 events with I_t  between 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.