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) traditional dendrochronological methods including studies based on tree-ring width and density, (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.

Convener: Kerstin Treydte | Co-conveners: Flurin Babst, Giovanna Battipaglia, Jan Esper
| Wed, 06 May, 14:00–18:00 (CEST)

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D3357 |
| solicited
Cyrille Rathgeber

As a consequence of recent climatic changes, many studies have reported an increase in tree growth, forest ecosystem net primary productivity, and terrestrial biosphere carbon up-take, making forests one of the largest carbon sink on Earth. Direct and remote observations, as well as eco-physiological models, have suggested that it is mainly the rise in temperature and the resulting extended period of growth that is responsible for forest enhanced productivity. However, up to now, there is no comprehensive observation-based study deciphering the respective roles of the length of the growing season versus its intensity, to confirm this interpretation. Based on a large wood-formation-monitoring dataset, encompassing numerous sites from Mediterranean to Boreal conifer forests, we tested the hypothesis that the length of the growing period is more important than the rate of growth to explain tree-ring width. Moreover, we explored the influence of the environmental conditions on the variation in both timings and rates of xylem cell production.

We collected data from more than 50 sites spread at various altitudes and latitudes, on three continents (America, Europe, Asia), in the extra tropical parts of the Northern Hemisphere (Boreal, Temperate and Mediterranean bioclimatic zones). Wood formation was monitored at a weekly time-step using histological sections of forming xylem collected from the stems of more than 15 conifer species. The critical dates of xylem phenology were assessed at tree level using logistic regressions, while the rates of cell production were computed using Gompertz models. A basic physical model was developed relating the total number of xylem cells with the rate and duration of its production. A sensitivity analyses was performed to reveal the global ecological patterns of tree-ring formation, while mixed effect models were used to quantify the influences of the environmental factors.

The basic physical model of xylem cell production was applied successfully to the whole dataset (including Mediterranean sites) explaining more than 80 % of the observed variability. The sensitivity analysis showed that the rate of xylem cell production contributed a bit more than the duration to the variation in the final number of cells. Trees presented contrasted strategies according to the bioclimatic zone they belong to: while Boreal trees grew at a high speed during a short time; Mediterranean trees proceeded slowly, but for an extended period of time. Nevertheless, even for Mediterranean trees, the rate of growth remained the first driver of the final number of cells. Moreover, we showed that xylem phenology was consistently explained by the change in thermal conditions occurring with altitude or latitude, while growth rate was more related to species effect and site conditions.

Our results confirm that recent global warming may have resulted in extended period of growth explaining the recent increase in forest productivity. However, we also showed that the rate of xylem cell production is indeed the first driver of tree radial growth, therefore species behavior and site conditions should be considered in vegetation models to assess the impact of climate changes on forest productivity.

How to cite: Rathgeber, C.: Global ecological trends in wood cell production of coniferous trees, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22283, https://doi.org/10.5194/egusphere-egu2020-22283, 2020

D3358 |
Alexandre Florent Nolin, Jacques C. Tardif, France Conciatori, David M. Meko, and Yves Bergeron

The streamflow regimes of eastern boreal Canada are snow-melt and ice-melt driven with the highest flows occurring in spring. Over the last few decades, a positive streamflow trend has been observed, with increasing severity and frequency of spring flooding. Further changes in flood dynamics are projected as a consequence of global climate change. The validity of projections is restricted by the lack of long and spatially well-replicated observations. High-resolution proxy records are needed to better understand the natural range of variability in spring runoff and associated atmospheric controls.

Recent research has shown that riparian black ash trees (Fraxinus nigra Marsh.) exposed to periodic submersion produce “flood rings” whose earlywood cross-sectional vessel area is linearly associated with the severity of flooding. Twelve continuous chronologies of ring width and earlywood vessel anatomy were developed for Lake Duparquet to extend the record of Harricana River mean spring flow. A visually determined index of flood rings was also developed to determine i) the spatial coherency of the spring flood signal and ii) the coherency of the flood signal among natural, regulated and unflooded rivers.

The reconstruction spans the period 1770-2016 and captures more than 65% of the variance of Harricana river spring flow. Trend analysis indicates an increase in both magnitude and frequency of the major floods starting at the end of the Little Ice Age (LIA, 1850-1890), with highest peaks after 1950. Time-frequency analysis shows non-stationarity: a stable 30-year periodicity during the LIA is replaced by a decadal pattern starting around 1850, and evolves into a more high-frequency pattern after 1930. The signal is strongly coherent between watersheds for natural rivers and weaker for regulated basins. Field correlations with gridded climate data indicate the broad spatially coherent pattern of spring high flows across much of central/eastern north Canada is positively associated with April-May precipitation and snow cover, and negatively associated with March-April maximum temperature.

These large-scale associations support atmospheric forcing of inter-annual hydroclimatic variability. While the Artic and North Atlantic Oscillations have previously been found to influence winter and spring climate conditions in eastern Quebec, our results contrast with a significant negative association with El-Niño Southern Oscillation from January to May, and the Pacific Decadal Oscillation from December to February. In Lake Duparquet, warm and wet air from Pacific-South Ocean (El-Niño) are associated with early spring and small floods, while cold and dry air masses (La-Niña) correlate to late thaw and high floods in spring. The association with sea surface temperature and 200mb geopotential field heights reveal a clear atmospheric connection between eastern north boreal Canada and the tropical Pacific Ocean.

The novel application of wood-cell anatomy to hydroclimatology underscores an increase in flood frequency and severity since the end of the 18th century in northeastern Canada. More broadly, the application highlights how analysis of tree rings from riparian trees can be used to extend the flood history of boreal rivers.

How to cite: Nolin, A. F., Tardif, J. C., Conciatori, F., Meko, D. M., and Bergeron, Y.: Multi-Century Spring Flood Reconstruction in Eastern Boreal Canada from Novel Application of Wood-Cell Anatomy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5572, https://doi.org/10.5194/egusphere-egu2020-5572, 2020

D3359 |
Laia Andreu-Hayles, Rosanne D'Arrigo, Rose Oelkers, Kevin Anchukaitis, Greg Wiles, Rob Wilson, David Frank, and Nicole Davi

Tree ring-width (TRW) and Maximum Latewood Density (MXD) series have been largely used to develop high-resolution temperature reconstructions for the Northern Hemisphere. The divergence phenomenon, a weakening of the positive relationship between TRW and summer temperatures, has been observed particularly in northwestern North America chronologies. In contrast, MXD datasets have shown a more stable relationship with summer temperatures, but it is costly and labor-intensive to produce. Recently, methodological advances in image analyses have led to development of a less expensive and labor-intensive MXD proxy known as Blue Intensity (BI). Here, we compare 6 newly developed BI tree-ring chronologies of white spruce (Picea glauca [Moench] Voss) from high-latitude boreal forests in North America (Alaska in USA; Yukon and the Northwestern Territory in Canada), with MXD chronologies developed at the same sites. We assessed the quality of BI in relation to MXD based on mean correlation between trees, chronology reliability based on the Expressed Population Signal (EPS), spectral properties, and the strength and spatial extent of the temperature signal. Individual BI chronologies established significant correlations with summer temperatures showing a similar strength and spatial cover than MXD chronologies. Overall, the BI tree-ring data is emerging as a valuable proxy for generating high-resolution temperature spatial reconstructions over northwestern America.

How to cite: Andreu-Hayles, L., D'Arrigo, R., Oelkers, R., Anchukaitis, K., Wiles, G., Wilson, R., Frank, D., and Davi, N.: Comparison between Blue Intensity (BI) and Maximum Latewood Density (MXD) tree-ring chronologies from the North American Boreal forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21137, https://doi.org/10.5194/egusphere-egu2020-21137, 2020

D3360 |
Alexander Kirdyanov, Anatoly Prokushkin, Anastasia Knorre, Olga Churakova (Sidorova), Marina Fonti, Matthias Saurer, Rolf Siegwolf, Frederick Reinig, Anatoly Nikolaev, Alexey Kolmogorov, Vladimir Shishov, Alma Piermattei, Paul Krusic, and Ulf Büntgen

The world’s largest terrestrial biome, Boreal forest, is prone to the greatest rates of recent and predicted warming. Much of this circumpolar vegetation belt is underlain by permafrost, which further challenges our understanding of the direct and indirect consequences of increasing temperature on the functioning and productivity of these northern latitudinal forests.

Here, we present the results of an on-going study of tree-ring growth of conifers in Russia’s continuous permafrost zone in northern Siberia, from 61-72°N and 90-148°E. Tree-ring data from a variety of habitats between 20 and 600 m asl with different climate and thermo-hydrological regimes of soils are analyzed. While in some cases up to 60-70% of the year-to-year tree-ring width and maximum latewood density variability can be explained by summer temperature variations alone, we find that the seasonal dynamics of permafrost also plays an important role in defining the overall rate of radial tree growth. Wider rings are generally formed on sites with a deeper active soil layer, which itself depends on the geographical location of a site, as well as its ground vegetation, stand parameters and fire history. Waterlogged permafrost may further act as a source of water for trees under exceptionally dry summer seasons.

Our study indicates that the growth response of conifers to temperature and precipitation across the continuous permafrost zone of Siberia is both, site- and species-specific. This implies a range of possible scenarios of further development of northern forests under projected climate change. Seasonal dynamics of the active soil layer and possible permafrost degradation must be taken into account when modelling tree growth variability and forest productivity.

How to cite: Kirdyanov, A., Prokushkin, A., Knorre, A., Churakova (Sidorova), O., Fonti, M., Saurer, M., Siegwolf, R., Reinig, F., Nikolaev, A., Kolmogorov, A., Shishov, V., Piermattei, A., Krusic, P., and Büntgen, U.: Does permafrost matter? Permafrost related studies of conifer tree-ring growth in northern Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21434, https://doi.org/10.5194/egusphere-egu2020-21434, 2020

D3361 |
Claudia Hartl, Elisabeth Düthorn, Ernesto Tejedor Vargas, Andreas Kirchhefer, Mauri Timonen, Steffen Holzkämper, Ulf Büntgen, and Jan Esper

The long tradition in dendroclimatological studies across Fennoscandia is mainly due to the exceptional strong temperature sensitivity of tree growth, as well as the existence of well-preserved subfossil wood in shallow lakes and extent peat bogs. Although some of the world’s advanced multi-millennial-long ring width and density based climate reconstructions have been developed in northern Fennoscandia, it is still unclear if differences in micro-site ecology have been considered sufficiently in previous studies. In order to assess the effects of moist lakeshores versus drier inlands on forest productivity, we present a Fennoscandia-wide network of 44 Scots pine ring width chronologies from 22 locations between 59°-70°N and 16°-31°E. Clustering into coastal settings in northern Norway, continental sites in the lee of the Scands north of the polar circle, and locations south of the polar circle, our network reveals a general dependency of pine growth rates on latitude and July temperature. Differences between moist and dry sites are likely caused by associated effects on soil temperature. While trees at moist micro-sites at western locations exhibit higher growth rates, this pattern inverses under the more continental conditions of the east, where increased ring widths are found at drier sites. In addition to the latitudinal increase in growth sensitivity to July temperature, pines at moist sites tend to show a higher dependency to summer warmth. The highest temperature sensitivity and growth coherency is found in those regions where July temperatures range between 11.5 and 13.5°C and May precipitation totals fall below 100mm. This study not only emphasizes the effects of micro-site ecology on Fennoscandian tree growth, but also provides guidance for the selection of sampling sites for climate reconstructions.

How to cite: Hartl, C., Düthorn, E., Tejedor Vargas, E., Kirchhefer, A., Timonen, M., Holzkämper, S., Büntgen, U., and Esper, J.: Disentangling the effects of micro-site ecology on Fennoscandian tree growth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8783, https://doi.org/10.5194/egusphere-egu2020-8783, 2020

D3362 |
Vladimir Shishov, Victor Il'in, Ivan Tychkov, Margarita Popkova, and Daria Belousova

Improvement of our understanding of tree-growth processes and accurate interpretations of climatic signals in tree rings have recently become possible through the application of process-based models, e.g., Biome3, MAIDEN,  ASTANEA, CAMBIUM, PRYSM, VS-lite and others, which simulate tree growth based on non-linear effects of environmental conditions. The process-based Vaganov–Shashkin model (VS-model) is one such model which describes tree-ring formation as a result of multivariate affects of local climate (temperature, soil moisture and solar irradiance). As with most of the process-based models, the VS-model is a complex tool that requires a considerable number of model parameters that should be reasonably estimated for each forest stand. This leads to problem of accurate model parameterization, namely estimations of optimal values of the model parameters necessary to guarantee: (1) the best fit to the observed tree-ring measurements; (2) identification of the specific seasonal cell production and enlargement; (3) reasonable ecological interpretation in terms of processes involved in the model.

Based on differential evolution (DE) approach adopted to the model parameterization using the supercomputer facilities it was shown:

(1) a significant spatial variability of adjusted VS-parameter values (with corresponded ecological interpretation) that provide the best fit to the actual tree-ring chronologies from climatically contrasted sites distributed in the vast territories of Eurasia and as a result, the models ability to capture a significant diversity in non-linear tree-ring growth responses that are climatically induced,

(2) the high sensitivity of the models even for forest stands where mixed climatic signal affects on tree-ring growth during growing season,

(3) the high probability to obtain a "correct" model parameterization which explains up to 60% tree-ring variance by the climate forcing even for randomly generated "chronologies"  in case of incorrect usage of the calibration-verification strategy for multidimensional models.

How to cite: Shishov, V., Il'in, V., Tychkov, I., Popkova, M., and Belousova, D.: Parameterization of multidimensional process-based tree-ring models: Why it is important?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7641, https://doi.org/10.5194/egusphere-egu2020-7641, 2020

D3363 |
Jeanne Rezsöhazy, Hugues Goosse, and Joël Guiot

Trees are one of the main archives to reconstruct the climate of the last millennium at high resolution. The links between tree-ring proxies and climate have usually been estimated on the basis of statistical approaches, assuming linear and stationary relationships. Both assumptions can be inadequate and this issue can be overcome by ecophysiological models such as MAIDEN (Modeling and Analysis In DENdroecology), which simulates tree-ring growth starting from temperature and precipitation daily inputs. A protocol for the application of MAIDEN to potentially any site with tree-ring width data in the extratropical region has been developed in Rezsöhazy et al. (2019) (in review). In this study, the applicability of the model has been tested over the twentieth century using as a test case tree-ring observations from twenty-one Eastern Canadian taiga sites and three European sites. The paper highlights the potential of MAIDEN as a complex mechanistic proxy system model to analyse the links between tree growth and climatic conditions in paleoclimatic applications. Following on from this recent work, MAIDEN is here applied to the PAGES2k tree-ring width database over the last century using the protocol developed in Rezsöhazy et al. (2019) (in review). We show how this larger network allows refining our protocol. We identify the regions and sites where MAIDEN can be successfully applied, as well as estimate the uncertainty associated with the use of MAIDEN for a wide range of sites.


Rezsöhazy, J., Goosse, H., Guiot, J., Gennaretti, F., Boucher, E., André, F., and Jonard, M.: Application and evaluation of the dendroclimatic process-based model MAIDEN during the last century in Canada and Europe, Clim. Past Discuss., https://doi.org/10.5194/cp-2019-140, in review, 2019.

How to cite: Rezsöhazy, J., Goosse, H., and Guiot, J.: Evaluation of a dendroclimatic process-based model (MAIDEN) over the last century using the PAGES2k tree-ring width database, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8247, https://doi.org/10.5194/egusphere-egu2020-8247, 2020

D3364 |
| Highlight
Valerie Trouet, Matthew Meko, Lara Klippel, Flurin Babst, Jan Esper, Paul Krusic, Momchil Panayotov, and Rob Wilson

A recent increase in mid-latitude extreme weather events has been linked to anomalies in the position, strength, and waviness of the Northern Hemisphere polar jet stream. The latitudinal position of the North Atlantic Jet (NAJ) in particular drives climatic extremes over Europe, by controlling the location of the Atlantic storm track and by influencing the occurrence and duration of atmospheric blocking. To put recent NAJ trends in a historical perspective and to investigate non-linear relationships between jet stream position, mid-latitude extreme weather events, and anthropogenic climate change, long-term records of NAJ variability are needed. Here, we combine two tree-ring based summer temperature reconstructions from Scotland and from the Balkan Peninsula to reconstruct inter-annual variability in the latitudinal position of the summer NAJ back to 1200 CE. We find that over the past centuries, a northward summer NAJ position has resulted in heatwaves in northwestern Europe, whereas a southward position has promoted wildfires in southeastern Europe and floods in northwestern Europe. The great famine of 1315-1317 in northwestern Europe, for instance, was associated with prolonged flooding and cold summers that resulted in failed grain harvest and were related to a southern NAJ position. We further find an unprecedented increase in NAJ anomalies since the 1960s, which supports more sinuous jet stream patterns and quasi-resonant amplification as potential dynamic pathways for Arctic warming to influence midlatitude weather.

How to cite: Trouet, V., Meko, M., Klippel, L., Babst, F., Esper, J., Krusic, P., Panayotov, M., and Wilson, R.: Eight Hundred Years of North Atlantic Jet Stream Variability and its Influence on European Climate Extremes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12400, https://doi.org/10.5194/egusphere-egu2020-12400, 2020

D3365 |
Isabel Dorado-Liñán and Valerie Trouet and the European Beech Tree-ring Network

Dynamically-driven extreme weather events have large ecological, social and economic consequences including large tree-growth reductions and forest mortality. These events are likely to become globally more frequent and intense in the near future with increased anthropogenic forcing and associated changes in couple atmosphere-ocean circulation. The European continent is under the control of different atmospheric circulation patterns leading to geographical climatic gradients caused by their eventual position and strength, being the North Atlantic Oscillation (NAO) and the East Atlantic Pattern (EA) the main modes of North Atlantic climate variability (Barnston and Levezey 1987; Folland et al. 2009). Both, NAO and EA reflect jet stream changes as a consequence of variations in the eddy forcing, being the North Atlantic Jet (NAJ) the pattern connecting the large-scale atmospheric variability over the North Atlantic basin (Woollings, Hannachi, and Hoskins 2010). Thus, the identification and characterization of the links between forest productivity and the precursors of large-scale dynamics inducing extreme events may boost our capacity of assessing their predictability and enhancing forecasting skills.
Here, we scale forest response to climate to higher atmospheric levels by establishing the connection between extreme positive and negative anomalies in productivity of European forests to the latitudinal position of the NAJ. For that, we use a network of 344 European beech tree-ring chronologies extending from the Iberian Peninsula to the Carpathians and from Greece to northern UK.
Our results show a geographical gradient on tree growth across Europe explained either by the asymmetric forest response to homogeneous summer climate over Europe or to a distinct summer climate dipole leading to diverging climatic conditions in northeaster and southwestern Europe. In both cases, the continental-scale European-beech growth patterns are linked to the NAJ latitudinal position and its determinant influence on summer climate over Europe. The projected increase in the frequency of northward migrations of the NAJ for the next century may enhance the differences in forest productivity across Europe by inducing subcontinental-wide beech forest growth reduction.

Barnston, Anthony Gaston, and Robert E. Levezey. 1987. "Classification, seasonality and persistence of low-frequency atmospheric circulation patterns" Mon. Weather Rev. 115: 1083-1126.
Folland, Chris K, Jeff Knight, Hans W Linderholm, David Fereday, Sarah Ineson, and James W Hurrell. 2009. “The Summer North Atlantic Oscillation: Past, Present, and Future.” Journal of Climate 22 (5): 1082–1103. https://doi.org/10.1175/2008JCLI2459.1.
Woollings, Tim, Abdel Hannachi, and Brian Hoskins. 2010. “Variability of the North Atlantic Eddy-Driven Jet Stream.” Quarterly Journal of the Royal Meteorological Society 136 (649): 856–68. https://doi.org/10.1002/qj.625.


How to cite: Dorado-Liñán, I. and Trouet, V. and the European Beech Tree-ring Network: North Atlantic Jet position induces latitudinal decouplings in forest productivity in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19951, https://doi.org/10.5194/egusphere-egu2020-19951, 2020

D3366 |
Yu Liu and Wenju Cai

Affecting a multitude of ecological and agricultural systems, the Asia summer monsoon (ASM) is essential for biodiversity and the food security of billions of people. Understanding past changes of the ASM is important for the detection and attribution of its recent evolution and future projection in the context of global warming. However, proxy-based, high-resolution reconstructions of the ASM prior to the period of instrumental measurements that started in the 1950s in China are still missing. Here, we use an ensemble of ten tree-ring width chronologies from the northern margin of the ASM to estimate ASM strength back to 1566 AD. The reconstruction not only reveals severe large-scale droughts in 1586/87 and 1759, but also negative anomalies during persistent locus plagues in the 1860s. The record also shows an unprecedented decrease in ASM since the mid-20th century. Simulations from a coupled climate model suggest that the recent ASM decline could have been induced by increased anthropogenic aerosol emissions over the Northern Hemisphere.

How to cite: Liu, Y. and Cai, W.: Recent pronounced weakening of Asia summer monsoon over the past 450 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6332, https://doi.org/10.5194/egusphere-egu2020-6332, 2020

D3367 |
Heather A Haines, Jonathan G Palmer, Nathan B English, Quan Hua, Patricia S Gadd, Justine Kemp, and Jon M Olley

In Australia the majority of tropical and subtropical regions lack any long-term (multi-decadal to centennial scale) instrumental climate records highlighting a need for alternatives such as proxy climate reconstructions. Despite this need, only a limited number of terrestrial proxy sources are available. Tree-rings provide one of the few options for climate reconstructions yet very little dendrochronological investigation has been undertaken as early assessments of tropical Australian species in the 1970s and 1980s indicated most species had short life-spans, poorly preserved timbers, or were compromised by having many ring anomalies. There has also been limited effort into understanding the growth-climate relationships of these trees with only a few studies undertaken targeting specific species that have unfortunately been heavily cleared from the region (eg. Toona ciliata). One exception noted in the early species assessment suggested that trees in the Araucariaceae family, a common tree family along the tropical Australian east coast, is longer lived than many other species in the region, contains growth rings which are annual in nature, and grows in response to climatic conditions.

Here we describe the results from a stand of Araucaria cunninghamii trees located in Lamington National Park, a World Heritage listed rainforest in subtropical Southeast Queensland, Australia (a region known for experiencing extreme hydroclimatic events). Our assessment discovered the presence of false, faint, locally absent, and pinching rings. By combining traditional dendrochronological analysis (eg. crossdating) with more recent techniques such as age validation by bomb-pulse radiocarbon dating and tree-ring density analysis, a robust ring-width chronology from 1805-2014 was developed. Dendrometers installed on four trees at the Lamington site confirmed that tree growth was annual and that moisture sensitivity was driving growth. Further growth-climate analysis indicated that the strongest correlation to the tree-ring chronology was specifically related to drought conditions in the region. The strength of this response was compared to both local and regional spatial areas and to drought indices such as the self-calibrating Palmer Drought Severity Index (scPDSI), the Standardized Precipitation Evaporation Index (SPEI), and the long-term drought conditions shown by the Australian and New Zealand Drought Atlas (ANZDA). The combined analysis led to the development of a 200-year drought reconstruction for the region and demonstrates influences from both the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO).

How to cite: Haines, H. A., Palmer, J. G., English, N. B., Hua, Q., Gadd, P. S., Kemp, J., and Olley, J. M.: The use of multiple dendrochronological techniques to develop a 200-year drought record for subtropical Southeast Queensland, Australia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11768, https://doi.org/10.5194/egusphere-egu2020-11768, 2020

D3368 |
Soumaya Belmecheri, Paul szejner, David Frank, Steve Voelker, and Alienor Lavergne

Rising atmospheric CO2 concentrations are expected to stimulate plant carbon uptake (A) while also reducing transpiration via a decrease in stomatal conductance (gs), resulting in an increase in the intrinsic water use efficiency (iWUE, i.e. the ratio of A to gs). While there is overwhelming evidence of a secular iWUE increase in response to rising CO2 over the 20th-21st century, the magnitude of changes in iWUE reported so far in the literature strongly varies across climatic regions and biomes. Moreover, increasing iWUE has not systematically been translated into tree growth increment at many forested ecosystems, challenging the CO2 fertilization theory. There is thus a need to track down the key physiological and environmental mechanisms driving changes in iWUE.

Here we estimate the carbon isotopic discrimination (Δ13C) - defined as the difference between the stable carbon isotopic compositions (δ13C) measured in atmospheric CO2 and in tree rings – from 147 tree-ring δ13C chronologies to: 1) investigate the physiological responses of woody C3 plants to increasing atmospheric CO2 and, 2) disentangle climate vs CO2 effects on A and gs. We specifically study deviations of tree-ring Δ13C from the predicted Δ13C response to CO2 as reconstructed from a recent meta-analysis of paleo and elevated CO2 data. We identify the following: 1) negative deviations from the expected Δ13C for most records; 2) no apparent deviation from expected Δ13C or; 3) positive deviations, both in a small minority of records ; and 4) an apparent non-linear response with a switch from a more negative Δ13C deviations to a Δ13C-response consistent with predicted CO2-effects. The widespread negative Δ13C  deviations are consistent with gs having been reduced or A having not increased as much as expected for a given CO2-driven stimulation of A. The presented global tree-ring data analyses suggest that a warmer and often drier climate have had a stronger effect on Δ13C compared to that of rising CO2, and a substantial modulation of recent rises in iWUE by climate effects across the globe.

How to cite: Belmecheri, S., szejner, P., Frank, D., Voelker, S., and Lavergne, A.: Global trends of tree-ring carbon isotope discrimination under rising atmospheric CO2 and changing climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12240, https://doi.org/10.5194/egusphere-egu2020-12240, 2020

D3369 |
Valentina Vitali, Rosemarie Weigt, Stefan Klesse, Kerstin Treydte, Rolf Siegwolf, and Matthias Saurer

Picea abies and Fagus sylvatica, are two of the most important tree species in Europe, and their responses to climate are being extensively investigated, especially at the limits of their distribution. However, their physiology at temperate sites is not yet fully understood. In a European tree-ring network, 10 sites along a climate gradient were sampled throughout Central Europe, and tree-ring width and stable isotope chronologies (C and O) were measured. The year-to-year variability of the isotopes time series for the last 100 years was analyzed in relation to tree-ring growth, spatial distribution, and seasonal climate.

Climate sensitivity of radial growth of both species was rather variable and site-dependent, and was strongest at the driest sites. On the contrary, variability in the isotopic ratios consistently responded to summer climate, particularly to vapor pressure deficit. The high δ18O coherence of the short-term variability between sites and species highlights the strength of the environmental signal in the O chronology also across long distances. On the contrary, δ13C shows lower correlations between sites and species, showing a stronger site-dependency, and a lower intra-annual variability. The generally positive correlation between the year-to-year differences in δ13C and δ18O across most sites demonstrates the strong role of stomatal conductance in controlling leaf gas exchange for these species. However, in the last decades, sites showed a dissimilar shift in the isotopes relationships, with the warmer sites showing an increase of either or both δ13C and δ18O and consequent decrease of photosynthetic rates and stomatal conductance, highlighting their dependency to atmospheric moisture demand and soil water availability.

Understanding the underlying physiological mechanisms controlling the short-term variation in tree-ring records will help with defining the performance of these ecologically and economically important tree species under future climate conditions.

How to cite: Vitali, V., Weigt, R., Klesse, S., Treydte, K., Siegwolf, R., and Saurer, M.: High frequency stable isotope signals as proxy for physiological responses to climate - Dual isotope approach at a European scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8104, https://doi.org/10.5194/egusphere-egu2020-8104, 2020

D3370 |
Marco M. Lehmann, Velentina Vitali, Philipp Schuler, and Matthias Saurer

Carbon and oxygen stable isotopes in tree-rings are successfully used in climate and environmental research, for instance for the reconstruction of past climatic conditions and corresponding physiological responses of trees to local climate. In contrast, hydrogen isotope ratios (δ2H), available also in the cellulose molecule of tree-rings, have been largely neglected. Mostly due to methodological reasons, but also because various studies found a rather poor climate information in the δ2H of tree rings. Recent studies show that the latter might be caused by isotope fractionation mechanisms that are related to plant physiological and biochemical processes rather than to climate or hydrological changes. These results also suggest that a relative use of carbon reserves and photosynthetic assimilates may explain δ2H variations in tree-rings. We therefore investigated the literature and observed strong relationships between δ2H and tree growth chronologies across various species in Switzerland, Germany, Norway, China, and India. The relationships between tree-ring growth and δ2H show a dependence to site-specific factors, climatic conditions (e.g. temperature, precipitation), and competition/light effects. Based on our findings we set up a novel conceptual framework that may allow the reconstruction of physiological responses such as carbon use strategies under varying environmental conditions. This new tool may find widespread application to identify and date, with high resolution, stressful conditions or stress-release phases that a tree or a forest ecosystem has experienced in the past.

How to cite: Lehmann, M. M., Vitali, V., Schuler, P., and Saurer, M.: A new conceptual framework for the use of hydrogen isotopes in tree rings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16223, https://doi.org/10.5194/egusphere-egu2020-16223, 2020

D3371 |
Flurin Babst, Richard L. Peters, Rafel O. Wüest, Margaret E.K. Evans, Ulf Büntgen, Andrew J. Hacket-Pain, Christoforos Pappas, Alexander V. Kirdyanov, Stefan Klesse, Volodymyr Trotsiuk, Jesper Björklund, Jodi Axelson, Jill Harvey, Dan Smith, Christian Zang, Dirk N. Karger, and Niklaus E. Zimmermann

Warming alters the variability and trajectories of tree growth around the world by intensifying or alleviating energy and water limitation. This insight from regional to global-scale research emphasizes the susceptibility of forest ecosystems and resources to climate change. However, globally-derived trends are not necessarily meaningful for local nature conservation or management considerations, if they lack specific information on present or prospective tree species. This is particularly the case towards the edge of their distribution, where shifts in growth trajectories may be imminent or already occurring.

Importantly, the geographic and bioclimatic space (or “niche”) occupied by a tree species is not only constrained by climate, but often reflects biotic pressure such as competition for resources with other species. This aspect is underrepresented in many species distribution models that define the niche as a climatic envelope, which is then allowed to shift in response to changes in ambient conditions. Hence, distinguishing climatic from competitive niche boundaries becomes a central challenge to identifying areas where tree species are most susceptible to climate change.

Here we employ a novel concept to characterize each position within a species’ bioclimatic niche based on two criteria: a climate sensitivity index (CSI) and a habitat suitability index (HSI). The CSI is derived from step-wise multiple linear regression models that explain variability in annual radial tree growth as a function of monthly climate anomalies. The HSI is based on an ensemble of five species distribution models calculated from a combination of observed species occurrences and twenty-five bioclimatic variables. We calculated these two indices for 11 major tree species across the Northern Hemisphere.

The combination of climate sensitivity and habitat suitability indicated hotspots of change, where tree growth is mainly limited by competition (low HSI and low CSI), as well as areas that are particularly sensitive to climate variability (low HSI and high CSI). In the former, we expect that forest management geared towards adjusting the competitive balance between several candidate species will be most effective under changing environmental conditions. In the latter areas, selecting particularly drought-tolerant accessions of a given species may reduce forest susceptibility to the predicted warming and drying.

How to cite: Babst, F., Peters, R. L., Wüest, R. O., Evans, M. E. K., Büntgen, U., Hacket-Pain, A. J., Pappas, C., Kirdyanov, A. V., Klesse, S., Trotsiuk, V., Björklund, J., Axelson, J., Harvey, J., Smith, D., Zang, C., Karger, D. N., and Zimmermann, N. E.: Hotspots of change in major tree species under climate warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22325, https://doi.org/10.5194/egusphere-egu2020-22325, 2020

D3372 |
Heather Shupe, Kai Jensen, and Kristin Ludewig

Anthropogenic land use and landscape change has dramatically decreased the presence of hardwood floodplain forests (HFF) globally. In Germany, it is estimated that only 1% of the former HFFs still exist today. Natural HFFs provide an abundance of ecosystem services such as the mitigation of climate change through the sequestration of atmospheric carbon. In order to confidently quantify global carbon fluxes, local in-situ investigations are required. This research aims to quantify and compare carbon sequestration rates (CSRs) of temperate HFFs at a local scale. Traditional dendrochronological methods are applied to tree cores collected from oak (Quercus robur) and elm (Ulmus laevis) trees located within 35 HFF plots differing in age classes and hydrological situations along 100 km of the Middle Elbe river. Tree ring widths (TRW) from both tree species are measured and used to estimate basal area increments (BAI) and CSRs. Preliminary results show that CSRs are higher in oaks than in elms. While CSRs seem not to differ between hydrological situations in trees with ages between 60 and 150 years, we found pronounced effects of hydrological conditions on CSRs in the oldest trees (> 180 years). Interestingly, highest mean CSRs were found for old trees in regularly flooded HFF with a dense canopy cover. These results are in agreement with recent research that have overturned the old paradigm that old forests are less productive than young forests. We conclude that HFFs remain active carbon sinks as they age and that the preservation or even expansion of HFFs can contribute to other global strategies for climate change mitigation.

How to cite: Shupe, H., Jensen, K., and Ludewig, K.: Using tree rings to estimate the annual carbon sequestration of hardwood floodplain forests along the Middle Elbe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10554, https://doi.org/10.5194/egusphere-egu2020-10554, 2020

D3373 |
Etienne Boucher, Ignacio Hermoso de Mendoza, and Fabio Gennaretti

The ecophysiological forest model MAIDENiso (Modeling and Analysis In + isotopes) uses a set of mechanistic rules to simulate the production, allocation and growth of virtual trees. MAIDENiso is adapted to the boreal tree species Picea mariana Mill. (Black spruce), but lacks a hydrological module adapted for boreal meteorological conditions. With the recent addition of a snow/ice module, MAIDENiso is now capable of realistically simulating snow cover and discharge in high latitude regions, while at the same time capturing climate-sensitive processes such as the enrichment of heavy water isotopes due to snow sublimation. The more realistic outputs of the model can be compared to tree ring records (ring widths and stable isotopes). This allows us to use an inversion algorithm (based on a Metropolis Hastings random walk) to estimate past hydroclimate conditions that are in line with physiological and hydrological processes of high boreal regions. We apply this methodology to a millennial chronology of tree ring width and cellulose isotopes from sub-fossil tree remains in North-Quebec, and produce an updated hydroclimate reconstruction of the last 1000 years in this region.


How to cite: Boucher, E., Hermoso de Mendoza, I., and Gennaretti, F.: MAIDENiso: a mechanistic approach to the reconstruction of past climate from tree chronologies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20535, https://doi.org/10.5194/egusphere-egu2020-20535, 2020

D3374 |
Tom De Mil, Matthew Salzer, Charlotte Pearson, Valerie Trouet, and Jan Van den Bulcke

Great Basin Bristlecone pine (Pinus longaeva) is known for its trees that attain old age. The longest chronology is more than 9000 years long, and the temperature-sensitive upper treeline chronology extends back to 5000 years. The ring width pattern of upper treeline bristlecone pine trees are strongly influenced by temperature variability at decadal to centennial scales. To infer a climate signal on annual scales, MXD is shown to be a better temperature proxy. Here, we present a preliminary Maximum Latewood Density (MXD) chronology of bristlecone pine to investigate the temperature signal in upper treeline and below. Maximum latewood density (MXD) from 24 dated cores (from various sites ranging from the upper treeline and below, oldest sample dates back to 776 AD) was determined with an X-ray CT toolchain. Ring and fibre angles were corrected and a MXD chronology was constructed. The resulting MXD chronology will be correlated to summer temperature. Future scanning will allow constructing a + 5000 year MXD chronology and could reveal the cooling effect of volcanic eruptions through this period.

How to cite: De Mil, T., Salzer, M., Pearson, C., Trouet, V., and Van den Bulcke, J.: Maximum latewood density records of the oldest trees in the world: Great Basin Bristlecone pine (Pinus Longaeva), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19868, https://doi.org/10.5194/egusphere-egu2020-19868, 2020

D3375 |
Jan Esper, Lara Klippel, Paul J. Krusic, Oliver Konter, Christoph Raible, Elena Xoplaki, Jürg Luterbacher, and Ulf Büntgen

The Mediterranean has been identified as particularly vulnerable to climate change, yet a high-resolution temperature reconstruction extending back into the Medieval Warm Period is still lacking. Here we present such a record from a high-elevation site on Mt. Smolikas in northern Greece, where some of Europe’s oldest trees provide evidence of warm season temperature variability back to 730 CE. The reconstruction is derived from 192 annually resolved, latewood density series from ancient living and relict Pinus heldreichii trees calibrating at r1911-2015 = 0.73 against regional July-September (JAS) temperatures. Although the recent 1985-2014 period was the warmest 30-year interval (JAS Twrt.1961-90 = +0.71°C) since the 11th century, temperatures during the 9-10th centuries were even warmer, including the warmest reconstructed 30-year period from 876-905 (+0.78°C). These differences between warm periods are statistically insignificant though. Several distinct cold episodes punctuate the Little Ice Age, albeit the coldest 30-year period is centered during high medieval times from 997-1026 (-1.63°C). Comparison with reconstructions from the Alps and Scandinavia shows that a similar cold episode occurred in central Europe but was absent at northern latitudes. The reconstructions also reveal different millennial-scale temperature trends (NEur = -0.73°C/1000 years, CEur = -0.13 °C, SEur = +0.23°C) potentially triggered by latitudinal changes in summer insolation due to orbital forcing. These features, the opposing millennial-scale temperature trends and the medieval multi-decadal cooling recorded in Central Europe and the Mediterranean, are not well captured in state-of-the-art climate model simulations.

How to cite: Esper, J., Klippel, L., Krusic, P. J., Konter, O., Raible, C., Xoplaki, E., Luterbacher, J., and Büntgen, U.: A millennium-length temperature reconstruction for the eastern Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3927, https://doi.org/10.5194/egusphere-egu2020-3927, 2020

D3376 |
Viorica Nagavciuc, Cătălin-Constantin Roibu, Monica Ionita, Andrei Mursa, Mihai-Gabriel Cotos, and Ionel Popa

The aim of this study was to compare the climatic responses of three tree rings proxies: tree ring width (TRW),
maximum latewood density (MXD), and blue intensity (BI). For this study, 20 cores of Pinus sylvestris covering
the period 1886–2015 were extracted from living non-damaged trees from the Eastern Carpathian Mountains
(Romania). Each chronology was compared to monthly and daily climate data. All tree ring proxies had a
stronger correlation with the daily climate data compared to monthly data. The highest correlation coefficient
was obtained between the MXD chronology and daily maximum temperature over the period beginning with the
end of July and ending in the middle of September (r=0.64). The optimal intervals for the temperature signature
were 01 Aug – 24 Sept for the MXD chronology, 05 Aug – 25 Aug for the BI chronology, and both 16 Nov
of the previous year – 16 March of the current year and 15 Apr – 05 May for the TRW chronology. The results
from our study indicate that MXD can be used as a proxy indicator for summer maximum temperature, while
TRW can be used as a proxy indicator for just March maximum temperature. The weak and unstable relationship
between BI and maximum temperature indicates that BI is not a good proxy indicator for climate reconstructions
over the analysed region.

How to cite: Nagavciuc, V., Roibu, C.-C., Ionita, M., Mursa, A., Cotos, M.-G., and Popa, I.: Different climate response of three tree ring proxies of Pinus sylvestris from the Eastern Carpathians, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20524, https://doi.org/10.5194/egusphere-egu2020-20524, 2020

Chat time: Wednesday, 6 May 2020, 16:15–18:00

D3377 |
| Highlight
Oliver Konter and Jan Esper

Tree-ring growth of conifer trees originating from central European low mountain ranges often reveal indistinct growth-climate relationships. Temperature variations can play a crucial role, whereas water availability can also control the annual growth and become the main dominating factor. The low mountain range Pfälzerwald in the Palatinate region represents the largest contiguous forested area in Germany and features at its most eastern limitation a unique ecological setting due to its sandy soils and reduced water availability. In addition, its north-south orientation and associated lee-effects due to predominating westerlies together with altitudinal differences of more than 300 m lead to higher temperatures, lower precipitation amounts, and, as a forest management consequence, to a proportion of up to 80 % of pine trees. Despite these exceptional ecological and climatological prerequisites, calibrating tree-ring width data from 487 Pinus sylvestris core samples against regional meteorological stations (1950-2011) and gridded data (1901-2011) confirm alternating climate control mechanisms. Comparison with drought-related indices (scPDSI), combining precipitation and temperature, unfolds highest correlations with May-July conditions (r1901-2011=0.34, p<0.05), however, lacking temporal robustness in the early 20th century.

The vegetation outside the forested areas in the plain can be characterized as agricultural croplands with vineyards, representing one of the largest wine-growing regions in Germany. We collected and analyzed a 24 datasets of 57 consecutive years (1959-2015) of must sugar content, acidity, alcohol content, and sugar-free extracts in Riesling, Pinot Gris, Pinot Blanc, and Silvaner wines, originating from 15 wineries adjoining the forested area into the plain. Correlation of Riesling must sugar content against regional April-August temperature data reveals a highly significant signal (r1981-2015=0.73, p<0.01; high-pass filtered r=0.49, p<0.01). Sugar-free extract variations of Pinot Gris are significantly controlled by March-September precipitation (r2004-2014=0.76, p<0.01; high-pass filtered r=0.77, p<0.01).

In this low mountain range, tree-ring growth from conifers is not solely controlled by one climatic variable, though it is that combining tree-rings with must sugar content and sugar-free extract data from Riesling and Pinot Gris wine can further elucidate our understanding of longer-term climate variability in the Palatinate region.

How to cite: Konter, O. and Esper, J.: Integrating tree-ring and wine data from the Palatinate (Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21983, https://doi.org/10.5194/egusphere-egu2020-21983, 2020

D3378 |
Milena Godoy-Veiga, Giuliano Locosselli, Lior Regev, Elisabetta Boaretto, and Gregório Ceccantini

Tree-ring chronologies are an excellent climate archive for their spatial and temporal resolution. While networks of chronologies have been built outside the tropics helping to understand past regional climate trends, tropical regions still lag behind in terms of spatial coverage. Dendrochronological studies, however, may succeed in seasonally dry tropical forests where the growing season is well defined. Amburana cearensis, found in both dry and wet forests in South America, is poorly explored for dendrochronological purposes, with no previous study in Brazil. Therefore, we sampled trees growing in a seasonally dry forest in a karstic area in Central-Eastern Brazil, under the South American Monsoon domain, in order to explore this species potential for dendroclimatological studies in the region. We build a tree-ring width chronology using 26 trees. We found a strong common growth signal among trees, with an r-bar of 0.51 and an average mean sensitivity of 0.50. The standard tree-ring width chronology showed a significant negative correlation with Vapor-Pressure Deficit during the entire wet season (0.54), negative correlation with temperature at the end of the wet season (0.45), and a positive correlation with the sum of precipitation during the wet season (0.46). Further stable isotopic analysis will provide additional records of climate variability in the region. Since Amburana cearensis occurs across most of the seasonally dry forests and savannas from South America, it has a great potential to be used to develop climate reconstructions and verify the effects of climate change currently affecting the region.

How to cite: Godoy-Veiga, M., Locosselli, G., Regev, L., Boaretto, E., and Ceccantini, G.: First Amburana cearensis (Fabaceae) tree-ring chronology in Brazil in a dry forest shows great potential for climate reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11379, https://doi.org/10.5194/egusphere-egu2020-11379, 2020

D3379 |
Huiming Song and Yu Liu

The tree-ring densitometric studies conducted in the semiarid regions are rare, among them, minimum earlywood density (MND) records the strongest climate signals than other density parameters. In contrast, maximum density of latewood (MXD) in cold and humid regions usually shows the most significant association with summer temperatures. Density parameters of Purplecone Spruce (Picea purpurea Mast.) in Mt. Shouyang, northwestern China, a typical semiarid region were obtained to test the density-climate relationships. It is showed that MXD has strong positive correlations with temperatures and a negative correlation with precipitation in the late growing season from July to September. MND is significantly positively correlated with temperature and positively correlated with precipitation during the early growing season. During early growing season, spring droughts always occur due to low precipitation. A narrow ring is built under moisture stress, since tree growth is inhibited by decreasing cell division and cell enlargement. With the intensification of monsoon, more precipitation is available, which can basically meet the needs of tree growth. During strong monsoon season with humid conditions, trees are less affected by moisture stress. In this case, high temperature could increase cell wall thickness in the latewood which strongly affects the tree-ring maximum density. It could explain why there is a significant positive correlation between MXD and summer-fall temperature.

How to cite: Song, H. and Liu, Y.: Climatic response of tree-ring densitometric records in a semiarid site of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6384, https://doi.org/10.5194/egusphere-egu2020-6384, 2020

D3380 |
Qiufang Cai and Yu Liu

Tree ring plays an important role in deciphering the paleoclimatic signals over the past 100-10000 years. However, tree-ring studies from tropical to subtropical regions are rarer than that from extratropical regions, which greatly limit our understanding of some critical climate change issues. Based on tree-ring-width chronologies in different area of Subtropical China (SC), seasonal temperature history of different seasons over the past 200 years were reconstructed. In addition to the warm and cold fluctuations in the reconstructed temperature series, main conclusions are drawn in the following two aspects: 1) Winter-half year temperature had good agreement with summer-time temperature variation in SC at decadal scale, while the winter-half year warming in recent decades was more evident than summer-time. 2) Comparison of the tree-ring based temperature series indicated that the start time of the recent warming in eastern China was regional different. It delayed gradually from north to south, starting at least around 1940 AD in the north part, around 1970 AD in the central part and around 1980s in the south part.

How to cite: Cai, Q. and Liu, Y.: Seasonal and regional temperature differences in subtropical China during the past 200 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12603, https://doi.org/10.5194/egusphere-egu2020-12603, 2020

D3381 |
Giovanna Battipaglia, Arturo Pacheco, Julio Camarero, Marin Pompa-Garcia, Jordi Voltas, and Marco Carrer

An improvement of our understanding of how tree species will respond to warmer conditions and longer droughts requires comparing their responses across different environmental settings and considering a multi-proxy approach. We used different xylem traits (tree-ring width, formation of intra-annual density fluctuations –IADFs, wood anatomy, D13C and d18O records) to retrospectively quantify these responses in three conifers inhabiting two different drought-prone areas in northwestern Mexico. A fir species (Abies durangensis) was studied in a higher altitude and more humid site and two pine species were sampled in a nearby, drier site (Pinus engelmannii, Pinus cembroides). Tree-ring-width indices (TRWi) of all the species showed very similar year-to-year variability, likely indicating a common climatic signal throughout the whole region. Wood anatomy analyses, covering over 3.5 million measured cells, showed that P. cembroides lumen area was much smaller than in the other two species and it remained constant along all the studied period (over 64 years). Alternately, cell wall was ticker in P. engelmannii which also presented the highest amount of intra-annual density fluctuations. Climate and wood anatomy correlations pointed out that lumen area was positively affected by winter precipitation for all the species, while cell-wall thickness was negatively affected by current season precipitation in all species but P. cembroides, suggesting this taxon may be better adapted to withstand drought than its coexisting conifer with thinner cell walls resulting from wet winters. Stable isotope analysis showed in P. cembroides some of the lowest cellulose-Δ13C mean values ever reported in the literature for a forest tree species, although there were no particular trend differences between the studied species. As well, no significant δ18O differences where found between the three species, but they shared a common decreasing trend. With very distinct wood anatomical traits (smaller cells, compact morphology), P. cembroides stood out as the better-adapted species in its current environment and could be less affected by future drier climate. P. engelmannii and A. durangensis showed high plasticity at wood anatomical level, allowing them to promptly respond to seasonal water availability, however this feature may provide few advantages on future climate scenarios with longer and more frequent drought spells. Further research, including xylogenesis analysis and monitoring of different populations of these tree species, would be still necessary to reach a clearer understanding of their future responses to weather patterns. Our multi-proxy approach could be used in other forests to characterize the in situ functioning of trees, e.g. growth, water use, and development of strategies for forest management under the current climate change scenarios.

How to cite: Battipaglia, G., Pacheco, A., Camarero, J., Pompa-Garcia, M., Voltas, J., and Carrer, M.: Growth, isotope records and quantitative wood anatomy reveal species-specific couplings in three Mexican conifers inhabiting drought-prone areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22409, https://doi.org/10.5194/egusphere-egu2020-22409, 2020

D3382 |
Qiang Li, Yu Liu, and Huiming Song

The Qinling Mountain is the most important mountain range in eastern China, and is the geographical boundary and the climatic boundary. We investigated tree-ring d18O variations in South and North Slope of the Qinling Mountain, and found that the variations of tree-ring  d18O were significantly correlated over the past two and a half centuries (r=0.641, n=247, p<0.001). And they are negatively correlated with relative humidity and precipitation, and positively correlated with temperature. Compared with the various hydroclimate-related time series in the surrounding area, it is found that both can represent the region's long-term hydroclimate change. The consistent changes in the interannual time scale may be due to the common modulation of ENSO. However, on the decadal time scale, there have been significant divergence between the two tree-ring  d18O series since 1981 and the divergence may be caused by changes in relative humidity at the sampling site, suggesting that in the context of global warming, although the warming range is the same, but the triggered relative humidity changes are not consistent. In addition, changes in PDO may be another cause of low-frequency difference.

How to cite: Li, Q., Liu, Y., and Song, H.: Low-frequency divergence of tree-ring d18O variations on both sides of climatic boundary mountain of eastern China since 1980s, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6467, https://doi.org/10.5194/egusphere-egu2020-6467, 2020

D3383 |
Danny Vargas, Darwin Pucha-Cofrep, Angélica Burneo, Lisseth Carlosama, Madison Herrera, Sheila Serrano, Marco Cerna, A.J. Timothy Jull, Mihály Molnár, István Futó, Anikó Horváth, Marjan Temovski, and László Palcsu

The neotropical tree genus Cedrela (Meliaceae) had originated in dry forest under seasonal climates in North America, then spread to South America during the Oligocene/Early Miocene and finally adapted to deciduous forest in the Pliocene Epoch. At present, Cedrela comprises 17 species distributed in the Neotropics (24N-27S) and in Ecuador; the species Cedrela nebulosa (T.D.Penn. & Daza) generally develops in the altitudinal range of 1100-2400 m a.s.l. The town of Mera, Pastaza in Central Ecuador was the first lowland Amazonian site from which paleoecological data were acquired. It brought about the hypothesis of a 4.5 oC temperature depression during glacial times recently supported by a paleolimnological record in the area. However, despite the dry events during glacial periods there was not a loss of forest structure owing to the importance of cloud cover formation enhanced by the lower temperatures (Montoya et al., 2018).

Our research aims to study the role that cloud cover plays in the pre-montane forest of Mera, located at the Andean eastern flank (1º24'25 S, 78º03'10 W, 1200 m a.s.l) and its coupling with modern climate variations. It is expected that cloud cover will continue moving upwards and narrowing as temperature rises overriding its buffering effect against changes in precipitation, a scenario that threatens the forest stability achieved even during glacial periods. Dendroclimatological methods will be applied with trees of Cedrela nebulosa which receive moisture and constant temperature throughout the year. Interpretations of the phenomenon are expected to be drawn using oxygen isotopes in tree-ring cellulose (δ18OTR) and precipitation (δ18OW), as well as air temperature (T), for which monitoring has been established in the study area. The formation of annual rings in the species has been preliminary validated by radiocarbon dating (14C) using the bomb peak.

The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’.

Reference: Montoya et al., 2018. Front. Plant Sci., 9, 196; doi: 10.3389/fpls.2018.00196

How to cite: Vargas, D., Pucha-Cofrep, D., Burneo, A., Carlosama, L., Herrera, M., Serrano, S., Cerna, M., Jull, A. J. T., Molnár, M., Futó, I., Horváth, A., Temovski, M., and Palcsu, L.: Impact of cloud coverage on growth dynamics of Cedrela nebulosa from an Amazonian pre-montane forest in Central Ecuador, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7730, https://doi.org/10.5194/egusphere-egu2020-7730, 2020

D3384 |
Alvaro Gonzalez-Reyes, Duncan Christie, Carlos LeQuesne, Moises Rojas-Badilla, Tomas Muñoz, and Ariel Muñoz

Soil moisture is a key variable into the earth surface dynamics, however long-term in situ measurements are globally scarce. In the Mediterranean Andes of Chile (30° - 37°S) grow the long-lived conifer “Ciprés de la Cordillera” (Austrocedrus chilensis), which is a demonstrated hydroclimatic proxy capable to cover the last millennium. Previous paleoclimatic studies have documented a high sensitivity between tree species and several hydroclimatic variables such as precipitation, streamflow, snowpack and aridity indexes, but the lack of in situ soil moisture observations has precluded an assessment of the spatial growth responses to high-resolution soil moisture variability. Here, we use three A. chilensis chronologies to determine linkages with the satellite-based surface soil moisture product v04.5 generated by ESA. We found significant relationships between tree-growth an a soil moisture field across the 32° - 34°S spatial domain of western South America from January to September during 1985 – 2013 period (r = 0.65; P < 0.001). Temporal relationships between tree-growth and soil moisture satellite observations exhibit a significant spectral coherence associated to cycles around 7 years (P < 0.10) and a clear decadal variability. Based on our preliminary results and the present extensive network of A. chilensis tree-ring chronologies, this species appears as a promising proxy to reconstruct surface soil moisture variability derived from remote sensing over the last millennium in a topographically complex Andean region of South America.



How to cite: Gonzalez-Reyes, A., Christie, D., LeQuesne, C., Rojas-Badilla, M., Muñoz, T., and Muñoz, A.: Linking tree rings with satellite observations of soil moisture: toward the reconstruction of water availability in the Mediterranean Andes region , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3975, https://doi.org/10.5194/egusphere-egu2020-3975, 2020

D3385 |
Karolina Janecka, Ryszard Kaczka, Holger Gärtner, Jill E. Harvey, and Kerstin Treydte

Compression wood is a common tissue present in the trunk, branches and roots of mechanically stressed coniferous trees. Its main role is to increase the mechanical strength and regain the vertical orientation of a leaning stem. Compression wood is thought to influence the climate signal in different tree-ring measures. Hence trees containing compression wood are mostly excluded from tree-ring studies reconstructing past climate variability. There is a large gap of systematic work testing the potential effect of compression wood on the strength of the climate signal in different tree-ring parameters, and especially stable isotope records.

Here we test for the first time the effect of compression wood contained in montane Norway spruce (Picea abies L. Karst) on both δ13C and δ18O tree-ring cellulose records by analyzing compression and opposite wood radii from several disturbed trees together with samples from undisturbed reference trees. We selected four trees tilted by geomorphic processes that were felled by wind, and four undisturbed reference trees in the Tatra Mountains, Poland. We qualitatively classified the strength of compression wood using wood cell anatomical characteristics (tracheid shape, cell wall thickness and presence of intercellular spaces). Then we developed tree-ring width, δ13C and δ18O chronologies from the compression wood radii and the opposite radii of the tilted trees, and from the radii of the reference trees. We tested the effect of compression wood on tree-ring cellulose δ13C and δ18O variability and on the climate signal strength. Only minor differences were found in the means of δ13C and δ18O compression, opposite and reference radii. The statistical relationships between climate variables, δ13C and δ18O remained consistent among all chronologies. Our findings suggest that moderately tilted trees containing compression wood can be used to both reconstruct past geomorphic activity, and stable-isotope based dendroclimatological research.

How to cite: Janecka, K., Kaczka, R., Gärtner, H., Harvey, J. E., and Treydte, K.: Compression wood has a minor effect on the climate signal in tree-ring stable isotopes of montane Norway spruce, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9173, https://doi.org/10.5194/egusphere-egu2020-9173, 2020

D3386 |
Kerstin Treydte, Lukas Bächli, Daniel Nievergelt, Christopher Sargeant, Marina Fonti, Matthias Saurer, Marco M. Lehmann, Arthur Gessler, and Katrin Meusburger

Tree species differ in their ability to utilize existing soil water pools due to their root architecture, but also due to their capacity to react on spatiotemporal variations of the supply. The interplay between variations of water availability and species-specific utilization plays a crucial role in determining the water balance and cycle of ecosystems. Despite a large number of studies on the various aspects of ecosystem water relations, there exists still uncertainty regarding the plasticity of tree roots to take up water from different soil depths in relation to the mechanisms and patterns of water infiltration into the root zone.

We will present results from a holistic tracer irrigation experiment in the Lötschental, Swiss Alps. A subalpine forest plot (150 m2) of Larix decidua and Picea abies was irrigated with, relative to natural soil abundance 18O and 2H depleted glacier water during 10 subsequent days in summer 2019. Water was taken from a nearby glacier river. Irrigation was conducted through a dripping system installed on the ground to increase and keep soil water content at field capacity during the experiment. Throughout the irrigation, soil moisture at three locations in the experimental as well as in a control plot was monitored in 15-minutes intervals in two soil depths. Four larch and four spruce trees per plot were selected and equipped with continuously measuring sapflow sensors. Sampling of soil and tree tissues took place on a daily basis always before noon: Soil samples were taken in close distance to the soil moisture sensors from at least three soil depths, needles and twigs from all experimental trees were sampled in the canopy of the sun-exposed crowns. Every third day xylem samples were taken from the tree stems with a 5mm increment corer. All samples were immediately cooled until the isotopic analysis. In parallel to the soil and tree sampling, physiological measurements were performed on the same trees with a Licor. In addition, also pre-dawn leaf water potentials were measured every third day. Finally, also micro cores were taken several times before, during and after the experiment for monitoring of xylem cell growth as a basis for high-resolution tree-ring isotope analysis at a later project phase. From all soil, needle, twig and stem core samples water was extracted by cryogenic vacuum distillation and d18O and d2H measured.

The data of this experiment together with mechanistic modelling will elucidate the spatiotemporal pattern of soil water dynamics, water uptake by roots and tree-water relations of two species that have ecologically different life forms but are both highly representative for subalpine regions. Understanding their ability to react and capitalize on soil rewetting after dry periods will be crucial for the estimation of their survival potential and competitiveness under future dry and wet extreme events.

How to cite: Treydte, K., Bächli, L., Nievergelt, D., Sargeant, C., Fonti, M., Saurer, M., Lehmann, M. M., Gessler, A., and Meusburger, K.: Soil water uptake of larch and spruce recorded by stable isotope tracing in the Swiss Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18994, https://doi.org/10.5194/egusphere-egu2020-18994, 2020

D3387 |
Gonzalo Peres-De-Lis, Cyrille Rathgeber, and Stéphane Ponton

Despite a long-standing interest in retrieving intra-annual environmental information from tree-ring features, none of the approaches developed so far for accurately dating intra-ring sector has been validated on observations. Here, we investigated space-for-time association across regular intra-ring sectors for which we estimated the timing of formation. For this purpose, a unique dataset containing quantitative wood anatomy measurements and kinetics of tracheid differentiation was compiled for 45 trees grown in North-East France (three years of wood formation monitoring, for five trees, from three different conifer species). Tracheid dimensions were measured directly on the best anatomical sections at the end of the growing season, while the kinetics of xylem cell differentiation were provided at tree-level by an empirical model of wood formation dynamics. Our results confirmed that the time taken to form sectors of the same width increased from earlywood (composed of wide thin-walled tracheids) to latewood (composed of narrow thick-walled tracheids). This mainly reflected the increase of the duration of cell wall deposition through the growing season, and, to a lesser extent, the augmentation of the number of tracheids per sectors. However, our results also show that regular intra-ring sectors, which were well separated in space, overlapped in time. The overlapping culminated during the summer period, reaching 40 % for 10 sectors. It could be reduced to approx. 30 % by increasing the number of sectors (from 10 to 25, for example), but it cannot be removed. Therefore, successive intra-ring sectors could not be attributed to a succession of separated time intervals by simply using their relative position along the ring. However, the formation of sectors of equivalent ranks were noticeably synchronous between the different trees and years, reaching 80 % of synchronicity for the process of wall thickening. This suggest that data from regular intra-ring sectors could be reliably used to build mean chronologies expressing the common signal of tree populations. Our results show the limits that the xylogenesis process itself imposes on the dating of intra-ring features. They also argue for an in-depth understanding of the association between cell differentiation processes (enlargement, wall thickening and lignification) and wood characteristics (density, anatomy, stable isotope composition).

How to cite: Peres-De-Lis, G., Rathgeber, C., and Ponton, S.: Cutting time slices of tree rings —How intra-annual dynamics of wood formation help to decipher space for time conversion in tree-ring sciences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22286, https://doi.org/10.5194/egusphere-egu2020-22286, 2020

D3388 |
Frederick Reinig, Giulia Guidobaldi, Daniel Nievergelt, Anne Verstege, Fritz Schweingruber, Alan Crivellaro, Lukas Wacker, Jan Esper, and Ulf Büntgen

Trees that were killed and buried by volcanic eruptions can be used to date an eruption with annual or even sub-annual resolution. The detection and measurement of subfossil tree-ring widths (TRW), however, often remains challenging if the material was carbonized during the eruption. Here, we show that the application of X-ray densitometry can improve the assessment of charcoal. Measuring the wood density of carbonized trees killed by the Laacher See Eruption ~13,000 years ago, facilitates the identification of the outermost rings that were formed just before the eruption. Our results suggest that anatomical techniques should be routinely applied in the assessment of historical, archaeological and subfossil wood.

How to cite: Reinig, F., Guidobaldi, G., Nievergelt, D., Verstege, A., Schweingruber, F., Crivellaro, A., Wacker, L., Esper, J., and Büntgen, U.: Using X-ray densitometry of carbonized wood to refine the date of past volcanic eruptions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10372, https://doi.org/10.5194/egusphere-egu2020-10372, 2020

D3389 |
Andrew Friend

Despite its importance for the study of past climates, as well as its significance for carbon sequestration, we lack a mechanistic explanation for how temperature controls wood anatomy. A model of xylogenesis is presented and used to analyse observed tree ring anatomy-temperature relationships in Scots pine (Pinus sylvestris). The model treats the daily proliferation of new cells in the cambium and their subequent differentiation through expansion and secondary wall thickening phases. Control on size at division in the cambium follows recent work on the Arabidopsis shoot apical meristem, and cell enlargement rates in the cambium and enlargement zone are controlled by temperature. The duration of post-cambial enlargement is partially controlled by the rate at which cells pass through the enlargement zone, and partially by the size of this zone, which is controlled by daylength. This set of assumptions is sufficient to generate observed profiles of cell sizes across radial files, with characteristic transitions from earlywood to latewood. After they leave the enlarging zone, cells enter the wall thickening zone, the width of which is also dependent on daylength. A temperature-dependent rate of wall material deposition is insufficient to reproduce the observed gradient in mass density across the radial file, and fails to fully capture the observed seasonality of the correlation between maximum latewood density and temperature. Inclusion of a control on the rate of wall deposition from substrate (sugar) supply, diffusing from the phloem across the radial file, corrects these deficiencies. The resulting model provides a mechanistic explanation of temperature-tree ring relationships, and has the potential to underpin understanding of how climate and CO2 interact in determining the amount of carbon sequestered in trees.

How to cite: Friend, A.: Mechanistic modelling of the influence of temperature on the wood anatomy of Scots pine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9455, https://doi.org/10.5194/egusphere-egu2020-9455, 2020

D3390 |
Jacques C. Tardif, Heather Dickson, France Conciatori, Alexandre Florent Nolin, and Yves Bergeron

Flood rings (FR) in ring-porous species have been widely used to identify flood events in boreal and temperate regions. Flood rings also have been experimentally reproduced in both Quercus and Fraxinus species. More recently, continuous measurement of earlywood cross-sectional vessel area in riparian black ash trees (Fraxinus nigra Marsh.) have shown that not only were FR associated with flood events but that the year-to-year variation in chronologies derived from earlywood cross-sectional vessel area also reflected that in mean spring flow data. These findings led to the reconstruction of the Harricana river spring flow for the period 1770-2016 with more than 65% of the variance in the gauge streamflow data captured (See Nolin et al. presentation at EGU2020). Compared to ring-porous species, anatomical variations in diffuse-porous species in relation to flood events has been little studied.

In this study, both ring-porous black ash and diffuse-porous [trembling aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.)] trees were sampled in three floodplain sites located on the shore of Lake Duparquet, northern Quebec. Within each floodplain site, trees were selected so to represent a gradient of exposure to spring flooding. Given that the response of black ash to flooding is well documented (FR), paired sampling was used so each Populus tree was paired with a nearby black ash tree. When feasible, cross-sections from dead trees were also collected. For each tree, the elevation of the tree base to lake water level and the height of extracted cores were noted.  The main objective of the study was to assess if diffuse-porous trembling aspen and balsam poplar growing on floodplains responded like ring-porous black ash to annual spring flooding.

All wood samples were prepared following standard dendrochronological procedures with visual crossdating validated using program COFECHA. In addition to ring-width measurements, a visual determination of the intensity of FR was done for each black ash tree. In diffuse-porous species, a newly observed tree-ring anomaly referred to as tree ring with “periodic tangential band of vessels” (PTBV) were systematically compiled using a two-part numerical code; the first digit corresponding to the start position of the banding sequence within a tree ring and the second digit referring to the number of consecutive bands within a sequence. Two observers independently compiled their observations. The main hypotheses were that years recording PTBV will correspond to FR years and that they will also be associated with those hydroclimatic variables leading to major spring floods. Preliminary analyses indicated that FR and PTBV years display synchronicity. Both anomalies are also associated with hydroclimatic conditions leading to major spring flooding. The absence of a perfect match between ring-porous and diffuse-porous species however as well as the observed variability in the banding patterns still need to be analyzed in relation to flood exposure and core height. The discovery of a new potential flood marker in diffuse-porous tree species opens the door for the novel application of wood-cell anatomy in dendrohydrology and especially when ring-porous species are absent.  

How to cite: Tardif, J. C., Dickson, H., Conciatori, F., Nolin, A. F., and Bergeron, Y.: Are periodic tangential band of vessels a new anatomical marker of floods in diffuse-porous tree rings?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5326, https://doi.org/10.5194/egusphere-egu2020-5326, 2020

D3391 |
Stefan Klesse, Georg von Arx, Martin Gossner, Christian Hug, Andreas Rigling, and Valentin Queloz

Since the 1990s the invasive fungus Hymenoscyphus fraxineus has led to severe crown dieback and high mortality rates in Fraxinus excelsior in Europe. In addition to a strong genetic control of tolerance to the fungus, previous studies have found high landscape variability in the severity of dieback symptoms. However, apart from heat and humidity-related climate conditions favoring fungal development the mechanistic understanding of why smaller or slower growing trees are more susceptible to dieback remains less well understood.

Here, we analyzed three stands in Switzerland with a unique setting of eight years of intra-annual diameter growth and annual crown health assessments, together with ring-width and quantitative wood anatomical measurements preceding the monitoring, to investigate if wood anatomical adjustments can help better explaining the size-related dieback phenomenon.

We found that slower growing trees or trees with smaller crowns already before the arrival of the fungus were more susceptible to dieback and mortality. We show that defoliation directly reduces growth as well as maximum earlywood vessel size, and that the positive relationship between vessel size and growth rate causes a positive feedback amplifying crown dieback. Because leaf necrosis happens during late summer when ring formation has already finished, photosynthesis is heavily reduced during a time when non-structural carbohydrates (NSCs, sugars and starch) are stored. Thus, we hypothesize that a lack of NSCs (mainly sugars) leads to lower turgor pressure and smaller earlywood vessels in the next year impeding efficient water transport and photosynthesis, and is responsible why smaller and slower growing trees show stronger symptoms of dieback and higher mortality rates.

How to cite: Klesse, S., von Arx, G., Gossner, M., Hug, C., Rigling, A., and Queloz, V.: Growth and wood anatomical adjustments of Fraxinus excelsior to the infestation of the invasive fungus Hymenoscyphus fraxineus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22520, https://doi.org/10.5194/egusphere-egu2020-22520, 2020

D3392 |
| Highlight
Francesco Niccoli, Veronica De Micco, Simona Castaldi, Riccardo Valentini, and Giovanna Battipaglia

In the Mediterranean Basin, fire incidence has increased dramatically during the past decades and fire is expected to become more severe in the future due to climate change. The effects of fires on forest ecosystems can last several years: the survival of fire-injured trees depend not only on the adaptive traits of individual species, but also on the ability of trees to tolerate post-fire environmental constraints.

Several trees, although initially resisting the strong heat injury caused by the high temperatures of the flames, can reduce their vigor and finally die after a few years after fire, due to serious damage at the canopy level or due to the difficult conditions arising in the surrounding stands. The study of long-term trends of the eco-physiological processes in plants subjected to fire are of fundamental importance in planning management actions and restoration strategies of burned areas.

In this context, our research aims to identify and understand the impacts that post-fire conditions can have on the growth and eco-physiology of Pinus pinaster Aiton, through the study of a forest stand hit by a devastating fire that affected the Vesuvius National Park, in Southern Italy, in July 2017. This study combines the dendrochronological analyses with the monitoring of xylogenesis, supported by the measurements in continuum of the eco-physiological parameters of the individual plants through the use of the innovative TreeTalker device.

The results of the dendrochronological analyses showed that, at the end of 2018, despite the strong stress suffered and a significant decrease in growth, the plants showed a very limited mortality rate: only 2-10% of the individuals reduced their vigor. However, preliminary data on xyologenesis, collected from spring 2019 to nowadays, suggest how, after two years, the fire of 2017 is still influencing the cambium activity of individual plants: the productivity and the differentiation kinetics of xylem cells are strongly influenced by the damages suffered at the canopy level.

The monitoring activities will continue for the next few years in order to identify the recovery times of the plant to return to normal vital functions, as well as, eventually, understand the eco-physiological processes that lead to a reduction in productivity or even to death.

How to cite: Niccoli, F., De Micco, V., Castaldi, S., Valentini, R., and Battipaglia, G.: An integrated approach for monitoring the post-fire responses of Pinus pinaster Aiton, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7395, https://doi.org/10.5194/egusphere-egu2020-7395, 2020

D3393 |
Elio Fierravanti, Serena Antonucci, Giovanni Santopuoli, Roberto Tognetti, and Marco Marchetti

The area of the Mediterranean basin is expected to be threatened by more severe and prolonged droughts and heat waves. Therefore, a more exhaustive knowledge about growth-climate responses in forest trees is necessary in order to adopt mitigation and adaptation strategies in forest management and planning. Climate change will cause shifts of the climate envelope for tree species, potentially leading to migration of species distribution. Under these circumstances, investigations on growth-climate relationships in trees of different provenances of the same species are important for the success of climate-smart forestry. Provenance trials are useful for understanding the response of this species to drought stress. We studied growth-climate relationships in 40-year-old trees of maritime pine (Pinus pinaster Ait.) from five provenances (Corsica, Portugal, Tuscany, and two native ones: Telti and Limbara) grown on four different sites in Sardinia island (Montes, Montarbu, Uatzo and Usinavà), Italy. In details, for all trees in each site, measurements of stem diameter at breast height (DBH) and plant height (H) were collected. For each site-provenance combination, two incremental cores were collected for each tree; successively, samples were cross-dated and standardized. Weather data (temperature and precipitation) were collected from CRU data online (http://www.cru.uea.ac.uk/). Differences in DBH and H were found among sites. In particular, the highest values for DBH and H were found in Montes and Uatzo, respectively. Instead, Montarbu showed the lowest mean values for both parameters. Differences among provenances were also observed. Specifically, in Montarbu, the greatest H were found for Tuscany and the lowest for Corsica (p<0.0001). The same pattern was also found for DBH, but without statistical significance (p>0.5). In Uatzo, Corsica showed the highest mean values for both H and DBH, while the lowest DBH was observed for Tuscany (p=0.0008), and the lowest H was found for Limbara (p<0.0001) provenance, respectively. No significant differences were found for both H and DBH in Montes. Finally, in Usinavà, Limbara showed significant higher values, for both H and DBH, compared to the other provenances (p<0.001). Temperature had a greater influence on growth traits in Montarbu, especially for spring-summer period, with Telti and Tuscany having the most significant correlation. Precipitation, instead, mostly affected Usinavà. On the other hand, in Montes and Uatzo, no significant correlations between climate and growth were observed. However, different climate-growth relationships were observed among provenances. In conclusion, our results suggest that, after 40 years of growth, greater H and DBH were found in the sites with lower temperature and higher precipitation (Uatzo and Montes). Interestingly, in Uatzo, Corsica showed the highest values of both DBH and H, while Limbara presented the lowest growth. Noteworthy, Limbara showed greater H in Usinavà (the warmest and driest site), whereas in the previous survey, Limbara had the lowest H. These results represent a further step in identifying potential genetic variation in tree growth and drought tolerance of maritime pine in Mediterranean conditions. Data collected in long-term experimental plots and repeated measurements are confirmed of fundamental importance to estimate the resilience of forest species to climatic changes.

How to cite: Fierravanti, E., Antonucci, S., Santopuoli, G., Tognetti, R., and Marchetti, M.: Forty years of growth-climate relationships in a progeny test of Pinus pinaster in Sardinia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11598, https://doi.org/10.5194/egusphere-egu2020-11598, 2020

D3394 |
Combining tree-ring and stable isotope analyses to differentiate between the effects of weather and edaphic factors on tree growth
Frank Thomas
D3395 |
Walter Oberhuber, Ursula Bendler, Vanessa Gamper, Jacob Geier, Anna Hölzl, Werner Kofler, Hanna Krismer, Barbara Waldboth, and Gerhard Wieser

It is well established, that tree growth at high elevations is mainly limited by low temperature during the growing season and climate warming was frequently found to lead to more growth and expansion of trees into alpine tundra. However, dendroclimatological studies revealed contradictory growth response to recent climate warming at the upper elevational limit of tree growth, and transplant experiments unveiled that high elevation tree provenances are not adequately benefiting from higher temperatures when planted at lower elevation. We therefore re-evaluated growth response of trees to recent climate warming by developing tree ring series of co-occurring conifers (Swiss stone pine (Pinus cembra), European larch (Larix decidua), and Norway spruce (Picea abies)) along several altitudinal transects stretching from the subalpine zone to the krummholz-limit (1630–2290 m asl; n=503 trees) in the Central European Alps (CEA). We evaluated whether trends in basal area increment (BAI) are in line with two phases of climate warming which occurred from 1915–1953 and from mid-1970s until 2015. We expected that BAI of all species shows an increasing trend consistent with distinct climate warming during the study period (1915–2015) amounting to >2 °C. Although enhanced tree growth was detected in all species in response to climate warming, results revealed that at subalpine sites (i) intensified climate warming since mid-1970s did not lead to corresponding increase in BAI, and (ii) increase in summer temperature primarily favored growth of Norway spruce, although Swiss stone pine dominates at high altitude in the CEA and therefore was expected to mainly benefit from climate warming. At treeline BAI increase was above the determined age trend in all species, whereas at the krummholz-limit only deciduous larch showed minor growth increase. We explain missing adequate growth response to recent climate warming (i) by strengthened competition for resources (primarily nutrients and light) in increasingly denser stands at subalpine sites leading to changes in carbon allocation among tree organs, and (ii) by frost desiccation injuries of evergreen tree species at the krummholz-limit. Our findings indicate that tree growth response to climate warming at high elevation is possibly nonlinear, and that increasing competition for resources and the influence of climate factors beyond the growing season impair stem growth. 

How to cite: Oberhuber, W., Bendler, U., Gamper, V., Geier, J., Hölzl, A., Kofler, W., Krismer, H., Waldboth, B., and Wieser, G.: Climate warming does not adequately translate to increased radial stem growth of coniferous species along the Alpine treeline ecotone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8232, https://doi.org/10.5194/egusphere-egu2020-8232, 2020

D3396 |
Rolf Siegwolf, Renée Brooks, John Roden, and Matthias Saurer

We are editing a new book in the Springer Tree Physiology Series entitled “Stable Isotopes in Tree Rings: Inferring Physiological, Climatic and Environmental Responses” due out in 2020. Because trees produce annual growth increments that can be precisely dated, annual and interannual variations in tree ring width and stable carbon, oxygen and hydrogen isotopes provide detailed records of past physiological responses to biotic and abiotic impacts over many decades and centuries. In contrast to non-living chronologies (ice cores, stalagmites etc.), trees modify base physical inputs in response to local microclimates through their physiological response to light, temperature, humidity, water availability, CO2 and nutrients. Although this can make interpretation of isotopic variation in organic matter more complicated, it also means that these proxies can provide a wealth of additional information. Thus, an understanding of the combined physical and biological drivers of isotope fractionation in tree rings is crucial for paleoclimate interpretation. In addition, tree rings and stable isotopes contained therein integrate dynamic environmental, phenological and developmental variation that can be used to study present organism function and recent anthropogenic influences apart from their use as proxies for conditions in the distant past. The last few decades have seen tremendous progress in understanding the mechanisms by which tree physiology modifies stable isotope fractionation in organic matter.

This book will be the first to comprehensively cover the field of tree ring stable isotopes. This volume highlights how tree ring stable isotopes have been used to address a range of environmental issues from paleoclimatology to forest management, and anthropogenic impacts on forest growth. It evaluates strengths and weaknesses of isotope applications in tree rings. This book focuses on physiological mechanisms that influence isotopic signals and reflect environmental impacts. Each of the 25 chapters has been authored by leading experts providing the most recent developments in the area.

How to cite: Siegwolf, R., Brooks, R., Roden, J., and Saurer, M.: Stable Isotopes in Tree Rings: Inferring Physiological, Climatic and Environmental Responses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3680, https://doi.org/10.5194/egusphere-egu2020-3680, 2020