CL1.18

Assessing the characteristic of water transport in wood is challenged by the complexity of its tissue composed by numerous different-sized and interconnected conduits. Current methods for measuring conductivity or flow resistance performed on a piece of wood usually have no direct link to the anatomy of the single conduits. Thus, despite the large application of these assessment for ecological studies, this integrated tissue-level approach hampers the possibility to extend the hydraulic assessment across time by using dated series of tree rings.

In this contribution we make use of tracheid versus pit isometry to propose a new hydraulic model merging existing morphological-based components of tracheid hydraulic to upscale water transport properties across time and environments. By using linear relations between tracheid dimeter and pit size as described in the literature, we applied our model to tracheids of increasing size to show that our assessments of the pit and tracheid resistances match with estimations performed in independent studies. We then apply the model to tracheid anatomical measurements from Larix sibirica tree-rings (from 1986 to 2015) formed under harsh conditions in southern Siberia to show the potential to reconstruct hydraulic properties across tree-rings and to quantify their intra- and inter-annual variability.

The proposed model (see 10.1093/jxb/eraa595 for more details on the performed study) not only provide means to derive realistic conduits hydraulic properties via accessible measures of cross-sectional tracheid size, but it also allows assessing how different-sized tracheid’s components contribute to the overall hydraulic properties. In particular, our up-scaled results from the study case with trees from Southern Siberia showed that the natural inter- and intra-ring anatomical variations had a substantial impact on the ring hydraulic properties and can consequently be applied to assess the impact of cell structural characteristics on the hydraulic functioning of trees.

We therefore conclude that this model, despite its early developmental stage, has the potential to provides a novel basis to investigate xylem structure-function relations across time and environmental conditions.

How to cite: Fonti, P., Vaganov, E. A., Fonti, M. V., and Sviderskaya, I. V.: Using tracheid isometry to upscale water transport from pit to tree-rings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10269, https://doi.org/10.5194/egusphere-egu21-10269, 2021.

Our understanding of plant responses to climate change, and their feedbacks to the climate system, rely heavily on consistent long-term observations. Yet, measuring tropical plant species is particularly demanding and results in a lack of spatial and temporal coverage to build relationships between forest dynamics and climatology in the central Congo Basin. Here dendrochronology and wood chemical analyses might provide important ecophysiological information addressing this knowledge gap, especially in tropical forests where the lack of a pronounced seasonality often makes it difficult to discern variability in xylem cell size and density. Conventional optical dendrochronology measurements therefore have strong limitations within these ecosystems, however chemical and elemental analysis can provide additional information. For example, seasonal fluctuations in the carbon (δ13C) and oxygen (δ18O) stable isotope composition of cellulose is linked to variations in local climate and changes in physiological function. A fewstudies have shown that intra-annual and inter-annual variations in the content of calcium [Ca] in tropical tree rings can be used to age tropical trees without rings, constraining estimates of biomass accumulation. Other studies have linked calcium accumulation in different plant organs to the rate of transpiration in trees making it a powerful predictor of inter-annual variability in rainfall for monsoon regions and a strong novel proxy for drought stress.

Here we present the first results of X-ray Fluorescence (XRF) measurements conducted at the SOLEIL synchrotron and analysis of [Ca] and [Sr], combined with ancillary data such as anatomical, stable isotope and climatological measurements for three tropical tree species. Most species show variability in calcium corresponding to previous proxy measurements, corroborating previous results and showing the potential of non-destructive XRF measurements of wood samples in support of ecophysiological research. The potential of high throughput scanning, in contrast to stable isotope measurements, opens possibilities to gather data on the large scale required to understand diverse tropical forest ecosystems and their responses to (drought) disturbances.

How to cite: Hufkens, K., Reguer, S., Rivard, C., Van den Bulcke, J., Beeckman, H., De Mil, T., and Wingate, L.: Calcium [Ca] tracers using X-Ray fluorescence (XRF) as a potential high throughput measurement technique in ringless highly diverse tropical ecosystems., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5077, https://doi.org/10.5194/egusphere-egu21-5077, 2021.

Trees can provide annual records of ecosystem changes connected with human activity over several decades. These changes can be recorded in the pattern of variation of tree-rings widths and in the variation in the elemental composition of wood. Analysis of trace metal pollution is based on the assumption that element concentrations in tree foliage and tree rings represent element availability in the environment.

We determined the chemical composition of pine needles and annual tree rings to monitor environmental contamination in an urban forest environment in the most industrialized part of southern Poland.

The concentrations of trace elements (Cr, Co, Ni, Cu, Zn, Pb) and the Pb isotope composition were measured in needles from Pinus sylvestris L. growing in nine urban forests near five factories. Trace elemental concentration and Pb isotope ratio were determined by ICP-MS and MC-ICP-MS, respectively. The needles were characterized based on the concentrations of Cr, ranging from 0.05 to 0.7 mg/kg, Co, from 0.005 to 0.075 mg/kg, Ni, from 0.12 to 0.66 mg/kg, Cu, from 0.49 to 1.0 mg/kg, Zn, from 3.9 to 14 mg/kg, and Pb, from 0.06 to 0.53 mg/kg. The ²⁰⁸Pb/²⁰⁶Pb ratio ranged from 2.08 to 2.11 and the ²⁰⁶Pb/²⁰⁷Pb ratio between 1.15 and 1.17. The heterogeneity of Pb isotope ratio indicates that there are different sources affecting the Pb isotopic composition of pine needles (Sensuła et al., 2021).

In one of the investigated site, a radial trace-element profiles were determined by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (Laser ablation: New Wave Research UP-193 FX Fast Excimer, ICP-MS: Thermo Scientific X-Series2 with CCT -Collision Cell Technology) at Royal Museum for Central Africa (Belgium). LA-ICP-MS provides a repeatable, minimally destructive, sensitive method for determining many elements in wood tissue, with relatively high spatial resolution.Temporal variations of element concentration (median) in annual tree-rings of pines were compared with time series of wet deposition of pollutant and air pollutant concentration in the investigated area. The similar trends of magnitudes changes can be observed between analysed elements concentration (Na, Mg, Fe, Ni, Zn) and total wet deposition of these elements in the environment during vegetation period or these elements concentration in the rain (Sensuła et al. 2017). 

Different space-time patterns of element accumulation in pine needles and annaul tree rings were observed. The variation in isotopic composition reflects a mix between different anthropogenic sources.

References:

Sensuła, B., Wilczyński, S., Monin, L., Allan, M., Pazdur, A., & Fagel, N. (2017). Variations of tree ring width and chemical composition of wood of pine growing in the area nearby chemical factories, Geochronometria, 44(1), 226-239. doi: https://doi.org/10.1515/geochr-2015-0064

Sensuła, B., Fagel, N., & Michczyński, A. (2021). Radiocarbon, trace elements and pb isotope composition of pine needles from a highly industrialized region in southern Poland. Radiocarbon, 1-14. doi:10.1017/RDC.2020.132

How to cite: Sensuła, B. and Fagel, N.: Trace elements and Pb isotope composition of annual tree rings and pine needles growing in highly industrialized region in southern Poland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9587, https://doi.org/10.5194/egusphere-egu21-9587, 2021.

Records of environmental change are often temporally short, perhaps spanning a few decades.  For many environmental issues impacting the world today, we have very limited observations or data concerning those changes.  Therefore, we need to supplement the short observational and instrumental records of environmental change with proxy data sources.  Tree-ring growth records are one type of proxy data source that can be examined at annual timescales to track changes in the environment across longer periods than afforded by relatively short observations and instrumental data records.  Changes in the composition of some gases in the atmosphere, are one example of environmental change that can be elucidated using tree-ring records.  Trees utilize various forms of carbon dioxide during photosynthesis, including radiocarbon (¹⁴C).  Naturally, ¹⁴C in the atmosphere varies through time due to cosmic ray flux and ocean-atmosphere dynamics.  The concentration of ¹⁴C also varies due to anthropogenic activities, including burning of fossil fuels, nuclear bomb testing, and the operation of nuclear power plants (NPPs).  Tree rings record atmospheric ¹⁴C concentration during the growing season and are an effective tool to trace ¹⁴C in the atmosphere from a variety of sources, including NPPs.

In Southern Ontario, Canada there are 15 operational CANDU reactors at three NPPs (Bruce (8), Darlington (1) and Pickering (6)).  Southern Ontario is also one of the most densely populated regions of Canada and is a major source of fossil fuel derived carbon that is depleted in ¹⁴C. Monitoring of atmospheric ¹⁴C in Ontario is conducted at the Centre for Atmospheric Research Experiments, operated by Environment and Climate Change Canada (ECCC).  The facility is considered a clean air site, located approximately halfway between the Bruce and Darlington NPPs. 

We measured the Δ¹⁴C in tree rings from white spruce (Picea glauca) trees sampled across a west-east geographic transect between the NPPs with the aim of better understanding how the atmospheric concentration of ¹⁴C has varied locally in this region, while also attempting to pinpoint sources of ¹⁴C emissions. Data from our clean-air sites track globally derived ¹⁴C data from the  Jungfraujoch clean-air atmospheric sampling site in Switzerland.  Tree-ring ¹⁴Cmeasurements from our most densely populated site near the city of Toronto are depleted in ¹⁴C, reflecting fossil fuel combustion. Conversely, ¹⁴C measurements at our site nearest the Pickering and Darlington NPPs are the most enriched. Our results give insight into how tree rings record ¹⁴C and how well they compare to established atmospheric sampling techniques. 

How to cite: Pisaric, M., Crann, C., and Vogel, F.: Tracking atmospheric carbon emissions in southern Ontario, Canada using dendrochronological records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10031, https://doi.org/10.5194/egusphere-egu21-10031, 2021.

Tree-rings, was an extraordinary information base of climate. The global climatic change has been modifying ecosystem, it is important to understand mechanism of how plants respond to climate change. The carbon isotope composition of tree-rings corrected to the value before industrial revolution (δ¹³C_ring) can provide climatic information and carbon and water balance relationship of plants. However, it was still a challenge to disentangle the influence of different environmental parameters on δ¹³C_ring among different tree types. We collected published data of δ¹³C_ring from published papers and study how angiosperms and gymnosperms responsed to different environmental parameters. The results showed that the δ¹³C_ring of angiosperms and gymnosperms were significantly different and there was a decrasing trend in δ¹³C_ring of angiosperms and gymnosperms. In this study, we found that atmospheric concentration (C_a) was not the mainly factor to influence the δ¹³C_ring, and the MAT and PRE were the most important environmental parameters to influence the decreasing trend of δ¹³C_ring for angiosperms and gymnosperms, respectively. Additionally, the global isoscapes of δ¹³C_ring were not established, in this study, three machine learning methods to predict the spatial distribution of δ¹³C_ring were done, the results showed that RF was the best model to established the isoscapes of δ¹³C_ring.

How to cite: Li, X., Chen, G., Qin, W., Wang, P., and Wang, X.: Tree-rings δ13C different responses to environmental factors in angiosperms and gymnosperms at global scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5365, https://doi.org/10.5194/egusphere-egu21-5365, 2021.

All hydrogen in plant compounds derives from plant water; however, fractionation and isotopic exchange with local tissue water theoretically occurs in the synthesis of sucrose, and during downstream metabolic steps before the eventual synthesis of cellulose in sink tissue. The net result is that the relationship between the hydrogen isotope composition (d²H) of cellulose and plant water may be weak. Whilst isotopic exchange and biosynthetic fractionation complicate our ability to recover the hydroclimate signal, the potential for d²H variation to provide information on plant metabolic responses to environment is gaining traction.

Not all the fractionation factors associated with metabolic reactions are known for hydrogen, and even if they were, the apparent isotopic effect is dependent on the flux through the pathway. However, some generalisations have been made: 1) triose phosphate from the Calvin cycle is proposed to have a d²H lower than leaf water due to the transfer of hydrogen from NADPH to glyceradehyde-3-phosphate being highly ²H-depleted; 2) as plant water is enriched compared with primary photosynthetic products, isotopic exchange with water will generally result in a ²H-enrichment of downstream sugars; and, 3) the more times sugars pass through fractionating reactions, the more enriched the resulting sugar pool has been hypothesised to become. This has led to two general hypotheses relating to plant C-use: 1) when sink demand for sugars is low compared with source availability, the residence time of sugars in sink cells may increase leading to greater isotopic exchange. In other words, cellulose would be relatively ²H-enriched under high vs under low source-to-sink ratio; and 2) long-term starch stores may be ²H-enriched relative to current assimilates, assuming starch undergoes greater isotopic exchange prior to being stored or reflecting on-going metabolic exchange between local sugar-starch pools in parenchyma cells. In other words, cellulose would be relatively ²H-enriched where the contribution of stored C compared to current assimilates to cellulose synthesis, is greater.

To test these ideas, we are currently investigating how d²H varies inter-annually and vertically within mature trees of Fagus sylvatica and Picea abies collected at the Canopy Crane Site II, Hölstein, Switzerland. Assessment is initially being made in samples collected from the top and base of the main stem as well as in collar roots, for the years 2017, 2018 and 2019. Previous studies have observed that under water-stress conditions, C allocation below the canopy can be reduced. The summer of 2018 was exceptionally hot and dry; thus, we anticipate that the inter-annual d²H patterns will contrast by vertical position, particularly in 2018 compared with 2017 and 2019. Relative changes in the vertical distribution of C will be determined through assessment of the tree-ring width and circumference. For a direct appraisal of hypothesis 2, we are currently developing analytical capacity to measure the d²H of plant extracted sucrose and starch.

How to cite: Kahmen, A., Treydte, K., and Holloway-Phillips, M.: Can hydrogen isotopes ratios in plants be used to inform the metabolic consequences of C allocation patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14429, https://doi.org/10.5194/egusphere-egu21-14429, 2021.

Trees are one of the main archives to reconstruct past climate variability at the interannual scale. The links between tree-ring proxies and climate have usually been estimated on the basis of statistical approaches, assuming linear and stationary relationships. Yet, both assumptions can be inadequate. This issue can be overcome by the use of process-based dendroclimatic models. For example, MAIDEN (Modeling and Analysis In DENdroecology) is a mechanistic tree-growth model that simulates tree-ring growth starting from surface air temperature, precipitation and CO₂  daily inputs. VS-Lite (Vaganov-Shashkin Lite) is a simplified model that is more generally used in global applications and simulates unitless tree-growth indexes with monthly temperature and precipitation as inputs. In this study, we provide a climate reconstruction of continental temperature, precipitation and winds in the mid to high latitudes of the Southern Hemisphere over the last millennium that takes into account explicitly the links between climate and tree growth with process-based dendroclimatic models. To this end, an offline data assimilation procedure is used to combine the information from the physics of the climate system, as included in climate models, and paleoclimate records, in particular tree-ring width and ice cores records (snow accumulation and δ¹⁸O). Those records are the best available continental proxies in the Southern Hemisphere continents (South America, Australia, Tasmania, New Zealand and Antarctica) for reconstructing the past climate. MAIDEN and VS-Lite are used here as proxy system models, also referred to as observation operators in data assimilation framework, to make the link between climate model outputs and indirect climate observations from tree-rings. The ice cores records are directly compared to the outputs of the climate model. More specifically, we evaluate the benefits of using tree-growth models such as VS-Lite and MAIDEN for reconstructing past climate with data assimilation compared to the commonly used linear regression.

How to cite: Rezsöhazy, J., Goosse, H., Guiot, J., Klein, F., and Dalaiden, Q.: Reconstruction of the Southern Hemisphere climate over the past millennium taking into account explicitly the links between climate and tree growth with process-based dendroclimatic models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2151, https://doi.org/10.5194/egusphere-egu21-2151, 2021.

The Tree Ring Width (TRW) records are one of the main paleoclimate proxies that estimate the past climate variability. TRW measurements pave the way for scientists to produce sequences from various kinds of trees and reconstruct climate variables over the past years. Understanding the relation between TRW and climate variables in the past would help us analyze climate change events. This study has applied multi-gridded datasets to find the relations and model TRW data with different climate variables in South Korea's northeast. We utilized TRW data related to our case study that is available on the NOAA website; furthermore, we have checked three primary gauges, namely Agmerra (The Modern-Era Retrospective Analysis for Research and Applications), CRU TS4.03 (Climatic Research Unit Time-Series version 4.03), and APHRODITE's (Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation) for climate variables. In the first step, we have checked the relation between the gauges' precipitation data and observation TRW. According to the obtained efficiency criteria, CRU performed the best consequences. In the second step, we have tried to model observation TRW as a dependent variable and four climate variables of CRU (precipitation, minimum temperature, potential evapotranspiration, and diurnal temperature range) as independent ones over 1969-1998. We have created a linear regression model and determined the accurate coefficients for each climate variable. Besides, we have examined the observation TRW and modeled TRW data. The results showed that with R²  ≈ 0.40 and a p-value of 0.0323, the regression line was linearly significant at the 95 percent significance level. It represents that our model is acceptable. We will extend our model with Artificial Intelligence methods and try to apply other TRW stations in the future step. In this way, we may produce highly accurate models and fill the gaps for future researches.

How to cite: Salehnia, N. and Ahn, J.: Assessing the relation of tree ring width with climate variables in South Korea through multi-gridded dataset, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3845, https://doi.org/10.5194/egusphere-egu21-3845, 2021.

Original dendrochronological research has developed rapidly over the last few decades to cover a wide range of environmental reconstruction, not only mean climate conditions but also climate extremes (e.g. floods, droughts) and other environmental hazards (e.g. landslides, debris flows, sea-level rise, volcanic eruptions). Similarly, the focus has expanded its geographical coverage from the temperate and high latitudes to lower latitudes (e.g.  the Himalaya, Tibet Plateau). Analysis of the two main dedicated dendrochronology journals (Dendrochronologia (2002-) and Tree Ring Research (2015-)) shows that the focus of the majority of published papers has been temperate and high latitudes and many fewer have considered lower latitudes such as the Himalaya. This may be due to the long-lasting controversy and doubt of the existence of tree-rings in lower latitude trees and the lower scientific acceptance of seasonal tree growth in such regions. However, such regions have some of the most preferred tree species (e.g. Larix griffithii, Abies spectabilis, Betula utilis, Juniperus polycarpos etc) for dendrochronological analysis making them suitable for tree-ring research and for answering questions regarding century-scale and longer environmental changes in regions with a relatively short history of instrumented recording of environmental parameters.

Perhaps the most interesting development in tree ring research is the realization that tree cellulose can be used to acquire information not only of climatic significance but also hydrological significance, by using environmental isotopes. To date, despite of being one of the most climate and geopolitically sensitive regions, the Himalaya has got very less or no attention for combined research of isotopes and anatomical analysis of tree rings. Based on its huge significance, it is critical to combine these two methods to allow us to make linkages between historical climate fluctuations and associated hydrological response. In this poster, we present the conception of a project to do this in a large catchment (4264 km²) in the Sikkim Himalaya with the purpose to understand how climate change is simultaneously impacting both water-related risks and water-related resources and crucially how far downstream which is highly significant as millions of people living downstream get freshwater from the seasonal snow and glacier-melt in this part of the Himalayas.

How to cite: Islam, N., Vennemann, T., and Lane, S. N.: Tree ring research in the Himalayas – a key resource for extending environmental records into the pre-instrumental period, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9237, https://doi.org/10.5194/egusphere-egu21-9237, 2021.

Tree-ring interannual pattern variation is crucial in dendrochronology, allowing the identification of possible limiting factors on growth. Thus, trees exposed to sub-tropical or tropical climates without a marked seasonality, may show a low degree of interannual variation, impeding a straightforward dendroclimatological approach. Meanwhile, subtropical regions, and areas in transitional climates such as the Azores archipelago, are widely unexplored in terms of dendroclimatology, providing opportunities to work with endemic trees, including the dominant Azorean tree Juniperus brevifolia (Seub.) Antoine. To evaluate the dendrochronological potential of J. brevifolia, we analyzed wood anatomy and tree-ring patterns, cross-dating capabilities, and correlation with climate parameters. We sampled 48 individual trees from 2 natural populations (São Miguel and Terceira islands) using an increment borer. In addition, a Trephor tool was used to obtain wood microcores for micro-anatomical analysis. Tree-ring widths were measured with CooRecorder (Cybis) and cross-dated with the PAST-5 software (SCIEM). After detrending, master chronologies were built and correlated with aggregated daily temperature and precipitation data using the dendroTools R package. Microcores were prepared following standard protocols to obtain high resolution images. Our results showed the transition from latewood to earlywood marked by thick-walled fibers, . However, there were also unclear ring transitions or partially indistinct ring boundaries and wedging rings, complicating the cross-dating process. Our preliminary climate-growth correlations indicated significant positive correlations with precipitation at the end of the growing season. Our results suggest an acceptable dendrochronological potential for Juniperus brevifolia, which could be further used in distribution modelling or in recent climatic reconstructions, for which more samples will have to be analyzed.

How to cite: C Pavão, D., Jevšenak, J., Camarinho, R., Rodrigues, A., Borges Silva, L., B Elias, R., and Silva, L.: Dendrochronological potential of the Azorean endemic gymnosperm Juniperus brevifolia (Seub.) Antoine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10168, https://doi.org/10.5194/egusphere-egu21-10168, 2021.

Tropical and subtropical ecosystems are primarily responsible for the large inter-annual variability (IAV) in the global carbon land sink. The response of tropical vegetation productivity to climatic variation likely drives this IAV, but the climate sensitivity of key productivity components are poorly understood. Tree-ring analysis can help fill this knowledge gap by estimating IAV in woody biomass growth, the major carbon accumulation process in tropical vegetation.

Here, we evaluate the climate responses of woody biomass growth throughout the global tropics. Using an unprecedented compilation of tropical tree-ring data, we test hypotheses that (1) precipitation (P) and maximum temperature (T_max) have opposite and additive effects on annual tree growth, (2) these climate responses amplify with increasing aridity and (3) wet-season climate is a more important driver of growth than dry-season climate.

We established a network of 347 tree-ring width chronologies compiled from (sub-)tropical latitudes, representing 99 tree species on five continents and obtained from contributors (n=112) and the International Tree-Ring Data Bank (ITRDB; n=235). Our network is climatologically representative for 66% of the pantropical land area with woody vegetation.

To test hypotheses we re-developed standardized ring-width index (RWI) chronologies and assessed climate responses using SOM cluster analysis (monthly P and T_max) and multiple regression analysis (seasonal P and T_max). Our results were consistent with hypothesis 1: effects of monthly or seasonal P and T_max on tree growth were indeed additive and opposite, suggesting water availability to be the primary driver of tropical tree growth. In accordance with hypothesis 2, these climate responses were stronger at sites with lower mean annual precipitation or a larger annual water deficit. However, our results contrast those expected under hypothesis 3. Three of the four clusters show a dominant role of dry-season climate on annual tree growth and regression analyses confirmed this strong dry-season role.

The strong dry-season effect on tropical tree growth seemingly contrasts the general notion that tropical vegetation productivity peaks during the wet season but is consistent with studies showing that climatologically benign dry seasons increase reserve storage and xylem growth. We posit that dry-season climate constrains the magnitude of woody biomass growth that takes place during the following wet season, and thus contributes to IAV in tree growth.

By providing field-based insights on climate sensitivity of tropical vegetation productivity, our study contributes to the major task in Earth system science of quantifying, understanding, and predicting the IAV of the carbon land sink.

How to cite: Zuidema, P., Babst, F., Groenendijk, P., and Trouet, V.: Dry-season climate drives interannual variability in tropical tree growth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14895, https://doi.org/10.5194/egusphere-egu21-14895, 2021.

Climate changes and raising atmospheric CO₂ concentrations are expected to influence tree and forest development. However, the direction and intensity of the tree and forest responses are diverse, and long-term studies are scarce.  Here, we studied responses of Quercus mongolica to climate over the last 117 years based on the tree-ring width, δ¹³C-derived physiological parameters (Δ¹³C, C_i and iWUE) and δ¹⁸O in Jeju Island, South Korea. Trend and change point analyses were performed to the radial tree growth, physiology and climate, and tree responses-climate relationships were analysed temporally and spatially. iWUE significantly increased since 1900 but decadal variations were observed in 1950, 1975 and 2010, revealing an evolving physiological response. iWUE was mainly driven by stimulated photosynthesis under no water limitations. This photosynthetic stimulation was driven mainly by the atmospheric CO₂ fertilization, warming and higher radiation, probably through the simultaneous influence on the phenology and physiology of trees. At a local scale, higher radiation combined with less cloudy conditions were the factors with the greatest positive influence on tree growth, while at a regional scale land and sea surface temperatures positively influenced both tree growth and physiology. Moreover, all these responses strongly intensified after the 1970s, showing that tree responses are not temporary stable. Altogether, the present results indicated that the physiology and growth of Q. mongolica from eastern Asia are driven by a combination of climatic, ecological and anthropogenic factors. Moreover, the significant, rapid and unprecedented changes in the tree responses indicated that trees may benefit from recent global changes, showing a physiology-driven growth enhancement. This represents a key understanding of trees and forests ecosystems responses to future climate changes, which is relevant to assess and design global change mitigation strategies.

How to cite: Arco Molina, J. G., Treydte, K., Maredova, N., Saurer, M., Dolezal, J., Song, J.-S., and Altman, J.: Long-term physiological and growth responses of oak trees under climate warming in eastern Asia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7207, https://doi.org/10.5194/egusphere-egu21-7207, 2021.

Detecting pointer years in tree-ring data is a central aspect of extreme-event ecology. Pointer years usually represent extraordinary secondary tree growth, which can often be interpreted as response to extraordinary environmental conditions such as late-frosts or droughts. Identifying pointer-years in larger tree-ring networks and relating those to specific climatic conditions may allow for a deeper understanding of how trees perform under extreme climate and consequently, under anticipated climate change (Meyer et al., 2020; Rehschuh et al., 2017).  

Recently, Buras et al. (2020) demonstrated how frequently used pointer-year detection methods are suboptimal for such large-scale analyses due to an either too low or sometimes too high sensitivity in detecting extraordinary growth. In their study, Buras et al. (2020) proposed a novel approach for detecting pointer years – the standardized growth change (SGC) method. Despite a higher success rate with regards to identifying artificially introduced pointer years in simulated tree-ring data, Buras et al. (2020) concluded that the SGC method could be further refined to capture pointer years following a gradual growth decline. Moreover, they discussed the possibility to incorporate growth changes at higher lags, thereby allowing the duration of the recovery period following a pointer year to be estimated.

Under this framework, we here present a refined version of the SGC-method – the bias-adjusted standardized growth change method (BSGC). The methodological adjustment to the SGC approach incorporates conflated probabilities of time-step specific growth changes with probabilities of time-step independent growth changes. Application of BSGC to simulated and measured tree-ring data indicated a successful bias adjustment which now allows for the identification of pointer years following years of successive growth decline. Moreover, the length of simulated recovery periods was well reproduced and revealed plausible results for existing tree-ring data. Based on these validations, BSGC can be considered a further refinement of pointer-year detection, allowing for a more precise detection and consequently better understanding of the radial growth response of trees to extreme events.

Buras, A., Rammig, A., Zang, C.S., 2020. A novel approach for the identification of pointer years. Dendrochronologia 125746. https://doi.org/10.1016/j.dendro.2020.125746

Meyer, B.F., Buras, A., Rammig, A., Zang, C.S., 2020. Higher susceptibility of beech to drought in comparison to oak. Dendrochronologia 64, 125780. https://doi.org/10.1016/j.dendro.2020.125780

Rehschuh, R., Mette, T., Menzel, A., Buras, A., 2017. Soil properties affect the drought susceptibility of Norway spruce. Dendrochronologia 45, 81–89. https://doi.org/10.1016/j.dendro.2017.07.003

How to cite: Buras, A., Ovenden, T., Rammig, A., and Zang, C.: Refining the standardized growth change method for pointer year detection: bias-adjustment and definition of the recovery period, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3299, https://doi.org/10.5194/egusphere-egu21-3299, 2021.

Large scale losses in forest productivity linked to extreme drought are now being documented globally. With climate change set to increase the frequency, intensity and duration of future extreme events, understanding the impact of drought on forest productivity and the post-drought recovery dynamics of these systems is becoming increasingly important. However, current approaches to quantifying resilience limit our understanding of forest response dynamics, recovery trajectories and drought legacies by constraining and simplifying the temporal scale and resolution of assessment. To advance beyond one of the most commonly used approaches to estimating resilience, we first compared estimates of resilience for Pinus sylvestris trees following an extreme drought by comparing the same resilience index calculated over different pre- and post-drought time scales. We then developed an alternative approach using dynamic regression to capture each individual tree’s relationship between climate and growth, which was then used to forecast tree growth annually for the drought year and nine subsequent years, in a scenario where no drought had occurred. Here we present the results of this work, comparing observed tree growth with growth forecasted using dynamic regression at multiple stem heights and stand densities. This approach allowed us to increase the temporal scale and resolution of resilience assessment and follow tree and stand level growth relative to a no-drought scenario throughout recovery and into a post-recovery phase, where we find evidence for significant compensatory growth. The existence of compensatory growth post-recovery reduced estimates of drought induced losses of radial growth, indicating that current approaches risk underestimating tree and stand resilience to drought and overestimate losses in above-ground biomass. Similarly, we provide evidence for a temporal dependency in the stage during recovery at which pre-drought tree and stand attributes such as growth rates, basal area and stand densities were associated with growth resilience. Our results have wide reaching implications for both forest management targeted at increasing resilience, carbon budgeting and our understanding of drought legacy.

How to cite: Ovenden, T., Perks, M., Clarke, T.-K., Mencuccini, M., and Jump, A.: Life after recovery: new insights into post-drought compensatory growth and forest recovery dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5765, https://doi.org/10.5194/egusphere-egu21-5765, 2021.

Hotter droughts will have an increasingly influential role in shaping forest ecosystems in the future. Risks include decreases in species richness, altered species distributions, forest dieback and changed function as carbon sink. A common method to study the impacts of droughts on forests is the quantification of reductions in biomass productivity via secondary growth – approximated by ring-width measurements –, including duration until growth rates return to pre-drought levels, so-called legacy periods. However, while these metrics are practical and relatively easy to measure, the underlying governing mechanisms are not, and thus poorly understood. Consequently, it is uncertain if drought-induced reductions in secondary growth are due to corresponding decreases in total physiological function or high plasticity, and if recovery times are due to lasting damage or adaptation with more carbon allocated to drought-mitigating structures.

The principle of the most limiting factor for tree-growth can be used to track temporal variations in climate-growth relationships. Similarly, the considerable strain hotter drought constitutes for tree-growth, and the need to repair damaged structures or alter carbon allocation, may imply temporary climate sensitivity deviations during legacy periods. Identifying their existence and quantifying subsequent differences in these deviations can help to shed light on strategies used by trees to respond to droughts.

Here, we detect and quantify deviations in climate-growth relationships during hotter drought legacy periods and assess how they differ according to clade (angiosperms – gymnosperms), site aridity and hydraulic safety margin. We do this by applying a linear mixed model on all ring-width indices (RWI) in the global-scale International Tree-Ring Data Bank (ITRDB) which exhibit a positive correlation with Standardized Precipitation-Evapotranspiration Index (SPEI). We apply a combined climatological and ecological definition for drought events and use site-dependent SPEI time-scales to allow for specific climate dependencies.

Results show heterogeneous post-drought climate sensitivity deviations, which are broadly categorized in three groups: 1) angiosperms growing in arid sites become increasingly sensitive to climate for 2 – 4 years; 2) angiosperms in mesic sites and or with high hydraulic safety margin show abrupt and complete disruption of the climate-growth relationship for the first year after droughts, which turn into a decrease in climate sensitivity for an additional 1 – 3 years; 3) gymnosperms in arid sites become less sensitive to climate for 2 – 4 years, although without the abrupt disruption seen in group 2. We discuss these results and their implications in an ecophysiological context, including future research avenues.

In conclusion, the results clearly show a functional legacy effect that is not detected through measurements of reductions in biomass accumulation alone, hinting at differential strategies employed by trees to cope with hotter droughts. This is a first step towards a better understanding of the mechanisms underlying hotter drought legacies which may help to improve ecosystem models and better predict how trees will respond to drought in a warming future climate.

How to cite: Leifsson, C., Buras, A., Rammig, A., and Zang, C.: Large scale assessment of post-drought climate sensitivity of tree-growth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7989, https://doi.org/10.5194/egusphere-egu21-7989, 2021.

Warmer climate and more frequent extreme droughts will pose major threats to forest ecosystems. Persistence of intra-specific populations of tree species will depend on their tolerance and adaptive capacities to forthcoming climate conditions. However, past demography processes due to post-glacial recolonization can also contribute to the genetic-based differences in growth responses among provenances. In this study, we investigated the impact of climatic conditions on growth traits among 18 provenances of silver fir (Abies alba Mill.) from west, south and eastern Europe growing in two provenance trials established in Switzerland in 1980s. We further assessed whether the differences in growth-related traits across provenances were linked to their genetic differences due to recolonization history and natural selection processes.

In total 250 individuals were measured and cored for dendrochronological analyses, and different growth-related traits were calculated: i) total tree height and diameter at breast height (DBH), ii) growth-climate relationships using correlations between tree-ring width and monthly climate parameters as well as levels of autocorrelation, and iii) short-term responses to extreme drought using resilience components (resilience, resistance, and recovery) to the severe drought that occurred in the study area in 2003. We also genotyped all the individuals in 150 putatively neutral single nucleotide polymorphisms to define the neutral genetic structure of the population, the neutral genetic differentiation among provenances (F_ST) and the genetic variation among provenances in relation to the total genetic variance in a trait (Q_ST). Signs of natural selection were assessed by two approaches: i) Pearson correlations between the least-square means of provenances of the traits and bioclimatic variables from the seed origin, and ii) Q_ST-F_ST comparison.

The studied provenances grouped into three longitudinal clusters reassembling the genetic lineages of refugia from the last glacial maximum: the provenance of the Pyrenees as a sole member of the westernmost cluster, the Central European provenances representing the central cluster and all the eastern European provenances forming the eastern cluster. These three lineages showed differences in growth performance traits (height and DBH), with the trees from the eastern cluster being the top performers. The Pyrenees cluster showed significantly lower recovery and resilience to the extreme drought of 2003 as well as lower values of growth autocorrelation. A Q_ST-F_ST and correlation analyses with climate of provenance origin suggest that the differences among provenances found in some traits result from natural selection. Our study suggests that post-glacial re-colonization and natural selection are the major drivers explaining the intra-specific variability in growth of silver fir across Europe. These findings provide insights to support assisted gene flow to ensure the persistence of the species in European forests.

How to cite: Martínez-Sancho, E., Rellstab, C., Guillaume, F., Bigler, C., Fonti, P., Wohlgemuth, T., and Vitasse, Y.: Post-glacial re-colonization and natural selection have shaped growth responses of silver fir across Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12650, https://doi.org/10.5194/egusphere-egu21-12650, 2021.

Forests are vital ecosystem service providers and are thought to play an important role as carbon sinks in climate-warming mitigation. Climate change can modify environmental forcing of tree growth, bringing changes in growth performance and ultimately in ecosystem community composition. Thus, studying how trees and forests react to a changing environment is required to preserve and manage them sustainably. It is largely unexplored how extreme weather events, such as the so called “hotter-droughts”, interact with silvicultural interventions (thinning). To address this problem, we explore a monitoring data set from 2017-2020 of three broadleaved species native to the Central European temperate forest (Fagus sylvatica L., Quercus robur L., Betula pendula Roth). To investigate the effect of thinning interventions and weather conditions on intra-annual growth, an experimental gap was created at the end of 2016 in the studied stands. Trees standing next to the gap and others on closed-stand conditions were equipped with band-dendrometers, which were read out bi-weekly throughout the four vegetation periods. The obtained growth-curves were used to compare absolute and relative growth between experimental conditions (gap vs. closed), and non-linear models were fitted to derive the phenology of stem-growth. In general, trees under gap conditions revealed smaller increments than trees in closed stands during the drought years 2018/2019, but especially for 2019. Species differences indicate beech was most sensitive to the extreme summer drought, as expected given the conclusions of several dendroecological studies. The results indicate different sensitivities to extreme events on the years following silvicultural interventions between tree species. As gap-formation occurs also naturally in temperate forests, these results suggest a possible mechanism through which legacy-effects and variability in individual climate responses arise, which can help unravel climatic signals in tree-rings and explain how they are modulated by ecological conditions and management interventions. Monitoring of tree-growth in a high-temporal resolution seems a valuable approach to understand the impact of extreme events and climate change on tree-growth. The obtained insights are relevant for improving sustainable silvicultural management, as the suitability of a species for a site might change upon further warming and more frequent drought spells. We recommend continuing to explore tree-growth at finer time-scales to shed light on species performance under climate change.

How to cite: Cruz-García, R., Frieboese, L., Scharnweber, T., Siller-Aguillón, I. A., Kalbe, J., and Wilmking, M.: Forest management and hotter droughts: tree-growth monitoring during 2018/2019 in northeastern Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1126, https://doi.org/10.5194/egusphere-egu21-1126, 2021.