Tree rings are one of nature’s most versatile archives, providing insight into past environmental conditions at annual and intra-annual resolution and from local to global scales. Besides being valued proxies for historical climate, tree rings are also important indicators of plant physiological responses to changing environments and of long-term ecological processes. In this broad context we welcome contributions using one or more of the following approaches to either study the impact of environmental change on the growth and physiology of trees and forest ecosystems, or to assess and reconstruct past environmental change: (i) dendrochronological methods including studies based on tree-ring width, MXD or Blue Intensity, (ii) stable isotopes in tree rings and related plant compounds, (iii) dendrochemistry, (iv) quantitative wood anatomy, (v) ecophysiological data analyses, and (vi) mechanistic modelling, all across temporal and spatial scales.
vPICO presentations: Tue, 27 Apr
The current research on the dynamics of tree ring formation in conifers has provided new insights into how rate and duration xylem-cell production and development control the size of the xylem conduits leading to the formation of earlywood and latewood. So far, the physiology behind wood formation processes and the associated kinetics has rarely been considered, leading to the impossibility to grasp the drivers of wood density changes along the tree-rings. Despite the importance of wood density for carbon sequestration and tree hydraulics, little is known about the factors controlling variations in wood density across the tree ring, i.e. micro-density, at the intra-annual scale. We first developed a process-based mechanistic model that simulates the development of conifer tracheids from a simple sugar signal that we discuss together with the main kinetics and environmental variables leading to the formation of micro-density in black spruce, the main conifers species in the boreal forest of Canada. At the beginning of the growing season, low sugar availability in the cambium results in slow wall deposition that allows for a lengthier enlargement time thus producing large cells with thin walls (i.e. earlywood). In late summer and early autumn, high sugar availability produces narrower cells with thick cell walls (i.e. latewood). Wood formation dynamics had an indirect effect on micro-density. Micro-density increased under longer periods of cell wall deposition and shorter durations of enlargement. Cell diameter indirectly affected micro-density via cell wall thickness, which was the most important parameter affecting micro-density. Cell traits experienced the joint action of enlargement and secondary wall deposition in shaping the intra-annual patterns of tree rings. Our results point to the predictive power of a simple sugar signal. During the growing season, the amount of carbon allocated to wood formation largely influences the duration of cell differentiation, thus modulating cell diameter, cell wall thickness and by result tree-ring micro-density.
How to cite: Deslauriers, A., Buttò, V., Cartenì, F., Rossi, S., and Morin, H.: Developmental and environmental factors driving xylem anatomy and micro-density, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10423, https://doi.org/10.5194/egusphere-egu21-10423, 2021.
A bimodal radial grow pattern, i.e. growth peaks in spring and autumn, was repeatedly found in trees in Mediterranean regions, where summer drought causes reduction or cessation of cambial activity. In a dry inner Alpine valley of the Eastern Alps (Tyrol, Austria, c. 750 m asl), which is characterized by drought periods at the start of the growing season in spring and more favorable conditions during summer, Pinus sylvestris shows an unimodal growth pattern with onset and cessation of cambial activity in early April and late June, respectively. Although xylem cell differentiation (cell wall thickening) may last until end of August, a resumption of cambial activity after intense summer rainfall was not observed in this region. In a field experiment we therefore tested the hypothesis that early cessation of cambial activity under drought is an adaptation to limited water availability during the growing season (April through June), leading to an early and irreversible switch of carbon (C) allocation to belowground. To accomplish this, the C status of c. 20 year old Pinus sylvestris saplings (mean stem height 1.5 m) was manipulated at a xeric site by physical blockage of phloem transport (girdling) in mid-July (doy 199), i.e. c. four weeks after cessation of cambial cell division. The influence of manipulated C availability on radial growth was continuously recorded by stem dendrometers, which were mounted 5 cm above girdling. In response to blockage of phloem flow, resumption of radial growth was detected above the girdling zone after about 2 weeks, i.e., bimodal growth could be triggered above girdling by increasing C availability. Although the experimentally induced second growth surge lasted for the same period as in spring (i.e., c. 2 months), the increment was more than twice as large. Below girdling radial growth was not affected (i.e., no reactivation of cambial activity occurred), but cell wall thickness of last latewood cells was significantly reduced indicating lack of C after girdling. Intense radial growth resumption in Pinus sylvestris saplings after girdling indicates that cessation of stem cambial activity can be reversed by manipulating the C status of the stem suggesting a high belowground C demand on the drought-prone, nutrient deficient site. This work highlights the need of in-depth experimental studies in order to understand the impact of endogenous and exogenous factors on cambial activity more clearly.
The research was funded by the Austrian Science Fund (FWF; project number P25643-B16).
How to cite: Oberhuber, W., Landlinger-Weilbold, A., Gruber, A., and Wieser, G.: Blocking phloem transport triggers bimodal radial growth in Pinus sylvestris at a xeric site, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2095, https://doi.org/10.5194/egusphere-egu21-2095, 2021.
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.
European beech (Fagus sylvatica) is a widespread and economically important temperate tree species in Europe. Expected future warmer temperatures and severe drought events, especially in Mediterranean areas, could affect vitality and productivity of beech stands that historically were under intensive management in those areas. In this study, we aim to address the lack of knowledge on intra-annual wood anatomical responses of beech to environmental variability and silvicultural practices by investigating three beech stands along an elevational gradient (1200 to 1950 m a.s.l.) in the Apennines (Italy). Several wood cell anatomical features were quantified on increment cores collected from five trees per stand. Results showed that high-elevation trees are hydraulically limited, and mid-elevation trees meet their hydraulic requirements with a different anatomical setup/configuration compared to low and high sites. Maximum xylem vessel size and theoretical hydraulic conductivity were associated with the temperatures of previous summer, previous winter and current summer as well as precipitation at the onset of radial growth and at time of maximum growth rates. Cessation of coppicing did not trigger main intra-annual differences in wood anatomical traits. Similarly, years with extreme climate (e.g. mean temperature and/or precipitation values above or below one standard deviation) did not have strong effects on intra-annual wood anatomical traits, maybe due to buffering through the several active sapwood rings present in beech. In conclusion, elevation had a higher impact on intra-annual wood anatomical traits in the studied trees than either cessation of silvicultural practices or years with extreme climate.
How to cite: Miranda, J. C., Calderaro, C., Cocozza, C., Lasserre, B., Tognetti, R., and von Arx, G.: Intra-annual wood anatomical variability in European beech in response to elevation, management and climate in the Central Apennines, Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6405, https://doi.org/10.5194/egusphere-egu21-6405, 2021.
Air temperature increase and change in precipitation regime have a significant impact on northern forests leading to the ambiguous consequences due to the complex interaction between the ecosystem plant components and permafrost. One of the major interests in such circumstances is to understand how tree growth of the main forest species of the Siberian North will change under altering climatic conditions. In this work, we applied the process-based Vaganov-Shashkin model (VS - model) of tree growth in order to estimate the daily impact of climatic conditions on tree-ring width of larch trees in northeastern Yakutia (Larix cajanderi Mayr.) and eastern Taimyr (Larix gmelinii Rupr. (Rupr.) for the period 1956-2003, and to determine the extent to which the interaction of climatic factors (temperature and precipitation) is reflected in the tree-ring anatomical structure. Despite the location of the study sites in the harsh conditions of the north, and temperature as the main limiting factor, it was possible to identify a period during the growing season when tree growth was limited by lack of soil moisture. The application of the VS-model for the studied regions allowed establishing in which period of the growing season the water stress is most often manifest itself, and how phenological phases (beginning, cessation, and duration of larch growth) vary among the years.
The research was funded by RFBR, Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science, project number 20-44-240001 and by the Russian Ministry of Science and Higher Education (projects FSRZ-2020-0010).
How to cite: Fonti, M., Churakova (Sidorova), O., and Tychkov, I.: Intra-annual climatic signal in tree rings of Larix sp. based on the Vaganov-Shashkin model output, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9278, https://doi.org/10.5194/egusphere-egu21-9278, 2021.
It is uncertain how European beech (Fagus sylvatica L.) will perform under climate change. Several dendroclimatological studies suggest that increasing temperature will positively affect radial increments at sites optimal for its growth. However, it is not entirely clear how changing growth conditions will affect wood anatomy and thus wood properties. The aim of this study was therefore to analyse the relationships between climate conditions (temperature and precipitation) and wood anatomical traits in beech trees growing at optimal beech forest sites in Slovenia. Three forest sites representing the main Slovenian beech provenances were selected (Idrija, Javorniki, and Mašun). At each site, 16 increment cores were collected in 2016 and subsequently prepared for observation under the light microscope. Image analysis software (Image Pro-Plus and Roxas) were used for quantitative wood anatomy. Mean vessel area, vessel density, and relative conductive area were analysed in tree rings between 1960-2016. Furthermore, tree rings were divided into four quarters to assess the intra-annual variability in vessel features also in relation to weather conditions. The preliminary results indicated that there was a significant difference in tree-ring widths as well as in vessel features among the selected forest sites. Idrija, the late flushing provenance, had the narrowest tree rings, the highest vessel density and relative conductive area, and smallest mean vessel area. The other two sites had a similar mean vessel area, while the widest tree-ring width and the smallest vessel density and relative conductive area were observed at Mašun (the mid-flushing provenance). The response of tree-ring width and vessel features to changing climate conditions differed among sites/provenance. Tree-ring widths at Idrija and Javornik were positively affected by late winter temperature, while tree-ring widths at Mašun were mostly affected by summer precipitation. In the case of vessel features, the highest correlations with climate data were observed in the fourth quarter of the rings with late summer temperature and precipitation. In conclusion, early spring temperatures and summer precipitation proved to be the most important climatic factors affecting beech growth and vessel features.
How to cite: Arnič, D., Gričar, J., Jevšenak, J., Božič, G., von Arx, G., and Prislan, P.: Relationships between wood anatomical traits and climate conditions at three beech forest sites in Slovenia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9804, https://doi.org/10.5194/egusphere-egu21-9804, 2021.
Treeline ecosystems are of great scientific interest to study the direct and indirect influence of limiting environmental conditions on tree growth. However, tree growth is complex and multidimensional, and its responses to the environment depend on a large number of abiotic and biotic factors and their interactions.
In this study, we analyze the growth and xylem anatomy of white spruce trees (Picea glauca [Moench] Voss) from three treelines in Alaska (one warm and drought-limited, and two cold and temperature-limited treelines). We hypothesized (1) no difference between the treelines regarding the relationship between tree DBH and height, yet in general (2) faster growing trees at the warmer site. Additionally, we expected to find differences in xylem anatomical traits with trees from the drought-limited site having adapted to drought conditions by (3) forming smaller lumen diameter due to water deficit but (4) a higher xylem anatomical density due to higher temperatures and a longer vegetation period.
Regarding growth in height and diameter, trees at the drought-limited treeline grew relatively (1) taller and (2) faster compared to trees at the temperature-limited treelines. Raw xylem anatomical measurements showed (3) smaller lumen diameters and (4) higher density in trees at the drought-limited treeline. However, using linear mixed-effect models, we found that (i) traits related to water transport like lumen diameter were not significantly correlated with the actual amount of precipitation during the vegetation period but with tree height. We also found that (ii) traits related to mechanical support like density were mainly positively influenced by the mean temperature during the vegetation period.
The differences in lumen diameter found in the raw data can be explained by differences in the growth rates of the trees, since lumen diameter at the lower part of the tree stem needs to increase over time with increasing tree height. The greater wood density at the drought-limited treeline is probably caused by the higher temperature that leads to more biomass production, and potentially longer vegetation periods.
Our study shows that xylem anatomical traits in white spruce can be directly and indirectly controlled by environmental conditions. While lumen diameter is not directly influenced by environmental conditions but indirectly through tree height, other traits like anatomical density show a direct correlation with environmental conditions. Our results highlight the importance of approaching tree growth in a multidimensional way and considering direct and indirect effects of environmental forcing.
How to cite: Pampuch, T., Trouillier, M., Anadon-Rosell, A., Lange, J., and Wilmking, M.: Direct and indirect effects of environmental limitations on white spruce xylem anatomy at treeline, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15323, https://doi.org/10.5194/egusphere-egu21-15323, 2021.
In the tundra, bryophytes may be the dominant growth form covering the soil surface of shrub communities. They can modulate soil conditions through their capacity to retain moisture and nutrients and their chemical characteristics. The study of the interaction between shrubs and bryophytes is essential to understand the functioning of these shrub communities, which are expanding due to global change. In this study, we collected Betula nana and Empetrum hermaphroditum ramets growing in moss carpets dominated by Hylocomium splendens, Pleurozium schreberi or Sphagnum spp., which differ in growth habit, density of their carpets and water holding capacity, amongst others. We sampled three ramets per site and moss species in eight locations distributed along a precipitation gradient (571-1155 mm/year) in the subarctic alpine tundra near Abisko, Sweden. To investigate structural and functional responses to the dominant moss species and precipitation regime, we prepared microscopic sections of the shrubs stem base and measured growth rings and xylem anatomical parameters (vessel lumen area, vessel density and grouping, and theoretical hydraulic conductivity). We also measured shrub leaf C and N concentration and isotope composition (δ13C, δ15N). To understand moss effects on soil characteristics along the precipitation gradient, we measured soil pH and water and nutrient content (nitrate, ammonium, phosphate, dissolved organic C and dissolved organic N). Preliminary results on shrub leaf physiology and soil characteristics show a significant interaction between moss species and the precipitation gradient, indicating that mosses modulate the effects of climate conditions on shrubs. We discuss the importance of moss species combined with the precipitation regime for the performance of tundra shrubs in the context of a changing climate.
How to cite: Anadon-Rosell, A., Michelsen, A., Lett, S., Dorrepaal, E., von Arx, G., Tumajer, J., and Wilmking, M.: Effects of dominant moss species on shrub growth and xylem anatomy along a precipitation gradient in the subarctic tundra, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9969, https://doi.org/10.5194/egusphere-egu21-9969, 2021.
Modern society faced significant challenges in the last decades as a result of environmental pollution and climate change. The current study's objective was to establish a pattern for assimilating HM in normally and declined Quercus robur L. trees. Also, was identify the present state and historical changes in heavy metal elemental composition using different approaches: i) twenty matrices including water, soil, sediments, mushrooms, acorn, leaves, branches, bark and wood; ii) tree-rings elemental time-series trends. Our research of elemental distribution in pedunculate oak earlywood tree-rings brings new viewpoints for investigating chronic decline and dieback using (LA-ICP-MS), (ICP-MS) and (AAS) technics. Impressive amounts of heavy metals in the background environment, especially in water and mushrooms indicate high environmental risk for human health. The Levene's t-test shows significant differences (p-value<0.001) between the analysed matrices' heavy metal concentration. Infertile seeds had a superior concentration of metals in acorn core and lower in acorn pericarp and opposite ratio being observed for healthy ones. We noted the above concentration of high susceptibility elements related to past reports in the study area assigned to the climate-induced changes in temperature and evapotranspiration. In our present state of knowledge, is the first study indicating high variability of heavy metals in tree-rings explained through the individual typology of assimilating elements under different phases of trees decline. The Levene's t-test shows significant differences (p-value<0.001) between decreased and normally growing ring-width chronologies (EW, LW, and RW) only for 1960-2019. Overall declined, and normally increasing trees coexist in sites with heavy pollution, mentioning those with decline are less sensitive to environmental factors. We noted different patterns of responses to climatic factors for trees affected and unaffected by decline growth. Generally, oak trees correlated significantly with water from the soil and negative with temperature and evapotranspiration in spring. Also, it can be stated that heavy metals from tree rings indicate a significant relationship with drought effects and trends for several elemental time series increasing after 1980. Heavy metals correlated strongly between theme indicating similar uptake pathways in trees, respectively from the soil and common origins from industrial activities. Changes in the NDVI indices were strongly correlated with heavy metals from tree-rings highlighting the shift in trees phenology induced by decline.
This work was supported by the Romanian National Authority for Scientific Research and Innovation, Contract No. 12N/2019 (PN 19070502 "Evaluation by transdisciplinary techniques of the oak trees decline affected by actual environmental changes in the extra-Carpathian area – adaptation, mitigation and risks") and Contract No. 9N/2019 (PN 19110303" Advanced techniques for identifying sources of contamination and biochemical reactions in aquatic ecosystems" and PN19110302 "Research on the variation trends specific to stable isotopes in different tree species: deepening the fractionation mechanisms and the chemical processes interconnected on the soil-water-plant chain"), partially by CRESFORLIFE ID_40_380 - Subsidiary contract S16/2020.
How to cite: Nechita, C., Iordache, A. M., Pluhacek, T., Lemr, K., Levanič, T., Botoran, O. R., Zgavarogea, R., Ionete, R. E., and Musca, C. D.: Elemental levels in twenty environmental matrices and temporal trends in normally and declining trees growth from Copsa Mica, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7619, https://doi.org/10.5194/egusphere-egu21-7619, 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.
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.
The growth response of trees to climate can be altered by other environmental changes that a tree may face including pollution or fertilization. In this study, the effect of spatial and temporal patterns sulfur dioxide (SO2) emissions on climate-growth relationships of lodgepole pine (Pinus contorta) in two areas of Alberta, Canada was assessed. Twenty tree cores were collected in each of four stands per study area: two near a source of SO2 emissions (sour gas processing facility) and two far from the source of emissions. To select important climate variables, the average standardized tree ring width of all trees in each area were first compared to monthly average temperature and total precipitation variables. For each important climate variable, response function analysis was conducted between standardized tree ring widths and climate in each of three SO2 exposure time periods: a period pre-dating any emissions, a period of high emissions, and a more recent period of reduced emissions. Linear mixed models were used to compare response coefficients of tree ring widths to climate between exposure space (near or far from the source of emissions) and exposure time (no emissions, high emissions, reduced emissions) and the interaction between them. The absolute values of predicted ring widths in each exposure space and exposure time in each area were used as a response variable in a linear mixed effects model to assess the effects of SO2 exposure on the magnitude of tree growth response to climate. SO2 exposure time was a significant term in all climate-growth relationship models. Exposure space was significant in 13 out of 20 models, and the interaction between exposure time and exposure space was significant in 14 out of 20 models. The effects of exposure time and exposure space on climate-growth relationships were not consistent between climate variables. Overall, tree growth responded most strongly to climate in the high exposure time period. The increase in magnitude of climate-growth relationships in the high SO2 exposure time period may indicate that trees stressed by sulfur deposition are not able to buffer the effects of climate, and are more susceptible to extreme weather conditions such as drought. However, the response to climate during the high emission period was greater far from the source of emissions than near the source of emissions; This could be because the historical addition of lime to stands near the sour gas processing facilities resulted in less sulfur stress. SO2 emissions in Alberta may alter climate-growth relationships of lodgepole pine.
How to cite: Earl, D., Norman, A.-L., and Reid, M.: Effects of SO2 emissions in Alberta, Canada on lodgepole pine climate-growth relationships, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14041, https://doi.org/10.5194/egusphere-egu21-14041, 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 (δ13Cring) 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 δ13Cring among different tree types. We collected published data of δ13Cring from published papers and study how angiosperms and gymnosperms responsed to different environmental parameters. The results showed that the δ13Cring of angiosperms and gymnosperms were significantly different and there was a decrasing trend in δ13Cring of angiosperms and gymnosperms. In this study, we found that atmospheric concentration (Ca) was not the mainly factor to influence the δ13Cring, and the MAT and PRE were the most important environmental parameters to influence the decreasing trend of δ13Cring for angiosperms and gymnosperms, respectively. Additionally, the global isoscapes of δ13Cring were not established, in this study, three machine learning methods to predict the spatial distribution of δ13Cring were done, the results showed that RF was the best model to established the isoscapes of δ13Cring.
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.
European forests stock 30% of the total carbon stored in the biomass of temperate forests globally. As essential components of the biosphere, these forests are highly influenced by land–atmosphere interactions and climate extremes that may alter carbon uptake and storage. In order to identify broad patterns of ecosystem responses to climate, changes in European forest productivity have been linked to the strength and phase (i.e., positive or negative) of large-scale atmospheric circulation patterns. However, a robust characterization of the physical coupling between ocean-atmosphere variability and terrestrial ecosystem productivity requires a more tangible and physically measurable representation of the atmospheric state. We propose that the latitudinal position of the jet-stream in the European-Atlantic sector (JSL) is such a measure and allows directly linking anomalies in terrestrial carbon fluxes with climate extremes. Importantly, JSL integrates not only co-variability between multiple climate parameters, but also the underlying atmospheric configuration.
In this study, we combine a network of 344 tree-ring width (TRW) chronologies, simulated ecosystem carbon uptake (i.e., gross primary production; GPP) from Dynamic Global Vegetation Models and atmospheric reanalysis data to characterize the spatiotemporal connection between forest productivity at the earth surface and summer JSL variability in the upper troposphere. The focus on extremes in both the atmospheric driver (JSL) and the ecosystem response (TRW, GPP) allows us to diagnose the synoptic-scale configuration and climatic fluctuations that trigger the most substantial carbon anomalies across temperate forests in Europe.
The impact of summer JSL migrations on the productivity of European forests is not uniform across the continent and shows a northwest-southeast polarity. Regional tree growth and GPP dipoles across Europe, particularly in extreme years, are tightly coupled to the position of the JSL and the occurrence of persistent and stationary weather patterns connected to persistent and strong anticyclonic anomalies (i.e., atmospheric blocking events). Productivity, and particularly forest growth, are the most impacted by changes in summer JSL over the continent, where atmospheric blocking frequency is the highest during summer. We observed synchronized changes in growth and GPP during summer JSL extremes, denoting common climatic constraints to both processes.
Our study emphasizes that JSL variability can trigger regional changes of up to 30% and 50% during extreme years in forest carbon uptake and growth of European forests, respectively. More importantly, these extremes on productivity are not uniform across Europe resulting in a continental productivity imbalance. Current and future net effect on continental forest productivity may depend on differences in forest resilience, forest density and rate of forest productivity across the continent.
How to cite: Dorado-Liñán, I., Ayarzagüena, B., Xu, G., and Trouet, V.: Jet stream position connected to atmospheric blocking drives regional anomalies in European forest productivity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12943, https://doi.org/10.5194/egusphere-egu21-12943, 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 Chao Phraya River Basin covers a third of Thailand’s area and is also home to a third of the country’s population. The Chao Phraya River serves multiple purposes: water supply, irrigation, hydropower production, cooling for thermoelectric power plants, among others. Water management in the basin could benefit from long term streamflow records that extend beyond the instrumental period. But to acquire practical relevance, streamflow reconstructions should have a sub-annual resolution—in line with the time step characterizing water management decisions. To this end, we reconstruct 253 years of monthly streamflow at all four major tributaries (Ping, Nan, Yon, and Wang) of the Chao Phraya. The reconstructions are developed using a network of tree rings and δ180 chronologies in Southeast Asia. Importantly, our reconstruction method ensures that the total monthly flow matches the annual flow closely. This mass balance criterion is necessary to avoid misguiding water management decisions, such as the allocation of water rights. All reconstructions are skillful. Better skills are obtained in the pre-monsoon months (March to May) than in the peak monsoon season (September, October). Overall, this work presents the most comprehensive record of high resolution and long term streamflow variability in the basin.
How to cite: Nguyen, H., Galelli, S., Xu, C., and Buckley, B.: Monthly streamflow reconstruction for the Chao Phraya River Basin with tree rings and δ180, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9029, https://doi.org/10.5194/egusphere-egu21-9029, 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 (Tmax) 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 Tmax) and multiple regression analysis (seasonal P and Tmax). Our results were consistent with hypothesis 1: effects of monthly or seasonal P and Tmax 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, Ci 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.
Increasing frequency of severe drought events under climate change is a major cause for concern for millions of hectares of forested land. One practical solution to improving forest resilience may be thinning. There may be several potential benefits, chief of which is that drought tolerance could be improved in the remaining trees due to lower competition for resources and increased precipitation throughfall. By improving resilience to drought, this may increase productivity of the remaining trees while lowering risks of mortality. Such potential benefits can effectively be quantified with data from statistically-sound, long-term field experiments, and tree rings provide a suitable avenue to compare treatments. We work with an experiment that applied different levels of tree retention to mature interior Douglas fir (Pseudotsuga menziesii var. glauca) in a dry ecosystem of western Canada. The treatments were applied in the winter of 2002/2003, coinciding with the aftermath of a severe natural drought event in 2002. We used tree-rings to quantify the extent to which thinning improves recovery and resilience of treated trees as compared to non-thinned controls. Tree-ring samples as well as height and diameter data were obtained from 83 trees from 8 treatment units of the randomized experimental design. Indicators for resilience to drought were calculated based on basal area increments. Thinning substantially increased basal area increments at the individual tree level, but more importantly, led to significantly higher recovery and resilience relative to the control. The results of this tree-ring analysis suggest that thinning may be a viable silvicultural intervention to counteract effects of severe drought events and to maintain tree cover.
How to cite: Montwé, D., Standish, A., Isaac-Renton, M., and Axelson, J.: Using tree rings to assess the potential of thinning to alleviate drought stress in a dry forest of western Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13182, https://doi.org/10.5194/egusphere-egu21-13182, 2021.
Climate-induced forest mortality is a critical issue in the Mediterranean basin, with major consequences for the functioning of these key ecosystems. Indeed, in Mediterranean ecosystems, where water stress is already the most limiting factor for tree performance, climatic changes are expected to entail an increase in water deficit. In this context, annual growth rings can provide short- (e.g., years) and long-term (e.g., decades) information on how trees respond to drought events. With climate change, Pinus pinaster and Pinus pinea L. are expected to reduce their distribution range in the region, being displaced at low altitudes by more drought tolerant taxa such as sub Mediterranean Quercus spp.
This study aims was to assess the physiological response of Pinus and Quercus species growing in the Vesuvio National park, located in Southern Italy and where an increase of temperature and drought events has been recorded in the recent years. Our preliminary results underlined the importance of temperature on the tree ring width of all the analyses species. The high temperatures can cause a change in the constant kinetics of the RuBisCo, leading to a consequent decrease in carboxylation rate and thus to a reduction in tree growth. On the other hand, also precipitation seemed to affect the growth of the sampled trees: indeed, in all the chronologies a reduction in growth was found after particular dry years: for example, the low rainfall in 1999 (455 mm/year) determined a drastic decline in growth in 2000 in all the species. In addition to the climatic factors, competition can also play an important role in the growth rate: dendrochronological analyzes have highlighted how stand specific properties (i.e. density, structure and composition) can influence individual tree responses to drought events. The knowledge of those researches should be integrated into sustainable forest management strategies to minimize the potential impacts of climate change on forest ecosystems.
How to cite: Battipaglia, G., Niccoli, F., and Pacheco-Solana, A.: The impact of drought on tree growth in Mediterranean sites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8635, https://doi.org/10.5194/egusphere-egu21-8635, 2021.
Latest drought events and their already visible damage to trees highlight the crucial need to assess the current state and resilience of forest ecosystems in southern Germany. However, commonly applied dendroclimatic approaches rarely take into account, how weather patterns affecting trees are modified by topographic conditions. For this purpose, three main tree species were studied at three low mountain ranges and three corresponding basins in the topographically complex province of Bavaria (southeast Germany). A response analysis between climate proxies and tree-ring widths was used to investigate climate-growth relationships over the past 50 years of both coniferous and deciduous tree species at each forest site. Temporal stability of tree responses to climate was compared for two 25-year periods to detect possible modifications in climate-growth correlations. A pointer year analysis was also conducted to analyze tree response to climatic extreme events. The results showed that Scots pine (Pinus sylvestris) was the most vulnerable and least drought-resistant of the investigated tree species. Although Norway spruce (Picea abies) and European beech (Fagus sylvatica) benefited from an extended growing season at high elevation sites, they showed higher drought sensitivity over the past 25 years. Beech responses were rather inhomogeneous and even differed in the optimal precipitation period. However, lower correlation coefficients for summer precipitation at the driest site may indicate the ability of beech to adapt to less summer precipitation. Nevertheless, increasing drought frequency, as predicted, poses a serious threat to all studied tree species, including even the colder and more humid sites. Hence, to more accurately estimate risk potentials under future weather conditions, we will combine dendroclimatological results with climate modelling scenarios, particularly expected future frequencies of critical weather types on the local scale.
How to cite: Debel, A. and Bräuning, A.: Current state and resilience of three main tree species in southern Germany with regard to drier and hotter weather conditions over the past 50 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11087, https://doi.org/10.5194/egusphere-egu21-11087, 2021.
Tree mortality due to climate change and particularly drought is a globally observed issue and has been studied widely. However, the underlying physiological mechanisms are still not fully understood. One approach to assess the drivers of drought-induced mortality is to retrospectively investigate predisposing factors that have led to tree death by utilizing tree rings. Here we combine annual stem growth, and stable carbon and oxygen isotopes (𝛿13C and 𝛿18O) in tree rings of recently died and living trees of two species, drought tolerant Pinus sylvestris and drought sensitive Fagus sylvatica, in the Rhone Valley (Valais), the driest part of Switzerland.
Irrespective of specific drought tolerance, growth patterns of now-dead and living trees were significantly different in both species. Now-dead trees showed higher growth rates than living trees, for at least half of their life span. In the last two decades this pattern was reversed and growth of now-dead trees was at a lower level compared to living trees. In this recent time period, 𝛿18O records of now-dead trees of both species showed a distinct decrease, while no systematic difference was found in the tree-ring 𝛿13C records of now-dead and living trees. Climate correlation analysis revealed that stem growth of now-dead trees was more sensitive to climate compared to living trees and that the relationship between isotope-derived leaf gas exchange and climate weakened in the late period prior to death.
Our findings suggest that now-dead trees followed a more conservative water-use strategy in their declining phase. Decreasing values and weakened relationships to climate indicate a reduction in stomatal conductance, accompanied by reduced photosynthetic activity, since the ratio of photosynthesis to stomatal conductance remained unchanged. Overall, our results suggest a combination of hydraulic failure and carbon starvation as initiators of tree death at our study sites, probably in different stages of tree life. It is obvious that recent climate conditions already strongly affected the trees, such that in a future environment negative effects will most likely increase.
How to cite: Rothenbühler, S., Walthert, L., Saurer, M., Gärtner, H., Gessler, A., Rigling, A., Tinner, W., Tenzin, K., and Treydte, K.: Assessing drought-induced mortality of European beech and Scots pine in the Valais, Switzerland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13226, https://doi.org/10.5194/egusphere-egu21-13226, 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 (FST) and the genetic variation among provenances in relation to the total genetic variance in a trait (QST). 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) QST-FST 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 QST-FST 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.
Severe drought events are affecting forests around the world, even in temperate climates. A viable climate change adaptation strategy may involve planting forests with trees more resilient to drought. The majority of the 300 million seedlings planted annually in western Canada are genetically-selected trees derived from tree breeding programs. Since tree breeding populations supply the seed that is deployed on the landscape, it is important to closely examine the degree of genetic control of drought resilience in these populations – yet methods for evaluating drought responses in mature experimental trials are limited. We evaluated the potential to use tree rings to infer genetic adaptation to drought. Specifically, we used annual growth increments to evaluate the genetic component behind variation in drought resilience. We also quantified potential genetic trade-offs between drought resilience and growth in long-term progeny trials. We worked with two economically and ecologically valuable sympatric conifers, coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) and western redcedar (Thuja plicata). Annual growth increment and tree height data were obtained from 1980 coastal Douglas-fir trees (93 polycross families on two well-replicated sites at age 19) and 1520 western redcedar trees (26 polycross families on three well-replicated sites at age 18). All trees showed substantial reduction in growth under drought, but there was clear variability in the longer-term response of families within each breeding population. The heritability (h2) of such drought resilience, or proportion of this variation explained by genetics, was high for Douglas-fir (h2 = 0.26, SE = 0.07) and moderate for redcedar (h2 = 0.13, SE = 0.04). Preliminary genetic correlations between tree height and drought resilience were also positive for both species (Douglas-fir: rg = 0.77, SE = 0.18; redcedar: rg = 0.62, SE = 0.17). Families that were both high-yielding and drought resilient could also be identified. Since growth response to drought is a variable and heritable trait, these traits are therefore under the control of the tree breeder. Moreover, the positive genetic correlations between tree height and an adaptive growth response to drought suggest that historic selection for tree height did not compromise drought resilience of planted seedlings. Tree rings appear to be an effective tool to screen these populations for drought resilience, which will help ensure that planted trees will remain healthy and productive under climate change.
How to cite: Isaac-Renton, M., Montwé, D., Stoehr, M., Degner, J., Hook, T., van der Merwe, L., Gamal El-Dien, O., Daniels, L., Yanchuk, A., and Campbell, E.: Tree rings and genetic control of drought resilience, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13156, https://doi.org/10.5194/egusphere-egu21-13156, 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.
Variable retention harvesting (VRH) is a silvicultural management practice that has been utilized to promote biodiversity, growth, and carbon sequestration in managed forests. VRH has been implemented as a climate mitigation strategy in response to increased climate warming and more erratic precipitation patterns which are occurring due to anthropogenic production of greenhouse gases. The aim of this study is to determine the impact of VRH and climate change on the inter-annual growth and carbon sequestration in a 20 ha red pine (Pinus resinosa) plantation forest located in southern Ontario, Canada over a 5-year period (2014-2018). The VRH treatment was implemented in 2014 within twenty, 1-hectare plots, which were subjected to one of four experimental thinning treatment types; 33% and 55% crown retention in an aggregated pattern (33A and 55A, respectively); and 33% and 55% crown retention in a dispersed pattern (33D and 55D, respectively), while four plots were maintained as unharvested control (CN) plots. In each plot, approximately sixty 5 mm increment cores were collected from residual trees during the spring and summer of 2019. These cores were processed for annual incremental growth according to standard dendrochronological methods to identify the climatic drivers on growth. Biomass and carbon sequestration were estimated using a species-specific allometric growth equation to quantify the impact of the different VRH treatments on red pine growth. Results of climate-growth assessments indicate that red pine growth in this region is dependent on maximum temperatures and total precipitation during the summer growing season. These relations were best captured in the May-July standard precipitation evapotranspiration index with a 3-month memory (SPEI3). May to August average maximum temperature and May to June total precipitation are also important drivers of red pine growth in all plots. We found that the dispersed crown retention patterns are the only VRH treatments that result in an increase in post-harvest growth; 8.12 ± 9.83% increase for 33D and 7.52 ± 5.71% increase for 55D. This suggests that dispersed retention may spatially optimize growth for the climatic conditions and be best suited for managing these forests under changing climatic conditions in the future. Aggregated treatments are found to have significantly less growth post-harvest; 33A had an average of 0.34 kg less biomass post-harvest (2.50 ± 1.94% decrease) and 55A had an average of 0.44 kg less biomass post-harvest (6.36 ± 3.82 % decrease). Our control sites showed that post-harvest growth showed an average of 0.56 kg less biomass post-harvest (6.01 ± 3.39% decrease). Within the aggregated treatments, exterior trees demonstrated increased growth, annual biomass accumulation, and carbon sequestration compared to trees growing in the interior of the aggregated plots. Our results suggest that dispersed crown retentions are most optimal when the goal of VRH is to increase growth or carbon sequestration. This research is ultimately important in informing future forest management practices in similar plantation forests across southern Ontario and elsewhere in the Great Lakes region and northeastern North America.
How to cite: Zugic, J., Pisaric, M. F. J., McKenzie, S. M., Arain, M. A., and Parker, W. C.: Assessing the short-term impacts of variable retention harvesting (VRH) and climatic drivers on carbon sequestration and growth of a red pine (Pinus resinosa) plantation in southern Ontario, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13539, https://doi.org/10.5194/egusphere-egu21-13539, 2021.
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