<p>In the work, a simple hypothesis was tested: whether treats of anatomica... more <p>In the work, a simple hypothesis was tested: whether treats of anatomical tree-ring structure of conifer (i.e. tracheidograms of rings) can be used for reconstruction of seasonal growth kinetics. Using the example of two sharply different growing seasons during which the seasonal growth of annual rings was measured with periodic sampling and dividing the forming annual ring into zones (cambium, enlargement zone, cell wall thickening zone and zone of matured tracheids) and the final tracheidograms, a simple scheme of recalculating the variability of radial cell size into cumulative and differential cell production curves was proposed. Statistical analysis of both correspondences and discrepancies between simulated and observed data shows the prospects of the proposed approach which can be testified for longer seasonal observations.</p>
& Key message This special issue of Annals of Forest Science compiles ten papers on "Wood formati... more & Key message This special issue of Annals of Forest Science compiles ten papers on "Wood formation and tree adaptation to climate", which were presented at "Le Studium" International Conference in May 2018 in Orléans (France). These papers present observational, experimental and modelling studies investigating the influence of climatic changes on tree growth from the hour to the century, and from the cell to the landscape.
More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic act... more More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic activity of the cambium. Nevertheless, there are few attempts to quantitatively describe cambium dynamics. In this study, we develop a state-of-the-art band model of cambium development, based on the kinetic heterogeneity of the cambial zone and the connectivity of the cell structure. The model describes seasonal cambium development based on an exponential function under climate forcing which can be effectively used to estimate the seasonal cell production for individual trees. It was shown that the model is able to simulate different cell production for fast-, middle- and slow-growing trees under the same climate forcing. Based on actual measurements of cell production for two contrasted trees, the model effectively reconstructed long-term cell production variability (up to 75% of explained variance) of both tree-ring characteristics over the period 1937−2012. The new model significantly s...
Improvement of dendrochronological crops yield reconstruction by separate application of earlywoo... more Improvement of dendrochronological crops yield reconstruction by separate application of earlywood and latewood width chronologies succeeded in rain-fed semiarid region. (1) Background: Tree-ring width chronologies have been successfully applied for crops yield reconstruction models. We propose application of separated earlywood and latewood width chronologies as possible predictors improving the fitness of reconstruction models. (2) Methods: The generalized yield series of main crops (spring wheat, spring barley, oats) were investigated in rain-fed and irrigated areas in semiarid steppes of South Siberia. Chronologies of earlywood, latewood, and total ring width of Siberian larch (Larix sibirica Ledeb.) growing in forest-steppe in the middle of the study area were tested as predictors of yield reconstruction models. (3) Results: In the rain-fed territory, separation of earlywood and latewood allowed increasing variation of yield explained by reconstruction model from 17.4 to 20.5%,...
Research Highlights: This study emphasized the importance of multi-parameter analyses along ecolo... more Research Highlights: This study emphasized the importance of multi-parameter analyses along ecological gradients for a more holistic understanding of the complex mechanism of tree-ring formation. Background and Objectives: The analysis of climatic signals from cell anatomical features measured along series of tree-rings provides mechanistic details on how environmental drivers rule tree-ring formation. However, the processes of cell development might not be independent, limiting the interpretation of the cell-based climatic signal. In this study, we investigated the variability, intercorrelations and climatic drivers of wood anatomical parameters, resulting from consequent cell developmental processes. Materials and Methods: The study was performed on thin cross-sections from wood cores sampled at ~1.3 m stem height from mature trees of Pinus sylvestris L. growing at five sampling sites along an ecological gradient from cold and wet to hot and dry within continental Southern Siberia...
We describe the implementation of the Vaganov-Shashkin tree-ring growth model (VSM) in MATLAB. VS... more We describe the implementation of the Vaganov-Shashkin tree-ring growth model (VSM) in MATLAB. VSM, originally written in Fortran, mimics subdaily and daily resolution processes of cambial growth as a function of soil moisture, air temperature, and insolation, with environmental forcing modeled as the principle of limiting factors. The re-implementation in a high level interpreted language, while sacrificing speed, provides opportunities to systematically evaluate model parameters, generate large ensembles of simulated tree-ring chronologies, and embed proxy system modeling within data assimilation approaches to climate reconstruction. We provide a versioned code repository and examples of model applications which permit process-level understanding of tree ring width variations in response to environmental variations and boundary conditions.
Intra-annual tree-ring parameters are increasingly used in dendroecology thanks to their high tem... more Intra-annual tree-ring parameters are increasingly used in dendroecology thanks to their high temporal resolution. To better understand the nature of intra-ring proxy signals, we compared old and young trees according to the different ways in which they respond to climate. The study was carried out in central Siberia (Russia, 60 • 75 N, 89 • 38 E) in two even-aged Pinus sylvestris L. stands of different ages (20 and 220 years). Ring width, cell size, and intra-annual δ 13 C were measured for 4 to 27 tree rings, depending on age group (young vs. old) and tree-ring parameter. Wood formation was monitored to link tree-ring position to its time of formation. Results indicated more distinct intra-annual δ 13 C patterns at both the beginning and end of the ring of young trees compared to old ones. Older trees showed a stronger significant correlation between δ 13 C across the ring border, indicating a stronger carry-over effect of the previous year's growing conditions on current year wood production. This suggests that tree age/size influences the magnitude of the transfer of mobile carbon reserves across the years.
The response of vegetation to climate change is of special interest in regions where rapid warmin... more The response of vegetation to climate change is of special interest in regions where rapid warming is coupled with moisture deficit. This raises the question of the limits in plants’ acclimation ability and the consequent shifts of the vegetation cover. Radial growth dynamics and climatic response were studied in Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.) in the forest-steppe, and for Siberian elm (Ulmus pumila L.) in the steppe of South Siberia, as indicators of vegetation state and dynamics. Climate–growth relationships were analyzed by the following two approaches: (1) correlations between tree-ring width chronologies and short-term moving climatic series, and (2) optimization of the parameters of the Vaganov–Shashkin tree growth simulation model to assess the ecophysiological characteristics of species. Regional warming was accompanied by a slower increase of the average moisture deficit, but not in the sever...
Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree ri... more Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree rings can provide valuable climatic information on these impacts across different spatial and temporal scales. Here we explore the suitability of tree-ring width (TRW), maximum latewood density (MXD), cell wall thickness (CWT), and δ 13 C and δ 18 O in tree-ring cellulose for the detection of climatic changes in northeastern Yakutia (YAK), eastern Taimyr (TAY) and Russian Altai (ALT) sites caused by six largest Common Era stratospheric volcanic eruptions (535,
In mountain ecosystems, plants are sensitive to climate changes, and an entire range of species d... more In mountain ecosystems, plants are sensitive to climate changes, and an entire range of species distribution can be observed in a small area. Therefore, mountains are of great interest for climate-growth relationship analysis. In this study, the Siberian spruce"s (Picea obovata Ledeb.) radial growth and its climatic response were investigated in the Western Sayan Mountains, near the Sayano-Shushenskoe Reservoir. Sampling was performed at three sites along an elevational gradient: at the lower border of the species range, in the middle, and at the treeline. Divergence of growth trends between individual trees was observed at each site, with microsite landscape-soil conditions as the most probable driver of this phenomenon. Cluster analysis of individual treering width series based on inter-serial correlation was carried out, resulting in two subset chronologies being developed for each site. These chronologies appear to have substantial differences in their climatic responses, mainly during the cold season. This response was not constant due to regional climatic change and the local influence of the nearby Sayano-Shushenskoe Reservoir. The main response of spruce to growing season conditions has a typical elevational pattern expected in mountains: impact of temperature shifts with elevation from positive to negative, and impact of precipitation shifts in the opposite direction. Chronologies of trees, growing under more severe micro-conditions, are very sensitive to temperature during September-April and to precipitation during October-December, and they record both inter-annual and long-term climatic variation. Consequently, it would be interesting to test if they indicate the Siberian High anticyclone, which is the main driver of these climatic factors.
... The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temp... more ... The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temperature for recent decades1,2, compared to earlier this century, are unknown. ... Earlysummer temperature. ² Winter precipitation (October±April).
Wood formation allows trees to adjust in a changing climate. Understanding what determine its adj... more Wood formation allows trees to adjust in a changing climate. Understanding what determine its adjustment is crucial to evaluate impacts of climatic changes on trees and forests growth. Despite efforts to characterize wood formation, little is known on its impact on the xylem cellular structure. In this study we apply the Vaganov-Shashkin model to generate synthetic tracheidograms and verify its use to investigate the formation of intra-annual density fluctuations (IADF), one of the most frequent climate tree-ring markers in drought-exposed sites. Results indicate that the model can produce realistic tracheidograms, except for narrow rings (<1 mm), when cambial activity stops due to an excess of drought or a lack of growth vigor. These observations suggest that IADFs are caused by a release of drought limitation to cells formation in the first half of the growing season, but that narrow rings are indicators of an even more extreme and persistent water stress. Taking the example of...
Proceedings of the National Academy of Sciences of the United States of America, Jul 19, 2017
Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have... more Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have received much attention. However, divergent results from the analyses of remote sensing data have been obtained for the Tibetan Plateau (TP), the world's largest high-elevation region. This study provides a perspective on vegetation phenology shifts during 1960-2014, gained using an innovative approach based on a well-validated, process-based, tree-ring growth model that is independent of temporal changes in technical properties and image quality of remote sensing products. Twenty composite site chronologies were analyzed, comprising about 3,000 trees from forested areas across the TP. We found that the start of the growing season (SOS) has advanced, on average, by 0.28 d/y over the period 1960-2014. The end of the growing season (EOS) has been delayed, by an estimated 0.33 d/y during 1982-2014. No significant changes in SOS or EOS were observed during 1960-1981. April-June and Augu...
Response of climate warming on tree-ring formation has attracted much attention during recent yea... more Response of climate warming on tree-ring formation has attracted much attention during recent years. However, most studies are based on statistical analysis, lacking understanding of tree-physiological processes, especially in the mountainous regions of the Tibetan Plateau (TP). Herein, we firstly use an updated new version of the tree-ring process-based Vaganov-Shashkin model (VS-oscilloscope) to simulate tree-ring formation and its relationships with climate factors during the past six decades. Our analyses covered 341 sampled trees growing within elevations ranging from 2750 to 4575 m a.s.l. at five sampling sites across the TP. Simulated tree-ring width series are significantly (p &amp;lt; 0.01) correlated with actual tree-ring width chronologies during their common interval periods. Starting dates of tree-ring formation are determined by temperature at all five sampling sites. After the initiation of tree stem cambial activity, soil moisture content has a significant effect on tree radial growth. Ending dates of cambial activity are driven by temperature over the whole study region. Simulated results indicate differences between wide and narrow tree-rings are mostly induced by soil moisture content, especially during the first half of the growing season, when effects from temperature variations are minor. Interestingly, we detected significantly (p &amp;lt; 0.001) increased relative growth rates due to higher soil moisture content after the year 1985 at the five sampling sites. However, the variability of mean relative growth rates due to temperature is negligible before and after that. Based on the successful application of VS-oscilloscope modeling on the high-elevation tree stands on the TP, our study provides a new perspective on tree radial growth process and their varying relationships to climate factors during the past six decades.
The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropog... more The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropogenic pollution and climate change. We examined long-term changes in wood chemistry of the dominant tree species of Siberian forests with inductively coupled plasma mass spectrometry analysis to study interaction between climate change and environmental trace elements. Variance and correspondence of 26 element concentrations of larch tree rings from the Taymyr Peninsula were statistically analyzed from AD 1300 to 2000. Unexpectedly, the tree rings reveal pronounced depletion of xylem Ca and Mg concentrations and enrichment of P, K, Mn, Rb, Sr and Ba concentrations after ca. 1950. The significant trends are unprecedented for the last 700 years, but the environmental mechanism triggering the change is not obvious. We hypothesize that the declining xylem calcium and manganese is a response to soil acidification from to air pollution as seen in experimental acidification elsewhere. The increase of P, K, and Mn concentrations, however, seems more likely a result of changes in root efficiency and excess water-soluble minerals liberated by the permafrost thaw and warming temperatures. Changes in wood chemistry altered by soil nutrient availability may signal mounting stress on arctic vegetation.
We explore the extent to which the Vaganov-Shashkin (VS) model of conifer tree-ring formation can... more We explore the extent to which the Vaganov-Shashkin (VS) model of conifer tree-ring formation can explain evidence for changing relationships between climate and tree growth over recent decades. The VS model is driven by daily environmental forcing (temperature, soil moisture, and solar radiation), and simulates tree-ring growth cell-by-cell as a function of the most limiting environmental control. This simplified representation of tree physiology allows us to examine using a selection of case studies whether instances of divergence may be explained in terms of changes in limiting environmental dependencies or transient climate change. Identification of model-data differences permits further exploration of the effects of tree-ring standardization, atmospheric composition, and additional non-climatic factors.
&amp;lt;p&amp;gt;In the work, a simple hypothesis was tested: whether treats of anatomica... more &amp;lt;p&amp;gt;In the work, a simple hypothesis was tested: whether treats of anatomical tree-ring structure of conifer (i.e. tracheidograms of rings) can be used for reconstruction of seasonal growth kinetics. Using the example of two sharply different growing seasons during which the seasonal growth of annual rings was measured with periodic sampling and dividing the forming annual ring into zones (cambium, enlargement zone, cell wall thickening zone and zone of matured tracheids) and the final tracheidograms, a simple scheme of recalculating the variability of radial cell size into cumulative and differential cell production curves was proposed. Statistical analysis of both correspondences and discrepancies between simulated and observed data shows the prospects of the proposed approach which can be testified for longer seasonal observations.&amp;lt;/p&amp;gt;
& Key message This special issue of Annals of Forest Science compiles ten papers on "Wood formati... more & Key message This special issue of Annals of Forest Science compiles ten papers on "Wood formation and tree adaptation to climate", which were presented at "Le Studium" International Conference in May 2018 in Orléans (France). These papers present observational, experimental and modelling studies investigating the influence of climatic changes on tree growth from the hour to the century, and from the cell to the landscape.
More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic act... more More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic activity of the cambium. Nevertheless, there are few attempts to quantitatively describe cambium dynamics. In this study, we develop a state-of-the-art band model of cambium development, based on the kinetic heterogeneity of the cambial zone and the connectivity of the cell structure. The model describes seasonal cambium development based on an exponential function under climate forcing which can be effectively used to estimate the seasonal cell production for individual trees. It was shown that the model is able to simulate different cell production for fast-, middle- and slow-growing trees under the same climate forcing. Based on actual measurements of cell production for two contrasted trees, the model effectively reconstructed long-term cell production variability (up to 75% of explained variance) of both tree-ring characteristics over the period 1937−2012. The new model significantly s...
Improvement of dendrochronological crops yield reconstruction by separate application of earlywoo... more Improvement of dendrochronological crops yield reconstruction by separate application of earlywood and latewood width chronologies succeeded in rain-fed semiarid region. (1) Background: Tree-ring width chronologies have been successfully applied for crops yield reconstruction models. We propose application of separated earlywood and latewood width chronologies as possible predictors improving the fitness of reconstruction models. (2) Methods: The generalized yield series of main crops (spring wheat, spring barley, oats) were investigated in rain-fed and irrigated areas in semiarid steppes of South Siberia. Chronologies of earlywood, latewood, and total ring width of Siberian larch (Larix sibirica Ledeb.) growing in forest-steppe in the middle of the study area were tested as predictors of yield reconstruction models. (3) Results: In the rain-fed territory, separation of earlywood and latewood allowed increasing variation of yield explained by reconstruction model from 17.4 to 20.5%,...
Research Highlights: This study emphasized the importance of multi-parameter analyses along ecolo... more Research Highlights: This study emphasized the importance of multi-parameter analyses along ecological gradients for a more holistic understanding of the complex mechanism of tree-ring formation. Background and Objectives: The analysis of climatic signals from cell anatomical features measured along series of tree-rings provides mechanistic details on how environmental drivers rule tree-ring formation. However, the processes of cell development might not be independent, limiting the interpretation of the cell-based climatic signal. In this study, we investigated the variability, intercorrelations and climatic drivers of wood anatomical parameters, resulting from consequent cell developmental processes. Materials and Methods: The study was performed on thin cross-sections from wood cores sampled at ~1.3 m stem height from mature trees of Pinus sylvestris L. growing at five sampling sites along an ecological gradient from cold and wet to hot and dry within continental Southern Siberia...
We describe the implementation of the Vaganov-Shashkin tree-ring growth model (VSM) in MATLAB. VS... more We describe the implementation of the Vaganov-Shashkin tree-ring growth model (VSM) in MATLAB. VSM, originally written in Fortran, mimics subdaily and daily resolution processes of cambial growth as a function of soil moisture, air temperature, and insolation, with environmental forcing modeled as the principle of limiting factors. The re-implementation in a high level interpreted language, while sacrificing speed, provides opportunities to systematically evaluate model parameters, generate large ensembles of simulated tree-ring chronologies, and embed proxy system modeling within data assimilation approaches to climate reconstruction. We provide a versioned code repository and examples of model applications which permit process-level understanding of tree ring width variations in response to environmental variations and boundary conditions.
Intra-annual tree-ring parameters are increasingly used in dendroecology thanks to their high tem... more Intra-annual tree-ring parameters are increasingly used in dendroecology thanks to their high temporal resolution. To better understand the nature of intra-ring proxy signals, we compared old and young trees according to the different ways in which they respond to climate. The study was carried out in central Siberia (Russia, 60 • 75 N, 89 • 38 E) in two even-aged Pinus sylvestris L. stands of different ages (20 and 220 years). Ring width, cell size, and intra-annual δ 13 C were measured for 4 to 27 tree rings, depending on age group (young vs. old) and tree-ring parameter. Wood formation was monitored to link tree-ring position to its time of formation. Results indicated more distinct intra-annual δ 13 C patterns at both the beginning and end of the ring of young trees compared to old ones. Older trees showed a stronger significant correlation between δ 13 C across the ring border, indicating a stronger carry-over effect of the previous year's growing conditions on current year wood production. This suggests that tree age/size influences the magnitude of the transfer of mobile carbon reserves across the years.
The response of vegetation to climate change is of special interest in regions where rapid warmin... more The response of vegetation to climate change is of special interest in regions where rapid warming is coupled with moisture deficit. This raises the question of the limits in plants’ acclimation ability and the consequent shifts of the vegetation cover. Radial growth dynamics and climatic response were studied in Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.) in the forest-steppe, and for Siberian elm (Ulmus pumila L.) in the steppe of South Siberia, as indicators of vegetation state and dynamics. Climate–growth relationships were analyzed by the following two approaches: (1) correlations between tree-ring width chronologies and short-term moving climatic series, and (2) optimization of the parameters of the Vaganov–Shashkin tree growth simulation model to assess the ecophysiological characteristics of species. Regional warming was accompanied by a slower increase of the average moisture deficit, but not in the sever...
Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree ri... more Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree rings can provide valuable climatic information on these impacts across different spatial and temporal scales. Here we explore the suitability of tree-ring width (TRW), maximum latewood density (MXD), cell wall thickness (CWT), and δ 13 C and δ 18 O in tree-ring cellulose for the detection of climatic changes in northeastern Yakutia (YAK), eastern Taimyr (TAY) and Russian Altai (ALT) sites caused by six largest Common Era stratospheric volcanic eruptions (535,
In mountain ecosystems, plants are sensitive to climate changes, and an entire range of species d... more In mountain ecosystems, plants are sensitive to climate changes, and an entire range of species distribution can be observed in a small area. Therefore, mountains are of great interest for climate-growth relationship analysis. In this study, the Siberian spruce"s (Picea obovata Ledeb.) radial growth and its climatic response were investigated in the Western Sayan Mountains, near the Sayano-Shushenskoe Reservoir. Sampling was performed at three sites along an elevational gradient: at the lower border of the species range, in the middle, and at the treeline. Divergence of growth trends between individual trees was observed at each site, with microsite landscape-soil conditions as the most probable driver of this phenomenon. Cluster analysis of individual treering width series based on inter-serial correlation was carried out, resulting in two subset chronologies being developed for each site. These chronologies appear to have substantial differences in their climatic responses, mainly during the cold season. This response was not constant due to regional climatic change and the local influence of the nearby Sayano-Shushenskoe Reservoir. The main response of spruce to growing season conditions has a typical elevational pattern expected in mountains: impact of temperature shifts with elevation from positive to negative, and impact of precipitation shifts in the opposite direction. Chronologies of trees, growing under more severe micro-conditions, are very sensitive to temperature during September-April and to precipitation during October-December, and they record both inter-annual and long-term climatic variation. Consequently, it would be interesting to test if they indicate the Siberian High anticyclone, which is the main driver of these climatic factors.
... The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temp... more ... The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temperature for recent decades1,2, compared to earlier this century, are unknown. ... Earlysummer temperature. ² Winter precipitation (October±April).
Wood formation allows trees to adjust in a changing climate. Understanding what determine its adj... more Wood formation allows trees to adjust in a changing climate. Understanding what determine its adjustment is crucial to evaluate impacts of climatic changes on trees and forests growth. Despite efforts to characterize wood formation, little is known on its impact on the xylem cellular structure. In this study we apply the Vaganov-Shashkin model to generate synthetic tracheidograms and verify its use to investigate the formation of intra-annual density fluctuations (IADF), one of the most frequent climate tree-ring markers in drought-exposed sites. Results indicate that the model can produce realistic tracheidograms, except for narrow rings (<1 mm), when cambial activity stops due to an excess of drought or a lack of growth vigor. These observations suggest that IADFs are caused by a release of drought limitation to cells formation in the first half of the growing season, but that narrow rings are indicators of an even more extreme and persistent water stress. Taking the example of...
Proceedings of the National Academy of Sciences of the United States of America, Jul 19, 2017
Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have... more Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have received much attention. However, divergent results from the analyses of remote sensing data have been obtained for the Tibetan Plateau (TP), the world's largest high-elevation region. This study provides a perspective on vegetation phenology shifts during 1960-2014, gained using an innovative approach based on a well-validated, process-based, tree-ring growth model that is independent of temporal changes in technical properties and image quality of remote sensing products. Twenty composite site chronologies were analyzed, comprising about 3,000 trees from forested areas across the TP. We found that the start of the growing season (SOS) has advanced, on average, by 0.28 d/y over the period 1960-2014. The end of the growing season (EOS) has been delayed, by an estimated 0.33 d/y during 1982-2014. No significant changes in SOS or EOS were observed during 1960-1981. April-June and Augu...
Response of climate warming on tree-ring formation has attracted much attention during recent yea... more Response of climate warming on tree-ring formation has attracted much attention during recent years. However, most studies are based on statistical analysis, lacking understanding of tree-physiological processes, especially in the mountainous regions of the Tibetan Plateau (TP). Herein, we firstly use an updated new version of the tree-ring process-based Vaganov-Shashkin model (VS-oscilloscope) to simulate tree-ring formation and its relationships with climate factors during the past six decades. Our analyses covered 341 sampled trees growing within elevations ranging from 2750 to 4575 m a.s.l. at five sampling sites across the TP. Simulated tree-ring width series are significantly (p &amp;lt; 0.01) correlated with actual tree-ring width chronologies during their common interval periods. Starting dates of tree-ring formation are determined by temperature at all five sampling sites. After the initiation of tree stem cambial activity, soil moisture content has a significant effect on tree radial growth. Ending dates of cambial activity are driven by temperature over the whole study region. Simulated results indicate differences between wide and narrow tree-rings are mostly induced by soil moisture content, especially during the first half of the growing season, when effects from temperature variations are minor. Interestingly, we detected significantly (p &amp;lt; 0.001) increased relative growth rates due to higher soil moisture content after the year 1985 at the five sampling sites. However, the variability of mean relative growth rates due to temperature is negligible before and after that. Based on the successful application of VS-oscilloscope modeling on the high-elevation tree stands on the TP, our study provides a new perspective on tree radial growth process and their varying relationships to climate factors during the past six decades.
The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropog... more The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropogenic pollution and climate change. We examined long-term changes in wood chemistry of the dominant tree species of Siberian forests with inductively coupled plasma mass spectrometry analysis to study interaction between climate change and environmental trace elements. Variance and correspondence of 26 element concentrations of larch tree rings from the Taymyr Peninsula were statistically analyzed from AD 1300 to 2000. Unexpectedly, the tree rings reveal pronounced depletion of xylem Ca and Mg concentrations and enrichment of P, K, Mn, Rb, Sr and Ba concentrations after ca. 1950. The significant trends are unprecedented for the last 700 years, but the environmental mechanism triggering the change is not obvious. We hypothesize that the declining xylem calcium and manganese is a response to soil acidification from to air pollution as seen in experimental acidification elsewhere. The increase of P, K, and Mn concentrations, however, seems more likely a result of changes in root efficiency and excess water-soluble minerals liberated by the permafrost thaw and warming temperatures. Changes in wood chemistry altered by soil nutrient availability may signal mounting stress on arctic vegetation.
We explore the extent to which the Vaganov-Shashkin (VS) model of conifer tree-ring formation can... more We explore the extent to which the Vaganov-Shashkin (VS) model of conifer tree-ring formation can explain evidence for changing relationships between climate and tree growth over recent decades. The VS model is driven by daily environmental forcing (temperature, soil moisture, and solar radiation), and simulates tree-ring growth cell-by-cell as a function of the most limiting environmental control. This simplified representation of tree physiology allows us to examine using a selection of case studies whether instances of divergence may be explained in terms of changes in limiting environmental dependencies or transient climate change. Identification of model-data differences permits further exploration of the effects of tree-ring standardization, atmospheric composition, and additional non-climatic factors.
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Papers by Eugene Vaganov