Vladimir V. Shishov

Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia

This paper describes variability in trends of annual tree growth at several locations in the high latitudes of Eurasia, providing a wide regional comparison over a 2000-year period. The study focuses on the nature of local and widespread tree-growth responses to recent warming seen in instrumental observations, available in northern regions for periods ranging from decades to a century. Instrumental temperature data demonstrate differences in seasonal scale of Eurasian warming and the complexity and spatial diversity of tree-growing-season trends in recent decades. A set of long tree-ring chronologies provides empirical evidence of association between inter-annual tree growth and local, primarily summer, temperature variability at each location. These data show no evidence of a recent breakdown in this association as has been found at other high-latitude Northern Hemisphere locations. Using Kendalls concordance, we quantify the time-dependent relationship between growth trends of the long chronologies as a group. This provides strong evidence that the extent of recent widespread warming across northwest Eurasia, with respect to 100- to 200-year trends, is unprecedented in the last 2000 years. An equivalent analysis of simulated temperatures using the HadCM3 model fails to show a similar increase in concordance expected as a consequence of anthropogenic forcing.

Comparing forest measurements from tree rings and a space-based index of vegetation activity in Siberia

Different methods have been developed for measuring carbon stocks and fluxes in the northern high latitudes, ranging from intensively measured small plots to space-based methods that use reflectance data to drive production efficiency models. The field of dendroecology has used samples of tree growth from radial increments to quantify long-term variability in ecosystem productivity, but these have very limited spatial domains. Since the cambium material in tree cores is itself a product of photosynthesis in the canopy, it would be ideal to link these two approaches. We examine the associations between the normalized differenced vegetation index (NDVI) and tree growth using 19 pairs of tree-ring widths (TRW) and maximum latewood density (MXD) across much of Siberia. We find consistent correlations between NDVI and both measures of tree growth and no systematic difference between MXD and TRW. At the regional level we note strong correspondence between the first principal component of tree growth and NDVI for MXD and TRW in a temperature-limited bioregion, indicating that canopy reflectance and cambial production are broadly linked. Using a network of 21 TRW chronologies from south of Lake Baikal, we find a similarly strong regional correspondence with NDVI in a markedly drier region. We show that tree growth is dominated by variation at decadal and multidecadal time periods, which the satellite record is incapable of recording given its relatively short record.

New perspective on spring vegetation phenology and global climate change based on Tibetan Plateau tree-ring data

Significance Inconsistent results regarding the rate of change in spring phenology and its relation to climatic drivers on the Tibetan Plateau have been obtained in the past. We introduce and describe here an innovative approach based on tree-ring data, which converts daily weather data into indices of the start (and end) of the growing season. This method provides a unique long-term record of vegetation phenological variability over the period 1960–2014. This approach could further be extended to other forested regions of the world. Scaling up the analysis would provide additional information on phenological responses of terrestrial ecosystems to the ongoing climate change across the Northern Hemisphere. 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 August–September minimum temperatures are the main climatic drivers for SOS and EOS, respectively. An increase of 1 °C in April–June minimum temperature shifted the dates of xylem phenology by 6 to 7 d, lengthening the period of tree-ring formation. This study extends the chronology of TP phenology farther back in time and reconciles the disparate views on SOS derived from remote sensing data. Scaling up this analysis may improve understanding of climate change effects and related phenological and plant productivity on a global scale.

Spatial patterns of eastern Mediterranean climate influence on tree growth

The first large-scale network of 79 tree-ring chronologies in the Eastern Mediterranean and Near East (EMNE; 33°N–42°N, 21°E–43°E) is described and analyzed to identify the seasonal climatic signal in indices of annual ring width. Correlation analysis and cluster analysis are applied to tree-ring data and gridded climate data to assess the climate signal embedded in the network in preparation for climate field reconstructions and formal proxy/model intercomparison experiments. The lengths of the 79 combined chronologies range from 89 to 990 years. The monthly correlations and partial correlations reveal a pervasive positive association with May, June, and sometimes July precipitation, positive correlations with winter and spring (December through April) temperatures, and negative relationships with May through July temperature, although as expected, there are site-to-site exceptions to these general patterns. Cluster analysis suggests three groups of sites based on their association with climate. The chronologies for the EMNE have coherent seasonal precipitation and temperature signals across a fairly broad geographical domain. The predominant signal is a positive growth response to May–June precipitation. Collectively, the findings suggest that the network can be exploited to develop season-specific field reconstructions of precipitation and drought history in the EMNE.

Competitive Strength Effect In the Climate Response of Scots Pine Radial Growth In South-Central Siberia Forest-Steppe

ABSTRACT This paper presents a method for classification of trees in groups depending on parameters of the age trend in tree-ring width. The method is tested on a sample containing 194 trees of Scots pine (Pinus sylvestris L.) growing in the forest-steppe zone of the South of Central Siberia. The climatic response of tree-ring width in such climatic conditions is complex. The influence of temperature in May-September is negative (moisture reducing). Warm-season precipitation serving as a source of moisture is a positive factor. Another positive factor is cold-season precipitation as frost protection. We determined the dependence of this response on the local conditions (soil, landscape and anthropogenic factors). The competitive strength of the trees influences both the sensitivity of individual trees to extreme climatic factors and the timing of growth processes. The latter implies the duration of the period of significant response to climate. It appears promising to take this influence into account in dendroclimatic reconstructions by using separate clusters of trees based on the competitive strength and having the maximum response to the reconstructed factor.

AUGUST TO JULY PRECIPITATION FROM TREE RINGS IN THE FOREST-STEPPE ZONE OF CENTRAL SIBERIA (RUSSIA)

ABSTRACT The goal of this research report is to describe annual precipitation reconstruction from Pinus sylvestris trees on three sites in the Abakan region, located in the Minusinsk Depression, at the confluence of the Yenisei and Abakan Rivers, Russia. The study was performed during the 4th annual international summer course “Tree Rings, Climate, Natural Resources and Human Interaction” held in Abakan, 5-19 August 2013. The reconstruction, for the 12-month total precipitation ending in July of the growth year, is based on a reliable and replicable statistical relationship between precipitation and tree-ring growth, and shows climate variability on both interannual and interdecadal time scales. The regional tree-ring chronology accounts for 56% of the variance of observed annual precipitation in a linear regression model, with the strongest monthly precipitation signal concentrated in May and June of the current growing season. Composite 500 mb height-anomaly maps suggest that the tree-ring data from this site, supplemented by other regional tree-ring data, could yield information on long-term atmospheric circulation variability over the study area and surrounding region.

Trends In Elemental Concentrations of Tree Rings From the Siberian Arctic

ABSTRACT The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropogenic pollution and climate change. We used ICP-MS to measure concentrations of 26 elements in the AD 1300–2000 tree rings of larch from the Taymyr Peninsula in northern Siberia for studying the interaction between environmental change and wood chemistry. We applied a two-stage data reduction technique to identify trends in the noisy measurement data. Statistical assessment of variance of normalized time series reveals pronounced depletion of xylem Ca, Mg, Cl, Bi and Si concentrations and enrichment of P, K, Mn, Rb, Sr and Ba concentrations after ca. AD 1900. The trends are unprecedented in the 700-year records, but multiple mechanisms may be at work and difficult to attribute with certainty. The declining xylem Ca and Mg may be a response to soil acidification from air pollution, whereas increasing P, K, and Mn concentrations may signal changes in root efficiency and excess water-soluble minerals liberated by the permafrost thaw. The changes seem consistent with mounting stress on Arctic vegetation. This study supports the potential of tree rings for monitoring past and ongoing changes in biogeochemistry of Arctic ecosystems related to pollution and permafrost thaw.

Elevation-layered dendroclimatic signal in eastern Mediterranean tree rings

The authors wish to thank the Forestry Departments in Turkey, Greece, Cyprus, Lebanon, and Syria for their great help and support in making this study possible. We would like to thank the Cyprus Meteorological Service for providing us with climate data. We thank Professor Alexandros P Dimitrakopoulos, of the Laboratory of Forest Protection, School of Forestry and Natural Environment, Aristotle University of Thessaloniki, Greece, for his help and support. We thank Christopher Baisan, Russell Biggs, and Gurudas C Bock for their valuable assistance in the field. We also thank Russell Biggs, Victoria L Frazier, Alicia Stout, Gurudas C Bock, Jessica L Little, and Anthony P Trujillo for their assistance in sample preparation and measurement. We wish to thank the anonymous reviewers for their constructive comments and suggestions on the manuscript. Funding was provided by the US National Science Foundation under Grant Earth System History (Grant No. 0075956), ATM-GEO/ATM-Paleoclimate Program 0758486, and Paleo Perspectives on Climate Change (Award No. 1103314). V. Shishov (software development and data analysis) was supported by the Russian Science Foundation (Grant # 14-14-00219). The tree-ring data will be available at the International Tree-Ring Data Bank (ITRDB) web site (https://www.ncdc.noaa.gov/paleo/study/19016).

The construction of oxygen isotope chronologies from tree-ring series sampled at different temporal resolution and its use as climate proxies: statistical aspects

Tree-ring oxygen stable isotope data series from conifers growing on the Dachstein Plateau (Austrian Alps) were selected to demonstrate the applicability of the serial pooling method using shifted 5-year tree-ring blocks for summer temperature reconstruction. The addressed method allows the construction of long isotope chronologies with significant climate correlation and well preserved climate sensitivity applying the irreducible sample replication of five trees. The linear regression model for temperature reconstruction is verifiable and the predicted data are well correlated with instrumental data, especially reproducing the long-term temperature trend. However, the reduced mean variance leads to loss of extreme years, which can be regulated by the combination of one data series in annual resolution with five shifted 5-year block data series. This significantly improves the variance of the mean chronology, sufficiently to identify extremes. Therefore, we recommend the use of mixed data sets as a compromise between essential sample replication and economic considerations.

Elemental composition of tree rings: A new perspective in biogeochemistry

Chemical elements that are associated with the ionic composition of the cytoplasm of cells are crucial components of higher plants. They enable various pro� cesses throughout the lifetime of plants associated with cellular energy, operation of a large number of enzymes, etc. (1). Entering the plant from the soil, chemical elements perform their functions in the plant and with its demise close important biogeochemical cycles (2). Longliving woody plants are themselves components of biogeochemical cycles with varying characteristic times: from one year to centuries. Tree rings that form each year in woody plants record the current climatic conditions on one hand, and they accumulate information about longterm changes of their environment (3) on the other. Wood cells mature in one growing season as cell walls lignify, and upon death, they serve as a waterconducting system. Chemical elements that are rigidly linked to the com� ponents of the cell walls of wood and that preserve this link for many decades are thus valuable. They can be used as a potential source of information about the processes and factors that govern their content that took place during the maturing of wood cells. In this paper we present for the first time the changes in biologicallyimportant elements (P, K, Ca, Mg, Sr, Ba, Cl, Si) from 1300 to 2000 AD in the annual rings of larch ( Larix gmelinii Rupr.) from the Taimyr Peninsula (polar boundary of forest vegetation, 72° N). In this study we only consider selected elements that are considered most informative, although the method allowed us to determine the concentration of a total of 40 elements. There are many publications dedicated to the elemental composition of tree rings over short time intervals, however the potential of using the signal of the elements for making long reconstructions of the paleoenvironmental conditions remains unfulfilled. Such a long dendrochemical record for the elements is obtained for the first time. The conditions of tree growth on the permafrost soils of the Taimyr Peninsula are strictly limited by temperature. Wood samples (tree discs) were collected in 2006. Dating of discs was car� ried out using a long master chronology that was pre� viously obtained for this area (4). The actual lifespan of the trees was no more than 350-400 years; for each calendar period 3-6 samples from discs of different ages were measured. Covering the time interval of 700 years was achieved by using samples from both liv� ing and very well preserved dead trees. The total num� ber of samples analyzed from sixteen trees was 351. A single sample contained a 5�year or 10�year period of growth (5 or 10 calendardated tree rings). Chemi� cal analysis was carried out using the method of mass spectrometry with inductively coupled plasma (ICPMS) employing a quadrupole spectrometer Agilent 7500ce. Measurements were made on solu� tions obtained by dissolving wood specimens in con� centrated nitric acid and their subsequent dilution with water. The method of processing wood samples, their dissolution, and the subsequent sample prepara� tion and measurement is described in detail in (5). The longterm average values as well as the range of changes of concentrations of the elements in wood samples are given in the table. The most abundant ele� ments in the wood samples are K + and Ca 2+ , which are important components of the cytoplasm. Ba and Sr, which are the chemical analogs of Ca and Mg, have the lowest concentrations. Based on the temporal vari� ability of all investigated elements, they can be divided into three groups. The first group consists of K and P, which are characterized by the following dynamics: a relatively stable level of concentration during the period from 1300 to 1950 and then a sharp increase in