Elena A. Babushkina

Climatic signal in radial increment of conifers in forest-steppe of southern Siberia and its dependence on local growing conditions

Radial increments have been studied in Siberian larch (Larix sibirica Ledeb.) and Scots pine (Pinus sylvestris L.) growing in the forest-steppe zone of southern Siberia in areas with different landscapes and levels of soil moisture supply but uniform climatic conditions. It has been shown that the radial increment significantly depends on climatic factors, primarily temperatures in April to July and September, sums of precipitation in April to July and September to November, and hydrothermal coefficient in May. The climatiC response in the wood of conifers in the forest-steppe zone differs depending on their species-specific features and local growing conditions.

Transformation of climatic response in radial increment of trees depending on topoecological conditions of their occurrence

We report the research results derived from identifying the regional climatic signal contained in the coniferous tree ring-width variability for different topoecological conditions in the forest-steppe of the Republic of Khakassia. It is found that under different growth conditions for trees of the same species the climatic signal undergoes a significant transformation. We demonstrate the possibility of using a combination of tree-ring chronologies of different tree species for an adequate dendroclimatic reconstruction of the leading climatic variables.

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.

Modeled Tracheidograms Disclose Drought Influence on Pinus sylvestris Tree-Rings Structure From Siberian Forest-Steppe

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 IADFs formation, this study demonstrated that the Vaganov-Shashkin model is a useful tool to study the climatic impact on tree-ring structures. The ability to produce synthetic tracheidogram represents an unavoidable step to link climate to tree growth and xylem functioning under future scenarios.

Climatic Response of Conifer Radial Growth in Forest-Steppes of South Siberia: Comparison of Three Approaches

We compared three approaches to study climatic signals of Pinus sylvestris and Larix sibirica treering width chronologies from the forest-steppe zone of South Siberia, where both temperature and precipitation limit the conifer tree growth: 1—paired correlation of chronologies with monthly climatic variables; 2— paired and partial correlations with monthly and seasonal series of primary and secondary climatic factors, calculated in the Seascorr program; 3—paired correlation with a 15-day moving average series of climatic variables. The comparison showed that simple paired correlation with monthly series as the simplest approach could be used for a wide range of dendroclimatic studies, both as a main procedure and for preliminary analysis. The Seascorr analysis is the most suitable for assessing climate-growth relationship in extreme growth conditions and for reconstructions of extremes, e.g. droughts, and of their impact periods. The application of the 15-day moving average series is limited by availability of daily climatic data, but it describes the seasonal window of climatic response with high precision. Altogether, the combination of three approaches allowed to explore the spatial-temporal pattern of the conifers radial growth climatic response in South Siberia.

Variation of the hydrological regime of Bele-Shira closed basin in Southern Siberia and its reflection in the radial growth of Larix sibirica

This study analyses dynamics of the hydrological regime of Bele-Shira closed basin and evaluates the potential for using radial growth of Siberian larch (Larix sibirica) for its assessment. We investigated the relationships between different characteristics of the water level variation of Lake Shira, precipitation amount and long-term regional chronologies developed from 56 living trees and 32 dead trees on three sites across this basin. Graphical and correlation analysis indicate that the interannual change (June minus previous June) of the water level of Lake Shira is strongly positively related to the annual sum of precipitation from July to June and the radial growth of larch. It was shown that this hydrological characteristic integrates the current dynamics of the regional precipitation and moisture regime as a whole of the Bele-Shira closed basin on interannual and decadal scales. The water level of Lake Shira fluctuates on a multi-year timescale in synchrony with the cumulative sum of the tree-ring chronology and also has strong positive long-term trend, probably driven by the continual groundwater inflow from neighboring Lake Itkul. Delayed relationships of precipitation and radial growth with the Lake Shira level change are interpreted with reference to a water balance model of the closed basin. Results offer the possibility of reconstructing interannual and decadal variation of the hydrological regime during the last few centuries through regression models using tree-ring chronologies or the dynamics of climatic variables recovered from them.

Precipitation reconstruction for the Khakassia region, Siberia, from tree rings

A nested July–June precipitation reconstruction for the period AD 1777–2012 was developed from multi-century tree-ring records of Pinus sylvestris L. (Scots pine) for the Republic of Khakassia in Siberia, Russia. Calibration and verification statistics for the period 1948–2012 show a high level of skill and account for a significant portion of the observed variance (>50%) irrespective of which period is used to develop or verify the regression model. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1948–2012). Thresholds (25th and 75th percentiles) based on the empirical cumulative distribution of 1948–2012 observed precipitation were used to delineate dry years and wet years of the long-term reconstruction. The longest reconstructed dry period, defined as consecutive years with less than 25th percentile of observed July–June precipitation, was 3 years (1861–1863). There was no significant difference in the number dry and wet periods during the 236 years of the reconstructed precipitation. Maps of geopotential height anomalies indicate that dry years differ from wet years primarily in the location of an anomalous 500-mb ridge approximately over the study area.

Radial increment dynamics of Scots pine (Pinus sylvestris L.) as an indicator of hydrothermal regime of the Western Transbaikalia forest steppe

The radial increment of Scots pine growing in the forest-steppe zone of Western Transbaikalia at five sites is studied. For each site, additional samples are collected, which allows us to increase reliability and build two regional chronologies. An analysis of chronology correlations with monthly temperatures, precipitation, and Selyaninov hydrothermal coefficient is carried out. The analysis of 10-day moving climatic series makes it possible to clarify the periods of climate impact on the increment: the main limitation of pine increment in the region is observed by moisture supply, including conditions during previous (from late July to late September) and current (May to mid-July) vegetative seasons. Fluctuations of 23–35 years in the dynamics of climatic factors and radial increment of the pine are found.

How can the parameterization of a process-based model help us understand real tree-ring growth?

Key messageThis study shows great potential of the well-validated VS-Oscilloscope (a visual accurate parameterization of the VS-model) for assessment of spatial–temporal cambium phenology, which is illustrated based on the analysis of comprehensive datasets from central Siberia.AbstractTree-growth response to changing climate varies depending on tree species, forest type, and geographical region. Process-based models can help us better understand and anticipate these outcomes. To characterize growth sensitivity to different climate parameters, we applied the VS-Oscilloscope analytical package, as a precise visual parameterization tool of the Vaganov–Shashkin model, to two contrasting habitats: one with tree-ring growth limitation by soil moisture (in the southern part of central Siberia) and the another with temperature limitation (in the middle part of central Siberia). We speculate that specific parameter values of the Vaganov–Shashkin model and their variability under local conditions and species are the key to understand different physiological processes in conifers. According to the simulation results for the temperature-limited site, wider rings of Picea obovata can result from a longer growing season. However, for the soil moisture-limited site, the final sizes of the tree rings of Pinus sylvestris were not affected by the length of the growing season but were primarily defined by the intra-seasonal variations in soil moisture, even under cold conditions. For the two sites, we obtained a 20-day difference between the two phenological dates, in which the early date could be associated with cambial initiation and the late date with the appearance of the first enlarging cell. In the case of central Siberia, the time period was half that of the southern Siberia. Such differences could be explained by both geography and species-specific responses to phenology. To test this hypothesis, additional tree-ring and climatic data for contrasted habitats would be needed.