DENDROCLIMOTOLOGICAL RESEARCH OF SCOTS PINE IN STAND OF THE LEFT-BANK FOREST-STEPPE OF UKRAINE

Purpose of this research was to detect influence of climatic change on pine radial increment in stand in the Left-bank Forest-steppe of Ukraine as example 100-years-old stand at State Enterprise 'Kharkiv forest scientific research station’. Methods. Dendrochronological. Method of correlation function and multiple regressions (response function) were used to analyze the influence of climatic factors on tree radial increment. For this purpose computer program RESPO was used. Results. Tree ring series were built and were used for correlation analysis between climatic factors and pine radial increment for two periods: 1960-1988 and 1988-2016.Years of minimum (1933, 1942, 1956, 1972, 1976, 1976, 1987, 1992, 2002, 2006 та 2012) and maximum (1933, 1942, 1956, 1972, 1975, 1976, 1979, 1979, 1979, 1987, 1992, 2002 та 2012) of radial increment were detected. Depressions of pine radial increment were as a result of negative weather conditions: low and high winter and early-spring temperature, droughts during vegetation period. Maximums of radial increments were depended on favorable weather conditions for pine radial growth. Correlation and Response analysis for two periods showed that increase of temperature and precipitation, excluding winter precipitation, changed response of forest ecosystems to climatic change: if in first period (1960-1988) radial increment limited by April temperature and together July temperature positively influenced on radial growth, in second period (1988-2016) June temperature negatively infuenced on radial increment. Slight increase precipitation during vegetation period could not soften impact if high temperature during vegetatation period on tree radial increment. Conclusions. At comparison 1960-1988 and 1988-2016 it was detected that during first period positive influence of summer temperature on radial growth was distinctive and for second period one started to limit increment (negative influence) were detected. Slight increase of precipitation for vegetation period in second period significantly didn’t influence on pine radial growth. In second period increase of winter temperature and number of thaws negatively influenced on soil moisture, decreased of tree ring widths.


Introduction
For the past 100 years temperature increases by 0.4-0.6°С in Ukraine [1].This climatic change will be able to move natural habitats and borders of forest areas, changes of dominant tree species and level of resistance of forest ecosystems [3]. As result of growing of stands in relatively favourable climatic and soil conditions, to reveal complex of factors limited tree growth sometimes enough difficult because it changes during calendar year.
In previous studies it was elicited tree ring formation in stands growing in conditions of temperate climate are limited by temperatures of the growing period, early spring and winter, as well precipitation for the growing period [4,5,6,8,9].
The current increase of average temperature caused to necessity of adaptation of forest ecosystems to new conditions. Study of change of response of forest ecosystems to change of climate is very important. By reason of tree rings record not only information about changes in natural environment, also the tree response to these changes. So tree rings will able to be as biological indicators and integral factor of state of forest ecosystems.
Aim of this study was elicitation of influence of climate change on pine radial growth in stands of the Left-bank Forest-steppe in Ukraine on example 100 year old pine stand in South forestry.
Cores were taken by Pressler borer at 1.3 m of trunk of dominant and undamaged trees. The widths of early and late wood were measured using LINTAB (measuring system is widely used in dendrochronology) and the TSAP software in dendrochronological laboratory at Institute of Geography, Friedrich-Alexander-Universität Erlangen-Nürnberg. Dating of tree rings was carried out to determine calendar date of formation for each tree ring. Quality of tree ring dating was checked using the program COFECHA [9,10]. Common tree ring chronology was built on the base of tree ring chronologies for tree ring width for each tree by averaging ones.
Indexing of tree-ring chronologies was realized using the program ARSTAN to move away age trend. This makes it possible to analyze response of pine radial growth to climatic factors using the program RESP from the program set DPL [10]. We used index tree ring STANDART to analyze influence of climate on pine radial growth because the best results were gotten with this tree ring index chronology.
Correlation analysis and multiple regressions were used for revelation of influence of climate on radial growth by the program RE-SPO. Values of STANDART chronology were used as independent variables while the aver-age monthly air temperature values and the average monthly precipitation values for 1959-2016 for the period from June to September of the current year, have been applied as variables. The data of the Kharkiv meteorological station at the airport (49 ° 55'N, 36 ° 17'E, 152 m altitude) for the period 1959-2016 was used. The average monthly temperature and monthly precipitation values for the Kharkiv meteorological station are presented on fig. 1. The most warm (21.9 °С) and humid (70 mm) month was July, and the coldest month -January (-4.6 °С). The minimum precipitation was noted in March.
Depression of the pine radial growth was due to negative weather conditions (low and high winter and early spring temperature; droughts during the growing season). Maximum radial growth was as result favorable weather conditions (Fig. 2, 3, 4).
Climatic indicators during two periods (1960-1988 and 1988-2016) were compared. In the last years of 1988-2016, compared with 1960-1988, the average annual temperature increased by 1.2 ° С, during the growing season -by 0.9 ° С, during the winter -by 1.7 ° С and in March -at 2.1 ° С. Low increase in precipitation for growing period (by 19 mm), and at the same time, the winter precipitation decreased by 15 mm were noted ( Table 1). The biggest changes occurred for winter and early autumn temperatures.
For 2009-2016 a significant increase in temperatures during the growing season was noted, which negatively affected the radial increment (Fig. 1, 2.). Deviation from the norm of this temperature was 9% (1.7 ° C), while the indices of radial growth decreased by 4% during this period.  The correlation coefficient (0.44) between tree ring chronologies for all trees allows realization of correlation analysis between radial growth and climatic factors ( Table 2).
The coefficient of autocorrelation of the first order, which characterizes how closely tree ring width of the annual ring of this year is related to the tree ring width of the previous year [11], was high ( Table 2). This indicates the favorable forest and climatic conditions for growing pine stands. The correlation analysis and the response function for two periods showed that with the increase of temperatures and precipitation (the exception is winter precipitation), the reaction of forest ecosystems to the influence of climate changes, as in 1960-1988, the radial growth was limited the low April and high July temperatures, then later, in 1988-2016 negatively affected the radial increase of September tem-peratures of the previous year which are influence on winter wet accumulation, and the negative influence of June temperatures. There was a slight increase in precipitation, but on the background of high temperatures negative correlations between the indices of radial growth and precipitation became more in the second period than in the first one (Fig. 5). In the first period of 1960-1988, there was a positive effect of precipitation on radial growth in the 1960-1988 because on the background of low winter temperatures there was moisture accumulation in the soil, but in the next years 1988-2016 this influence became opposite -negative, which is probably due to an increase in winter and early spring temperatures, which did not contribute to the formation of a constant snow cover. As a result of thawing during the winter there was no moisture accumulation at the level of the past 1960-1988., which negatively affected the formation of tree ring widths.
D.V. Tishin [7] also showed an increase in the negative effects of winter precipitation on radial growth, due to the increase in winter temperatures and flooding over the past years. Such a reaction of radial growth to the influence of winter precipitation can be due not only to climate fluctuations, but also to changes in groundwater levels.

Conclusions
At comparison 1960-1988 and 1988-2016, it was revealed that for the first period, the positive influence of summer temperatures on the radial growth is characteristic, while for the second period they begin to limit the radial growth. A slight increase in precipitation for growing period could not mitigate the negative influence of high temperatures on the formation of tree rings. In the second period, the increase of the negative influence of winter precipitation on growth, which was caused by an increase in winter temperatures and thaw, was found to have a negative effect on the wet accumulation of soil and the formation of annual pine rings.
Acknowledgements. The authors are most grateful to Iris Burchardt from Dendrochronological laboratory at Institute of Geography at Friedrich-Alexander-Universität Erlangen-Nürnberg, who helped a lot with measurement and dating tree rings.