| Pinus sylvestris var.mongolica forest is naturally distributed in Great Xing'an Mountains.912 tree-ring samples were collected from 13 sites in southern and northern P.sylvestris var.mongolica natural forest distribution.Based on the theory of dendroclimatology,13 tree ring width residual chronologies were developed by using negative exponent curve or linear regression.According to the climatic conditions,the ecotype of P.sylvestris var.mongolica and the correlation between chronologies,all chronologies were divided into two categories:the south and north.To facilitate statistical analysis,two region residual chronologies were developed by averaging all chronologies of the southern and northern sample sites,respectively.The relationships between chronologies and local climate factors were studied by correlation analysis and the growth variation was estimated by basal area increment from 1960 to 2013 to investigate the different response of Pinus sylvestris var.mongolica to climate change in southern and northern Great Xing'an Mountains.The main results are as follows:1.According to the results of correlation analysis between tree ring width and monthly mean temperature,monthly mean maximum temperature,monthly mean minimum temperature,monthly precipitation,and standardized precipitation evapotranspiration index(SPEI),the response of P.sylvestris var.mongolica radial growth to climate factors is different in the southern and northern regions.Tree-ring width of two regions are both significantly positively correlated(P<0.05)with total precipitation and average SPEI from April to September,so the response to moisture is consistent.But the response of Pinus sylvestris var.mongolica to moisture in the south is stronger than that in the north.Except for the negative response of tree ring width to mean temperature and mean maximum temperature in June,there are different responses at different degree in most of the other months.Most of the correlation coefficients are opposite.Tree-ring width of all the sites is significantly negatively correlated with mean maximum temperature in the southern area,while it is significantly positively correlated in the northern area.The southern trees suffer from water stress,whereas the northern trees suffer from low temperature stress.Thus,the southern tree radial growth is mainly limited by moisture from April to September,but the northern is mostly affected by the monthly mean minimum temperature of the same period.2.The results of moving correlation analysis of temperature and tree ring width data for long time series suggest that the relationship between temperature and tree growth is not stable.As temperature increases significantly after 1960(P<0.01),P.sylvestris var.mongolica growth is more sensitive to temperature in both southern and northern regions.Tree radial growth shows an increasingly negative correlation with mean maximum temperature from April to September in the southern region and an increasingly positive correlation with the mean minimum temperature in the northern region.3.The estimation results of BAI show that the variety of growth differed significantly between two regions over the past 54 years.The mean BAI trends are declining rapidly in the south.Further study determines that mean maximum temperature for April to September contributes most to southern average BAI variability from 1960 to 2013(r=-0.698,P<0.01),so increasing drought stress caused by high temperature is the main reason for growth decline.And climate warming inhibites radial growth of the southern P.sylvestris var.mongolica.But the average BAI trends are rising basically in the north.And it may be closely related to the increase of mean minimum temperature and total precipitation in April-September.So to some extent climate warming is beneficial to growth of the northern P.sylvestris var.mongolica.If the warming is sustained,the distribution area of P.sylvestris var.mongolica may move northward in the future. |
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