The Influences Of Growing Period Variation On Pinus Sylvestris Var. Mongolica Radial Growth In Northern Great Xing`an Mountains

Global warming is obvious and extreme events occur frequently,which effect the hydrothermal regime of the climate system and have a profound effect on the ecosystem.Rising temperature will change growing period of plants.It remains to clarify that the effects on tree growth according to the growing period lengthened.Based on the theory of dendrochronology methods,the tree-ring samples were collected in the concentrated distribution area of the Pinus sylvestris var.mongolica in the northern part of the Great Xing`an Mountains.The Regional curve standardization(RCS)function of the RCSSig Free program was used detrending and standarding to set up the chronology of tree(whole ring,earlywood and latewood).A total of 42 tree-ring width indices of single sample site and compound chronology were developed as needed.Daily temperature data of 1972-2015 was used to calculate the start of growing season(SOS),the end of growing season(EOS),duration of the growing season(DOS),active accumulated temperature(AAT)at 0 to 15? to analysis the regional changes in different growing periods.The correlation between annual ring width and climatic factors,different growing periods of Pinus sylvestris var.mongolica were analyzed and the influences of growing period variations on the radial growth of Pinus sylvestris var.mongolica in the northern part of the Great Xing`an Mountains was discussed.The main results are as follows:1.The first day of different temperatures of the growing period advance in the study area while the end day changes is not significant,duration is longer and active accumulated temperature is higher.2.The correlation between the climatic factors and the width of whole ring,earlywood and latewood of each sample site are basical consistent.By affecting the growth of earlywood,climate factors have an important influence the growth of whole tree ring.The response of latewood to climatic factors is quite different from that of earlywood and whole ring.3.The response of earlywood and whole ring width to different growing periods is approximately the same,and the sensitive temperature is slightly different.The SOS at 3-4.5? and the prolonged of DOS at 2-3? are benefit to the radial growth of Pinus sylvestris var.mongolica,whereas the earlier growth date of 14.5-15?,that is to say,the high temperature advance is unfavorable to the radial growth of Pinus sylvestris var.mongolica.4.The radial growth of trees is affected by both temperature and precipitation.Temperature inhibits the whole ring width of Pinus sylvestris var.mongolica in the early growing season and promotes it in the later growing season.The reason is that the correlation between ring width and temperature in May-September has not reached a significant level.Climate warming can promote the radial growth of Pinus sylvestris var.mongolica to some extent,it may also damage the growth if temperature beyond a certain range.The degree of promoting and inhibiting the growth needs to be quantified.In addition,although temperature is the main factor that triggers the cambium layer of Pinus sylvestris var.mongolica to begin to growth,the role of wood stopping growth remains to be clarified,such as the importance of water in the wood formation of Pinus sylvestris var.mongolica.