| Climate change profoundly affects the cambium activity and the xylem physiological growth process.Xylem growth is more sensitive to climate factors,so the past climate change is better recorded in the variation of tree-ring width.Tree-ring data had become one of the most important proxy data for reconstructing the last millennium climate change study because of it contain high resolution climatic signal.Recently,tree-ring data has become increasingly important in the field of global change research.Funiu Mountain,located in the western of Henan Province,belongs to the eastern branch of the Qinling Mountains.Meanwhile,it is located in the north-south climate transition zone of China,as well as the transition zone of two or three steps of terrain from west to east in China.Its unique geographical position and special transitional climate make its fragile ecosystem sensitive to climate change.In Mt.Funiu area,so much of the natural appearance was retained and has a very high forest coverage rate,which attracts the attentions of many scholars.The tree-ring research in Funiu Mountain area started relatively late,and only focuses on the dendroecology and dendroclimatology of Pinus tabulaeformis and Pinus armandii Franch..However,the research results are not enough,and further research is still neededIn this study,195 Pinus tabulaeformis trees of 360 cores(Finally selected 180 trees,320cores)from 7 sample sites were collected from Mt.Longchiman of Funiu Mountain area,the only original forest region in Henan Province,and a series of chronologies of 7 sample sites were established.The quality of chronologies was higher,and the standard chronologies that containing more information were selected to conduct the research.Through correlation and systematic clustering analysis,the correlation coefficient between standard chronologies are high,and the 7chronologies are finally divided into 4 categories,which were lower limit Pinus tabulaeformis(LCM＿A,1580-1620m)lower elevation Pinus tabulaeformis(LCM＿B,1650-1720m)higher elevation Pinus tabulaeformis(LCM＿C,1660-1750m)and upper limit Pinus tabulaeformis(LCM＿D,1760-1909m)and they have significant characteristics of altitude gradient.According to the systematic clustering analysis results,the four categories tree-ring chronologies were established and to analyze the four categories tree-growth differences from tree-ring raw width,and to discuss the response differences of four elevation gradient trees radial growth to the climate factors that south/north sides of Funiu Mountain area,so as to try to reconstruct the climate in Funiu Mountain based on tree-ring width.The main findings are as follows:(1)The standard chronologies of 7 sampling sites in Mt.Longchiman statistical characteristics MS,SNR,SD and EPS values are higher,indicating that these chronologies quality are high and it containing more environmental information.The MS,SNR values of chronologies increased with the increase of altitude,indicating that the tree-ring at high altitude contains more environmental signals(climatical signals).The average tree-ring width at all elevations were decreased during the period of 1980-2018,and tree-ring width’s decreasing rate significantly increased with the increase of altitude.(2)The results of correlation analysis between Pinus tabulaeformis tree-ring index and climate factors in the south and north of Funiu Mountain area showed: Pinus tabulaeformis growth at different elevations had better response to the temperature in the south side of Mt.Funiu and the precipitation in the north of Mt.Funiu.The hydrothermal factors in early growing season(May and June)were the main limiting factors for tree growth.Tree-ring index was negatively correlated with monthly mean temperature in May,May-June,positively correlated with precipitation in May,MayJune,and the high temperature in summer of last year had obvious "lag effect" on the tree growth at all elevations,and positively correlated with sc PDSI in May,June,July,May-July.High temperature in early growing season aggravated drought,which was an important factor restricting the annual growth of Pinus tabulaeformis in Funiu Mountain area.The stepwise regression growth models showed that the most important limiting factors for the tree growth of the other three categories(LCM＿A、B、C)were precipitation from April to June,and precipitation from May to June was the most important limiting factor at the upper limit(LCM＿D).(3)Therefore,the precipitation of May-June since 1850 in Mt.Funiu area was reconstructed based Pinus tabulaeformis tree-ring width at the upper limit.The reconstructed sequence showed that Funiu Mountain area had experienced 5 dry periods and 3 wet periods since1850,with a total of 33 dry years(including 11 extreme dry years)and 27 wet years(11 extreme wet years).The reconstructed sequence could capture the drought and wet events recorded in historical documents,such as the Ding-Wu disaster(1877-1878)and the great drought in northern China in the 20 th century,and had a high consistency with other reconstruction studies in terms of drought/wet periods.The reconstructed sequence has 3.36a(99%),3.9a(90%),10a(90%)and 13.9a(90%)quasi-cycle.The quasi-period 10 a cycle disappeared after 1900,after that,the quasi-period about 3-4a was became stronger.(4)The reconstructed sequence has a good spatial representation for the precipitation in Mt.Funiu area,the south of North China Plain,Shandong Peninsula and the central part of The Korean Peninsula from May to June;It is significantly positively correlated with the air temperature at 850 h Pa over the northern Indian Ocean,Indochina peninsula,south China sea and western equatorial Pacific,and it is significantly positively correlated with the radial wind at 850 h Pa over the coastal areas of Jiangsu and Shandong.Based on NCEP/NCAR reanalysis of wind vector data,it is found that during extremely wet years in Mt.Funiu area the northwest wind prevailed in the lower troposphere(850h Pa)and the south wind prevailed in the upper troposphere(200h Pa).During extreme drought year,southwest wind prevailed in the lower troposphere and northeast wind prevailed in the upper troposphere.The precipitation during May-June in Funiu Mountain area is mainly brought by the frontal systems formed when the cold air from high latitude moves southward and encounters the warm air in Funiu Mountain area.In this study,the response differences of Pinus tabulaeformis growth at different altitude to climate factors that in the north and south of Mt.Funiu area were systematically analyzed,which filled the gap of tree-ring precipitation reconstruction in Mt.Funiu area,and analyzed the precipitation formation mechanism during May to June in Funiu Mountain area,providing data for forest care and management in western Henan mountainous area and understanding the climate change background in Funiu Mountain area.However,there are still many deficiencies in the treering study in Funiu Mountain,and some jobs remains to be carried out in the future,such as through tree-ring isotope and density perspective,to explore the physiological mechanism of tree growth responding to climate change under the background of climate warming,so as to comprehensively and deeply understand the response of tree growth to climate change in Mt.Funiu transition zone. |
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