| In order to correctly evaluate the current climate change situation and accurately predict the future climate change situation,firstly,we must understand the past climate change.Due to the advantages of accurate dating,strong continuity,high resolution,easy access and large number of copies,tree-ring has become one of the important proxy indicators for the study of past climate change.Tongbai Mountain is located in the transition zone from subtropical zone to warm temperate zone,and is the northern distributed boundary of Pinus massoniana and is better response to climate change.Therefore,Tongbai Mountain is suitable for the studying the relationship between tree radial growth and climate change.According to the basic theory and method of tree-ring climatology,taking Pinus massoniana from 10 sampling points in Tongbai mountain area as the research object,this paper established the standard chronologies of earlywood width,latewood width and total ring width.The correlation analysis was carried out between all chronologies and the regional monthly mean temperature,mean maximum temperature,mean minimum temperature,precipitation,and mean relative humidity composed from Xinyang and Nanyang meteorological stations to determine the limiting factors of affecting tree growth in the Tongbai Mountain area,and establish Regional Pinus massoniana Ecological Model.Based on the results of the correlation analysis,the sequence of the mean minimum temperature in May-June(c5-6)in the past 100 years was reconstructed in the Tongbai Mountain area to provide reference data for the studing of climate change in the Tongbai Mountain area.The main conclusions are as follows:(1)Pinus massoniana was prone to water stress caused by high temperature in areas with lower altitudes in the northwest of Tongbai Mountain;the higher temperature in late summer,the more favorable it is for Pinus massoniana to carry out photosynthesis in areas with higher altitudes.The standard chronology of earlywood was significantly correlated with temperature and relative humidity in spring and summer at most sampling points,and the standard chronology of latewood was well correlated with temperature in autumn and winter.The growth of tree-ring in Northwest China was significantly negatively correlated with the average minimum temperature from May to June of that year,with a correlation coefficient of-0.577,and was significantly positively correlated with the average relative humidity from May to July of that year,with a correlation coefficient of 0.612.(2)The single chronology in the southeast of Tongbai mountain had a good correlation with the temperature and relative humidity in June and August.There were less precipitation and higher temperature in June.The high temperature made the plant transpiration strong and produced water stress.After the rainy season in August,the precipitation was sufficient and the temperature rose providing good hydrothermal conditions to promote the high growth of Masson pine.The annual tree-ring in the southeast region had a significant negative correlation with the average minimum temperature from May to June of that year,with a correlation coefficient of-0.640,and a significant positive correlation with the average relative humidity from January to July of that year,with a correlation coefficient of 0.578.(3)The annual ring growth of trees in Tongbai mountain area had a significant negative correlation with the average minimum temperature from May to June of that year,with a correlation coefficient of 0.646,and a significant positive correlation with the average relative humidity from March to August of that year,with a correlation coefficient of 0.617.The reason for the low growth of Pinus massoniana in recent years was that the relative humidity in the Tongbai Mountain area is on the decline,and the mean maximum and average minimum temperatures are on the rise.(4)The mean minimum temperature reconstruction sequence from May to June in Tongbai mountain area had seen three warm periods and two cold periods in the past century.The extreme high temperature years were 20 years,accounting for 20%,and the extreme low temperature years were 7 years,accounting for 7%.The reconstruction sequence had a significant period of 2.17 years similar to the change cycle of tropospheric quasi biennial oscillation(TBO),a significant period of 10.24 years similar to the10-year activity cycle of sunspots,and a significant period of 77.84 years similar to the North Atlantic interdecadal oscillation(AMO).There was a short period before 1928,and a long period after 1928(77.84years)was the main control period in Tongbai mountain area,especially after 1955.The reconstruction sequence was also closely related to the SST of the North Atlantic,the Western Pacific and the Indian Ocean;It could represent the variation of regional average minimum temperature in North China Plain.This study studied the response of Pinus massoniana in the northern boundary of growth to climate change in the ecological transition zone of Tongbai mountain,which can more accurately understand the response of ecosystem in the marginal zone under the background of global warming;In terms of tree-ring parameters,the earlywood and latewood tree ring width index is adopted,which has higher time resolution and can show a more refined relationship between tree ring and climate.There are also some problems and deficiencies in the research: the length of the chronology is short,the length of the reconstruction sequence is short,only a hundred years,and the basic data provided for the past climate change in this region is limited.The spatial correlation analysis of the reconstruction sequence has been carried out,some conclusions have been obtained,and simple explanations have been made,but its deeper causes and mechanisms need to be further explored. |
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