Study On The Climate Response Of Earlywood And Latewood Trees Of Pinus Taiwanensis At Different Altitudes In Mount Sanqing,Jiangxi

Paleoclimate reconstruction based on proxy indicators is an important way to study past climate changes.Tree-ring indicators are important data for reconstructing past millennium-scale annual resolution climate changes due to their accurate dating,high resolution and sensitivity to climate.The analysis of early and latewood formed in different seasons can study the history of climate change with high temporal resolution on an intra-annual scale.In the subtropical region of my country,the mountains and forests are widely distributed,the forest coverage rate is high,the tree ring width is large,and the boundaries between the early and late wood are obvious.There are also a large number of intra-annual density fluctuations(IADFs)in tree rings in this area,that is,there are cell bands similar to latewood in earlywood and cell bands similar to earlywood in latewood,which can be used to study more climate history with high temporal resolution.The purpose of this study was to select tree-ring early and latewood data distributed at different altitudes representing different climate zones,to study their response to climate change,and to provide a scientific basis for regional high-resolution tree-ring climate reconstruction.Pinus taiwanensis is a representative community in subtropical regions,distributed at an altitude of 750-2800 m.The altitude difference of Mount Sanqing in Jiangxi is large,and Pinus taiwanensis has a continuous distribution phenomenon at 1000-1800 m in this area.This paper takes Pinus taiwanensis in Mount Sanqing,Jiangxi as the research object,and studies the response characteristics of early and latewood and intra-year density fluctuations to climate change at different altitudes.1、In this study,four sampling points at different altitudes were set up in Mount Sanqing.Based on dendrochronological methods and principles,establish 12 width chronologies(full-round,earlywood,latewood)and 12 blue-light chronologies(earlywood blue-light chronology,latewood blue-light chronology,earlywood blue-light intensity difference chronology)..The characteristic parameters of the width chronology show that the sample core contains more environmental information,and the overall representativeness(EPS)of the sample size of each width chronology is higher than 0.85,and the quality of the chronology is high.Due to the low quality of the blue light intensity chronology and low sensitivity to climate,the follow-up analysis is mainly based on the width chronology.2.Combined with the average value of meteorological data for the past 60 years from three meteorological stations(Yushan,Jingdezhen,Tunxi)near the study area,study the relationship between the chronology of Pinus taiwanensis and climatic factors(The response characteristics of average temperature,maximum temperature,minimum temperature,precipitation,and Palmer Drought Index(PDSI),the study found that the overall width of Pinus taiwanensis at different altitudes has a positive correlation with temperature as a whole,and a negative correlation with precipitation..With the increase of altitude,the limiting effect of low temperature on the radial growth of Pinus taiwanensis became stronger.The radial growth of earlywood was more affected by the temperature in the previous year’s growing season,showing a more obvious "hysteresis effect";the radial growth of latewood was more affected by the temperature and precipitation in the current growing season.3.Statistical analysis of the annual density fluctuation of Pinus taiwanensis in Mount Sanqing found that the occurrence rate of the annual density fluctuation in the sample reached 68%,and the annual density fluctuation of Pinus taiwanensis in the study area was more frequent.In order to try to explore the environmental signals reflected by the density fluctuation phenomenon in the study area during the year,a corresponding type of frequency chronology was built.The results of correlation analysis showed that the intra-year density fluctuation of earlywood type was positively correlated with the precipitation in April,May and June,and negatively correlated with the average temperature in April,May and June.This indicates that the early growing season is the rainy season in the study area,and the sampling point is at a high altitude,and the relatively cold and wet environment promotes the occurrence of intra-year density fluctuations of earlywood types.The intra-year density fluctuation of the latewood type was positively correlated with the precipitation in September,and the phenomenon mostly occurred in the climate model with high temperature in the summer and more precipitation in the late growing season.Therefore.The increase in precipitation in September in this study may play a key role in the formation of intra-annual density fluctuations.In the study area,there was an obvious summer drought phenomenon from July to August,which led to the production of latewood cells.However,the increase in precipitation and the decrease in temperature in the later growing season eased the drought limitation,and the cells absorbed water and increased the turgor pressure,which drove the increase of cell diameter to form a similar earlywood cell.The cell band of the wood leads to the occurrence of density fluctuations during the year.