The Establishment Of Tree-Ring Chronology Of Cupressus Gigantea And Its Response To Climatic Factors

Cupressus gigantea is an endemic and endangered tree species in Tibet,which is naturally only distributed in some river valleys and hillsides in the middle and lower reaches of the Yajiang River.In order to explore the growth law of Cupressus gigantea,this paper adopts the growth cone sampling method,collects the tree cores of Cupressus gigantea as research materials,establishes a functional relationship between the DBH and tree age growth of Cupressus gigantea using mathematical model method,and analyzes the response of radial growth of Cupressus gigantea to climate factors,providing a certain theoretical basis for better protection of this rare resource.The main research results are as follows:（1）There is a significant positive correlation between DBH and tree age of Cupressus giganteus,and six model equations can be used to fit the relationship between DBH and tree age of Cupressus giganteus.Both the exponential equation and the parabolic equation can better reflect the relationship between the age and DBH of Cupressus gigantea.However,based on the comparison,it is concluded that the best fitting model between the DBH and the age of Cupressus gigantea is the exponential model（where x is the DBH and y is the DBH age）.The exponential model equation is applicable to the fitting estimation of the age of Cupressus gigantea with a DBH of d_1.3≤1 m.（2）The standard chronology of different types of Cupressus gigantea shows that the average sensitivity of Cupressus gigantea is above 0.190,and the high signal-to-noise ratio is greater than 15,indicating that the annual ring width of Cupressus gigantea is relatively sensitive to environmental reflection,with high environmental information content,and more climate information content,making it suitable for analyzing the response of tree annual rings to climate in this region.（3）The correlation coefficient between tree rings is used to indicate the consistency of tree growth within each sampling point.This study found that in the established standard chronology of Cupressus gigantea,the correlation coefficient between tree rings is relatively large and has good consistency.Therefore,the correlation relationship between Cupressus gigantea and environmental factors under different growth environments is universal.（4）In the comparison of the variance of the first principal component of different land types,the higher values of slope and terrace are both higher than 50%,indicating that the growth of Cupressus gigantea in these two areas has a good consistency;The low variance（21.7%）and large standard deviation（0.797）of the first principal component of the waterline type are both greater than those of the slope type（0.676）and the terrace type（0.652）,indicating that the growth of the waterline type Cupressus gigantea is greatly affected by environmental factors,and the intensity of the climatic signals recorded in the annual ring chronology series is much higher than that of the slope type and the terrace type.（5）According to the correlation analysis results of monthly precipitation,seasonal precipitation,and the annual ring width index of Cupressus gigantea,the correlation between precipitation in the study area and the annual ring width index of Cupressus gigantea is small,and only the monthly precipitation in July showed a significant negative correlation（P<0.05）,with a correlation coefficient of-0.305,indicating that precipitation is not the main factor limiting the growth of Cupressus gigantea.（6）The radial growth of Cupressus gigantea is mainly limited by temperature.Among them,the monthly average temperature and monthly average maximum temperature from June to September,as well as the average temperature and average maximum temperature in summer and autumn are the most restrictive factors for the radial growth of Cupressus gigantea.In conclusion,the best fitting model between DBH and tree age was an exponential function.The standard chronology of the ring of Cupressus gigantea contains more climatic information which is suitable for the study of radial growth.There was little correlation between radial growth and precipitation,and temperature was the biggest factor limiting radial growth of Cupressus gigantea,which reflected the strong drought resistance of Cupressus gigantea,and provided certain theoretical basis for climate reconstruction in this region in the future.