Timescale Effect Of Relationship Between Radial Growth Of Pinus Tabulaeformis And Climatic Factors At Different Altitudes In The Eastern Qilian Mountains

Plants are an important component of terrestrial ecosystems,and the response of trees to climate change is an important way to understand the dynamics of forest ecosystems.In the context of climate change,the sensitivity of radial growth of some trees to climate response is a divergence problem.In addition,there are different response characteristics of tree growth to the same climate factor at time and altitude scales.The eastern section of the Qilian Mountains,located in an important physiographic transition zone in China,provides an ideal site for conducting dendrochronological studies because of its unique geographical location.Therefore,this paper selects Pinus tabuliformis,the main dominant conifer species in this region,as the research object to conduct dendrochronological studies.In this paper,100 sample cores of 50 trees at two altitudes,high(2260m)and low(2055m),were collected on the basis of forest community surveys,and a chronology of P.tabuliformis tree-ring width was established for analyzing the response characteristics of P.tabuliformis growth to climate factors at different time scales(daily,dekad,monthly and annual).The paper reveals the time-scale effects and altitude differences of radial growth of P.tabuliformis,and also evaluates the stability of radial growth of P.tabuliformis in response to climatic factors,and portrays the changes of tree growth patterns.The main conclusions are as follows:(1)The statistical analysis of the chronology of the width of P.tabulaeformis and its parameters at the two altitude gradients showed that the values of some key indicators of P.tabulaeformis were relatively high(MS,EPS,AC1),which proved that the chronology of P.tabulaeformis obtained in this paper was of high quality,reliable and rich in climatic information,and also met the basic requirements for conducting ecological studies on tree chronology.By analyzing the trend change of the width chronology of the two altitudes of P.tabulaeformis,it is found that the growth trend of P.tabulaeformis in the study area increased first and then decreased.The growth of low-altitude P.tabulaeformis only showed a downward trend in the 1990 s.(2)Under the background of climate change,the inter-annual changes of air temperature and precipitation in the study area showed an upward trend,and the inter-annual growth trend of air temperature(0.428°C/10a)was significantly faster than that of precipitation(0.202 mm/10a).Through the Pearson correlation analysis,it was found that there were obvious altitude differences in the main climate factors controlling the radial growth of P.tabulaeformis in the study area.Among them,the growth of high-altitude P.tabulaeformis is mainly restricted by the temperature of the growing season in July,while the growth of low-altitude P.tabulaeformis is not only limited by the temperature at the end of the previous year’s growth season and in the early April and mid-July of the current year’s growth season,but also by precipitation constraints in July during the growing season.Moreover,the drought index SPEI was significantly positively correlated with the radial growth of P.tabulaeformis,indicating that drought was the main limiting factor for the growth of P.tabulaeformis in the study area.(3)The results of the response to the radial growth of P.tabulaeformis in the Qilian Mountains and climatic factors at different time scales showed that when the time scale studied changed,the growth of P.tabulaeformis showed different response results to climatic factors at different time scales.Among them,the response relationship between the growth of P.tabulaeformis and dekad-scale climatic factors in the study area is better than other three scales of year,month and day.The dekad performance is more concentrated and the relationship with precipitation is also well demonstrated.On the other hand,the absolute value of the significant correlation coefficient between the growth of P.tabulaeformis and climatic factors is higher on the dekad scale than the other three scales.(4)Through the moving correlation analysis of the temporal stability of the radial growth of P.tabulaeformis to the climate factors on the dekad time scale,it is found that the growth of P.tabulaeformis at high altitude has an obvious " divergence " to the climate factors on the dekad scale,which mainly showed that the growth of P.tabulaeformis in the historical period was constrained by the growing season temperature to the recent growth was not constrained by temperature,indicating that the constraint of high-altitude P.tabulaeformis by drought might be reduced.In contrast,the growth of low-altitude P.tabulaeformis is constrained by temperature and precipitation during the growing season,which is stable,mainly in the highest temperature and precipitation in early April and early July,indicating that the growth of low elevation P.tabulaeformis may be more severely restricted by drought in the future.