Study On The Response Of Picea Schrenkiana To Climate At Different Altitudes In Kashi River Basin

The study of tree-ring climate response is not only the basis for the reconstruction of paleoclimate,but also an important part of the research on climate change of forest ecosystems.As a typical representative of the large-scale mountain ecology in temperate arid regions of the world,the Tianshan Mountains are one of the most sensitive areas to climate change,and their environmental change reflect the laws of regional change under the background of global climate change.Therefore,this study chose the forest in the Nileke Kashi River Basin in the west of the Tianshan Mountains to collect 7 sample points of picea schrenkiana cores along different altitudes,establish standardized chronologies of tree ring,and analyze the relationship with its climate factors.Discussing the stability of different tree-ring parameters in response to climate and its altitude differences under the background of climate change are helpful to predict the possible future changes of forest ecosystems.The main conclusions are as follows:(1)From 1959 to 2017,the temperature and precipitation showed a significant upward trend,while the relative humidity showed a significant downward trend.The mutation test results show that the temperature and precipitation varied from low to high in 1997 and 1991 separately,and the relative humidity varied from high to low in2007.(2)Tree ring width chronologies of different altitudes contain a certain environmental information.The upper and lower forest edges of the forest contains more climate change information than the 2100-2200 m tree-ring chronologies in the forest.(3)The response analysis results of tree ring width chronologies and climatic factors at different altitudes show that precipitation had a "lag effect" on the growth of trees.The precipitation in July-August of the previous year and January to February of the current year was the restricts the growth of trees.The response of temperature and relative humidity to Picea schrenkiana varies in altitudes.In the upper forest,the tree-ring width above 2300 m were significantly negatively correlated with the temperature from July to August of the previous year,and were significantly positively correlated with the relative humidity from July to August of the previous year and June to August of the current year;tree ring width below 2000 m in the lower edge of the forest is significantly positively correlated with the temperature in August of the previous year and June to September of the current year,and negatively correlated with the relative humidity from June to August of the current year.In summary,the upper edge of the forest were limited by water conditions,and the lower edge of the forest were mainly affected by temperature and precipitation.(4)After precipitation mutation,the negative correlation between the tree ring chronologies above 2300 m and the temperature from July to August increased,and the positive correlation with the relative humidity from June to August also amplified,and the tree ring width index showed significant downtrend.The tree ring chronologies below 2000 m showed a significant increase in the overall positive correlation with the temperature from June to August,the positive correlation with precipitation weakened,the negative correlation with relative humidity increased,and the tree ring width index showed a significant uptrend.(5)The characteristic parameters of the tree-ring density chronologies are an order of magnitude lower than that of the width chronologies,and contain a certain amount of information about changes in the external environment,and the parameters do not show significant altitude differences.The four density chronologies at the same altitude were significantly correlated,and the density index changes are relatively synchronized,which may carry similar climate and environmental information.(6)The results of the response analysis of the tree ring density chronologies and climatic factors at different altitudes show that the tree ring early wood density and minimum density were significantly positively correlated with the air temperature from May to August,and the relative humidity was reversed.High temperature slows down the rate of cell division and expansion of tree ring cells due to insufficient water supply,resulting in individual cells becoming smaller and thicker,resulting in greater wood density.The density of latewood is mainly positively correlated with the temperature from July to September and the largest correlation coefficient appears in July.Higher air temperature promotes the accumulation of photosynthetic products,prolongs the process of cell wall thickening,and promotes the formation of larger density.(7)Under the background of rapid warming.The positive correlation between the density of early wood and the temperature from June to August is strengthened,and the relative humidity is conversely.The positive correlation between early wood density below 2000 m and July was significantly enhanced,and the negative correlation with July precipitation was significantly enhanced.The positive correlation between the density of late wood and the temperature from June to July was strengthened,and the relative humidity is conversely,and the occurrence of sample point below 2200 m has a negative response to the precipitation in July.It can be seen that the densities strongly reflects drought.