Response of radial growth of lakeshore tamarisk to changes in the water environment in extreme and arid regions

Using tree-ring chronology on samples from tamarisk,growing on beach bars at the shores of Lake West-Juyan,the terminal of the Heihe River in west China,the response of radial growth to the lake water environment has been measured and analysed by principal component analysis.The first principal component(PC1),which accounted for 53.3% of the total variance,reflects a common growth response of tree-rings,at three beach bars sites,to environmental factors.The second principle component(PC2) accounted for 30.7% of the variance and reflects tree-ring growth response at the three beach bars to other factors.Correlation analysis indicates that the relationship between PC1 and fluctuations in the lake water level during the growing season,from May to August,is statistically significant as is the relationship between PC2 and annual precipitation;PC2 seems slightly correlated with fluctuations in the groundwater level.The results show that fluctuations in the groundwater level are the major factor controlling tree-ring growth while groundwater is suitable for tree-ring growth.In contrast,precipitation is the major factor in maintaining basic growth of tamarisk. In this tree-ring chronology the response models of radial growth exhibit both spatial and temporal patterns.We are of the opinion that the difference between the maximum groundwater level and the water level in the Shiyang,Heihe and Talimu watersheds was brought about by the differences in local precipitation.