Climate response of radial growth of Picea crassifolia in Qilian Mountains of northwestern China.

To investigate the climate response of radial growth of Picea crassifolia at the lower tree line in the middle Qilian Mountains, northwestern China, relationships of standardized chronologies of annual, earlywood and latewood width to monthly mean temperature and monthly total precipitation were analyzed by methods of correlation and pointer year analysis. The results of the relationship between chronologies and temperatures and precipitation showed that width of annual ring, earlywood and latewood were significantly negatively correlated with monthly mean temperature in June and July. Annual and earlywood width were significantly positively correlated with monthly total precipitation in March, May and June, and negatively correlated with monthly total precipitation in September. Earlywood width was more sensitive to climate than latewood width, which was insignificant with precipitation. The results of pointer year analysis revealed that the summer temperatures in years when narrow rings formed were higher than the mean summer temperatures synchronization, while the summer precipitation in those years was lower than mean summer precipitation synchronization, and the reverse was also true in years when large rings were formed. The results indicate that more precipitation in spring and summer is helpful for radial growth while warmer summer restricts the radial growth of P. crassifolia at the lower tree line in the middle Qilian Mountains, northwestern China.