Abstract: Using tree-ring width chronology of Picea crassifolia in the middle region of Qilianshan Mountains, we studied the relationship between tree-ring and climate factors, and reconstructed spring precipitation and summer temperature in the middle region of Qilianshan Mountains. The results indicated that the tree-ring width is sensitive to spring precipitation, and summer temperature has influence of different degree on trees of different altitudes. High temperature of summer is harm to tree growth. There is positive correlation between tree-ring width and spring precipitation. In spring, the rainy season has yet not arrived, and precipitation is deficient. The soil water becomes the limited factor to tree-ring growth. Little precipitation leads to the shortage of soil water, so the tree-ring width is narrow. Summer temperature has negative influence on the growth of tree~ring. In summer, monsoon brings precipitation to the middle region of Qilianshan Mountains. In general, the tree is satisfied with the water situation, but high temperature results in intense evaporation. By influencing soil water, summer temperature limits tree-ring growth. So high temperature of summer corresponds to the narrow tree-ring. But summer temperature cannot limit the tree growth in middle altitude. Because, in summer, the altitude of maximum precipitation in Qilianshan Mountains is just at 2 700-2 800 m. Enough rain reduces the negative effect that high temperature imposes on the tree growth. The reconstructed spring precipitation had the periods of 69- and 21-year, and it indicated that the middle region of Qilianshan Mountains was mainly in a humid state since A. D. 1770. Summer temperature had 2-year to 4-year periods. Now, this area is dry and warm, and it shows the warmer and drier tendency.

Key words: Qilianshan mountains, tree-ring chronology, response relationship, climate reconstruction