Effect of Spline Function Step Size on Relationship between Tree-ring Width Chronology and Climate

Tree-ring samples collected from four sites in Toutun River and Santun River basins on the north slope of middle Tianshan Mountains were used to develop tree-ring width chronologies at different spline function step size.Analysis on the effect of different spline function step size on correlation between tree-ring width chronology and climate showed:(1)With increase of spline function step size,the curves of correlation coefficient between two tree-ring width chronologies at low forest limit and precipitation during prior July to current June of a related meteorological station all showed changes of increase in former part and decline in posterior part,but with local differences.The best step sizes were 40 years and 30 years,respectively.(2)With increase of spline function step size,the curves of correlation coefficient between two tree-ring width chronologies at up forest limit and temperature during current February to March of a related meteorological station all showed a smooth logarithmic form with increase in former part and no change in latter part.The best step sizes were 220 years and 185 years,respectively.(3)It was found that the best step size of spline function conserved more information than the ones which were given on base of traditional method or half of length of public tree-ring chronology series.