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The monthly mean temperature for October in the Fenglin National Natural Reserve of Wuying,in Heilongjiang province,was reconstructed for the period running from 1796 to 2004 using RES tree ring chronology.The explained variance of the reconstruction is 34.8%.In the past 209 years,there are 4 colder and 4 warmer periods according to the reconstructed series.A period of 3.33-year is found significant based on the power spectrum method.Abrupt changes are also detected in the reconstructed series with 30-year time scale based on the smoothing t-test,smoothing F-test and Le Page test methods.Significant abrupt changes in mean value are observed for around 1871 and 1900,and a significant abrupt change in standard deviation is observed for around 1851.