Response to ENSO Events in the Radial Growth of Picea wilsonii in Guandi Mountains,China
Guandi Mountains are situated in the climate transition zone(CTZ)of North China,which is strongly influ-enced by ENSO events.Analyzing the relationship between radial growth of Picea wilsonii in this mountain and ENSO e-vents can enhance our understanding of the impact of climate change on tree growth in montane forests within the CTZ.Re-sidual tree-ring width chronologies(RES)were established for P.wilsonii at an altitude of 2 000-2 200 m using collected tree-ring samples from Guandi Mountains.Pearson correlation analysis was employed to examine the correlation between tree-ring width index(RWI)and monthly mean temperature(MMT),monthly precipitation(MTP),as well as the multi-variate ENSO index(MEI).Cross-wavelet transform analysis(XWT)was utilized to determine the temporal frequency of ENSO events within the residual chronology of P.wilsonii.Paired t-tests were conducted to compare the difference in spruce response to ENSO events between wide and narrow tree-rings.Superimposed epoch analysis(SEA)was applied to identify changes in radial growth pattern of P.wilsonii following typical ENSO events.The main findings are as follows:(1)Radial growth of spruce trees was primarily influenced by MMT during the previous pre-growing season(p3-p5),as well as the current growing season(c7,c9).Additionally,it showed a positive response to MTP at both the start(pp5)and the end(pp9)stages of the two previous years'growing seasons.(2)The RES chronology of P.wilsonii exhibited a significantly negative correlation with the MEI from previous May to current March(p5-c3)(P＜0.05),indicating a co-periodic oscillation lasting 2-5.5-years.(3)The wide-rings predominantly occurred during La Nina events while the nar-row-rings with El Nino events,moreover,significant slowdowns in radial growth were observed during both El Nino event years(P＜0.01)and three subsequent years after such an event occurred(P＜0.01)for P.wilsonii in Guandi Mountains.
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