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 influenced by ENSO events. Analyzing the relationship between radial growth of Picea wilsonii in this mountain and ENSO events can enhance our understanding of the impact of climate change on tree growth in montane forests within the CTZ. Residual 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 multivariate 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 Niña events while the narrow-rings with El Niño events, moreover, significant slowdowns in radial growth were observed during both El Niño event years (P < 0.01) and three subsequent years after such an event occurred (P < 0.01) for P. wilsonii in Guandi Mountains.