A wetness index derived from tree-rings in the Mt. Yishan area of China since 1755 AD and its agricultural implications

Dendroclimatological techniques were employed to investigate the relationship between Chinese Pinus (Pinus tabulaeformis Carr.) growth and climatic variability in the Mt. Yishan region of Shandong Province, China, over the past 253 years. Using regression analysis, the wetness index (WI) was reconstructed for the Mt. Yishan area for the period 1755–2007 AD based on tree-ring widths; predictor variables accounted for 40 % of the variance. The reconstructed time-series displayed an increasing trend after the late 1960s. Both the estimated and the observed WI for May–August were better correlated with precipitation than temperature during the period 1958–2007 AD, indicating that the contribution of precipitation to the WI was larger than temperature in the study area. The reconstructed WI was compared with the dryness/wetness index of China and land areas that were affected by droughts and floods using the agricultural statistics for Shandong Province. In addition, the WI time-series corresponded well with the peanut yield in Shandong Province at high frequency, which may be reasonable in the context of agriculture in Shandong. The 3-, 5- to 6- and 9- to 10-year periodicities detected in the time-series suggested that the reconstructed WI in the Mt. Yishan area may be related to large-scale climate variations.