Summer climate implications of tree-ring latewood width: a case study of Tsuga longibracteata in South China

Summer climate variability in South China at decadal scales is not well understood due to the relatively short meteorological records and the scarcity of paleo-proxies. Herein, we explore the potential of using tree-ring latewood width (LWW) from Tsuga longibracteata to reconstruct summer climatic factors. Latewood usually forms in the mid- to late growing season, at least partly during summer. Tree-ring samples were collected at three sites (HS, QSZ, and SJD) close to the northern boundary of Guangxi province. We built three LWW chronologies and three adjusted LWW chronologies (LWWadj) after the removal of the influence of earlywood on latewood growth. Bootstrapped correlation and response analyses indicate that the LWW chronologies are significantly correlated with summer climatic factors, and the LWWadj chronologies show much higher correlations. The extent to which summer climatic signals can be extracted from LWWadj is site-dependent. At the well-drained sites (QSZ and SJD) with abundant sunshine, LWWadj shows significant positive correlations with July–August Standardised Precipitation-Evapotranspiration Index (SPEI), owing to the positive response to precipitation and the negative response to temperature. In contrast, LWWadj only exhibits positive responses to July temperature on north-oriented slope (HS) with high water-holding capacity. Nearly 37% of the variance in the regional SPEI can be explained by the LWWadj chronology from the forest stand (QSZ) on well-drained southeast-facing slope with less endogenous disturbances. These results indicate that there is a great potential of using LWWadj to reconstruct summer SPEI in South China when suitable sampling sites are selected.