Abstract: Background, aim, and scope Due to the lack of clear ring boundaries in most tropical tree species, tree ring studies in tropical region are still rare. Tree ring stable isotopes variations generally record stronger climatic signals compared with ring width, thus have great potential in dendroclimatical study in tropical region. Moreover, intra-annual variations of tree ring stable isotopes could provide seasonal climatic information. The present study aims to investigate the potential of tree ring width and stable oxygen isotope variations of a tropical pine species in Xishuangbanna, southwestern China. Materials and MethodsThe present study developed tree ring-width and stable oxygen isotope chronologies in earlywood (δ18OEW) and latewood (δ18OLW) of Pinus kesiya Royle ex Gordon (Simao pine) in Xishuangbanna. We performed correlation analyses between tree ring width, δ18OEW and δ18OLW and climatic factors such as monthly mean temperature, monthly precipitation and Standardized Precipitation Evapotranspiration Index (SPEI) during the period 1985—2018. Spatial representatives were investigated by correlating δ18OEW and δ18OLW with regional precipitation. The relationships between tree ring oxygen isotope and El Niño-Southern Oscillation (ENSO) were also investigated. Results The mean values of δ18OEW and δ18OLW were 23.08‰ and 23.83‰, respectively, and both δ18OEW and δ18OLW showed decreasing trends. Tree ring-width chronology of P. kesiya in Xishuangbanna correlated negatively with the temperature and positively with precipitation in July of the previous year. δ18OEW chronology were negatively correlated with precipitation in the early growing season (May), whereas δ18OLW mainly recorded precipitation signal at the end of the growing season (August). δ18OEW was positively correlated with SPEI in April, and negatively correlated with SPEI in May, whereas δ18OLW was negatively correlated with SPEI in August. Both δ18OEW and δ18OLW were positively correlated with El Niño and negatively correlated with Southern Oscillation Index. Discussion Our study showed that tree growth of P. kesiya in Xishuangbanna is not sensitive to climate variables. The mean value of δ18OEW (23.08‰) and δ18OLW (23.83‰) is similar, which may due to the low variability of rainfall δ18O during the growing season. The decreasing trends of both δ18OEW and δ18OLW could be related to the decreasing of the contribution of fog water to the tree water use in Xishuangbanna. δ18OEW and δ18OLW were negatively correlated with regional precipitation in May and August, respectively. Strong correlation between tree-ring δ18O and regional precipitation confirmed that tree ring δ18O has the potential to reconstruct regional precipitation variability in the tropical regions. Moreover, tree ring δ18O showed high correlation with ENSO index, which implies that ENSO has an important influence on the hydro-climate in the study region. Conclusions Tree ring δ18OEW mainly records precipitation signal in May of the early growing season, while δ18OLW mainly records precipitation signal in August at the end of the growing season (latewood formation period). The δ18OEW and δ18OLW can represent the regional precipitation patterns in May and August, respectively. Tree-ring was δ18O mainly positively correlated with El Niño and negative correlation with the Southern Oscillation Index. Recommendations and Perspectives This study indicates that earlywood and latewood δ18O of P. kesiya in this region have high potential to reconstruct hydro-climate history in different seasons.
Keywords: Asian tropics; stable oxygen isotope; earlywood and latewood; climate response; spatial correlation