Climate-growth Relationships Of Spruce-fir And Their Connection With Large-scale Climate Change In Xiaoxing’an Mountains, China

Spruce-fir forests are one of the most important forests in Xiaoxing’an Mountains. In recent decades, growth declines of valley spruce-fir forests in this area are very significant. It is critical to explore spruce-fir growth-climate relationships for better understanding the effects of global warming on boreal forest ecosystem and forest declines. Three tree-ring standard chronologies of Abies nephrolepis and two Picea koraiensis at different elevations in Fenglin National Nature Reserve from Xiaoxing’an Mountains were developed by using standard dendrochronological methods.Relationships between these three Abies nephrolepis chronologies and local (mainly temperature and precipitation) and large-scale climatic factors were analyzed. Results showed that radial growth of Abies nephrolepis in this region is mainly limited by air temperature, while the effect of precipitation is relatively weak. Three Abies nephrolepis chronologies were negatively correlated with minimum and mean temperatures in the current growth season (p<0.01) and total precipitations in March (p<0.05). Radial growths of Abies nephrolepis in different elevations, however, respond differently to monthly mean temperatures and total precipitations. The effects of climatic factors (monthly temperature and precipitation) on tree growths in high elevations are significantly stronger than that in low elevations. Correlation analysis between three Abies nephrolepis chronologies and the index of Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) indicated that radial growths of Abies nephrolepis could be connected with large-scale climate changes in Pacific and Atlantic. A greater effect of AMO on tree growths appeared in low elevation sites, while greater effect of PDO on tree growths was in two high elevation sites. The declines of valley spruce-fir forests in this region in recent years could be related to phase changes of AMO and PDO, which change the regime of temperature and precipitation in this region. Higher minimum temperatures in growing season caused by large-scale climate (AMO and PDO) changes decrease net photosynthesis and increase respirations of Abies nephrolepis in this area. Thus, the physiological recession of tree growth will appear. In addition, higher temperatures may result in the disappearance of patchy permafrosts in valleys, which will decrease water availability of soil in growing seasons. Therefore, spruce-fir forest declines in valleys in this region will occur.Two Picea koraiensis chronologies analyzed showed that radial growth of Picea koraiensis in this region is mainly limited by air temperature, while the effect of precipitation is relatively weak. Two Picea koraiensis chronologies were negatively correlated with minimum temperatures in the current growth season (p<0.05). Correlation analysis between two Picea koraiensis chronologies and the index of PDO and AMO indicated that radial growths of Picea koraiensis could be connected with large-scale climate changes in Pacific and Atlantic. A greater effect of PDO on tree growths appeared in low elevation sites, while greater effect of AMO on tree growths was in high elevation sites. The declines of valley spruce-fir forests in this region in recent years could be related to phase changes of AMO and PDO, which change the regime of temperature and precipitation in this region. Higher minimum temperatures in growing season caused by large-scale climate (AMO and PDO) changes decrease net photosynthesis and increase respirations of Picea koraiensis also in this area. Thus, the physiological recession of tree growth will appear. In addition, higher temperatures may result in the disappearance of patchy permafrosts in valleys, which will decrease water availability of soil in growing seasons. Therefore, spruce-fir forest declines in valleys in this region will occur.In this study, through the the PDSI index Picea koraiensis chronology analysis found that1980warming and drying phenomenon may be the dominant factor for this incentive, segment climate response to the results of the analysis also shows that the warming after1980may be the main cause of the region spruce large area recession.