Spatial patterns of precipitation-induced moisture availability and their effects on the divergence of conifer stem growth in the western and eastern parts of China’s semi-arid region

Abstract

Conifer forests in semi-arid regions are fragile and sensitive to climate change. As the climate changes, more frequent drought and higher temperatures may reduce conifer stem growth in these regions, but moistening and lengthening of the growing season may improve tree growth conditions. The relative influences of specific climate parameters on conifer stem growth, however, remain poorly quantified in Asian regions. We analyzed conifer stem growth responses to climate in the semi-arid region of China. Our analyses show a wetting trend since 1960 in the western part of this region, versus a drying trend in the east. We used tree-ring width data from a network of 33 forests as inputs for the process-based Vaganov–Shashkin-Lite growth model to assess how moisture patterns have affected tree growth in this region, and then used the resulting model to predict changes in tree growth during the 21st century. Tree-ring growth in our study region is mainly controlled by precipitation and soil moisture, and shows significant impacts of antecedent moisture conditions (the “water memory effect”). However, the contribution of soil moisture to tree growth was stronger in the eastern vs. western sub-regions (77% vs. 69%). Pointer-year analysis showed significantly stronger growth responses to soil moisture in the early growing season (April to June) in positive pointer years in the eastern sub-region, but showed no difference in the western sub-region. These results indicate that tree-ring growth in the eastern sub-region is more vulnerable to moisture availability. Our simulations suggest that tree growth will increase slightly under the RCP 4.5 and RCP 8.5 scenarios in both sub-regions, possibly due to the prolongation of the growing season caused by climate warming.