Extreme droughts decrease the growth and resilience of Juniperus rigida in the northern edge but not in the southern

Abstract

Impending climate change is anticipated to exacerbate the frequency and severity of extreme droughts, significantly affecting tree growth and distribution ranges. A critical endeavor in predicting how tree species will respond to more frequent and intense severe droughts is assessing the drought sensitivity and resilience of tree growth across a species' different range. However, the variation in tree growth resistance and resilience to extreme droughts across different distribution range edges have received little attention. In this study, we analyzed tree ring width data from 596 trees across 19 sites, encompassing the northernmost and southernmost distribution limits of Juniperus rigida in China. Our objectives were to delineate patterns of growth resistance, recovery and resilience to extreme droughts between northern and southern populations, and to assess their driving factors. Our findings revealed that the drought events significantly reduced the tree growth. Specifically, the tree growth has exhibited a decreasing trend in the northern distribution range limit, but an increasing trend at southern range limit since 1996, due to the more frequent and severe droughts in the northern region than in the southern. Furthermore, although the tree growth resistance and resilience were significantly higher in the northern limits than those in the southern, more frequent droughts will reduce their resistance and resilience. In addition, the growth resistance and resilience were also affected by factors such as tree age, pre-drought growth (e.g. mean growth rate and variability), and the interaction between drought characteristics and pre-drought growth. We conclude that J. rigida trees exhibit greater resistance and resilience to drought at their northern range limits compared to their southern counterparts. However, the increasing frequency and severity of droughts in the northern expose these trees to more persistent drought conditions, which could ultimately result in a decline in resilience and growth.