Increasing climate sensitivity of subtropical conifers along an aridity gradient

Abstract Subtropical forests are an important but still poorly understood component of the global carbon cycle and global biodiversity. If climate continues to change as anticipated, increasing drought may affect the composition and structure of many subtropical forests. Understanding the environmental conditions that determine drought sensitivity across subtropical ecosystems and trees species will help accurately predict their response to climate change and inform the best mitigation and protection strategies. To identify the broad-scale drivers of drought sensitivity, we collected a large network of ring-width chronologies along a broad climate gradient that spans from east to west of the Yunnan-Guizhou Plateau (YGP), in southwestern China. Our network includes growth data from 10 trees species in 28 old growth subtropical coniferous sites. We used tree ring analyses, Redundancy Analysis (RDA), and linear mixed effects models to assess how drought responses varied geographically, climatically, and taxonomically. We found that aridity exerted the strongest limitation in our study area, implying that subtropical forest responses to drought may be more complex than commonly assumed. Moreover, we found that drought intensity during dry season, proxied by aridity index, is a stronger driver of drought sensitivity than stand characteristics and microenvironment. Further increases in drought frequency and dry season drought intensity in the region associated with climate change may pose a larger-than-expected threat to the growth, and ultimately persistence, of many subtropical coniferous forests.