Subtropical forests are an important but poorly understood component of the global carbon cycle and global biodiversity. If climates continue to dry as anticipated, drought may change the composition and structure of subtropical forests in ways that can feed back to accelerate climate change. Therefore, understanding the environmental conditions that determine drought sensitivity of trees is critical to accurately predicting forest ecosystem responses to environmental change and supporting future mitigation and protection strategies. We addressed this goal by using a network of ring–width chronologies from 10 different trees species in 28 old growth subtropical coniferous sites along a broad climate gradient that spans from east to west of the Yunnan-Guizhou Plateau (YGP) in southwest China. We then used dendroecological analyses to identify the broad-scale drivers of drought sensitivity for the conifer trees in the region. We also used Principal Components Analysis (PCA) and linear mixed effects model (LMM) to assess how drought responses varied among differentspecies and different geographic locations.
Results/Conclusions
We found that carry-over effects of dry season drought had the strongest negative impacts on conifer growth, with weaker effects of winter-spring temperature. However, this effect was particularly strong in drier areas, suggesting that drought more strongly limits growth in subtropical coniferous forests than is commonly expected. Despite the large differences in species and habitats across the YGP, spatial heterogeneity in growth responses to climate were largely caused by spatial differences inclimate rather than species or microenvironment differences, implying that drought-coping mechanisms and limitations on growth are shared by species across different habitats. Our study highlights that subtropical forests in the YGP are a transition zone, separating drought-constrained forest populations to the west and temperature-constrained ones to the east. Our results also suggest that the expected increase in the frequency and intensity of droughts in the region associated with climate change may pose a largerthreat to the growth, and ultimately persistence, of subtropical coniferous forests than we commonly assumed.