Diverse responses of radial growth to climate across the southern part of the Asian boreal forests in northeast China

In the context of rapid warming, a better understanding of the spatially varying growth-climate responses of widely-distributed forests is essential for predicting the warming effects on trees, so as to guide the forest management. Here, we characterized the growth-climate relationships of the southern part of Asian boreal forests in northeast China at multiple levels to deduce how warming impacts tree growth. Specially, we aimed to distinguish climatic limitations to growth and clarify how local climate determines the response pattern. We established a tree-ring network, which includes 516 trees from 20 populations across the study area. We then correlated regional, population, and tree chronologies with climate data. In the north of the study area, radial growth responded positively to temperature before the growing season and precipitation during the growing season. In contrast, growth in the south responded positively to precipitation and negatively to temperature during the growing season. Thus, diverse growth patterns exist in response to climate. The extent to which growth was limited by climate varied along the latitudinal climate gradient. The north parts were limited by both frost and moisture, whereas the central-south parts were limited by moisture deficit induced by high temperature. The growth-climate response was quantified as the percentage of significant tree-level correlations. Through associating this quantitative index of each population with local climate, we confirmed the decisive role of local temperature in forming the spatial heterogeneity of response. We also confirmed that warming negatively affected tree growth across the study area. Our models predict that as warming continues, the trees threatened by high temperature in summer will increase by 45.5%–63.6% by the end of this century. All these findings warn of growth declines in Asian boreal forests, and suggest the need for urgent efficient regionally-specific measures to sustain the forest productivity in this region.