Laurentian Forestry Centre, Canadian Forest Service, Natural Resources Canada, Quebec City, QC, G1V 4C7, Canada.
Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, AB, T6H 3S5, Canada.
Proc Natl Acad Sci U S A. 2022 May 3;119(18):e2117464119. doi: 10.1073/pnas.2117464119. Epub 2022 Apr 27.
As northern latitudes experience rapid winter warming, there is an urgent need to assess the effect of varying winter conditions on tree growth and forest carbon sequestration potential. We examined tree growth responses to variability in cold-season (November–April) frequency of freeze days (FFD) over 1951 to 2018 using tree-ring data from 35,217 trees and 57 species at 4,375 sites distributed across Canada. We found that annual radial growth responses to FFD varied by species, with some commonalities across genera and clades. The growth of gymnosperms with late spring leaf-out strategies was negatively related to FFD; years with high FFD were most detrimental to the annual growth of Pinus banksiana, Pinus contorta, Larix lyalli, Abies amabilis, and Abies lasiocarpa. In contrast, the growth of angiosperms with early leaf-out strategies, namely, Populus tremuloides and Betula papyrifera, was better in the coldest years, and gymnosperms with intermediate leaf-out timing, such as widespread Picea mariana and Picea glauca, had no consistent relationship to FFD. Tree growth responses to FFD were further modulated by tree size, tree age, regional climate (i.e., mean cold-season temperature), and local site conditions. Overall, our results suggest that moderately warming winters may temporarily improve the growth of widespread pines and some high-elevation conifers in western Canada, whereas warming winters may be detrimental to the growth of widespread boreal angiosperms. Our findings also highlight the value of using species-specific climate-growth relationships to refine predictions of forest carbon dynamics.
随着北方纬度地区冬季迅速变暖，迫切需要评估冬季条件变化对树木生长和森林碳固存潜力的影响。我们利用加拿大 4375 个地点的 35217 棵树和 57 个树种的树木年轮数据，研究了 1951 年至 2018 年冷季（11 月至 4 月）冻雨日（FFD）频率变化对树木生长的响应。我们发现，物种对 FFD 的年径向生长响应存在差异，有些共性存在于属和进化枝中。具有晚春展叶策略的裸子植物的生长与 FFD 呈负相关；FFD 较高的年份对 Pinus banksiana、Pinus contorta、Larix lyalli、Abies amabilis 和 Abies lasiocarpa 的年生长最为不利。相比之下，具有早展叶策略的被子植物的生长，即 Populus tremuloides 和 Betula papyrifera，在最冷的年份更好，而展叶时间居中的裸子植物，如广泛分布的 Picea mariana 和 Picea glauca，则与 FFD 没有一致的关系。FFD 对树木生长的响应进一步受到树木大小、树龄、区域气候（即冷季平均温度）和局部地点条件的调节。总的来说，我们的结果表明，适度变暖的冬季可能会暂时改善加拿大西部广泛分布的松树和一些高海拔针叶树的生长，而变暖的冬季可能会对广泛分布的北方被子植物的生长不利。我们的研究结果还强调了使用特定物种的气候-生长关系来改进森林碳动态预测的价值。
