Department of Biology, University of Western Ontario, London, Ontario, Canada; Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, Quebec City, QC, Canada.
Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, Quebec City, QC, Canada.
Sci Total Environ. 2022 Dec 10;851(Pt 2):158062. doi: 10.1016/j.scitotenv.2022.158062. Epub 2022 Aug 15.
Understanding boreal/hemi-boreal forest growth sensitivity to seasonal variations in temperature and water availability provides important basis for projecting the potential impacts of climate change on the productivity of these ecosystems. Our best available information currently comes from a limited number of field experiments and terrestrial biosphere model (TBM) simulations of varying predictive accuracy. Here, we assessed the sensitivity of annual boreal/hemi-boreal forest growth in Canada to yearly fluctuations in seasonal climate variables using a large tree-ring dataset and compared this to the climate sensitivity of annual net primary productivity (NPP) estimates obtained from fourteen TBMs. We found that boreal/hemi-boreal forest growth sensitivity to fluctuations in seasonal temperature and precipitation variables changed along a southwestern to northeastern gradient, with growth limited almost entirely by temperature in the northeast and west and by water availability in the southwest. We also found a lag in growth climate sensitivity, with growth largely determined by the climate during the summer prior to ring formation. Analyses of NPP sensitivity to the same climate variables produced a similar southwest to northeast gradient in growth climate sensitivity for NPP estimates from all but three TBMs. However, analyses of growth from tree-ring data and analyses of NPP from TBMs produced contrasting evidence concerning the key climate variables limiting growth. While analyses of NPP primarily indicated a positive relationship between growth and seasonal temperature, tree-ring analyses indicated negative growth relationships to temperature. Also, the positive effect of precipitation on NPP derived from most TBMs was weaker than the positive effect of precipitation on tree-ring based growth: temperature had a more important limiting effect on NPP than tree-ring data indicated. These mismatches regarding the key climate variables limiting growth suggested that characterization of tree growth in TBMs might need revision, particularly regarding the effects of stomatal conductance and carbohydrate reserve dynamics.
了解北方/温带森林对季节性温度和水分变化的生长敏感性，为预测气候变化对这些生态系统生产力的潜在影响提供了重要依据。我们目前最好的信息来自数量有限的实地实验和不同预测精度的陆地生物圈模型（TBM）模拟。在这里，我们使用大量树木年轮数据集评估了加拿大北方/温带森林年生长对季节性气候变量年波动的敏感性，并将其与从 14 个 TBM 获得的年净初级生产力（NPP）估计的气候敏感性进行了比较。我们发现，北方/温带森林对季节性温度和降水变量波动的生长敏感性沿着西南到东北梯度变化，在东北和西部，生长几乎完全受温度限制，在西南部受水分可用性限制。我们还发现了生长气候敏感性的滞后，生长主要由形成年轮前夏季的气候决定。对相同气候变量的 NPP 敏感性分析产生了类似的 NPP 估计从除三个 TBM 之外的所有 TBM 产生的从西南到东北的生长气候敏感性梯度。然而，树木年轮数据分析和 TBM 分析的 NPP 敏感性分析表明，限制生长的关键气候变量存在矛盾的证据。虽然 NPP 分析主要表明生长与季节性温度之间存在正相关关系，但树木年轮分析表明温度与生长呈负相关关系。此外，大多数 TBM 中降水对 NPP 的积极影响弱于降水对基于树木年轮的生长的积极影响：温度对 NPP 的限制作用比树木年轮数据所表明的更为重要。这些关于限制生长的关键气候变量的不匹配表明，TBM 中树木生长的特征可能需要修订，特别是关于气孔导度和碳水化合物储备动态的影响。
