Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton E3B 5A3, Canada.
Proc Natl Acad Sci U S A. 2023 Jan 10;120(2):e2212780120. doi: 10.1073/pnas.2212780120. Epub 2023 Jan 3.
Large projected increases in forest disturbance pose a major threat to future wood fiber supply and carbon sequestration in the cold-limited, Canadian boreal forest ecosystem. Given the large sensitivity of tree growth to temperature, warming-induced increases in forest productivity have the potential to reduce these threats, but research efforts to date have yielded contradictory results attributed to limited data availability, methodological biases, and regional variability in forest dynamics. Here, we apply a machine learning algorithm to an unprecedented network of over 1 million tree growth records (1958 to 2018) from 20,089 permanent sample plots distributed across both Canada and the United States, spanning a 16.5 °C climatic gradient. Fitted models were then used to project the near-term (2050 s time period) growth of the six most abundant tree species in the Canadian boreal forest. Our results reveal a large, positive effect of increasing thermal energy on tree growth for most of the target species, leading to 20.5 to 22.7% projected gains in growth with climate change under RCP 4.5 and 8.5. The magnitude of these gains, which peak in the colder and wetter regions of the boreal forest, suggests that warming-induced growth increases should no longer be considered marginal but may in fact significantly offset some of the negative impacts of projected increases in drought and wildfire on wood supply and carbon sequestration and have major implications on ecological forecasts and the global economy.
未来，森林干扰的大幅增加，将对寒冷限制的加拿大北方森林生态系统的未来木材纤维供应和碳固存构成重大威胁。鉴于树木生长对温度的高度敏感，变暖引起的森林生产力增加，有可能减少这些威胁，但迄今为止的研究工作产生了相互矛盾的结果，原因是数据可用性有限、方法偏差以及森林动态的区域差异。在这里，我们应用机器学习算法，分析了来自加拿大和美国 20,089 个永久性样地超过 100 万条树木生长记录（1958 年至 2018 年）的空前网络，这些记录分布在跨越 16.5°C 的气候梯度上。然后，使用拟合模型来预测加拿大北方森林中最丰富的六种树种的近期（2050 年代）生长情况。我们的研究结果表明，对于大多数目标物种，热能的增加对树木生长有很大的积极影响，导致在 RCP4.5 和 8.5 下，气候变化导致树木生长增加 20.5%至 22.7%。这些增长的幅度在北方森林的较冷和较湿润地区达到峰值，这表明变暖引起的生长增加不应再被视为微不足道，实际上可能会显著抵消预计增加的干旱和野火对木材供应和碳固存的负面影响，并对生态预测和全球经济产生重大影响。
