Institute of Culture and Environment, Alaska Pacific University, Anchorage, AK, USA.
Environment and Natural Resources Institute, University of Alaska Anchorage, Anchorage, AK, USA.
Nature. 2022 Aug;608(7923):546-551. doi: 10.1038/s41586-022-05093-2. Epub 2022 Aug 10.
Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra, thereby reducing albedo, altering carbon cycling and further changing climate, yet the patterns and processes of this biome shift remain unclear. Climate warming, required for previous boreal advances, is not sufficient by itself for modern range expansion of conifers forming forest-tundra ecotones. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented advancing at rates following the last glacial maximum (LGM). Here we describe a population of white spruce (Picea glauca) advancing at post-LGM rates across an Arctic basin distant from established treelines and provide evidence of mechanisms sustaining the advance. The population doubles each decade, with exponential radial growth in the main stems of individual trees correlating positively with July air temperature. Lateral branches in adults and terminal leaders in large juveniles grow almost twice as fast as those at established treelines. We conclude that surpassing temperature thresholds, together with winter winds facilitating long-distance dispersal, deeper snowpack and increased soil nutrient availability promoting recruitment and growth, provides sufficient conditions for boreal forest advance. These observations enable forecast modelling with important insights into the environmental conditions converting tundra into forest.
预计前所未有的现代变暖速度将使北方森林推进到北极苔原，从而降低反照率，改变碳循环，并进一步改变气候，但这种生物群落转变的模式和过程尚不清楚。以前北方森林推进所需要的气候变暖本身不足以支持形成森林-苔原生态过渡带的针叶树现代范围的扩张。以前，没有记录到高纬度的针叶树种群（北美北极树线的主要分类群）以末次冰盛期（LGM）之后的速度推进。在这里，我们描述了一个白冷杉（Picea glauca）种群以末次冰盛期之后的速度在远离现有树线的北极盆地推进，并提供了维持这种推进的机制的证据。该种群每十年翻一番，个体树木的主干呈指数级径向生长与 7 月气温呈正相关。成年树木的侧枝和大幼树的顶梢比现有树线的生长速度快近一倍。我们的结论是，超过温度阈值，加上冬季风有利于远距离扩散，更深的积雪层和增加的土壤养分供应促进了繁殖和生长，为北方森林的推进提供了足够的条件。这些观察结果使我们能够进行预测建模，深入了解将苔原转化为森林的环境条件。
