Sufficient conditions for climate-driven range expansion of a boreal conifer, Alaska, 2019-2021

Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra, thereby reducing albedo, altering C-cycling (carbon-cycling), and changing global climate, yet the patterns and processes of this biome shift remain unclear. We describe the 20th century colonization of an Arctic basin by a widespread boreal conifer, Picea glauca, 40 km (kilometer) north of the nearest established treelines. The population approximately doubled each decade, with radial growth in main stems increasing exponentially and correlating positively to July air temperature. Juvenile height and adult lateral growth were 90% faster than at established treelines. This climate-forced range expansion, cast in the context of invasion theory, informs forecast models of vegetation change with the ecological conditions driving this biome shift. While surpassing temperature thresholds is a necessary condition for boreal forest advance, our empirical results indicate high soil nutrient availability, deep snow, and winter winds facilitate long-distance dispersal and promote recruitment.

前所未有的现代增温速率预计将推动北方森林（boreal forest）向北扩张至北极苔原（Arctic tundra），从而降低反照率（albedo）、改变碳循环（C-cycling/carbon-cycling）并影响全球气候，但该生物群系（biome）转变的模式与过程仍不明朗。本研究报道了20世纪以来，一种广泛分布的北方针叶树种——白云杉（Picea glauca）在距离最近现存林线（treelines）40公里的北极盆地实现定植的现象。该种群数量每十年约翻一番，其主茎的径向生长呈指数增长趋势，且与七月气温呈显著正相关。幼树高度与成年个体的侧向生长速率均比现存林线处快90%。本研究结合入侵理论（invasion theory）对这一气候驱动的分布区扩张展开分析，为揭示驱动该生物群系转变的生态条件提供了植被变化预测模型的构建依据。尽管突破温度阈值是北方森林向北扩张的必要条件，但本研究的实证结果表明，高土壤养分有效性、深厚积雪与冬季风能够促进长距离扩散并助力种群补充（recruitment）。