Data from: Frost hollows of the boreal forest: a spatiotemporal perspective

1. Frost hollows (FH) are small, confined lichen-dominated ecosystems surrounded by lichen woodlands. FH are impacted by repetitive frosts occurring during the growing season. We evaluated the dynamics of FH across the boreal forest in eastern Canada and assessed the influence of latitude as the main geoclimatic factor controlling their development. 2. The distribution and abundance of FH along 39 longitudinal transects were based on aerial photographs and field validation. Black spruce (Picea mariana) in FH and adjacent woodlands were sampled for age determination, year of tree establishment, height growth rate of spruce, and intensity and frequency of frost rings. 3. Most FH are located in the southern part of the boreal forest, in depressions bordered by dry, open, lichen woodlands. The inception and development of FH are not dependent on latitude but rather on the presence of lichen woodlands. Frost-induced thúfurs and frost rings were more frequent and abundant in the southernmost FH, whereas the northernmost FH were devoid of thúfurs. Black spruce established synchronously in FH across the boreal forest, an indication of a climatic control associated with cloudier, humid conditions reducing radiative frost activity. Most FH spruce established after 1933 and peaked in the 1980s. Fewer frost events were recorded in the 1980s than in the 1990s. In the latter decade, frost events became more frequent, intense and synchronous across the boreal forest. 4. Synthesis. The distribution of frost hollows (FH) is related to the presence of dry lichen woodlands that exacerbate frost activity during the growing season. Synchronous frost-ring frequency across the biome also suggests that shared climatic conditions, in particular freezing temperature, humidity and cloudiness, are at the origin of the dynamics of FH. A longer growing season creates propitious conditions for a higher frequency of frost events and more intense soil cryoturbation. FH are climate-sensitive ecosystems which can be used as proxies of the impact of global change on the boreal biome.

1. 霜洼（Frost hollows, FH）是一类小型、封闭的以地衣为主导的生态系统，被地衣林地环绕。霜洼会受到生长季内重复霜冻的干扰。本研究对加拿大东部寒温带针叶林内的霜洼动态开展系统评估，并以纬度作为调控霜洼发育的核心地球气候因子，分析其影响效应。
2. 本研究通过航空影像结合野外验证，对沿39条经度样带分布的霜洼的分布范围与种群丰度进行了统计。针对霜洼及其邻近林地中的黑云杉（Picea mariana）开展采样工作，测定其树龄、林木定植年份、云杉高生长速率，以及霜环的强度与发生频率。
3. 绝大多数霜洼分布于寒温带针叶林的南部区域，坐落于以干燥开阔的地衣林地为边界的洼地之中。霜洼的起始与发育并不受纬度调控，而是依赖于地衣林地的存在。霜冻诱导的霜冻土丘与霜环在最南部的霜洼中更为频发且丰度更高，而最北部的霜洼则未出现霜冻土丘。寒温带针叶林内的黑云杉在霜洼中同步完成定植，这表明气候调控作用显著：多云湿润的环境会抑制辐射霜冻的发生。绝大多数霜洼内的黑云杉于1933年后完成定植，并在20世纪80年代达到定植峰值。20世纪80年代记录到的霜冻事件少于90年代；在90年代这十年间，寒温带针叶林内的霜冻事件愈发频繁、强烈，且发生同步性更强。
4. 综合分析结果显示：霜洼（FH）的分布与干燥地衣林地的存在密切相关，这类林地会加剧生长季内的霜冻活动。寒温带针叶林生物群区内同步发生的霜环频率也表明，共同的气候条件——尤其是低温、湿度与云量状况——是驱动霜洼动态变化的核心成因。更长的生长季会为霜冻事件的高频发生与更强的土壤冻融扰动创造有利条件。霜洼是一类气候敏感型生态系统，可作为全球变化对寒温带针叶林生物群区影响的代用指标。