AIM: Trees need to avoid frost damage to their young leaves by leafing out after the occurrence of the last frost, yet they also need to start photosynthesis early in the season to achieve sufficient growth. This trade‐off leads to the hypothesis that ‘safety margins’ against spring frost should become shorter, the longer the winter duration, perhaps reaching an asymptotic limit where frost damage would occur in most years. Physiologically, shorter safety margins in high‐latitude ecotypes might be achieved by lower degree‐day requirements for leaf‐out, compared to low‐latitude ecotypes. LOCATION: Europe. TIME PERIOD: 1902–2009. MAJOR TAXA STUDIED: Temperate trees. METHODS: Using herbarium collections of Acer platanoides, Carpinus betulus, Fagus sylvatica and Prunus spinosa made over 108 years at 40° to 60° N latitude, we related historic leaf‐out dates to winter and spring temperatures (chilling and degree‐days), winter duration, and date of last frost occurrence in the relevant years and locations. RESULTS: In all species, frost safety margins decreased towards high‐latitude regions with long winters, with each day increase in winter duration reducing frost safety margins by 0.48 days in Fagus and 0.32–0.21 days in Prunus, Acer and Carpinus. These latitudinal differences correlate with northern ecotypes’ shorter degree‐day requirements for leaf‐out. MAIN CONCLUSIONS: The decline in spring frost safety margins in regions with long winters supports the new hypothesis that species may reach their geographic range limit where they ‘bump up’ against experiencing regular frost injury to their young leaves. Larger datasets are necessary to further corroborate our hypothesis and future efforts should thus be directed toward increasing the latitudinal range of existing phenological databases.

中文翻译：

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北方生态型广泛树木的叶子脱落需要较少的春季变暖，从而增加了寒冷范围限制春季霜冻的风险

目的：树木需要在最后一次霜冻发生后通过生叶来避免对其幼叶的霜害，但它们也需要在季节早期开始光合作用以实现足够的生长。这种权衡导致假设春季霜冻的“安全裕度”应该变短，冬季持续时间越长，可能达到一个渐近极限，在大多数年份都会发生霜冻损害。从生理上讲，与低纬度生态型相比，高纬度生态型中较短的安全裕度可能通过较低的脱叶度日要求来实现。地点：欧洲。时间段：1902-2009。研究的主要分类群：温带树木。方法：使用北纬 40° 至 60° 108 年来收集的 Acer platanoides、Carpinus betulus、Fagus sylvatica 和 Prunus spinosa 的植物标本馆，我们将历史上的落叶日期与相关年份和地点的冬季和春季温度（寒冷和度数）、冬季持续时间以及最后一次霜冻发生的日期相关联。结果：在所有物种中，冬季长的高纬度地区的霜冻安全边际降低，冬季持续时间每增加一天，山毛榉的霜冻安全边际减少 0.48 天，李属、宏碁和松果树的霜冻安全边际减少 0.32-0.21 天。这些纬度差异与北方生态型对叶出的较短度日要求相关。主要结论：冬季漫长地区春季霜冻安全边际的下降支持了新假设，即物种可能会达到其地理范围限制，在那里它们“撞上”幼叶遭受定期霜冻伤害。