Climate change effects on tree reproduction are poorly understood, even though the resilience of populations relies on sufficient regeneration to balance increasing rates of mortality. Forest‐forming tree species often mast, i.e. reproduce through synchronised year‐to‐year variation in seed production, which improves pollination and reduces seed predation. Recent observations in European beech show, however, that current climate change can dampen interannual variation and synchrony of seed production and that this masting breakdown drastically reduces the viability of seed crops. Importantly, it is unclear under which conditions masting breakdown occurs and how widespread breakdown is in this pan‐European species. Here, we analysed 50 long‐term datasets of population‐level seed production, sampled across the distribution of European beech, and identified increasing summer temperatures as the general driver of masting breakdown. Specifically, increases in site‐specific mean maximum temperatures during June and July were observed across most of the species range, while the interannual variability of population‐level seed production (CVp) decreased. The declines in CVp were greatest, where temperatures increased most rapidly. Additionally, the occurrence of crop failures and low seed years has decreased during the last four decades, signalling altered starvation effects of masting on seed predators. Notably, CVp did not vary among sites according to site mean summer temperature. Instead, masting breakdown occurs in response to warming local temperatures (i.e. increasing relative temperatures), such that the risk is not restricted to populations growing in warm average conditions. As lowered CVp can reduce viable seed production despite the overall increase in seed count, our results warn that a covert mechanism is underway that may hinder the regeneration potential of European beech under climate change, with great potential to alter forest functioning and community dynamics.

中文翻译：

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由于夏季气温上升，欧洲山毛榉的桅杆普遍受损

尽管人口的恢复力依赖于足够的再生来平衡不断上升的死亡率，但人们对气候变化对树木繁殖的影响知之甚少。森林形成树种通常肥大，即通过种子产量的逐年同步变化进行繁殖，从而改善授粉并减少种子捕食。然而，最近对欧洲山毛榉的观察表明，当前的气候变化会抑制种子生产的年际变化和同步性，并且这种肥大崩溃会大大降低种子作物的生存能力。重要的是，目前还不清楚在什么条件下会发生桅杆故障，以及这种泛欧洲物种的桅杆故障有多普遍。在这里，我们分析了 50 个人口水平种子产量的长期数据集，在欧洲山毛榉的分布范围内进行了采样，并确定夏季气温升高是导致肥大崩溃的一般驱动因素。具体来说，在大多数物种范围内，六月和七月期间特定地点的平均最高温度有所增加，而种群水平种子产量（CVp）的年际变异性则下降。 CVp 下降幅度最大，温度上升最快。此外，在过去四十年中，农作物歉收和低种子年份的发生率有所减少，这表明肥大对种子捕食者的饥饿影响发生了变化。值得注意的是，不同地点的 CVp 并没有根据夏季平均温度而变化。相反，桅杆崩溃是由于局部温度升高（即相对温度升高）而发生的，因此风险不仅限于在温暖的平均条件下生长的种群。尽管种子数量总体增加，但 CVp 降低会减少可行的种子产量，因此我们的结果警告说，一种秘密机制正在形成，可能会阻碍欧洲山毛榉在气候变化下的再生潜力，并具有改变森林功能和群落动态的巨大潜力。