人们对气候变化对树木繁殖的影响知之甚少,即使种群的复原力依赖于足够的再生来平衡死亡率的增加。形成森林的树种经常桅杆,即通过种子产量的逐年同步变化进行繁殖,这改善了授粉并减少了种子捕食。欧洲山毛榉最近的观察显示,然而,当前的气候变化可以抑制种子生产的年际变化和同步性,并且这种糊状分解会大大降低种子作物的生存能力。重要的是,目前尚不清楚在这种泛欧物种中,在哪种条件下发生了糊状分解,以及分解的广泛程度。这里,我们分析了50个群体级种子生产的长期数据集,对欧洲山毛榉分布进行采样,并确定夏季气温的升高是造成故障的主要原因。具体来说,在大多数物种范围内观察到6月和7月特定地点平均最高温度的升高,而种群级种子产量(CVp)的年际变异性降低。CVp的下降幅度最大,温度上升最快的地方。此外,在过去的四十年中,作物歉收和种子年数减少了,信号改变了桅杆对种子捕食者的饥饿效应。值得注意的是,CVp根据站点夏季平均温度在站点之间没有变化。相反,随着局部温度的升高(即相对温度的升高),因此,这种风险不仅限于在温暖的平均条件下增长的人口。尽管种子数量总体增加,但降低的CVp可以降低可行的种子产量,我们的研究结果警告说,一种秘密机制正在进行中,这可能会阻碍欧洲山毛榉在气候变化下的再生潜力,具有改变森林功能和社区动态的巨大潜力。
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.