Hanley Mick E, Cook Benjamin I, Fenner Michael
School of Biological Sciences, The University of Plymouth, Plymouth, UK.
NASA Goddard Institute for Space Studies, New York, New York, USA.
J Plant Ecol. 2019 Jun;12(3):542-549. doi: 10.1093/jpe/rty046. Epub 2018 Nov 15.
AIMS -: Annually variable, but synchronous production of large seed crops ('masting') is a widespread phenomenon in temperate trees. Mounting concerns about the impacts of anthropogenic climate change (ACC) on plant reproduction, gives urgency to our need to understand better the role of climate on tree reproduction, and in particular, mast events. Unlike our understanding of reproductive phenology however, there is little consensus regarding how climate affects plant reproductive effort, or indeed the actual environmental triggers that underpin masting behaviour.
METHODS -: We used a 27-year record of acorn yield from a population of 12 trees located in southern England to compare masting frequency and post-dispersal acorn yield each year for each tree, with long-term weather data over the same period. We focussed on discrete or sequential climate cues (temperature, precipitation, and frost days) as likely predictors of oak reproduction.
IMPORTANT FINDINGS -: Annual post-dispersal acorn crop varied greatly; i.e. no acorns in 14 of the 27 years, but there was no sequential pattern of crop versus non-crop years indicating that weather, rather than resource limitation alone, dictated the timing of reproduction. Crop years were instead most closely associated with relatively cool late summer conditions in the preceding year, followed by anomalous summer warmth within crop year. Acorn yield increased following dry April and above average May and June temperatures within crop year. Although our results support a general association between warm late spring and summer conditions, and crop frequency and yield respectively, the influence of cooler later summer conditions in the year prior to masting highlights how a combination of weather cues may dictate the occurrence of mast years. Consequently, our results corroborate not only the hypothesis that temperature differentials between consecutive years, not absolute temperatures, may be the better predictor of mast seeding events, but lend support also to the suggestion that reproductive failure and resource accumulation resulting from a climate-linked environmental veto, drives future reproductive synchronization in temperate tree species.
每年产量变化但同步产生大量种子作物（“大年结实”）是温带树木中普遍存在的现象。人们日益担忧人为气候变化（ACC）对植物繁殖的影响，这使得我们迫切需要更好地了解气候对树木繁殖的作用，尤其是大年结实事件。然而，与我们对生殖物候的理解不同，关于气候如何影响植物繁殖努力，或者实际上支撑大年结实行为的实际环境触发因素，几乎没有共识。
我们利用来自英格兰南部12棵橡树种群的27年橡子产量记录，将每棵树每年的大年结实频率和种子传播后的橡子产量与同期的长期天气数据进行比较。我们关注离散或连续的气候线索（温度、降水和霜冻日），将其作为橡树繁殖的可能预测指标。
种子传播后的年度橡子产量差异很大；即在27年中有14年没有橡子，但没有丰年与非丰年的连续模式，这表明天气而非仅资源限制决定了繁殖时间。相反，丰年与前一年夏末相对凉爽的条件最为密切相关，其次是丰年期间夏季异常温暖。在丰年，4月干燥以及5月和6月温度高于平均水平后，橡子产量增加。尽管我们的结果支持晚春和夏季温暖条件与丰年频率和产量之间的一般关联，但大年结实前一年夏末较凉爽条件的影响突出了天气线索的组合可能如何决定大年的发生。因此，我们的结果不仅证实了连续年份之间的温度差异而非绝对温度可能是大年结实事件更好预测指标的假设，而且还支持了这样的观点，即与气候相关的环境否决导致的繁殖失败和资源积累推动了温带树种未来的繁殖同步。
