BackgroundClimate‐change‐induced shifts in the timing of leaf emergence during spring have been widely documented and have important ecological consequences. However, mechanistic knowledge regarding what controls the timing of spring leaf emergence is incomplete. Field‐based studies under natural conditions suggest that climate‐warming‐induced decreases in cold temperature accumulation (chilling) have expanded the dormancy duration or reduced the sensitivity of plants to warming temperatures (thermal forcing) during spring, thereby slowing the rate at which the timing of leaf emergence is shifting earlier in response to ongoing climate change. However, recent studies have argued that the apparent reductions in temperature sensitivity may arise from artefacts in the way that temperature sensitivity is calculated, while other studies based on statistical and mechanistic models specifically designed to quantify the role of chilling have shown conflicting results.MethodsWe analysed four commonly used combinations of phenology and temperature datasets obtained from remote sensing and ground observations to elucidate whether current model‐based approaches robustly quantify how chilling, in concert with thermal forcing, controls the timing of leaf emergence during spring under current climate conditions.ResultsWe show that widely used modeling approaches that are calibrated using field‐based observations misspecify the role of chilling under current climate conditions as a result of statistical artefacts inherent to the way that chilling is parameterised. Our results highlight the limitations of existing modelling approaches and observational data in quantifying how chilling affects the timing of spring leaf emergence and suggest that decreasing chilling arising from climate warming may not constrain near‐future shifts towards earlier leaf emergence in extra‐tropical ecosystems worldwide.

中文翻译：

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热强迫与冷却？春季物候模型中温度控制的错误


背景气候变化引起的春季叶片出现时间的变化已被广泛记录，并具有重要的生态后果。然而，关于什么控制春叶出现时间的机械知识是不完整的。自然条件下的实地研究表明，气候变暖引起的低温积累（寒冷）减少延长了休眠时间或降低了植物在春季对变暖温度（热强迫）的敏感性，从而减缓了叶片出现时间提前变化的速度，以响应持续的气候变化。然而，最近的研究认为，温度敏感性的明显降低可能是由计算温度敏感性方式的人工制品引起的，而其他基于专门设计用于量化冷却作用的统计和机理模型的研究则显示出相互矛盾的结果。方法我们分析了从遥感和地面观测中获得的物候和温度数据集的四种常用组合，以阐明当前基于模型的方法是否稳健地量化了在当前气候条件下，寒冷如何与热强迫一起控制春季叶片出现的时间。结果我们表明，由于寒冷参数化方式固有的统计伪影，使用基于实地的观测进行校准的广泛使用的建模方法错误地指定了当前气候条件下寒冷的作用。 我们的研究结果强调了现有建模方法和观测数据在量化寒冷如何影响春叶出现时间方面的局限性，并表明气候变暖引起的寒冷减少可能不会限制全球温带生态系统在不久的将来向叶子提前出现的转变。