We studied the growth reaction of silver poplar trees (Populus alba) to a large flood in November 2014 in the semi-arid High Atlas Mountains, Morocco. The flood resulted in half of the studied trees developing wider tree rings in 2015 and the other half developing narrower rings in 2015, next year after the flood. For 57.1% of trees which released growth in 2015, this was the most significant increase of ring width during their whole lives (in whole tree-ring chronologies), and for 23.8% of trees which reduced growth in 2015, this was the most significant decrease of ring width. Tree-ring reductions in next year after the 2014 flood resulted from environmental stress related to burying stems with alluvia deposited during the flood. Fresh sediments cut off air access from the root system, and for some of the sampled trees, this stress was strong enough to control their radial growth. Growth releases that follow the 2014 flood are a record of trees benefitting from a sudden supply of water, a rare opportunity in dry study area, where water is usually scarce. The study demonstrates that floods in high mountains of arid zone can cause dual, opposite growth reaction of affected trees. Such dual record is characteristic for environmental impulses, which exert stress on trees, but, at the same time, improve other conditions of tree growth. Environmental events that cause simultaneous positive and negative reactions among a population of trees, like studied flood, can easily be overlooked in chronologies based on average widths of tree rings each year. For trees affected during studied flood arithmetical mean of ring widths in 2015 is average and does not stand out from arithmetical means for other years. However, when analysed in detail, the year 2015 is significantly different from other years, as is demonstrated by high values of dispersion indicators (standard deviation and coefficient of variation) calculated for all sampled trees. This study demonstrates that following the standard procedure (developing tree-ring chronology from average ring widths) is not a reliable solution for reconstructions of environmental impulses which cause dual, opposite reaction among sampled trees. Even strong events of this type will not be emphasised in standard chronologies, which can lead to underestimating frequency and magnitude of processes and, in the case of floods, to underestimating hazard and risk.

我们研究了白杨树（Populus alba) 到 2014 年 11 月在摩洛哥半干旱的高阿特拉斯山脉发生的大洪水。洪水导致一半的研究树木在 2015 年形成了更宽的年轮，而另一半在 2015 年（即洪水过后的第二年）形成了更窄的年轮。对于 2015 年释放增长的 57.1% 的树木来说，这是其整个生命周期中年轮宽度的最显着增长（在整个年轮年表中），而对于 23.8% 的 2015 年增长减少的树木来说，这是最显着的环宽度减小。2014 年洪水过后，明年的年轮减少是由于与洪水期间沉积的冲积物掩埋茎干有关的环境压力造成的。新鲜的沉积物切断了根系的空气通路，对于一些采样的树木，这种压力足以控制它们的径向生长。2014 年洪水之后的生长释放记录了树木从突然供水中受益的记录，这在干旱的研究区是难得的机会，那里通常缺水。研究表明，干旱地区高山的洪水会导致受影响树木的双重、相反的生长反应。这种双重记录是环境冲动的特征，它对树木施加压力，但同时也改善了树木生长的其他条件。在树木种群中同时引起积极和消极反应的环境事件，如研究的洪水，很容易在基于每年年轮平均宽度的年表中被忽略。对于受洪水影响的树木，2015 年年轮宽度的算术平均值为平均值，与其他年份的算术平均值不显着。然而，详细分析后，2015 年与其他年份有显着差异，这可以从为所有采样树木计算的高值离散指标（标准偏差和变异系数）证明。这项研究表明，遵循标准程序（从平均年轮宽度开发树木年轮年表）并不是重建环境脉冲的可靠解决方案，环境脉冲会导致采样树木之间的双重、相反的反应。即使是这种类型的强烈事件也不会在标准年表中得到强调，这可能导致低估过程的频率和幅度，并且在洪水的情况下，会低估危害和风险。正如为所有采样的树木计算的离散指标（标准偏差和变异系数）的高值所证明的那样。这项研究表明，遵循标准程序（从平均年轮宽度开发树木年轮年表）并不是重建环境脉冲的可靠解决方案，环境脉冲会导致采样树木之间的双重、相反的反应。即使是这种类型的强烈事件也不会在标准年表中得到强调，这可能导致低估过程的频率和幅度，并且在洪水的情况下，会低估危害和风险。正如为所有采样的树木计算的离散指标（标准偏差和变异系数）的高值所证明的那样。这项研究表明，遵循标准程序（从平均年轮宽度开发树木年轮年表）并不是重建环境脉冲的可靠解决方案，环境脉冲会导致采样树木之间的双重、相反的反应。即使是这种类型的强烈事件也不会在标准年表中得到强调，这可能导致低估过程的频率和幅度，并且在洪水的情况下，会低估危害和风险。这项研究表明，遵循标准程序（从平均年轮宽度开发树木年轮年表）并不是重建环境脉冲的可靠解决方案，环境脉冲会导致采样树木之间的双重、相反的反应。即使是这种类型的强烈事件也不会在标准年表中得到强调，这可能导致低估过程的频率和幅度，并且在洪水的情况下，会低估危害和风险。这项研究表明，遵循标准程序（从平均年轮宽度开发树木年轮年表）并不是重建环境脉冲的可靠解决方案，环境脉冲会导致采样树木之间的双重、相反的反应。即使是这种类型的强烈事件也不会在标准年表中得到强调，这可能导致低估过程的频率和幅度，并且在洪水的情况下，会低估危害和风险。