Rear-edge tree populations forming the equatorward limit of distribution of temperate species are assumed to be more adapted to climate variability than central (core) populations. However, climate is expected to become more variable and the frequency of climate extremes is forecasted to increase. Climatic extreme events such as heat waves, dry spells and spring frosts could become more frequent, and negatively impact and jeopardize rear-edge stands. To evaluate these ideas, we analyzed the growth response of trees to successive spring frosts in a mixed forest, where two temperate deciduous species, Fagus sylvatica (European beech) and Quercus petraea (sessile oak), both at their southernmost edge, coexist with the Mediterranean Quercus pyrenaica (Pyrenean oak). Growth reductions in spring-frost years ranked across species as F. sylvatica > Q. petraea > Q. pyrenaica. Leaf flushing occurred earlier in F. sylvatica and later in Q. pyrenaica, suggesting that leaf phenology was a strong determinant of spring frost damage and stem growth reduction. The frost impact depended on prior climate conditions, since warmer days prior to frost occurrence predisposed to frost damage. Autumn Normalized Difference Vegetation Index (NDVI) data showed delayed leaf senescence in spring-frost years and subsequent years as compared with pre-frost years. In the studied forest, the negative impact of spring frosts on Q. petraea and especially on F. sylvatica growth was considerably higher than the impacts due to drought. The succession of four spring frosts in the last two decades determined a trend of decreasing resistance of radial growth to frosts in F. sylvatica. The increased frequency of spring frosts might prevent the expansion and persistence of F. sylvatica in this rear-edge Mediterranean population.

中文翻译：

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连续春季霜冻对西班牙中部气候要求不同的三种落叶树种叶片物候和径向生长的影响

假设形成温带物种分布赤道界限的后缘树木种群比中央（核心）种群更适应气候变化。然而，预计气候将变得更加多变，预计极端气候事件的频率将增加。热浪、干旱和春季霜冻等极端气候事件可能会变得更加频繁，并对后缘看台产生负面影响和危害。为了评估这些想法，我们分析了树木对混交林中连续春季霜冻的生长反应，其中两种温带落叶树种Fagus sylvatica（欧洲山毛榉）和Quercus petraea（无梗橡树）都在它们的最南端，与地中海栎栎（比利牛斯橡木）。春霜年的生长减少在不同物种中排名为F. sylvatica  >  Q. petraea  >  Q. pyrenaica。F. sylvatica叶片潮红发生较早，Q. pyrenaica较晚，这表明叶片物候是春季霜冻损害和茎生长减少的重要决定因素。霜冻的影响取决于先前的气候条件，因为在霜冻发生之前的温暖日子容易遭受霜冻损害。秋季归一化差异植被指数（NDVI）数据显示，与霜前年份相比，春季霜冻年份和随后年份的叶片衰老延迟。在所研究的森林中，春季霜冻对Q. petraea尤其是对F. sylvatica的生长明显高于干旱的影响。近20年来4次春季霜冻的连续发生决定了林木径向生长对霜冻​​的抵抗力下降的趋势。春季霜冻频率的增加可能会阻止F. sylvatica在这个地中海后缘种群中的扩张和持续存在。