Unitat d'Ecologia, Department Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Barcelona), Spain.
Tree Physiol. 2012 Apr;32(4):478-89. doi: 10.1093/treephys/tps025. Epub 2012 Apr 11.
Severe droughts may increase physiological stress on long-lived woody vegetation, occasionally leading to rapid defoliation and progressive increase in mortality of overstorey trees. Over the last few years, episodes of drought-induced tree dieback have been documented in a variety of woodlands and forests around the world. However, the factors determining tree survival and subsequent recovery are still poorly understood, especially in resprouter species. We have studied the effects of a single drought episode on crown condition in a holm oak (Quercus ilex L.) forest located in NE Spain 7 years after the drought event. Generalized linear models were used to study the environmental correlates of forest crown condition 7 years after the drought event. Additionally, we evaluated the association between crown condition and the carbon and nutrient reserves stored in lignotubers 7 years after the drought. Our study reveals the multifactor nature of a drought-driven forest dieback in which soil depth and the characteristics of individual trees, particularly their number of stems, determined a complex spatial pattern of tree-level responses. This dieback was associated with a depletion of the carbon reserves in lignotubers 7 years after the episode, representing a reduction of up to 60% in highly drought-damaged trees. Interestingly, in the absence of new acute droughts, successive surveys in 2007-11 showed a direct association between carbon reserves depletion and further deterioration of crown condition. More frequent droughts, as predicted by climate change projections, may lead to a progressive depletion of carbon reserves and to a loss of resilience in Mediterranean resprouter species.
严重的干旱可能会增加长寿木本植物的生理压力，偶尔导致快速落叶和上层树木死亡率的逐渐增加。在过去的几年中，世界各地的各种林地和森林都记录了与干旱相关的树木衰退事件。然而，决定树木存活和随后恢复的因素仍知之甚少，特别是在再生植物物种中。我们研究了在西班牙东北部的一片圣栎（Quercus ilex L.）林，在干旱事件发生 7 年后，单次干旱事件对树冠状况的影响。我们使用广义线性模型来研究干旱事件发生 7 年后森林树冠状况的环境相关性。此外，我们评估了树冠状况与干旱发生 7 年后木质部碳和养分储量之间的关系。我们的研究揭示了干旱驱动的森林衰退的多因素性质，其中土壤深度和树木个体的特征，特别是它们的茎数，决定了树木层面响应的复杂空间模式。这种衰退与木质部碳储量的枯竭有关，在受干旱严重影响的树木中，碳储量减少了高达 60%。有趣的是，在没有新的急性干旱的情况下，2007-11 年的连续调查显示，碳储量的枯竭与树冠状况的进一步恶化之间存在直接关联。气候变化预测所预测的更频繁的干旱可能会导致碳储量的逐渐枯竭，并导致地中海再生植物物种的恢复力丧失。
