The Mediterranean basin has been proposed as an area especially vulnerable to the effect of global climate change, with a greater probability of extreme drought events which can trigger massive forest decline episodes. The impact of extreme droughts on tree mortality in these territories can be magnified by several local factors, such as soil depth, which can predispose some species or individuals to be the damaged. During the summer of 2011 and 2012 many individuals of the deciduous Q. subpyrenaica in the Spanish Pre-Pyrenees showed a premature leaf withering in patches interspersed with non-affected areas. In this study, we have demonstrated that during 2011 and 2012 an extreme drought episode coincided with this phenomenon. The ultimate mechanism explaining the premature withering in Q. subpyrenaica was the hydraulic failure in the vascular system of the leaves in those trees growing in the poorest soil conditions. This mechanism, identified as an example of vulnerability segmentation, preserved the integrity of the stems and buds and allowed the new foliage production during the following spring. As a negative consequence, this drought avoidance strategy shortens the vegetative period, which may threaten the long-term growth and survival of these trees.