Mediterranean mountainous areas of shallow soil often display a mosaic of tree clumps surrounded by grass. The combined role and dynamics of water extracted from the underlying rock, and the competition between adjacent patches of trees and grass, has not been investigated. We quantified the role rock water plays in the seasonal dynamics of evapotranspiration (ET), over a patchy landscape in the context of current and past seasonal climate changes, and land‐cover change strategies. Soil water budget suggests deep water uptake by roots of trees (0.8–0.9 mm/d), penetrating into the fractured basalt, subsidized grass transpiration in spring through hydraulic redistribution. However, in summer trees used all the rock water absorbed (0.79 mm/d). A 15‐year data set shows that, with increasing seasonal drought‐severity (potential ET/precipitation) to >1.04, the vertical water flux through the bottom of the thin soil layer transitions from drainage to uptake in support of ET. A hypothetical grass‐covered landscape, with no access to deep water, would require 0.68–0.85 mm/d more than is available, forcing shortened growing season and/or reduced leaf area. Long‐term decreasing winter precipitation and increasing spring potential ET suggest drying climate, so far with stable vegetation mosaic but progressively earlier peak of grass leaf area. Intervention policies to increase water yield by reducing tree cover will curtail grass access to rock moisture, while attempting to increase tree‐related products (including carbon sequestration) by increasing forest cover will limit water availability per tree leaf area. Both changes may further reduce ecosystem stability.

中文翻译：

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岩水是浅层土壤上斑驳生态系统的关键资源：挖深树丛补贴了周围的表层草

地中海山区的浅层土壤经常显示出被草丛包围的树丛马赛克。从底层岩石中提取的水的综合作用和动力学，以及相邻树木和草丛之间的竞争，尚未得到研究。我们量化了岩水在蒸散量（ET）季节动态中的作用。），当前和过去的季节性气候变化以及土地覆被变化策略的背景下的一片片片景观。土壤水收支状况表明，树木根部吸收深水（0.8-0.9 mm / d），渗透到断裂的玄武岩中，并通过水力重新分配来补贴春季的草蒸腾作用。然而，在夏季，树木吸收了所有吸收的岩水（0.79 mm / d）。一个15年的数据集表明，随着季节性干旱的严重程度（潜在的ET /降水）增加到> 1.04，通过薄土层底部的垂直水通量从排水过渡到吸收以支持ET。假想的草覆盖的景观，无法获得深水，将比现有的需要多0.68–0.85 mm / d，从而迫使缩短生长季节和/或减少叶面积。长期减少的冬季降水和春季潜在的ET升高表明气候干燥，到目前为止，植被镶嵌稳定，但草叶面积逐渐达到峰值。通过减少树木覆盖率来增加水分产量的干预政策将减少草类获得岩石水分的机会，而通过增加森林覆盖率来增加与树木相关的产品（包括碳固存）的尝试将限制每片树叶的水供应量。两种变化都可能进一步降低生态系统的稳定性。