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Climate projections predict higher precipitation variability with more frequent dry extremes 1. CO 2 assimilation of forests decreases during drought, either by stomatal closure 2 or by direct environmental control of sink tissue activities 3. Ultimately, drought effects on forests depend on the ability of forests to recover, but the mechanisms controlling ecosystem resilience are uncertain 4. Here, we have investigated the effects of drought and drought release on the carbon balances in beech trees by combining CO 2 flux measurements, metabolomics and 13 CO 2 pulse labelling. During drought, net photosynthesis (A N), soil respiration (R S) and the allocation of recent assimilates below ground were reduced. Carbohydrates accumulated in metabolically resting roots but not in leaves, indicating sink control of the tree carbon balance. After drought release, R S recovered faster than A N and CO 2 fluxes exceeded those …