Atmospheric aridity drives functional reorganisation and resilience loss in global forests

Abstract Global forests are gaining productivity while losing resilience, yet the mechanisms underlying this divergence remain unclear. Here we show, using multi-source remote sensing data spanning 2001–2021, that over one-third of global forests simultaneously gain gross primary productivity and lose resilience, linked to shifts in ecosystem functional coupling. Rising vapour pressure deficit was the primary driver of resilience loss. This resilience erosion weakened the coupling between gross primary productivity and ecosystem photosynthetic efficiency in boreal forests. By contrast, vapour pressure deficit directly strengthened gross primary productivity-water use efficiency covariation in tropical and boreal forests. This tighter coupling reflects stomatal constraint on transpiration variability rather than improved carbon-water coordination. In intact forests, vapour pressure deficit instead weakened this coupling. Non-intact forests were twice as sensitive to resilience loss as intact forests, indicating that structural simplification disproportionately amplifies climate-driven vulnerability to atmospheric aridity. These findings call for integrating resilience and functional coupling into forest monitoring to safeguard carbon sink stability.