SCALE-UP – Understanding VPD impacts on forests across scales to advance the next generation of Earth-system models

Vapor pressure deficit (VPD) is rising globally, but its effects on gas exchange, tree growth, mortality, and forest carbon and water fluxes remain unclear. Key uncertainties exist regarding species-specific responses, interactions with soil drought, and acclimation across time and spatial scales. These gaps undermine confidence in models predicting vegetation dynamics and carbon cycle changes, limiting our ability to implement climate-smart management. SCALE-UP will investigate (1) species-specific VPD impacts on gas exchange, growth, and mortality, (2) interactions with soil drought, (3) acclimation potential to rising VPD, and (4) mechanistic insights to improve predictive models of forest responses to VPD.