Forest ecosystems and their resilience to climate extremes across Europe

Over the past several decades European forest have played a major role in slowing the pace of climate change by sequestering vast amounts of CO2 from the atmosphere and storing it as wood. However, growing evidence suggests that this carbon sink is now weakening, with potentially disastrous consequences for international efforts to keep global warming within 2 degrees C. This recent dip in the strength of the forest carbon sink is thought to be linked, at least in part, to a rise in the frequency and intensity of hot dry summers in Europe - including the record-breaking heatwaves of 2003, 2010 and 2018-19. If Europe's forests are to continue being part of the solution for transitioning to a low-carbon future, we urgently need to understand how these ecosystems are impacted by and recover from periods of extreme water stress. The overarching goal of the FORTRESS project is to generate the first complete picture of how extreme heat and drought impact the ability of European forests to sequester and store carbon: from the growth and survival of individual tree seedlings, to population dynamics across entire landscapes. Using a unique combination of manipulative experiments, long-term retrospective analyses of tree ring records, real-time ecophysiological data from a pan-European wireless tree sensor network, cutting-edge remote sensing and machine learning, this project aims to: (i) reveal which European tree species are most resilient to climate extremes and why; (ii) uncover how climate constrains tree growth and water use at daily, seasonal, annual and multi-decadal time scales; and (iii) develop the next generation of early warning signals that predict a tree's risk of mortality from hydraulic failure using a range of data, including satellite imagery. In doing so, the FORTRESS project will radically transform our ability to manage, monitor and model Europe's forest ecosystems into the future.