Large-scale forest responses to droughts using national forest inventories: a systematic review

Drought and temperature trends are shifting under recent climate change, resulting in decreased water availability. These changes are leading to widespread tree growth declines, increased mortality, and regeneration impairment, having direct implications for forest biodiversity and functioning. Despite growing evidence of drought-induced impacts on forests, characterising drought effects at large spatio-temporal scales remains challenging due to the limited availability of long-term continuous data over space and time and the multidimensional nature of drought. As a result, assessment of drought effects on forest responses varies widely across studies. National Forest Inventories (NFIs) systematically record forest structure and composition, enabling demography and biomass estimation. Their extensive spatial coverage and systematic data collection make NFIs invaluable tools for long-term monitoring of climate-driven spatio-temporal changes in forests. To understand how drought impacts on forests are assessed using NFIs, we systematically analysed the scientific literature on the use of NFIs to evaluate drought effects on forests. We conducted a scoping review using the Scopus database to identify studies published in English that explicitly link drought to forest responses based on NFIs. We found that most of the studies are conducted in North America and Europe, reflecting NFI data availability, and focused on species- or stand –level responses- growth or mortality- and accounted for only one drought dimension (e.g. intensity). Our review aimed to consolidate existing knowledge on drought impacts on forests using NFIs, identify dominant methodological approaches, and highlight critical gaps that must be addressed to improve understanding and prediction of forest responses to drought under ongoing climate change.