An outlook on the rapid decline of carbon sequestration and perspectives for an improved monitoring of French forests

In this study, we present and discuss changes in carbon storage in French forests from 1990 to 2022, derived from CITEPA statistics on forest carbon accounting. These statistics are primarily informed by National Forest Inventory (NFI) data collected from systematic samples of forest plots across Metropolitan France, as well as additional sources related to forest removals, soils or wood products. As NFI is designed to provide statistical estimations of forest growing stock, gains and losses only at the national or subnational levels but not to deliver detailed spatial outlooks on disturbances carbon losses from fires, droughts and insect attacks, we also outline a prospect for future improvements enabled by remote sensing and the development of multi-source inventories. At a national level, a continuing removal of CO 2 from the atmosphere occurred from 1990 to 2022, as harvest and mortality-induced CO 2 losses remained smaller than CO 2 removals by forest growth and the increase in forest area (ca. 80 000 ha per year since 2005 but insignificant in terms of increased carbon stocks at present). The CO 2 removal by forests was 49.3 MtCO 2 ·yr −1 in 1990, increased to reach a peak of 74.1 MtCO 2 ·yr −1 in 2008 and then quickly decreased down to 37.8 Mton CO 2 ·yr −1 in 2022. The changes in CO 2 removal by forests can be separated into three phases. From 1990 to 2013, the CO 2 removal increased alongside the increasing growth of living trees. A spike in carbon loss was caused by the passage of the Lothar and Martin extra-tropical cyclones but forests recovered rapidly within a few years. In contrast, from 2013 to 2017, the CO 2 removal by forests quickly decreased due to increasing CO 2 losses from harvest and natural mortality and a trend of decreasing productivity (Hertzog L. R. et al., Sci. Total Environ. 967 (2025), article no. 178843), each process contributing almost equally. After 2017, the sink remained low and mortality rates stayed larger than during any of the previous years. The recent period is marked by climate shocks such as summer droughts and heatwaves in 2015, 2018, 2022, 2023. The full impacts of the droughts in 2022 and 2023 are not yet covered with full precision, as some of the sites measured by the national inventory before those droughts are still pending a second visit. Delayed tree mortality can also manifest years after a drought has occurred. At a regional level, contrasted trajectories were identified. Southern Mediterranean regions where forests have a low harvest rate have also experienced a lower increase in mortality and a sustained CO 2 uptake. Despite high harvest intensities, the Landes plantations also show an increasing CO 2 sink. In contrast, all northern regions and Corsica have seen a strong decline in their CO 2 removal rates, except in the Ile-de-France region (larger Paris area), where the CO 2 sink was constant during the last 30 years, possibly because many forests are used for recreation and are subjected to low harvest pressure. Two regions, the Hauts-de-France and Grand Est forests, stand out as becoming net emitters of CO 2 to the atmosphere. Other regions where the CO 2 sink declined and is now close to zero are Normandy, Corsica, and Bourgogne-Franche-Comté. A detailed analysis was conducted to identify where trees are dying in France, the regions with increased mortality, and which species and tree sizes are most affected. We conclude with a perspective on how traditional sample-based statistical estimation of forest carbon changes, as implemented in classical NFI approaches, can be complemented by high-resolution satellite and LiDAR data, together with denser monitoring of mortality processes. Progress in remote sensing technologies supports both model-based approaches aimed at mapping the carbon budget and enhanced inventory techniques for accurate estimation at finer spatial scales. Given the limited continuity of some long-term forest flux estimates, we finally outline potential pathways to strengthen carbon sink quantification in the near future.