GEDI observations of foliar height diversity track regrowth trends in the humid tropical forests of the Democratic Republic of Congo

Abstract

The humid tropical forests of the Democratic Republic of Congo (DRC) cover 1.15 million km2 and are highly biodiverse but under threat. The European Union Tropical Moist Forest (TMF) Landsat-based forest cover monitoring product reports that >25% of DRC forests experienced deforestation and degradation in the last 30 years. The NASA Global Ecosystem Dynamics Investigation (GEDI) is the first spaceborne LiDAR designed to provide information on forest canopy structure, including a 25 m diameter footprint foliage height diversity (FHD) product that quantifies the distribution of plant material from the ground to the canopy top. This study provides the first assessment of forest structural diversity change in regrowing DRC humid tropical forests. Local validation of the GEDI FHD product against Airborne Laser Scanning data confirmed its utility in capturing forest structural diversity (relative RMSE = 10.32%), particularly when stringently filtered for potential geolocation and canopy penetration issues (relative RMSE = 5.91%). The GEDI FHD was used with TMF-mapped 1990–2023 regrowing forest locations to examine the relationship between FHD and post-deforestation regrowing forest age. An FHD regrowth trajectory, defined from the data at 7102 DRC humid tropical forest locations, indicates a rapid increase in structural diversity within the first ∼20 years of regrowth, followed by a decelerating but sustained increase with age, and that by 34 years the regrowing forest FHD had not recovered to the median undisturbed forest value. These results suggest that leaving forests to regrow provides opportunities, not just for carbon sequestration, but also for biodiversity recovery.