Stand-density optimization could substantially increase aboveground biomass in China’s planted forests without land expansion

Expanding forest cover is a cornerstone of land-based climate mitigation, yet its future contribution is increasingly limited by competition for land and by broader policy and social constraints. Making better use of the forests already planted, therefore, offers a mitigation opportunity that requires no additional land. Here we show how much aboveground biomass China’s planted forests could gain by optimizing stand density, drawing on nationwide unmanned aerial vehicle (UAV) and satellite LiDAR, tree density maps, and multiple biomass datasets. Across 6226 paired UAV-satellite observations, aboveground biomass exhibits a hump-shaped response to tree density, mediated in part by forest canopy complexity. Matching density to local environmental conditions could raise the biomass these forests hold by roughly 8.84 Pg, achieved by planting in sparse stands and thinning in crowded ones with little net change in total tree numbers. Under future climate, the most productive densities shift geographically, underscoring the need for adaptive management. Optimizing stand density through targeted planting and thinning could increase aboveground biomass in China’s planted forests by approximately 8.8 Pg without additional land, according to analyses of paired UAV and satellite LiDAR observations, tree density maps, and multiple biomass datasets.