Larger Forest Patches Exhibit Greater Per-Area Productivity in the U.S. and Worldwide

Forest fragmentation is accelerating worldwide as large, continuous forests are divided into increasingly smaller and more isolated patches. While the impacts of fragmentation on biomass storage are well documented, its consequences for forest productivity and carbon sequestration rates remain uncertain. Here, we analyse all ~17 million forest patches across the conterminous United States (CONUS) using a spatial mixed-effects framework to control for broad-scale socio-environmental heterogeneity and spatial autocorrelation. We find that larger forest patches consistently exhibit higher vegetation reflectance and significantly greater per-area net primary productivity (NPP) and gross primary productivity (GPP) than smaller patches under comparable conditions. This produces a robust superlinear scaling of total forest productivity with patch size. On average, a hectare embedded within a 100,000 km² forest is approximately 38% more productive than an isolated hectare in similar environments, and this size-related boost accounts for nearly one-quarter of total annual forest productivity across CONUS. Extending the workflow globally revealed consistent relationships across major forest biomes and continents, indicating that the phenomenon extends beyond CONUS. These findings highlight that fragmentation can substantially reduce carbon uptake even without net forest-area loss, underscoring the need for forest policies that consider spatial configuration alongside total area.