The overlooked contribution of trees outside forests to tree cover and woody biomass across Europe

Abstract Trees are an integral part of almost all European landscapes, but only forest resources are systematically assessed by national inventories, and the extent to which trees in urban and agricultural areas contribute to biomass and carbon stocks at the national level remains largely unknown. Here we make use of nanosatellite imagery to generate canopy cover, height, and above-ground biomass maps for the entire European continent from 3-m resolution imagery. Our country-scale biomass estimates have a systematic bias of only 7.6% (overestimation; R = 0.98) when compared to national inventories of 30 countries, and our new dataset is sufficiently highly resolved spatially to support the inclusion of tree biomass outside forests, which we quantify to 0.8 Pg. Although this represents only 2% of the total European tree biomass on average, large variations between countries are found (for example 10% for UK) and trees in urban areas contribute substantially to national carbon stocks (for example 8% for the Netherlands). The good agreement with national inventory data, the scalability, and the high level of detail across landscapes, including trees outside forests, make our approach attractive for operational implementation to support national carbon stock inventory schemes.