A global map of root biomass across the world's forests

. As a key component of the Earth system, root plays the key role in linking Earth's lithosphere, hydrosphere, biosphere, and atmosphere. Here we combine 10307 field measurements of forest root biomass worldwide with global observations of forest structure, climatic conditions, topography, land management and soil characteristics to derive a spatially explicit global high-resolution (~1 km) root biomass dataset, including fine and coarse roots. In total, 142 ± 25 (95 % CI) Pg of live dry matter biomass is stored below-ground, representing a global average root:shoot biomass ratio of 0.25 ± 0.10. Our estimations of total root biomass in tropical, temperate and boreal forests are 44–226 % smaller than earlier studies (Jackson et al., 1997; Robinson, 2007; Saugier et al., 2001). The smaller estimation is attributable to the updated forest area, spatially explicit above-ground biomass density used to predict the patterns of root biomass, new root measurements and upscaling methodology. We show specifically that the root shoot allometry is one underlying driver that leads to methodological overestimation of root biomass in previous estimations. Raw datasets and global maps generated in this study are deposited at the open access repository Figshare (https://figshare.com/articles/Supporting_data_and_code_for_A_global_map_of_root_biomass_across_the_world_s_forests/ 12199637).