This EnviroAtlas dataset includes the summed below ground live tree root dry biomass estimate by 12-digit Hydrologic Unit (HUC) in metric tons (megagrams) from the 2000 National Biomass and Carbon Dataset (Version 2.0) developed by the Woods Hole Research Center, released in October, 2012. This dataset was produced by the US EPA to support research and online mapping activities related to EnviroAtlas. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the contiguous United States. The dataset is available as downloadable data (https://edg.epa.gov/data/Public/ORD/EnviroAtlas) or as an EnviroAtlas map service. Additional descriptive information about each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).