The living biomass of roots greater than 2 mm diameter.
Glossary. M.S. Ashton et al. (eds.), Managing Forest Carbon in a Changing Climate, DOI 10.1007/978-94-007-2232-3, © Springer Science+Business Media B.V. 2012
All biomass of live roots. Fine roots of less than 2 mm diameter are excluded because these often cannot be distinguished empirically from soil organic matter or litter.
Terms and Definitions - FRA 2015, Forest Resources Assessment Working Paper 180, FAO, 2015 (http://www.fao.org/docrep/017/ap862e/ap862e00.pdf).