Methods are provided for the efficient fractionation of lignocellulosic biomasses into cellulosic, hemicellulosic and lignin fractions, wherein concentrated organic acid vapors are applied to the biomass at elevated temperatures at the location(s) or near the location(s) where the biomass has been harvested and gathered, to at least partly depolymerize or substantially solubilize the hemicelluloses and lignins in the biomass. The organic acid-treated biomass is in either case then dried and pelletized for extended bulk storage and/or for shipment to a second facility some distance away. The organic acid-treated biomass may be processed into desired chemicals, fuels and/or fuel additives at the local processing site or at a second facility away from the local processing site, or the pelletized material may be used as a ruminant feed locally or at a feedlot some distance removed from the local processing site.
