Primary mills are those that convert roundwood products (i.e., tree trunks and logs) into other wood products and include sawmills that produce lumber, pulp mills, veneer mills, etc. In the process of converting trees into wood products, waste residues are generated consisting of bark, fine wood residues, and coarse wood residues which are used for energy, to make fiber products (e.g., pulp for paper and cardboard; engineered wood products such as fiberboard, oriented strandboard, medium density fiberboard), and for other uses (e.g., mulch and bedding).
An estimated 86.7 million dry tons of primary mill residues were produced in RPA survey year 2007. Residues are relatively clean and concentrated at the site of production resulting in all but 1.3 million dry tons (1.5%) not used. The remaining residues were used for fuel (42%), fiber products (41%), or other products (15%).