Predicting logging residue volumes in the Pacific Northwest

Pacific Northwest forest managers seek estimates of post-timber-harvest woody residue volumes and biomass that can be related to readily available site- and tree-level attributes. To better predict residue production, researchers investigated variability in residue ratios, growing-stock residue volume per mill-delivered volume, across Idaho, Montana, Oregon, and Washington. This project presented unique sample design challenges, and the authors adopted model-based sampling to calculate the growing-stock logging residue ratio for the four-state region and produced models that relate the residue ratio to individual tree- and stand-level variables meaningful to land managers. The regionwide residue ratio was 0.0269, i.e., 26.9 ft³ of growing-stock logging residue per 1,000 ft³ (26.9 m³ per 1,000 m³) of mill-delivered volume. Residue ratios were related to tree- and site-level variables with predictive models. Residue ratios were predicted to increase with larger small-end used diameter and decline exponentially with increasing dbh. Ratios were predicted to drop when pulp logs were removed and when timber was mechanically felled. Results from this study could be used to produce or improve residue prediction tools for land managers.