The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest

Many species of birds, mammals, amphibians, and reptiles use coarse woody debris (i.e., standing and downed dead wood) for nesting, roosting, foraging, and shelter. Woodpeckers depend on decayed wood to excavate nest and roost cavities in standing trees. Secondary cavity nesters then claim the abandoned cavities for their nesting or roosting. Many of the woodpeckers and secondary cavity nesters use dead wood to forage on forest insects, including bark beetles and defoliators. Characteristics that affect the type and extent of vertebrate use of dead wood include the physical orientation, size, decay state, tree species, and overall abundance. Some species of heartwood decaying fungi create hollow chambers in living trees, which eventually die to become hollow, standing dead trees. Standing trees with hollow chambers are used by Vaux’s swifts (Chaetura vauxi) for nesting and roosting, pileated woodpeckers (Dryocopus pileatus) for roosting, black bears (Ursus americanus) for overwintering, American martens (Martes americana) for denning and resting, and many other species of small mammals for shelter. Once the trees fall, many of the same species continue to use the hollow structures, except the avian species. Solid logs provide cover or travel lanes for small mammals. Accumulations of logs stacked on top of each other provide important habitat in the open spaces formed under the snow where martens and small mammals spend much of the winter. Large-diameter logs are used extensively by pileated woodpeckers and black bears for foraging on carpenter ants. Extensively decayed logs provide habitat for amphibians and reptiles.