Cavity-Nester Habitat Development in Artificially Made Douglas-Fir Snags

Abstract

Standing dead trees, or snags, are a source of foraging habitat and nesting cavities for wildlife. We evaluated the efficacy of creating Douglas-fir (Pseudotsuga menziesii) snags (by girdling, silvicide treatment, and topping) and their influence on deterioration rate by describing bark beetle activity, fungal colonization, and use by cavity nesters. To compare the development of artificial with natural fungal infection, we inoculated snags with Fomitopsis pinicola, Fomitopsis cajanderi, Phellinus pini, and Phlebiopsis gigantea. Silvicide-treated and fully topped trees took just over 1 year to die; girdled trees took slightly over 2 years to die. Trees topped at mid-crown that died took almost 3 years. Top breakage began 4 years after treatment. Neither snag-creation methods nor artificial inoculation directly affected bark beetle (Dendroctonus spp., Ips spp.) activity or the presence of externally visible fungal fruiting bodies 4 years after treatment. Native decay fungi, particularly Trichaptum abietinum and Cryptoporus volvatus, extensively colonized snag sapwood. Snag-creation method and artificial inoculation did not appreciably affect woodpecker activity after 4 years. Rather, length of time the snag had been dead had the most influence on bird use. All snags except the living mid-crown topped trees provided foraging habitat and may be a suitable condition for cavity-nest excavation. Pileated woodpeckers (Dryocopus pileatus), hairy woodpeckers (Picoides villosus), and other species excavated and de-barked the created snags during foraging, and possibly during nesting activity.