Snag Abundance for Primary Cavity-nesting Birds on Nonfederal Forest Lands in Oregon and Washington

More than 100 species of vertebrates in the Pacific Northwest use standing dead trees (snags) at one time or another in their lifecycle (Thomas et al. 1979a, Neitro et al. 1985). With few exceptions, investigators have found significant correlations between snag density and the abundance of primary cavity-nesters in North American coniferous forests (Raphael and White 1984:47-53, Madsen 1985, Zarnowitz and Manuwal 1985, McComb et al. 1986, Land et al. 1989, Carey et al. 1991, Schreiber and deCalesta 1992). Similar relationships have been detected for secondary cavity-nesters (Schreiber and deCalesta 1992). Thomas et al. (1979a) and Neitro et al. (1985) suggested that timber management practices and changing land-use patterns in the Northwest are reducing snag abundance and thus dependent populations of wildlife species (also see Morrison et al. 1986 and Schreiber and deCalesta 1992). Snag abundance in unmanaged Douglas-fir (Pseudotsuga menziesii) forests >40 years old have been quantified by Spies et al. (1988), Carey et al. (1991), and Spies and Franklin (1991). However, patterns of snag abundance across a broader region, especially in young managed stands, are poorly understood. Regional assessments can help guide planning and policy for managing Northwest forests for wood production and wildlife in public and private forests. In this study we assessed patterns of snag abundance among plant communities and stand conditions in managed and natural forests on nonfederal lands in Oregon and Washington. Our objectives were to: (1) quantify densities and characteristics of snags across a range of forest conditions; (2) assess snag origin, whether from death of trees in the present stand or carried over from a previous stand; (3) use models of snag-bird relationships to predict the role that nonfederal lands might play in providing habitat for primary cavity-nesters; and (4) discuss implications for forest management in the Northwest.