Influence of Gambel Oak on Breeding Birds in Ponderosa Pine Forests of Northern Arizona

Abstract

Gambel oak (Quercus gambelii) is widely distributed in the Southwestern United States, where it frequently occurs in association with ponderosa pine (Pinus ponderosa). Fire suppression and fuelwood harvest likely have reduced oak abundance within the pine-oak type. Gambel oak occurs in multiple age-related growth forms, from small shrubs to large, old trees, and may provide important foraging and nesting habitat for breeding birds. I compared attributes of breeding bird communities in 16 northern Arizona ponderosa pine stands from 1993-1995, that were structurally similar except for the presence or absence of Gambel oak. Overlap in bird species composition was high; pine and pineoak stands had a mean Jaccard similarity value of 0.67. Five species were unique to pine stands, whereas 10 species were largely restricted to or only found in pine-oak stands. Overall bird diversity was significantly higher in pine-oak stands, which also had more species of Neotropical migrants, ground nesters, primary cavity excavators, and secondary cavity users than did pine stands. Pine and pine-oak stands had similar species evenness and similar rates of annual species turnover. Total bird abundance did not differ between cover types; however, primary cavity excavators were more abundant in pine-oak stands. Because of the apparent positive influence of oak on breeding birds, forest managers are encouraged to use treatments that retain and enhance the various growth forms of Gambel oak found in pine-oak stands.