Abstract:
Previous studies of bird communities in the mid-Willamette Valley, Oregon, indicated that Oregon white oak (Ouercus garryana) stands supported more cavity-using bird
species than sympatric stands of Douglas-fir (Pseudotsuga menziesii). Mature Oregon oak stands are being harvested and few are regenerating. I compared cavity availability for hole-using fauna among 10 types of stands in the mid-Willamette Valley and
adjacent Coast Range foothills (6 Oregon white oak, 3 Douglas-fir and 1 mixed Oregon oak/Douglas-fir). Thirty stands (3/type of stand) were classified by their predominant tree species, average diameter class (20.0-to-34.9 cm, 35.0-to-49.9 cm, and 50.0+ cm at breast height) and area (groves <4 ha, stands >4 ha). Origin, location and estimated size were recorded for 735 cavities found in 3300 trees. Sixty-three percent of the trees examined were Oregon oak, but 93.7% of the cavities were in Oregon oak. Most cavities (70%) were products of decay following infection. Two-thirds of the cavities had entrance hole
diameters between 2.5-to-5.0 cm. Groves of medium- and large- diameter oaks and stands of large-diameter oaks had the most cavities, Cavity availability was higher in the oak stands than in the Douglas-fir and mixed stands. Declines in densities of cavities through a progressive replacement of larger Oregon white oak by smaller, managed Douglas-fir will unquestionably reduce the abundance of cavities in the mid-Willamette Valley. Maintenance of existing oak stands and regeneration of
Oregon oak in the mid-Willamette Valley may be desirable to maintain habitat for indigenous cavity-using fauna.
