Restoration treatments reduce threats to oak ecosystems and provide immediate subtle benefits for oak-associated birds

摘要

Oak ecosystems support a high amount of biodiversity and are critical for avian conservation in the Pacific Northwest, yet most of the remaining habitat is in a degraded state. A landscape-scale restoration project in the Klamath Siskiyou Bioregion of southern Oregon and northern California reduced factors that stress oak trees while improving the function of oak-associated plant communities on 450 ha of private lands from 2011 to 2013. We implemented a before-after-control-impact study to measure changes in vegetation structure and composition, avian community composition, and individual avian species density within 23 restored and 23 control stands. Restoration resulted in reduced Douglas fir and western juniper tree cover and overall shrub cover, but generally did not cause notable shifts between vegetation types (e.g. oak-conifer forest did not become oak woodland). Oak-associated birds were positive indicator species following treatment at the restored sites; yet, the avian community composition shift toward an oak-associated community observed in the NMS ordination was not statistically significant. Furthermore, we observed only negligible change in individual species density of both conifer- and oak-associated birds following restoration. While restoration objectives at all sites sought to improve oak tree vigor and associated ecosystem health, the pre-restoration stand conditions and thus the specific prescriptions varied widely. More study is needed to disentangle how overstory and understory restoration actions interact to affect bird community response.