Over fifty percent of humans live in cities. The environmental cost of this is massive, as is the potential for utilizing privately held yards as an integral part of conservation in urban areas. The Backyard Habitat Certification Program (BHCP) in Portland, Oregon, was established to reduce invasive plants, support wildlife, and promote conservation. The program involves > 3000 yards certified at three tiers. While onsite inspections are required to verify compliance, there has never been an assessment of the value of these yards to wildlife. Chapter 1 examined the relationships between the urban landscape and bird distributions outside of yards. Chapter 2 evaluated the ability of the program to separate yards by assessing differences in vegetation structure and composition. Chapter 3 tested if avian abundance, richness and diversity in yards are a product of responses to yard or landscape vegetation structure. Avian data was collected at 146 yards and 73 random locations in 2013 and 2014. Public landscape data was used to collect yard data in the field. Avian abundance, richness, and diversity were affected negatively by urbanization (especially impervious surface) and population density, but positively by tree cover. The BHCP was effective at distinguishing platinum yards from others, but overlap was relatively high among gold, silver and uncertified yards. Avian abundance, richness and diversity within yards was less affected by yard vegetation than the structure of habitat in the surrounding landscape. Species responded individualistically to yard vegetation and the urban landscape, and response was a continuum of tolerance to urbanization. Ultimately, the ability of yards to support wildlife will depend on wide scale neighborhood participation.

The effects of urbanization and continual human disturbance on the plant and avian communities of Forest Park and forested lands surrounding Portland, Oregon, were studied. I examined characteristics of plant and avian communities at 25 sites, 24 which were in Forest Park and surrounding areas and one which was in the Ancient Forest Preserve (old-growth stand) northwest of Forest Park. Data were analyzed using multiple regression, ANOV A, and Bonferonni/Dunn. Seven variables were selected representing different urbanization gradients. An additional covariable coded for the old-growth stand, allowing it to be used as a control. Many tree variables, especially those related to shade-tolerant species, were positively correlated with both the distance from downtown Portland and the number of houses in the surrounding area, and negatively correlated with the distance from the nearest forest edge; however, many shrub and herbaceous variables were negatively correlated with the distance from downtown Portland. Species diversity for herbaceous and shrub species was greater at more urban sites, but diversity of trees was lower at more urban sites. There were significantly more non-native species of plants in the city section. I found significantly fewer saplings and small trees, especially shade-tolerant species, in the section of Forest Park closest to downtown Portland, although tree mortality was positively correlated with distance from Portland. Summer bird data revealed significant increases in the abundances of urban and edge species at more urban sites, with concomitant reductions in forest species. There were significantly more ground gleaning birds and short distance migratory species. I also found a significantly greater abundance of birds in the old-growth stand during the winter. This increase was positively correlated with the depth of snow in the nearby Cascade Mountains. My results indicate that Forest Park is apparently progressing in a normal successional pattern with the exception of the city section. The reduction in shade tolerant saplings and small trees in the city section suggest that rate of succession has been slower at more urban sites. Avian data suggest that urbanization affects bird species abundance and guild composition in the more urban areas.