We are studying the plants, arthropods, and birds that occur in “certified backyard habitats” in Portland, Oregon. We compared yards in three neighborhoods, each with different total tree cover but with the same relative proximity to a large greenspace. Our central research question investigated the role native plants might have in help maintain bird biodiversity, particularly how shrubs might provision urban birds with arthropod food in urban areas. We expected native plants to be more ecologically productive and have more arthropods overall than non-native plants, as the leaves of ornamental plants typically are less palatable to insects. However, as all yards tested contained a mixture of native and ornamental shrubs, we compared yards in the same neighborhoods having relative mixtures of native and ornamental plants, but having at least a minimum number of native shrubs. We collected shrub diversity measures using line transects placed along the side of the yard containing the most native plants. We collected arthropods from similar shrub species in each yard, using branch beating. Arthropods were subsequently identified in the lab. We collected bird diversity data using point counts from 50 m radius areas in yards over two spring seasons.
Results/Conclusions
Based on a small number (23) of yards, we determined that a mixture of native and ornamental plants; snowberry, Indian plum, non-native rhododendron and laurel, hosted a greater abundance of arthropods than other shrubs. Based on comparing three neighborhoods, we found overall tree cover had an influence on the abundance of arthropods and diversity of birds. Many of the arthropod species collected were not native, but were introduced, upending one of our original assumptions about the link between urban native plants and arthropods. The neighborhood having the highest conifer tree cover had higher bird species diversity when compared with neighborhoods with lower and primarily deciduous tree cover. A study of the contribution of plant structure as compared with species composition, arthropod collection from neaby greenspaces and from small trees in yards, and continuing studies about bird abundance including citizen science collected bird data are currently occurring.