Green Roofs in Willamette Valley Ecoregions

Abstract

This chapter covers case studies of four conservation sites and nine green roofs located in the Willamette Valley ecoregions of western Oregon. The region is geographically complex with multiple ecoregions including prairies, rocky outcrops, oak woodlands, mixed woodlands, forests, wetlands, and riparian habitats. Historically, grasslands were widespread in the valley, and these were intermixed with oak and conifer woodlands from Portland to Eugene. Less than 1% of the native prairie habitat remains intact. Precipitation averages 800–950 mm annually in the valley, and the region experiences warm to hot and dry summers and long wet winters, with infrequent snow. Much of the precipitation takes place from October through May. Although green roofs were introduced into the valley since early 2000, much of the vegetation on the over 500 green roofs in the Portland metro region has apparently not been intended to mitigate the displacement of native ecosystems by building construction. However, the nine ecoregional green roof case studies in this chapter demonstrate how 69 species of vegetation native to the Willamette Valley ecoregions can be employed on green roofs.