Other interactions between urban environments, soils, and local biotic communities have implications for restoration success. Particularly problematic to the practice of urban ecological restoration is the potential for urban soils to promote invasive species establishment. For example, in a study of urbanized riparian areas in Portland, Oregon, Sharp and Yeakley found that the effects of urbanization on soil properties increased colonization and dominance of riparian corridors by non-native plants (Sharp 2002; Yeakley 2006, Portland State University, personal communication). Urban riparian soils have increased bulk density, decreased soil organic matter contents, shallower surface horizons, and finer soil texture, likely the result of exposing subsurface layers by erosion or removal of surface soil layers during development. These soil changes favored non-native plant invasion at several sites. The authors speculate that local native plants may be adapted to soil conditions that existed in preurban Portland and are less competitive in the urban soil environment. In such cases, simple eradication of non-native species is likely to be ineffective and an integrated restoration approach that considers and ameliorates the soil conditions that promote invasibility should be more successful