Factors Influencing Non-Native Tree Species Distribution in Urban Landscapes

Non-native species are presumed to be pervasive across the urban landscape. Yet, we actually know very little about their actual distribution. For this study, vegetation plot data from Syracuse, NY and Baltimore, MD were used to examine non-native tree species distribution in urban landscapes. Data were collected from remnant and emergent forest patches on upland sites and riparian habitats. Non-native tree species were divided into three groups based on their frequency of occurrence: ubiquitous, common and infrequent. Unique species distributions were observed. For example, Acer platanoides was a common species on remnant forest patches but was an ubiquitous species on emergent forest patches. In riparian habitats, however, A. platanoides was infrequent. Site histories also played an important role, especially for infrequent species on upland sites. For example, Syringa vulgaris occurred only on abandoned residential sites. Surprisingly, riparian habitats had only four non-native tree species as compared to seven for remnant and 23 species for emergent forest patches on upland sites. No ubiquitous, non-native tree species were observed for riparian habitats and only one species Morus alba was common. It occurred on 11 of the 33 plots. The other three nonnative species on riparian sites occurred infrequently. For upland and riparian