The effects of urban land use and human disturbance on forested wetland invasibility

Patches of natural vegetation within urban landscapes are assumed to be highly disturbed, often by the incursion of exotic invasive species. However, categorizing the land usage adjacent to natural communities as simply "urban" does not convey the heterogeneity and complexity of influences that various types of urban land uses have on adjacent communities. The objective of this study is to correlate community composition and structure to types of adjacent land use and interior human use and determine the role these disturbances play in exotic species invasion. This study was conducted in forested wetlands of the highly urbanized Arthur Kill watershed, New Jersey, USA. I found that forested wetlands with different adjacent land uses that are otherwise similar in species composition and vegetation structure differ strikingly in their extent of invasion. Wetlands bordered by industrial land use were less invaded than wetlands within residential landscapes. This pattern is observed regardless of the size and shape of the wetland. Yet, the increase in exotic species was not a result of greater human activity within the residential wetlands. Adjacent human land use (% residential and industrial) had a greater influence on vegetation composition and structure than interior human use. Trail and ditch sample locations were more invaded than the interior transects, but trail area and ditch area were not correlated with measures of invasion. Measurements of the structure of edge indicated that residential edges are more open and less obstructed by vegetation than industrial edges. Both seed bank and seed rain collections concluded that residential wetlands received a greater number of native and exotic seeds total and generally averaged more native and exotic native species of seeds per plot than industrial wetlands. With a field and greenhouse germination study, I was able to conclude that Rosa multiflora , which has generally not invaded industrial wetlands but is found on the edges of industrial wetlands, is capable of germinating and growing in industrial wetland soil and within industrial wetlands. Therefore, adjacent land use is more important than internal human use or site conditions in determining invasibility by influencing edge structure and propagule pressure and dispersal.