Urban environments alter our natural world in ways that researchers have just begun to understand. The effects of urbanization on riparian zones are particularly important because these areas function as natural water filters. Access to potable water in some areas is becoming a greater concern than access to cheap energy supplies. Changes in overall composition and diversity can inhibit functioning and reduce the ecosystem services that these systems provide. In order to determine the effect of urbanization on riparian plant communities, I chose 3 adjacent catchments, subdividing each into subcatchments. Within each subcatchment, I determined the percent impervious surface (IS) and classified each as urban, suburban, and rural. I characterized and contrasted the overall plant species composition and diversity between urban, suburban, and rural environments by selecting one site location per subcatchment and laying down one transect extending up to 100 meters perpendicular to the stream channel. I placed up to 3 nested plots along each transect equidistant from each other. Within each plot I identified trees, saplings, and shrubs to species, recording diameter at base height (dbh) for trees, and stem counts for saplings and shrubs. Sampling was conducted in Summer 2005 and 2006. To classify the vegetation into plant community types, I conducted a non-metric multidimensional scaling (NMS) ordination and indicator species analysis using PCOrd software.
Results/Conclusions
The results of the ordination analysis revealed that overall species composition differed between urban and rural sites. Two species were strongly correlated with one NMS axis: exotic Amur honeysuckle (Lonicera maackii) and native Spicebush (Lindera benzoin). Indicator species analysis of the shrub layer showed these species differences to be indicative of an impervious surface gradient, with Amur honeysuckle having an indicator value of 60 (p=0.002) in urban subcatchments (> 30% IS), and Spicebush having an indicator value of 38 (p=0.013) in rural subcatchments (< 10% IS). Exotic shrub species, such as Amur honeysuckle, are gaining greater importance within urban areas, and native shrub species, such as Spicebush, are losing importance. Amur honeysuckle also has the potential to be used as an indicator species of particular environmental conditions which are associated with urban areas.
