Influence of urbanization on riparian forest diversity and structure in the Georgia Piedmont, US

Riparian forests are increasingly threatened by urban expansion and land use change worldwide. This study examined the relationships between landscape characteristics and woody plant diversity, structure, and composition of small order riparian corridors along an urban-rural land use gradient in the Georgia Piedmont, US. Riparian plant diversity, structure, and composition were related to landscape metrics and land use. Species richness was negatively associated with impervious surfaces and landscape diversity, and positively associated with forest cover and largest forest patch index. Shannon species diversity was strongly related to the biomass of non-native species, especially for the regeneration layer. Urban sites were characterized by high richness of non-native and pioneer species. Developing sites were dominated by the non-native shrub, Ligustrum sinense Lour., and several native overstory trees, mainly Acer negundo L. While agricultural and managed forest sites were composed of ubiquitous species, unmanaged forest sites had a structurally distinct midstory indicative of reduced disturbance. Urban and agricultural land uses showed decreased native stem densities and signs of overstory tree regeneration failure. Results from this study highlight the impact of the surrounding landscape matrix upon riparian forest plant diversity and structure.