PARENT SESSION
Contributed Oral Session 21: Urban Stream Ecosystems
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
Impacts of urbanization and land cover on riparian woody plant diversity, structure, and composition in the Piedmont of Georgia, USA.
Burton, Michele*,1, Samuelson, Lisa1, 1 Auburn University, Auburn, Alabama, USA
ABSTRACT- Changes in riparian woody plant assemblages are anticipated in the southeastern United States due to increases in urbanization rates. Because riparian forests serve important roles in maintaining water quality and biodiversity, understanding how they respond to urbanization is crucial. The objective of this study is to examine forest structure (leaf area index, density, diameter distribution, basal area, species form) and vegetation diversity indices such as importance values, Shannon-Wiener diversity and evenness of riparian woody plant species in response to a land use gradient in the Piedmont of Georgia, USA. Using digitized aerial photography taken of the 3-county study area in 2003, fifteen sub-watersheds (2000-400 ha) representing a gradient of land uses (mixed forest, pine plantation, agriculture, suburban, urban) were identified. In the summers of 2003-2004, woody vegetation (>2.54cm dbh) within a 3.5 ha plot was sampled in each riparian community. In addition, woody plant regeneration (<2.54 dbh) was sub-sampled. Trends in forest structure and diversity along the gradient were identified. Most notably, shifts in Shannon diversity were significantly related to abundance of non-native species and predominant land use within each watershed. The invasive, non-native shrub Ligustrum sinense was a dominant species in the forest stand and regeneration layer for urban, suburban, and agriculture riparian communities. As forest cover within each watershed shifted to agricultural and urban land use, density of overstory trees species decreased linearly, while mean tree diameter increased. Tree diameter distributions also differed among land uses. Moreover, DCA ordinations suggest species composition along the gradient may be shifting from native riparian species to generalist and nonnative species. Species composition shifts were most notable in the regeneration layer. Changes in riparian forest diversity, structure and composition may subdue the ability of communities to maintain ecosystem stability and complexity.
Key words: urbanization, riparian forests, biodiversity, invasive species