Environmental gradients and vegetation patterns on the Roanoke River floodplain, North Carolina

This research examined landscape-scale processes that influence vegetation patterns on the Roanoke River floodplain of North Carolina. The results include the development of spatially-explicit, quantitative representations of the major environmental factors that influence forest patterns and regeneration in the study area. The research has involved the following: development of a detailed vegetation classification of ecologically significant terrestrial and aquatic communities from multi-temporal Landsat TM imagery; creation of an extensive digital database with important environmental variables for research and resource management; development of a digital elevation model, from which models of potential flood inundation were derived; production of a model of potential hydroperiod regime, incorporating both spatial and temporal properties, using multi-temporal synthetic aperture radar (SAR) imagery; and integration of field data, GIS variables, and remote sensing analyses to examine species and community distributions on the lower Roanoke River floodplain.;SAR was used to successfully identify patterns of flood inundation beneath the forest canopy. These results were applied directly to analyses of the vegetation of the region, and helped explain community and species distributions on the floodplain. The analyses of vegetation data indicated a distinct series of gradients related to topographic position in the floodplain, hydroperiod, and alluvial processes (sedimentation, organic matter accumulation). Modeling of species distributions on the floodplain suggested that vegetation communities in many locations are mismatched with the current environmental processes. Specifically, the relatively flood-intolerant species Fagus grandifolia is modeled to be much more prominent on the floodplain than it presently is. The modeling results are corroborated by data on species regeneration, which indicate the widespread abundance of beech seedlings in forests that are currently dominated by other species. This indicates that the conditions under which the current forests established differ from those present today. There are several potential causes for vegetation change in the region, including, most prominently, changes in hydrology due to the construction of dams on the river upstream of the study area. This research represents the foundation for a watershed-scale analysis of the response of an ecosystem to regional and global change.