Flood Processes, Forest Dynamics, and Disturbance In the Congaree River Floodplain, South Carolina

Southeastern bottomland hardwood ecosystems thrive as a result of the biophysical linkages between the river and the floodplain. These ecosystems contain significant habitat heterogeneity and support rich diversity of species, but have been altered and manipulated by anthropogenic impacts. This study was designed to examine the forest development dynamics in abandoned meander landforms on the Congaree River floodplain, South Carolina in order to gain a better understanding of the forest successional responses to environmental gradients and historic logging disturbances. This study presents the innovative application of a 2D hydrodynamic flood model for simulating complex overland flow processes and quantifying hydrogeomorphic environmental data for use in ecological analysis. The 2D flood model is developed using high resolution terrain data and historical flows. The flood simulation model measures flood extent, depth, frequency and flood water retention capacity. These data were incorporated with structural and compositional forest surveys, additional environmental data, and historic logging information to compare forest patterns and other factors controlling succession in abandoned meander landforms. Forest development patterns varied as a function of the type of logging disturbance, hydrogeomorphic conditions, and environmental change. Three distinct successional patterns emerged that were linked with the following disturbance history: unlogged old-growth forests, selectively logged forests, and clear cut forests. Forest succession in old-growth environments exhibited a gradual transition from obligate wetland species to facultative species. In contrast, recovery patterns in clear-cut forests exhibited complete replacement of the original obligate wetland dominated community to a predominantly facultative community. Selectively logged sites showed the least amount of successional change, but they lacked recovery of the logged, Taxodium distichum component of the forest, which was replaced almost exclusively by Nyssa aquatica. Processes and patterns evidenced in the Congaree River floodplain provide a glimpse of the various controls and successional pathways that produce heterogeneous forest patterns. A 2D flood model proves to be a valuable tool for modeling complex overland flow processes for the Congaree floodplain and has many ecological applications. Flood and forest patterns revealed by this study can be used to help guide or redirect restoration efforts to match current or desired environmental conditions