In most forested landscapes, the organization of plant communities across stream valleys is thought to be regulated by a complex set of interactions including flooding, landform properties, and vegetation. However, few studies have directly examined the relative influence of frequent and infrequent flooding, as well as landform properties, on riparian plant community organization in moderately or deeply entrenched stream valleys where the magnitude and extent of frequent flooding may be constrained by local stream valley characteristics. Our approach, which we applied in an old-growth northern hardwood watershed, integrated detailed plant community surveys with a GIS and watershed surface hydrology model that allowed us to model water surface elevation associated with different flood magnitudes and recurrence intervals for specific locations across the old-growth watershed. Our results show that irrespective of stream valley geomorphology, the ground-flora exhibits a high rate of species replacement across the stream valley at low elevations, which are the most susceptible to frequent and more extreme infrequent flooding. However, over 50%of the major shifts in ground-flora community composition and almost all of the shifts in overstory composition occur beyond the direct influence of flooding, especially in the high-gradient moderately and deeply entrenched stream valleys. In these areas, landform boundaries and changes in the environmental properties associated with these boundaries appear to be the primary factors controlling changes in vegetation across the stream valley.
Northern hardwood forest ecosystems
Goebel, P. Charles; Pregitzer, Kurt S.; Palik, Brian J. 2012. Influence of flooding and landform properties on riparian plant communities in an old-growth northern hardwood watershed. Wetlands. 32(4): 679-691.