Dune and swale complexes have four distinct, alternating zones. These are the beach and foredune, the open interdunal swales, the forested dune ridges, and the forested swales. Dune and swale complexes can be quite extensive; one of the largest is the 40 mile long Tolston Beach complex along the southern Lake Michigan shoreline in Indiana and Illinois.
Bare sand and herbaceous vegetation characterize the foredune, and often two or three additional beach ridges farther inland. Marram grass is a major pioneering plant on the beach ridge closest to the shoreline.
The wetness of interdunal swales near the present lakeshore is determined by the Great Lakes water level. Swales farther from the shoreline can also be flooded, but these swales are typically flooded because of ground-water flow or seepage, not due to the lake’s water level.
Reduced sand accumulation in the dune and swale complex allows trees to establish without being buried. Large white and red pine on the ridges provide nest trees for bald eagles and ospreys.
The establishment of forests within the swales is much more gradual than the establishment of forests on the ridges. Herbs and shrubs are gradually replaced by swamp conifers as one proceeds further from the shoreline and as the swales become drier.