Ohio subset of Plant Communities of the Midwest ... - NatureServe

Sphagnum wulfianum, Sphagnum warnstorfii, Sphagnum magellanicum, and Sphagnum squarrosum) are commonly
found in the thick peat soils of the swale behind the shoreline (MNFI 1999).
As described by the MNFI (1999) summary description this complex, composed of upland and wetland features, is
found in embayments and sand spits along the Great Lakes shoreline. Most were formed in two stages, with
progressive dropping lake levels and post-glacial uplift beginning with the glacial Lake Algonquin levels (approx.
12,000 years ago), and again with the Lake Nipissing water levels 3000-4000 years ago. The receding lake levels
deposited a series of sandy beach ridges ranging from 0.5 to 4 m high. From the air these ridges appear as a series
of arcs, extending inland up to 2 miles, generally parallel to the present shoreline. In several examples, beach ridges
were also built up and re-sorted by wind, creating a higher, somewhat irregular dune ridge.
These complexes are often best developed where post-glacial streams entered an embayment and provide a
dependable sand source. The combination of along-shore currents, waves, and winds form foredunes along the
shoreline. With gradual long-term drops in water level, combined with post-glacial uplifting of the earth's crust, these
low dunes gradually rise above the direct influence of the lakes, and new foredunes replace them. Over several
thousand years, a series of ridges and swales is created. For most complexes, the flow of surface streams and
groundwater maintain the wet conditions in the swales. With time, plant succession has proceeded to the point where
the beach ridges are now forested while the wet swales are either forested or open wetlands. Along the Lake
Superior shoreline, where post-glacial uplift is greatest, many of the complexes consist primarily of dry, forested
swales (Comer and Albert 1993). The number and size of the dune ridges and swales differs depending on fetch and
the amount of sediment available.
Both swales and upland dune ridges have been studied (Comer and Albert 1993). Of the 17 sites where elevations
were measured from the shoreline inland, only 3 sites contained swales where the sandy bottoms of all or most of the
swales lay below the current Great Lakes water levels. This suggests that, except for a few examples, the influence
of Great Lakes water-level fluctuations is probably limited to the first few swales inland from the shoreline. For most of
the complexes, the water occupying the swales comes from streams flowing from the adjacent uplands or from
groundwater seepage (MNFI 1999).
Classic ecological studies have identified distinctive successional zones within the sand dune portion of the
complexes, determined on the basis of several factors, including distance from the lake, amount of soil development,
and available light (Olson 1958,Cowles 1899). Lichter's (1998) recent study of dune-and-swale complexes at
Wilderness State Park in northern Lower Michigan has identified similar successional trends. He found that, at the
Lake Michigan shoreline, young dunes had (1) stronger winds, (2) more sand burial and erosion, (3) higher levels of
sunlight, (4) higher rates of evaporation, and (5) lower available nitrogen and phosphorus than older beach ridges
farther inland, resulting in an open herbaceous-dominated plant community along the shore. Farther inland, with
greater protection from sun and wind and with greater soil development, there was succession from open dune, first
to grassland, then to shrubs, and finally to forests, with mesic northern hardwoods increasing in dominance on beach
ridges farther from the shoreline.
COMMENTS: 3, MCS. Because they contain a unique assemblage of physiographic, soil, and vegetative components,
and provide a high-quality habitat for numerous shoreline animal species, the Wooded Dune and Swale Complex is
considered a distinct complex that groups together a number of different associations, some restricted to the
complex, others more wide-ranging. The various zones of plant communities in each complex may include several of
the following, depending on the complex subtype and local site: Great Lakes Foredune, Interdunal Wetland, Great
Lakes Pine Barrens, Great Lakes Dune Pine Forest, Red Pine / Blueberry Dry Forest, White Pine - Red Oak Forest,
Great Lakes White Pine - Hemlock Forest, White Cedar - (Hemlock) Mesic Forest, White Cedar - Mixed Hardwood
Swamp, Black Ash - Mixed Hardwood Swamp, Speckled Alder Swamp, Bog Birch - Willow Rich Boreal Fen,
Leatherleaf Bog, Northern Poor Fen, Tussock Sedge Wet Meadow.
The complex can be further subdivided into five complex subtypes, reflecting north-south trend in plant species
distributions, from southern Lake Huron to western Lake Superior, along with the relative impact of wind-sorting
versus water-lain processes that formed the beach ridges of each complex. The five subtypes include the southern
Lake Huron subtype, the northern Lake Huron/Lake Michigan-Low Dune subtype, the Northern Lake Michigan-High
Dune subtype, the Lake Superior-High Dune subtype, and the Lake Superior-Low Dune subtype. Southern Lake
Michigan dune/swale complexes in Indiana and Illinois are currently very minor and not included here. It is possible
that these dune/swale complexes have mostly dried out and blown away (P. Comer pers. comm. 2000). Northward in
southern Michigan, the dunes are perched and complexes do not form. Rather, scattered Interdunal Wetlands occur.
Possible complexes in Lake Erie (Pennsylvania) and elsewhere in shorelines in Ontario may require additional
subtypes.
CONSERVATION RANK: G3. Wooded dune and swale complexes are restricted to the Great Lakes shoreline (Comer
and Albert 1991, 1993, Homoya et al. 1985). Although there are features of similar geological origin along the shorelines
of most oceans and seas, the biota of the marine systems is distinctly different (Wiedemann 1984). Residential
and recreational development has resulted in disrupted hydrological conditions and wetland destruction. Currently,
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