Wooded Dune and Swale Complex
Wooded dune and swale complex is a large complex of parallel wetland swales and upland beach ridges (dunes) found in coastal embayments and on large sand spits along the shorelines of the Great Lakes. The upland dune ridges are typically forested, while the low swales support a variety of herbaceous or forested wetland types, with open wetlands more common near the shoreline and forested wetlands more prevalent further from the lake. Wooded dune and swale complexes occur primarily in the northern Lower and Upper Peninsulas and Thumb region.
County Distribution Map
Global Rank: G3 - Vulnerable
State Rank: S3 - Vulnerable
Wooded dune and swale complexes are found in coastal embayments and on large sand spits along shorelines of the Great Lakes in Minnesota, Wisconsin, Michigan, Illinois, Pennsylvania, Ohio, and Ontario. They were formed in two stages by retreating water levels and post-glacial uplift beginning with glacial Lake Algonquin approximately 12,000 years ago. As lake levels progressively receded, they deposited a series of low, parallel, sandy beach ridges ranging in height from 0.5 m to 4.0 m. The alternating sequence of arced sand ridges and associated swales often extends up to two miles inland.
Given the complexity and variation of wooded dune and swale complexes, soils can range from calcareous sands in the foredunes to deep acidic peat or alkaline marl in well-established swales.
Wooded dune and swale complexes formed as a result of receding Great Lakes water levels and post-glacial uplift that created a series of parallel, arced, low sand ridges and swales. Vegetative succession has since created a distinct pattern of communities or zones across this landscape complex. The flow of surface streams and groundwater is critical for maintaining saturated to inundated conditions in swales. Because of the close proximity to the shoreline, windthrow is common, especially on the loose organic soils of swales where anaerobic conditions limit the rooting depth of trees. Along-shore currents, waves, and wind create and continuously re-work foredunes along the shoreline. Additional important components of the natural disturbance regime include fire, beaver flooding, and insect epidemics.
Wooded dune and swale complexes consist of a distinct series of successional vegetative zones or communities determined by factors such as distance from the lake, amount of soil development, groundwater input, and light availability. Component communities typically proceed from primary open dunes and interdunal wetlands along the shore to grassland, then shrubland, and finally forested dune ridges and swales farther inland. With increasing distance from the lakeshore, there is greater protection from wind and wave action and subsequently greater soil development and more complex natural communities.
Vegetation growing on the low foredunes along the shorelines commonly includes marram grass (Ammophila breviligulata), dune grass (Calamovilfa longifolia), autumn willow (Salix serissima), sand dune willow (S. cordata), and balsam poplar (Populus balsamifera).
Behind foredunes, where saturated lake-influenced, calcareous sands form the substrate, common species include twig-rush (Cladium mariscoides), sweet gale (Myrica gale), shrubby cinquefoil (Dasiphora fruticosa), bluejoint grass (Calamagrostis canadensis), Kalm's lobelia (Lobelia kalmii), false asphodel (Triantha glutinosa), grass-of-Parnassus (Parnassia glauca), rushes (i.e., Juncus balticus, J. pelocarpus, and J. nodosus), spike-rush (Eleocharis acicularis), and three-square (Schoenoplectus pungens).
A low dune field is often present and typically supports a scattered overstory of jack pine (Pinus banksiana), white pine (P. strobus), and red pine (P. resinosa) and an understory and ground layer of common juniper (Juniperus communis), creeping juniper (J. horizontalis), bearberry (Arctostaphylos uva-ursi), marram grass, and June grass (Koeleria macrantha).
Inland of the dune field, both the dune ridges and swales are typically forested, although open, herbaceous wetlands may be common in the swales closer to the shoreline. Moist swales typically contain saturated organic soils and support partial to closed canopies of northern white-cedar (Thuja occidentalis), tag alder (Alnus incana), willows (Salix spp.), and red maple (Acer rubrum).
Swales where standing water is present through most of the year typically lack an overstory and instead are dominated by sedges (Carex aquatilis and C. stricta), twig-rush, marsh marigold (Caltha palustris), swamp candles (Lysimachia terrestris), sweet gale (Myrica gale), and swamp cinquefoil (Comarum palustre). Where organic soils have accumulated to greater depths farther from the shoreline, vegetation in open swales may reflect more acid conditions and support species such as leatherleaf (Chamaedaphne calyculata), bog rosemary (Andromeda glaucophylla), Labrador tea (Rhododendron groenlandicum), bog laurel (Kalmia polifolia), large cranberry (Vaccinium macrocarpon), cottongrass (Eriophorum virginicum), pitcher-plant (Sarracenia purpurea), and sphagnum mosses (i.e., Sphagnum centrale, S. wulfianum, S. warnstorfii, S. magellanicum, and S. squarrosum). Shrub-dominated swales with scattered trees are also common and typically include species such as tag alder, black chokeberry (Aronia prunifolia), red-osier dogwood (Cornus sericea), bog birch (Betula pumila), as well as sedges (Carex lasiocarpa, C. oligosperma, C. aquatilis, and C. stricta), wool grass (Scirpus cyperinus), and marsh fern (Thelypteris palustris).
Forested beach ridges tend to be dominated by species common to dry-mesic northern forest and mesic northern forest including red pine, white pine, and red oak (Quercus rubra). Subcanopy dominants often include paper birch (Betula papyrifera), big-toothed aspen (Populus grandidentata), balsam fir (Abies balsamea), and red maple. Common species of the shrub and ground layers of inland beach ridges include bracken fern (Pteridium aquilinum), huckleberry (Gaylussacia baccata), Canada blueberry (Vaccinium myrtilloides), bunchberry (Cornus canadensis), and wintergreen (Gaultheria procumbens).
On lower dune ridges, where soils are moister, white pine may share dominance with white spruce (Picea glauca), black spruce (P. mariana), red maple, balsam fir, northern white-cedar, and occasionally tamarack (Larix laricina). Common shrub and ground layer species on the lower dune ridges may include American fly honeysuckle (Lonicera canadensis), mountain holly (Ilex mucronata), twinflower (Linnaea borealis), dwarf raspberry (Rubus pubescens), Canada mayflower (Maianthemum canadense), and starflower (Trientalis borealis).
Beaver (Castor canadensis) can dam streams that flow through wooded dune and swale complexes, causing vegetation in affected swales to shift from forest to emergent marsh and northern wet meadow.
- Armoracia lacustris (lakecress, state threatened)
- Carex albolutescens (greenish-white sedge, state threatened)
- Carex nigra (black sedge, state endangered)
- Calypso bulbosa (calypso, state threatened)
- Cirsium pitcheri (Pitcher’s thistle, state threatened)
- Crataegus douglasii (Douglas’ hawthorn, state special concern)
- Cypripedium arietinum (ram’s head lady’s-slipper, state special concern)
- Elymus glaucus (blue wild rye, state special concern)
- Elymus mollis (American dune wild-rye, state special concern)
- Iris lacustris (dwarf lake iris, state threatened)
- Orobanche fasciculata (fascicled broom-rape, state threatened)
- Pterospora andromedea (pine-drops, state threatened)
- Ranunculus lapponicus (Lapland buttercup, state threatened)
- Salix pellita (satiny willow, state special concern)
- Solidago houghtonii (Houghton’s goldenrod, federal/state threatened)
- Stellaria longipes (starwort, state special concern)
- Tanacetum huronense (Lake Huron tansy, state threatened)
- Accipiter gentilis (northern goshawk, state special concern)
- Buteo lineatus (red-shouldered hawk, state threatened)
- Canis lupus (gray wolf, state threatened)
- Charadrius melodus (piping plover, federal/state endangered)
- Euxoa aurulenta (dune cutworm, state special concern)
- Falco columbarius (merlin, state threatened)
- Haliaeetus leucocephalus (bald eagle, state threatened)
- Lanius ludovicianus migrans (migrant loggerhead strike, state endangered)
- Pandion haliaetus (osprey, state threatened)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
- Trimerotropis huroniana (Lake Huron locust, state threatened)
Biodiversity Management Considerations
Residential and recreational development and accompanying road building in and around wooded dune and swale complexes has resulted in disrupted hydrological conditions, wetland destruction, nutrient loading, and the introduction of invasive species. Conservation efforts should focus on protecting wooded dune and swale complexes from development and fragmentation, preserving natural hydrology, and controlling invasive species. Because of the wide diversity of habitats provided by wooded dune and swale complexes, invasive species that threaten the diversity and community structure include species from all ends of the moisture and light continuums. Particularly aggressive invasives to monitor and promptly remove if found include garlic mustard (Alliaria petiolata), Dame’s rocket (Hesperis matronalis), purple loosestrife (Lythrum salicaria), narrow-leaved cat-tail (Typha angustifolia), hybrid cat-tail (Typha xglauca), reed (Phragmites australis subsp. australis), reed canary grass (Phalaris arundinacea), European marsh thistle (Cirsium palustre), spotted knapweed (Centaurea stoebe), common buckthorn (Rhamnus cathartica), glossy buckthorn (Frangula alnus), autumn olive (Elaeagnus umbellata), Eurasian honeysuckles (especially Lonicera morrowii, L. tatarica, and L. xbella), multiflora rose (Rosa multiflora), and Norway maple (Acer platanoides).
The following five sub-types of wooded dune and swale complexes have been identified based on differences in geographic location, processes of beach ridge formation, and plant assemblages: Southern Lake Huron; Northern Lake Huron/Lake Michigan-Low Dune; Northern Lake Michigan-High Dune; Lake Superior-High Dune; and Lake Superior-Low Dune.
Similar Natural Communities
Wooded dune and swale complexes may encompass several natural communities, including emergent marsh, northern wet meadow, northern shrub thicket, northern fen, poor fen, coastal fen, Great Lakes barrens, interdunal wetland, rich conifer swamp, poor conifer swamp, hardwood-conifer swamp, bog, dry northern forest, dry-mesic northern forest, mesic northern forest, open dunes, and sand and gravel beach.
- Albert, D.A., and P.J. Comer. 1999. Natural community abstract for wooded dune and swale complex. Michigan Natural Features Inventory, Lansing, MI. 8 pp.
- Comer, P.J., and D.A. Albert. 1993. A survey of wooded dune and swale complexes in Michigan. Report to Michigan DNR, Land and Water Managment Division, Coastal Zone Management Program. 159 pp.
- Dorr, J.A., and D.F. Eschman. 1970. Geology of Michigan. University of Michigan Press, Ann Arbor, MI 476 pp.
- Lichter, J. 1998. Primary succession and forest development on coastal Lake Michigan sand dunes. Ecological Monographs 68(4): 487-510.
- Thompson, T.A. 1992. Beach-ridge development and lake-level variation in southern Lake Michigan. Sedimentary Geology 80: 305-318.
For a full list of references used to create this description, please refer to the natural community abstract for wooded dune and swale complex.
Kost, M.A., D.A. Albert, J.G. Cohen, B.S. Slaughter, R.K. Schillo, C.R. Weber, and K.A. Chapman. 2007. Natural Communities of Michigan: Classification and Description. Michigan Natural Features Inventory, Report No. 2007-21, Lansing, MI.