Southern Hardwood Swamp
Southern hardwood swamp is a minerotrophic forested wetland occurring in southern Lower Michigan on mineral or occasionally organic soils dominated by a mixture of lowland hardwoods. Conifers are absent or local. The community occupies shallow depressions and high-order stream drainages on a variety of landforms. The canopy is typically dominated by silver maple (Acer saccharinum), red maple (A. rubrum), green ash (Fraxinus pennsylvanica), and black ash (Fraxinus nigra).
County Distribution Map
Global Rank: G3 - Vulnerable
State Rank: S3 - Vulnerable
Southern hardwood swamp occurs in poorly drained depressions on glacial lakeplain, outwash plains and channels, end moraines, till plains, and perched dunes. Historically, the Maumee Lake Plain in southeastern Michigan supported large areas of lowland hardwood forest that bordered lakeplain prairie, lakeplain oak openings, wet-mesic flatwoods, and mesic southern forest. In large wetland complexes, southern hardwood swamp is typically associated with a variety of other herbaceous, shrub, and forested wetland communities. Upland communities bordering southern hardwood swamp are usually forested, with mesic southern forest being most common.
Soils are typically loam or silt loam, sometimes sandy loam or clay loam, of neutral to mildly alkaline pH (sandy substrates are more acidic), and sometimes covered by a thin layer of muck. An underlying impermeable clay lens is often present and allows for prolonged pooling of water. Occasionally the community occurs on deep sapric peat, especially inland, where stands may be associated with conifer or hardwood-conifer, minerotrophic peatlands.
Water levels fluctuate seasonally, with standing water typically occurring throughout winter and spring. Due to anaerobic conditions associated with prolonged inundation and a high water table, trees are shallowly rooted and prone to frequent blowdown. Windthrow creates a pit and mound microtopography, and variously sized canopy gaps, which promote regeneration of a diverse overstory. In addition, the pit and mound microtopography generates fine-scale gradients of soil moisture and soil chemistry and provides a diversity of microsites for plant establishment. As spring floodwater drains, both the residual mucky pools and exposed tip-up mounds provide different habitat conditions, fostering high plant diversity. Coarse woody debris, which typically lies above the zone of flooding, remains a continued source of saturated substrate for seed germination and seedling establishment through drier periods. Prolonged flooding, often associated with beaver activity, leads to tree mortality and dominance by light-requiring shrubs and ground flora, typically sedges and grasses. Groundwater seepage affects species composition and structure. Fire is likely rare to infrequent, but may impact some stands in periods of extended drought, particularly in areas characterized by fire-dependent upland natural communities (e.g., oak barrens).
Dominance patterns vary, based largely on substrate characteristics, hydrology, and regional floristic distribution patterns. Sites on mineral soil that experience significant periods of inundation and seasonal water level fluctuation are typically dominated by silver maple (Acer saccharinum) and green ash (Fraxinus pennsylvanica), with red maple and pin oak (Quercus palustris) often as important subdominants. Tree species typical of floodplain forest are often present, including hackberry (Celtis occidentalis), sycamore (Platanus occidentalis), and cottonwood (Populus deltoides). Other associates include sugar maple (Acer saccharum), white ash (Fraxinus americana), black ash (F. nigra), tulip tree (Liriodendron tulipifera), quaking aspen (Populus tremuloides), swamp white oak (Quercus bicolor), bur oak (Q. macrocarpa), red oak (Q. rubra), basswood (Tilia americana), and American elm (Ulmus americana). Prior to the introduction and spread of Dutch elm disease, American elm was an important canopy constituent, but is now largely relegated to the subcanopy and sapling layers. Other common understory species include saplings of canopy tree species (especially silver and red maple), musclewood (Carpinus caroliniana), and witch hazel (Hamamelis virginiana). Characteristic shrub species include spicebush (Lindera benzoin), elderberry (Sambucus canadensis), winterberry (Ilex verticillata), and buttonbush (Cephalanthus occidentalis). The ground layer is characteristically sparse due to prolonged inundation during the early growing season. Commonly encountered species include false nettle (Boehmeria cylindrica), marsh marigold (Caltha palustris), spring cress (Cardamine bulbosa), pink spring cress (C. douglassii), fowl manna grass (Glyceria striata), jewelweed (Impatiens capensis), swamp buttercup (Ranunculus hispidus), bishop’s cap (Mitella diphylla), wild geranium (Geranium maculatum), dwarf raspberry (Rubus pubescens), spinulose woodfern (Dryopteris carthusiana), cinnamon fern (Osmunda cinnamomea), sedges (Carex gracillima, C. intumescens, C. radiata, and C. stipata), poison ivy (Toxicodendron radicans), and Virginia creeper (Parthenocissus quinquefolia).
Sites on saturated organic soil of relatively stable hydrology are typically dominated by red maple and black ash. Common canopy associates include yellow birch (Betula alleghaniensis) and American elm; occasional associates include sugar maple, silver maple, American beech (Fagus grandifolia), white ash, green ash, tulip tree, quaking aspen, swamp white oak, sycamore, and basswood. Stands associated with hardwood-conifer swamp or rich tamarack swamp may occasionally contain scattered individuals of tamarack (Larix laricina), white pine (Pinus strobus), hemlock (Tsuga canadensis), or northern white-cedar (Thuja occidentalis). The subcanopy and tall shrub layers can range from open to closed, depending on canopy closure. The shrub layer is characterized by saplings of canopy species, in addition to musclewood, winterberry, poison ivy, nannyberry (Viburnum lentago), silky dogwood (Cornus amomum), gray dogwood (C. foemina), spicebush, elderberry, smooth highbush blueberry (Vaccinium corymbosum), and occasionally buttonbush in the most open and wettest swales. The ground layer ranges from sparse under the dense shade of hardwoods or in areas subject to seasonal inundation to dense in light gaps and openings. Stands are often characterized by the development of moss and litter-covered hummocks that are elevated above the saturated or inundated muck hollows. Characteristic species of hummocks and decomposing wood include spinulose woodfern, goldthread (Coptis trifolia), bishop’s cap, Canada mayflower (Maianthemum canadense), and dwarf raspberry. Typical species of hollows and open, mucky flats include skunk cabbage (Symplocarpus foetidus), pink spring cress, spring cress, jack-in-the-pulpit (Arisaema triphyllum), marsh marigold, fowl manna grass, sedges (Carex radiata, C. intumescens, C. stipata, etc.), northern bugle weed (Lycopus uniflorus), false nettle (Boehmeria cylindrica), marsh fern (Thelypteris palustris), cinnamon fern, sensitive fern (Onoclea sensibilis), jewelweed, and clearweed (Pilea spp.) Areas of standing water are sometimes dominated by small duckweed (Lemna minor) or, in the spring, by golden saxifrage (Chrysosplenium americanum).
Beaver can cause prolonged flooding that substantially alters wetland community structure, converting southern hardwood swamps to a broad range of wetland types, depending on landscape position, soils, and depth and duration of flooding.
- Betula murrayana (Murray birch, state special concern)
- Carex lupuliformis (false hop sedge, state threatened)
- Carex seorsa (sedge, state threatened)
- Carex straminea (straw sedge, state endangered)
- Cuscuta glomerata (rope dodder, state special concern)
- Cuscuta polygonorum (knotweed dodder, state special concern)
- Dryopteris celsa (log fern, state threatened)
- Eupatorium fistulosum (hollow-stemmed joe-pye-weed, state threatened)
- Fraxinus profunda (pumpkin ash, state threatened)
- Galearis spectabilis (showy orchis, state threatened)
- Hybanthus concolor (green violet, state special concern)
- Hydrastis canadensis (goldenseal, state threatened)
- Isotria medeoloides (smaller whorled pogonia, state endangered)
- Isotria verticillata (whorled pogonia, state threatened)
- Lysimachia hybrida (swamp candles, state special concern)
- Panax quinquefolius (ginseng, state threatened)
- Panicum microcarpon (small-fruited panic grass, state special concern)
- Plantago cordata (heart-leaved plantain, state endangered)
- Poa paludigena (bog bluegrass, state threatened)
- Polymnia uvedalia (large-flowered leafcup, state threatened)
- Populus heterophylla (swamp or black cottonwood, state endangered)
- Rudbeckia subtomentosa (sweet coneflower, presumed extirpated from Michigan)
- Trillium undulatum (painted trillium, state endangered)
- Valerianella umbilicata (corn-salad, state threatened)
- Viburnum prunifolium (black haw, state special concern)
- Woodwardia areolata (netted chain-fern, presumed extirpated from Michigan)
- Accipiter cooperii (Cooper’s hawk, state special concern)
- Acronicta falcula (corylus dagger moth, state special concern)
- Ambystoma opacum (marbled salamander, state threatened)
- Ambystoma texanum (smallmouth salamander, state endangered)
- Basilodes pepita (gold moth, state special concern)
- Buteo lineatus (red-shouldered hawk, state threatened)
- Catocala illecta (Magdalen underwing, state special concern)
- Clemmys guttata (spotted turtle, state threatened)
- Clonophis kirtlandii (Kirtland’s snake, state endangered)
- Emydoidea blandingii (Blanding’s turtle, state special concern)
- Euphyes dukesi (Dukes’ skipper, state threatened)
- Gomphus quadricolor (rapids clubtail, state special concern)
- Haliaeetus leucocephalus (bald eagle, state threatened)
- Heterocampa subrotata (small heterocampa, state special concern)
- Heteropacha rileyana (Riley’s lappet moth, state special concern)
- Incisalia henrici (Henry’s elfin, state special concern)
- Myotis sodalis (Indiana bat, federal/state endangered)
- Nerodia erythrogaster neglecta (copperbelly watersnake, federal threatened and state endangered)
- Nycticorax nycticorax (black-crowned night-heron, state special concern)
- Pandion haliaetus (osprey, state threatened)
- Papaipema cerina (golden borer, state special concern)
- Papaipema speciosissima (regal fern borer, state special concern)
- Protonotaria citrea (prothonotary warbler, state special concern)
- Seiurus motacilla (Louisiana waterthrush, state special concern)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
- Terrapene c. carolina (eastern box turtle, state special concern)
Biodiversity Management Considerations
Conservation of wetlands requires management and protection of adjacent upland communities aimed at maintaining hydrology, minimizing inputs of nutrient-rich runoff, and protecting and managing habitat for animal species that require both upland and wetland habitats. Hydrologic alteration associated with agriculture, roads, or other development can alter species composition and structure, and foster establishment of invasive species. Where the primary conservation objective is to maintain biodiversity in southern hardwood swamps, the best management is to leave large tracts unperturbed and allow natural processes such as flooding, windthrow, and senescence to operate unhindered.
Monitoring and control efforts to detect and remove invasive species are critical to the long-term viability of southern hardwood swamp. Invasive plant species that threaten the diversity and community structure include garlic mustard (Alliaria petiolata), reed canary grass (Phalaris arundinacea), reed (Phragmites australis subsp. australis), autumn olive (Elaeagnus umbellata), multiflora rose (Rosa multiflora), and glossy buckthorn (Frangula alnus). Light-requiring invasive plant species such as reed and reed canary grass can establish in canopy gaps and in openings along streams. Emerald ash borer, an invasive insect, has reduced or eliminated ash as an important component of upland and lowland forest types in southeastern Michigan and has the potential to significantly impact ash populations in forested wetlands and uplands throughout the state.
Dominance patterns among common canopy constituents vary based on site-specific factors. Silver maple and green ash indicate fluctuating hydrology and seasonal inundation, whereas areas dominated by red maple and black ash indicate a more stable hydrology influenced by persistent groundwater seepage. Stands that contain conifers may represent converted hardwood-conifer swamp, rich tamarack swamp, or rich conifer swamp. Conversion of conifer-dominated stands to hardwood dominance is frequently associated with anthropogenic disturbances such as logging, hydrologic alteration, and fire suppression. Small forested seeps embedded in a matrix of dry-mesic and mesic southern forest in southern Lower Michigan are currently placed in this classification, and sometimes include species otherwise absent in mixed hardwood swamp, including Ohio buckeye (Aesculus glabra), pawpaw (Asimina triloba), blue ash (Fraxinus quadrangulata), and hackberry.
Similar Natural Communities
- Abrams, M.D. 1998. The red maple paradox. BioScience 48: 355-364.
- Comer, P.J., D.A. Albert, H.A. Wells, B.L. Hart, J.B. Raab, D.L. Price, D.M. Kashian, R.A. Corner, and D.W. Schuen. 1995. Michigan’s presettlement vegetation, as interpreted from the General Land Office surveys 1816-1856. Michigan Natural Features Inventory, Lansing, MI. Digital map.
- Knopp, P.D. 1999. Landscape ecosystems of the Maumee Lake Plain, southeastern Lower Michigan: Interrelationships of physiography, soil, and vegetation. M.S. thesis, University of Michigan, Ann Arbor, MI. 100 pp.
- Lee, J.G. 2005. Landscape ecology of silver maple (Acer saccharinum L.) in wetlands of southeastern Michigan. M.S. thesis, University of Michigan, Ann Arbor, MI. 195 pp.
- Merkey, D.H. 2006. Characterization of wetland hydrodynamics using HGM and subclassification methods in southeastern Michigan, USA. Wetlands 26: 358-367.
- NatureServe. 2006. NatureServe Explorer: An online encyclopedia of life [Web application]. Version 6.1. NatureServe, Arlington, VA. Available http://www.natureserve.org/explorer. (Accessed: December 4, 2006.)
- Orr, S.P., J.A. Rudgers, and K. Clay. 2005. Invasive plants can inhibit native tree seedlings: Testing potential allelopathic mechanisms. Plant Ecology 181: 153-165.
- Riffell, S., T. Burton, and M. Murphy. 2006. Birds in depressional forested wetlands: Area and habitat requirements and model uncertainty. Wetlands 26: 107-118.
- Schneider, G.J., and K.E. Cochrane. 1998. Plant community survey of the Lake Erie Drainage. Ohio Department of Natural Resources, Division of Natural Areas and Preserves, Columbus, OH.
For a full list of references used to create this description, please refer to the natural community abstract for southern hardwood swamp.
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.