Rich Conifer Swamp
Rich conifer swamp is a groundwater-influenced, minerotrophic, forested wetland dominated by northern white-cedar (Thuja occidentalis) that occurs on organic soils (i.e., peat) primarily north of the climatic tension zone in the northern Lower and Upper Peninsulas. The community is also referred to as cedar swamp.
County Distribution Map
Global Rank: G4 - Apparently secure
State Rank: S3 - Vulnerable
Rich conifer swamp occurs in outwash channels, outwash plains, glacial lakeplains, and in depressions on coarse- to medium-textured ground moraines. It is common in outwash channels of drumlin fields and where groundwater seeps occur at the bases of moraines. Rich conifer swamp typically occurs in association with lakes and cold, groundwater-fed streams. It also occurs along the Great Lakes shoreline in old abandoned embayments and in swales between former beach ridges where it may be part of a wooded dune and swale complex.
Climatic conditions in the community are influenced by its northerly distribution, low topographic position, and thick layer of mosses, especially sphagnum (Sphagnum spp.), which insulate the organic soils. At night, cold air drains down from the surroundings uplands throughout the growing season, causing condensation to collect on plants. This constant source of nocturnal moisture helps sustain the community’s abundant lichen and bryophyte flora. The cold air drainage may also cause nighttime temperatures to drop below freezing throughout the growing season. The insulating properties of sphagnum moss allow ice to remain within the upper layers of soil until mid-June or July, but in the fall, soils remain unfrozen until after snowfall, and deep penetration of frost may not occur until February. Thus, rich conifer swamp has a shorter, cooler, and more humid growing season than the surrounding uplands, while winters are milder and more even in temperature.
The soils are composed of saturated, coarse woody peat and may vary significantly in depth of organic matter. The organic soils are typically neutral to moderately alkaline but may be very strongly acid near the surface where sphagnum mosses dominate the ground layer. The structure and species composition of rich conifer swamp are strongly influenced by the constant flow of mineral-rich, cold groundwater through the organic soils.
Seasonal water level fluctuations, beaver flooding, windthrow, and fire are all important forms of natural disturbance for rich conifer swamp. Although rich conifer swamp is primarily groundwater fed, seasonal water-level fluctuations are common with water levels highest in spring and lowest in late summer and fall. In response to seasonal water level fluctuations, the roots of northern white-cedar and tamarack form extensive mats that stand elevated above adjacent inundated muck-flats or carpets of moss, creating a varied microtopography. Beaver flooding can cause extensive mortality of northern white-cedar and other woody plants, significantly altering community structure and composition. Prolonged flooding can cause conversion to shallow pond, emergent marsh, northern wet meadow, northern fen, poor fen, or northern shrub thicket depending on the depth and duration of inundation, local topography, and groundwater chemistry.
Due to anaerobic conditions associated with a high water table and organic soils, trees growing in rich conifer swamps are shallowly rooted, making them susceptible to frequent small-scale windthrow. As a result, leaning, bent, or fallen trees are common, creating tip-up mounds, abandoned root pits, and coarse woody debris that contribute to the complex structure and microtopography of rich conifer swamp. Northern white-cedar is well adapted to windthrow because of its ability to reproduce both sexually, through seed, and asexually, by growing adventitious roots when its lateral branches are in contact with the ground (i.e., layering).
Fire may spread through the community during extensive periods of drought, killing many woody plants and in some instances, removing the upper layers of organic soil. Fire can also play a role in the community’s establishment. Seedlings of northern white-cedar can establish directly on burned-over organic soils or within alder thickets that originate following catastrophic fire in poor conifer swamp. Catastrophic fire and windfall in northern Lower Michigan conifer swamps are estimated to have occurred at intervals of approximately 3,000 years.
The structure of rich conifer swamp is shaped by northern white-cedar, the dominant tree species. Northern white-cedar is a relatively short tree (20 m or 66 ft) and often forms a dense, low canopy, which can prevent other tree species from establishing. Because windthrow is very common, portions of the community often appear as a dense tangle of fallen, leaning, and misshapen northern white-cedar. The complex community structure is further enhanced by the root hummocks of northern white-cedar, which are often elevated above adjacent saturated or flooded organic soil.
In addition to northern white-cedar, other common trees species may include balsam fir (Abies balsamea), tamarack (Larix laricina), black spruce (Picea mariana), white spruce (P. glauca), hemlock (Tsuga canadensis), white pine (Pinus strobus), black ash (Fraxinus nigra), red maple (Acer rubrum), yellow birch (Betula alleghaniensis), paper birch (Betula papyrifera), American elm (Ulmus americana), quaking aspen (Populus tremuloides), and balsam poplar (Populus balsamifera).
Shrubs can be very common, especially within recent windfalls. Tall shrub species occurring in rich conifer swamp include tag alder (Alnus incana), winterberry (Ilex verticillata), mountain holly (I. mucronata), red-osier dogwood (Cornus sericea), elderberry (Sambucus canadensis), red elderberry (S. racemosa), huckleberry (Gaylussacia baccata), autumn willow (Salix serissima), and Canadian yew (Taxus canadensis). Early accounts list Canadian yew as one of the most common understory species, but this plant has since been sharply reduced or extirpated from most cedar swamps as a result of herbivory by deer. Balsam fir also commonly occurs as part of the shrub layer, sometimes forming dense patches.
Low shrub species common to rich conifer swamp can include Labrador tea (Rhododendron groenlandicum), low sweet blueberry (Vaccinium angustifolium), Canada blueberry (V. myrtilloides), leatherleaf (Chamaedaphne calyculata), American fly honeysuckle (Lonicera canadensis), hairy honeysuckle (L. hirsuta), swamp fly honeysuckle (L. oblongifolia), wild black currant (Ribes americanum), swamp red current (R. triste), and swamp black current (R. lacustre). Common vine species in rich conifer swamp include poison ivy (Toxicodendron radicans) and red honeysuckle (Lonicera dioica).
The ground layer of rich conifer swamp can be especially diverse in sedges, ferns, orchids, forbs, liverworts, and mosses. Common sedges may include Carex gynocrates, C. leptalea, C. disperma, C. trisperma, C. interior, C. eburnea, and C. vaginata. Common fern species may include maidenhair fern (Adiantum pedatum), lady fern (Athyrium filix-femina), rattlesnake fern (Botrypus virginianus), bulblet fern (Cystopteris bulbifera), spinulose woodfern (Dryopteris carthusiana), crested woodfern (D. cristata), glandular woodfern (D. intermedia), oak fern (Gymnocarpium dryopteris), sensitive fern (Onoclea sensibilis), cinnamon fern (Osmunda cinnamomea), broad beech-fern (Phegopteris connectilis), New York fern (Thelyperis noveboracensis), and marsh fern (Thelypteris palustris). Common orchids may include early coralroot (Corallorhiza trifida), small yellow lady-slipper (Cypripedium parviflorum var. pubescens), showy lady-slipper (C. reginae), broad-leaved twayblade (Neottia convallarioides), heart-leaved twayblade (N. cordata), tall northern bog orchid (Platanthera aquilonis), tall white bog orchid (P. dilatata), and blunt-leaved orchid (P. obtusata). Additional common ground flora may include wild sarsaparilla (Aralia nudicaulis), Jack-in-the-pulpit (Arisaema triphyllum), marsh marigold (Caltha palustris), small enchanter’s nightshade (Circaea alpina), goldthread (Coptis trifolia), bunchberry (Cornus canadensis), water horsetail (Equisetum fluviatile), fragrant bedstraw (Galium triflorum), creeping snowberry (Gaultheria hispidula), wintergreen (G. procumbens), purple avens (Geum rivale), rattlesnake grass (Glyceria canadensis), fowl manna grass (G. striata), jewelweed (Impatiens capensis), wild blue flag (Iris versicolor), twinflower (Linnaea borealis), Canada mayflower (Maianthemum canadense), naked miterwort (Mitella nuda), one-flowered pyrola (Moneses uniflora), gay wings (Polygala paucifolia), round-leaved pyrola (Pyrola americana), pink pyrola (P. asarifolia), dwarf raspberry (Rubus pubescens), mad-dog skullcap (Scutellaria lateriflora), twisted-stalk (Streptopus amplexifolius), and starflower (Trientalis borealis).
Mat-forming mosses can cover large portions of rich conifer swamp. Nearly the entire surface of nurse logs can be covered by callicladium moss (Callicladium haldanianum) and feather moss (Pleurozium schreberi). Common sphagnum mosses that can cover large portions of the forest floor in some rich conifer swamps include Sphagnum centrale, S. squarrosum, S. girgensohnii, S. wulfinaum, S. warnstorfii, and S. centrale.
Rich conifer swamps provide critical winter habitat for deer and snowshoe hare. Beaver-induced flooding can result in widespread mortality of northern white-cedar and other species not adapted to prolonged flooding.
- Amerorchis rotundifolia (round-leaved orchis, state endangered)
- Aster modestus (great northern aster, state threatened)
- Calypso bulbosa (calypso orchid, state threatened)
- Carex heleonastes (Hudson Bay sedge, state endangered)
- Cypripedium arietinum (ram’s head lady’s-slipper, state special concern)
- Empetrum nigrum (black crowberry, state threatened)
- Erigeron hyssopifolius (hyssop-leaved fleabane, state threatened)
- Gymnocarpium robertianum (limestone oak fern, state threatened)
- Lonicera involucrata (black twinberry, state threatened)
- Mimulus glabratus var. michiganensis (Michigan monkey-flower, state endangered)
- Parnassia palustris (marsh-grass-of-Parnassus, state threatened)
- Pinguicula vulgaris (butterwort, state special concern)
- Ranunculus lapponicus (Lapland buttercup, state threatened)
- Senecio indecorus (rayless mountain ragwort, state threatened)
- Solidago houghtonii (Houghton’s goldenrod, federal/state threatened)
- Stellaria crassifolia (fleshy stitchwort, state threatened)
- Vaccinium vitis-idaea (mountain-cranberry, state endangered)
- Accipiter gentilis (northern goshawk, state special concern)
- Alces alces (moose, state special concern)
- Appalachina sayanus (spike-lip crater, state special concern)
- Asio otus (long-eared owl, state special concern)
- Buteo lineatus (red-shouldered hawk, state threatened)
- Canis lupus (gray wolf, state threatened)
- Clemmys insculpta (wood turtle, state threatened)
- Dendragapus canadensis (spruce grouse, state special concern)
- Felis concolor (cougar, state endangered)
- Hendersonia occulta (cherrystone drop, state threatened)
- Lynx canadensis (lynx, federal threatened and state endangered)
- Pandion haliaetus (osprey, state threatened)
- Picoides arcticus (black-backed woodpecker, state special concern)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
- Somatochlora hineana (Hine’s emerald, federal/state endangered)
Biodiversity Management Considerations
Rich conifer swamp is a self-maintaining, stable community that relies on gap-phase dynamics to regenerate long-lived, shade-tolerant, northern white-cedar. A major threat to natural regeneration of cedar in northern rich conifer swamps is high density of deer, which rely on cedar as a main winter-staple. Logging rich conifer swamps can facilitate its conversion to hardwood-conifer swamps, hardwood swamps, aspen, and alder thickets. Long-term conservation of rich conifer swamps will require reducing deer densities across the landscape and allowing natural disturbances such as windthrow to create the complex structure that creates habitat for late-successional species.
Invasive species that threaten the diversity and community structure of rich conifer swamp include glossy buckthorn (Frangula alnus), 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), and European marsh thistle (Cirsium palustre). Regular monitoring for these and other invasive species followed by prompt and sustained control efforts will help protect the ecological integrity of rich conifer swamp and adjacent natural communities.
Rich conifer swamp occurs throughout the upper Midwest and northeast United States and adjacent Canadian provinces. South of the climatic tension zone in southern Lower Michigan, tamarack typically becomes the dominant conifer in minerotrophic wetlands. Minerotrophic wetlands dominated by tamarack in southern Lower Michigan are classified as rich tamarack swamp.
Similar Natural Communities
- Christensen, E.M., J.J. (Jones) Clausen, and J.T. Curtis. 1959. Phytosociology of the lowland forests of northern Wisconsin. American Midland Naturalist 62: 232-247.
- Curtis, J.T. 1959. The vegetation of Wisconsin. University of Wisconsin Press, Madison, WI. 657 pp.
- Faber-Langendoen, D., ed. 2001. Plant communities of the Midwest: Classification in an ecological context. Association for Biodiversity Information, Arlington, VA. 61 pp. + appendix (705 pp.).
- Kost, M.A. 2002. Natural community abstract for rich conifer swamp. Michigan Natural Features Inventory, Lansing, MI. 9 pp.
- Kudray, G.M., and M.R. Gale. 1997. Relationships between groundwater characteristics, vegetation, and peatland type in the Hiawatha National Forest, Michigan. Pp. 89-96 in Northern forested wetlands: Ecology and management, ed. C.C. Trettin, M.F. Jurgensen, D.F. Grigal, M.R. Gale, and J.K. Jeglum. CRC Press, Boca Raton, FL. 486 pp.
- NatureServe Explorer. 2001. NatureServe Explorer: An online encyclopedia of life [Web application]. Version 1.6. NatureServe, Arlington, VA. Available http://www.natureserve.org/explorer. (Accessed: September 18, 2002.)
- Schwintzer, C.R. 1981. Vegetation and nutrient status of northern Michigan bogs and conifer swamps with a comparison to fens. Canadian Journal of Botany 59: 842-853.
- Van Deelen, T.R. 1999. Deer-cedar interactions during a period of mild winters: Implications for conservation of swamp deeryards in the Great Lakes region. Natural Areas Journal 19: 263-275.
- Van Deelen, T.R., K.S. Pregitzer, and J.B. Haufler. 1996. A comparison of presettlement and present-day forests in two northern Michigan deer yards. American Midland Naturalist 135: 181-194.
For a full list of references used to create this description, please refer to the natural community abstract for rich conifer 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.