Rich Tamarack Swamp
Rich tamarack swamp is a groundwater-influenced, minerotrophic, forested wetland dominated by tamarack (Larix laricina) that occurs on deep organic soils predominantly south of the climatic tension zone in southern Lower Michigan. This natural community type was known as relict conifer swamp in previous versions of the natural community classification.
County Distribution Map
Global Rank: G4 - Apparently secure
State Rank: S3 - Vulnerable
Rich tamarack swamp occurs in outwash channels, outwash plains, and kettle depressions throughout southern Lower Michigan. The community is often found where groundwater seeps occur at the bases of moraines. Rich tamarack swamps typically occur in association with headwater streams and adjacent to inland lakes. In large wetland complexes, rich tamarack swamp is typically associated with southern shrub-carr, prairie fen, southern wet meadow, and emergent marsh.
The organic soils underlying rich tamarack swamp are typically comprised of deep (> 2.5 m) peat containing large amounts of woody debris and occasionally layers of sedge-dominated peat. The soil profile often contains or is underlain by marl, a calcium carbonate precipitate that accumulates as sediment in shallow lake bottoms. Because glacial till in southern Michigan is typically high in calcium and magnesium, the groundwater discharge into rich tamarack swamp has high levels of alkalinity and dissolved calcium and magnesium carbonates.
Windthrow, insect outbreak, beaver flooding, and fire are all important forms of natural disturbance for rich tamarack swamp. Trees growing in the anaerobic conditions associated with a high water table and peat soils tend to be shallowly rooted and are thus, especially prone to windthrow. The light gaps created by windthrow help to regenerate tamarack and maintain the community’s dense shrub layer. In addition, the coarse woody debris and pit and mound microtopography that results from windthrow add to the community’s complex structure and floristic diversity.
Periodic outbreaks of larch sawfly (Pristophora erichsonii) and eastern larch beetle (Dendroctonus simplex), both native insect species, and the introduced tamarack casebearer (Coleophora laricella) can cause significant mortality of tamarack. The defoliation associated with an insect outbreak results in increased light reaching the understory, which may promote tamarack regeneration and high shrub-layer density. However, these defoliation events also promote the growth of red maple, which subsequently reduces the amount of light available to the understory and ground layers and results in lower species richness.
Due to the strong influence of groundwater, water levels in rich tamarack swamps tend to fluctuate less than in many other wetland types. However, the community is subject to seasonal water fluctuations and long-term flooding associated with beaver dams or blocked road culverts. Although the roots of tamarack form elevated hummocks that allow it to withstand small-scale water level fluctuations, prolonged flood events result in tamarack mortality and the conversion of rich tamarack swamp to emergent marsh, southern wet meadow, or southern shrub-carr.
While fire is not a frequent form of direct disturbance in rich tamarack swamps, its influence on the surrounding landscape is very important to the successional dynamics of this community. With the widespread absence of fire in southern Michigan, tamarack, a common tree within prairie fens, has completely colonized many sites that were previously occupied by prairie fen, thus forming many of the rich tamarack swamps we see today. Additionally, fire suppression in the surrounding landscape has facilitated the increase and dominance of red maple within upland forests. As a result, red maple is now more likely to colonize rich tamarack swamps and replace tamarack, especially following disturbances such as insect outbreaks and windthrows.
The structure of this community is largely shaped by tamarack, the dominant tree species. The roots of tamarack often form extensive mats that stand elevated above adjacent pools of standing water and provide a substrate for a diverse wetland ground flora that differs from that of the inundated mudflats between root hummocks. The varied microtopography fosters biocomplexity and high species richness. Tamarack windthrows and tip-up mounds also add to the heterogeneous structure of the ground and shrub layers. Because of the open branching and spire-like shape of tamarack, the shrub layer of rich tamarack swamp receives a high level of light and is typically both very dense and diverse. The shrub layer may contain as many as 28 species, with multiple species intertwined and over-topping one another so that total shrub-layer cover may reach 90 to 130%.
In addition to tamarack, other common tree species include black ash (Fraxinus nigra), yellow birch (Betula alleghaniensis), American elm (Ulmus americana), red maple (Acer rubrum), swamp white oak (Quercus bicolor), quaking aspen (Populus tremuloides), red cedar (Juniperus virginiana), and in some locations white pine (Pinus strobus) and northern white-cedar (Thuja occidentalis). Common tall shrub species include poison sumac (Toxicodendron vernix), winterberry (Ilex verticillata), smooth highbush blueberry (Vaccinium corymbosum), gray dogwood (Cornus foemina), silky dogwood (C. amomum), swamp rose (Rosa palustris), American hazelnut (Corylus americana), nannyberry (Viburnum lentago), juneberry (Amelanchier arborea), black chokeberry (Aronia prunifolia), and pussy willow (Salix discolor). Low shrub species common to rich tamarack swamp include swamp gooseberry (Ribes hirtellum), wild red raspberry (Rubus strigosus), bog birch (Betula pumila), sage willow (Salix candida), swamp fly honeysuckle (Lonicera oblongifolia), alder-leaved buckthorn (Rhamnus alnifolia), common juniper (Juniperus communis), shrubby cinquefoil (Dasiphora fruticosa), and bog willow (Salix pedicellaris). Common woody vines include poison ivy (Toxicodendron radicans), Virginia creeper (Parthenocissus quinquefolia), and riverbank grape (Vitis riparia).
Because of the high frequency of canopy disturbance and open structure of tamarack, the ground flora is composed of a heterogeneous mixture of shade-tolerant and intolerant wetland plants. In addition, the stark difference in moisture levels between the elevated root hummocks and saturated muck flats also significantly increases the diversity of wetland species found in the ground flora. Common ground flora in rich tamarack swamp include the following species: nodding bur-marigold (Bidens cernua), tall swamp-marigold (B. trichosperma), false nettle (Boehmeria cylindrica), bluejoint grass (Calamagrostis canadensis), marsh marigold (Caltha palustris), marsh bellflower (Campanula aparinoides), Pennsylvania bitter cress (Cardamine pensylvanica), sedges (Carex comosa, C. hystericina, C. lacustris, C. leptalea, and C. stricta), water hemlock (Cicuta bulbifera), spinulose woodfern (Dryopteris carthusiana), water horsetail (Equisetum fluviatile), rough bedstraw (Galium asprellum), bog bedstraw (G. labradoricum), stiff bedstraw (G. tinctorium), fowl manna grass (Glyceria striata), jewelweed (Impatiens capensis), cut grass (Leersia oryzoides), small duckweed (Lemna minor), northern bugle weed (Lycopus uniflorus), tufted loosestrife (Lysimachia thyrsiflora), Canada mayflower (Maianthemum canadense), false mayflower (M. trifolium),sensitive fern (Onoclea sensibilis), royal fern (Osmunda regalis), golden ragwort (Packera aurea), clearweed (Pilea pumila), dwarf raspberry (Rubus pubescens), common arrowhead (Sagittaria latifolia), mad-dog skullcap (Scutellaria lateriflora), swamp goldenrod (Solidago patula), rough goldenrod (S. rugosa), smooth swamp aster (Symphyotrichum firmum), eastern lined aster (S. lanceolatum), swamp aster (S. puniceum), skunk cabbage (Symplocarpus foetidus), marsh fern (Thelypteris palustris), starflower (Trientalis borealis), and violets (Viola spp.).
While mosses, especially brown mosses (Amblystegiaceae), are prevalent throughout the ground layer, sphagnum mosses (Sphagnum spp.) are usually only locally distributed.
Beaver-induced flooding can result in widespread mortality of tamarack and other species not adapted to inundated conditions. Periodic outbreaks of the larch sawfly (Pristophora erichsonii) and tamarack casebearer (Coleophora laricella) result in significant reductions in tamarack-cover, and repeated defoliation events can cause tamarack-mortality. Fall migrating songbirds and other resident birds and small mammals feed on the abundance of fruit produced by the dense shrub layer of rich tamarack swamp.
- Berula erecta (water parsnip, state threatened)
- Cacalia plantaginea (prairie Indian-plantain, state special concern)
- Calamagrostis stricta (narrow-leaved reedgrass, state threatened)
- Cypripedium candidum (white lady’s-slipper, state threatened)
- Drosera anglica (English sundew, state special concern)
- Filipendula rubra (queen-of-the-prairie, state threatened)
- Muhlenbergia richardsonis (mat muhly, state threatened)
- Phlox maculata (sweet william phlox, state threatened)
- Poa paludigena (bog bluegrass, state threatened)
- Polemonium reptans (Jacob’s ladder, state threatened)
- Sporobolus heterolepis (prairie dropseed, state special concern)
- Valeriana edulis var. ciliata (edible valerian, state threatened)
- Clemmys guttata (spotted turtle, state special concern)
- Emydoidea blandingii (Blanding’s turtle, state special concern)
- Oecanthus laricis (tamarack tree cricket, state special concern)
- Neonympha m. mitchellii (Mitchell’s satyr butterfly, federal/state endangered)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
Biodiversity Management Considerations
The presence of conifer-dominated wetlands in southern Michigan contributes significantly to the region’s overall biodiversity. Protecting the hydrology of rich tamarack swamp is critical for its continued existence and may include avoiding surface water inputs to the community from drainage ditches and agricultural fields, clearing blocked road culverts, which can cause prolonged flooding, and maintaining native vegetation types in the uplands surrounding the community.
Invasion by red maple can cause rich tamarack swamp to shift toward hardwood domination, resulting in a significant decrease in shrub-layer cover and loss of shade-intolerant species such as tamarack. Reducing red maple cover in rich tamarack swamps by girdling in conjunction with trunk-application of wetland-approved herbicide may be effective in limiting its dominance. Ideally, this type of management would accompany the use of prescribed fire and removal of red maple in the upland forests adjacent to the swamp as well as hydrologic restoration where necessary. Significantly reducing red maple cover within the swamp and adjacent upland will help ensure that characteristic natural disturbance events, such as windthrow and insect outbreaks, result in tamarack regeneration rather than further proliferation of red maple.
Invasive species that can reduce species diversity and alter community structure include glossy buckthorn (Frangula alnus), multiflora rose (Rosa multiflora), 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), the latter species mostly restricted to northern Michigan at present. Glossy buckthorn is probably the greatest threat to rich tamarack swamps as it is capable of completely dominating the shrub and ground layers. Removing glossy buckthorn can be accomplished with cutting, accompanied by herbicide application and by using spot-burning to eliminate seedlings. Regular monitoring for invasive species followed by prompt and sustained control efforts will help protect the ecological integrity of rich tamarack swamp and other adjacent natural communities.
Throughout northern Michigan and near the tension zone in mid-Michigan, northern white-cedar (Thuja occidentalis) replaces tamarack as the dominant tree species in groundwater-influenced, forested wetlands. Rainwater-fed (ombrotrophic) acidic, tamarack and black spruce swamps also occur in southern Michigan and are classified as poor conifer swamp. Many large wetland complexes contain zones of both minerotrophic tamarack swamp (e.g., rich tamarack swamp) near the upland edge where groundwater seeps occur, as well as ombrotrophic tamarack swamp (e.g., poor conifer swamp) near the center of the complex. In the ombrotrophic zone, deep peat separates the vegetation from the influence of groundwater and sphagnum mosses acidify the surface peat.
Similar Natural Communities
- Curtis, J.T. 1959. The vegetation of Wisconsin. University of Wisconsin Press, Madison, WI. 657 pp.
- Kost, M.A. 2001a. Natural community abstract for rich tamarack swamp. Michigan Natural Features Inventory, Lansing, MI. 6 pp.
- Kost, M.A. 2001b. Potential indicators for assessing biological integrity of forested, depressional wetlands in Southern Michigan. Michigan Natural Features Inventory, Lansing, MI. 69 pp.
- Merkey, D.A. 2001. Dominant water sources of six conifer swamps of southeastern Michigan. Report submitted to Michigan Natural Features Inventory, Lansing, MI. 13 pp.
- Reinartz, J.A. 1997. Controlling glossy buckthorn (Rhamnus frangula) with winter herbicide treatment of cut stumps. Natural Areas Journal 17:38-41.
For a full list of references used to create this description, please refer to the natural community abstract for rich tamarack 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.