Natural Communities:
Geological Features and Primary Communities
Click on community name for photo gallery.
Algific talus slope This rare community of southwestern Wisconsin’s Driftless Area consists of steep slopes of fractured limestone (dolomite) rock that retains ice and emits cold air throughout the growing season. The cold microhabitats enable the persistence of northern species and "periglacial relicts" such as northern monkshood (Aconitum noveboracense) and rare terrestrial snails. The woody overstory is often sparse, with scattered small black ash (Fraxinus nigra) and white birch (Betula papyrifera). Mountain maple (Acer spicatum), a northern shrub, may be frequent and extensive beds of bulblet fern (Cystopteris bulbifera) and mosses are characteristic.
Alkaline clay bluff Steep, clay bluffs occur along some stretches of the Great Lakes shorelines and less commonly inland on streams draining into Lake Superior and Lake Michigan. Vegetative cover ranges from forested with pines (Pinus resinosa and P. strobus), white cedar (Thuja occidentalis) and white birch (Betula papyrifera), to bare clay with only a few herbs present. Buffaloberry (Sheperdia canadensis) is a characteristic shrub, but more typically, alders(Alnus incana and A. crispa), as well as herbs such as Canada goldenrod (Solidago canadensis) and pearly everlasting (Anaphalis margaritacea) are dominant. Both native and exotic pioneers such as fireweed (Epilobium angustifolium) and Canada thistle (Cirsium arvense) are common, especially on unstable sites. But it is the semi-stabilized “weeping” bluffs that are of the greatest biological interest. Golden sedge (Carex aurea), orchids and calciphilic fen species may colonize such sites, which can be local repositories of rare or otherwise noteworthy species.
Alvar This rare community consists of areas of thin discontinuous soil overlying horizontal beds of limestone or dolomite in the vicinity of Great Lakes shorelines. They are characterized by relatively low tree cover and a distinctive biota which includes elements of rock pavement, prairie, savanna and boreal forest communities. Among these are regional endemics, some very rare. This community type is much more common and better-developed in Michigan and Ontario than in Wisconsin. Small coniferous and deciduous trees (cedar, fir, pine, oak, aspen, birch) are scattered among an assemblage of species that can include big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), Indian-grass (Sorghastrum nutans), and wood lily (Lilium philadelphicum), as well as shoreline plants such as silverweed (Potentilla anserina). and dwarf lake iris (Iris lacustris).
Bedrock glade These are xeric, sparsely vegetated non-vertical bedrock exposures with very thin, often discontinous soils. The rock types vary from quartzite (Baraboo Hills, McCaslin Mountain), to basalt (lower St. Croix River valley), to granite (northeastern Wisconsin). The flora can include prairie, savanna, or barrens components, some at their northern range limits. Trees and shrubs are sparse and may include pines, oaks, and cherries. Xerophytic pteridophytes such as rusty woodsia (Woodsia ilvensis) and rock spikemoss (Selaginella rupestris) are characteristic, as are lichens and mosses.
Felsenmeer Quartzite or other metamorphic or igneous rock talus slope or “felsenmeer” communities characterized by all-summer upwellings of cool, moist air near or at their bases. It is not certain whether year-round ice deposits are responsible for the upwelling. Glacière talus forms as the result of periglacial frost and ice-wedging; quartzite, in particular, is a brittle rock that is susceptible to frost-wedging. The talus slopes themselves consist of lichened boulders ranging from 0.25-1 m in diameter. Nearly all sites (except the one at Devils Lake, Wisconsin) occur in areas that were glaciated during the Pleistocene. At the best-developed examples (Ouimet and Cavern Lake Canyons in Ontario, the Blue Hills Felsenmeer in Wisconsin), a double talus slope embracing a V-shaped valley may be present.
Great Lakes beach This beach community usually occurs in association with active dune systems. The beaches of the Great Lakes are extremely dynamic features, strongly influenced by water level changes and storm events. They support a suite of very specialized organisms, although unprotected shorelines may be entirely unvegetated. The plant species found in this community include (along Lake Michigan) seaside spurge (Euphorbia polygonifolia) and American sea-rocket (Cakile edentula).
Inland beach The beaches of inland lakes that experience enough water level fluctuation to prevent the development of a stable shoreline forest or other community may, instead support a specialized biota adapted to sandy or gravelly littoral habitats. The shorelines of such lakes (usually seepage lakes) may be subject to fluctuations of as much as several meters over a few years or decades. The alternation of high and low periods maintains populations of the beach specialists over time, including some rare species of unusual geographic affinity such as the Atlantic Coastal Plain of the eastern United States.
