Hemlock Relict

Counties: Adams, Iowa, Jackson, Juneau, Monroe, Richland, and Sauk.

Description:

Hemlock relict is a type of natural community found in the state of Wisconsin in the United States. It is characterized by the presence of hemlock trees, which are coniferous trees that are native to the region. Hemlock relict communities are typically found in moist, cool areas with well-drained soils, such as ravines, slopes, and along streams.

Hemlock relicts are small patches of mesic forest composed mostly of species that are separated from and generally far south of their usual ranges. They are considered to be a type of “relict” community because they are found in areas that were once more widespread, but are now limited to a few scattered locations. This is due in part to the decline of hemlock trees, which have been impacted by the hemlock woolly adelgid, a non-native insect that feeds on the trees and can kill them.

Most documented relicts occur in southwestern Wisconsin’s Driftless Area, within the Western Coulees and Ridges Ecological Landscape. Typical sites are deep, steep-sided, moist ravines, with cool northern or eastern slope exposures. Exposures of bedrock, most often Cambrian sandstones, are typically present and contribute to the ability of this community to develop and persist in areas that would otherwise be vegetated with deciduous hardwood forests. The porous sandstone has a high capacity to hold water, which slowly moves through the rock and keeps conditions humid and cool.

Hemlock relicts are highly localized in southwestern Wisconsin. They are concentrated in a few areas, such as the drainages of the upper Kickapoo and Baraboo Rivers, and in a few of the deep gorges that cut into the flanks of the Baraboo Hills. Extremely isolated outliers are known from a few sites south of the Wisconsin River. Unusual plants and animals have been documented in several stands.

Hemlock relict communities are home to a variety of plant and animal species that are adapted to the moist, cool conditions found in these areas. These include periglacial relict species, that for various reasons, were unable to keep pace with changes to the vegetation as the climate changed following the last glacial advance, as well as a number of habitat specialists that are rare elsewhere in southern Wisconsin.

Some common plant species found in hemlock relict communities include eastern hemlock (Tsuga canadensis), Eastern white pine (Pinus strobus), yellow birch (Betula alleghaniensis), and paper birch (Betula papyrifera) are common northern canopy associates. Other trees present are usually those present in the adjoining hardwood forests. Shrubs and herbs with northern affinities are also important, and may include mountain maple, Canada yew (Taxus canadensis), showy mountain ash (Sorbus decora), blue-bead lily (Clintonia borealis), rose twisted-stalk (Streptopus roseus), shining club-moss (Huperzia lucidula), and spinulose wood fern (Dryopteris carthusiana). The dense shade of the hemlock combined with the northern aspect of many stands means that very little light reaches the forest floor causing a very sparse groundlayer.

Overall, hemlock relict communities are important components of the natural landscape in Wisconsin, providing habitat for an otherwise rare diversity of plant and animal species, as well as contributing to the overall health and diversity of the ecosystem.

Alternative Natural Community Names:

Hoffman	N/A
WI DNR	Hemlock Relict
US National Vegetation Classification	CEGL002597 Hemlock – Sugar Maple Relict Forest

Typical Plant Species:

Typical Animal Species:

References:

Curtis, John T. The Vegetation of Wisconsin.  University of Wisconsin Press. 1959.

Hoffman, Randolph M. Wisconsin’s Natural Communities: How to Recognize Them, Where to Find Them, second edition. University of Wisconsin Press. 2002.

Wisconsin Department of Natural Resources. Wisconsin Wetland Inventory Classification Guide. 1992.