Alvar

Definition

Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

This rare community consists of areas of thin, discontinuous soil overlying horizontal beds of limestone or dolomite in the vicinity of Great Lakes shorelines. These communities support an unusual blend of boreal and prairie species, which appear to be relicts of the cold period following the last glaciers and of the warmer, drier period that followed. 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 of which are globally very rare. This community type is much more common and better developed in Michigan and Ontario than in Wisconsin.

Small coniferous and deciduous trees such as northern white-cedar (Thuja occidentalis), balsam fir (Abies balsamea), pines (Pinus spp.), oaks (Quercus spp.), aspens (Populus spp.), and paper birch (Betula papyrifera) 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 anserine) and dwarf lake iris (Iris lacustris). Alvars are home to an unusual set of wildlife species as well, including the loggerhead shrike and a large number of distinctive invertebrates such as leaf-hoppers and land snails.

Rare animals

Species of Greatest Conservation Need

The following Species of Greatest Conservation Need are listed according to their level of association with the Alvar natural community type, based on the findings in Wisconsin's 2015 Wildlife Action Plan.

Scores: 3 = high association, 2 = moderate association, and 1 = low association. See the key to association scores for complete definitions.

Please see Section 2. Approach and Methods of the Wildlife Action Plan to learn how this information was developed.

Rare plants

The Natural Heritage Inventory has developed scores indicating the degree to which each of Wisconsin's rare plant species is associated with a particular natural community or ecological landscape. This information is similar to that found in the Wildlife Action Plan for animals. As this is a work in progress, we welcome your suggestions and feedback.

Landscapes

The following Ecological Landscapes have the best opportunities to manage for Alvar, based on the Ecological Landscapes of Wisconsin Handbook.

Major (3 on map)
A major opportunity for sustaining the natural community in the Ecological Landscape exists, either because many significant occurrences of the natural community have been recorded in the landscape or major restoration activities are likely to be successful maintaining the community's composition, structure, and ecological function over a longer period of time.

Important (2 on map)
Although the natural community does not occur extensively or commonly in the Ecological Landscape, one to several occurrences do occur and are important in sustaining the community in the state. In some cases, important opportunities may exist because the natural community may be restricted to just one or a few Ecological Landscapes within the state and there may be a lack of opportunities elsewhere.

Present (1 on map)
The natural community occurs in the Ecological Landscape, but better management opportunities appear to exist in other parts of the state.

Threats/Actions

What are conservation actions?

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for natural communities

Considerations

The following are additional considerations for Alvar in Ecological Landscapes with opportunities for protection, restoration, and/or management. For more information, see the Wildlife Action Plan.

Central Lake Michigan Coastal

Red Banks Escarpment and Glades (Brown County) is the most prominent alvar community in Wisconsin. This site contains one of the most diverse snail communities known in the Midwest and is one of the most important areas in Wisconsin for land snails. Colonies of 25 different groups of glacial relict snails can be found from the base to the top of the escarpment. Of interest are the number of rare and glacial relict snail taxa that are present including the cherrystone drop and the Midwest Pleistocene vertigo snail.

Northern Lake Michigan Coastal

Idlewild Alvar (Door County) is a lower quality site that may nonetheless offer some potential conservation opportunity.

Photos

Click to view a larger version. Please considering donating your photos to the Natural Heritage Conservation Program for educational uses. Photo use

Alvar Photos

Note: photos are provided to illustrate various examples of natural community types. A single photograph cannot represent the range of variability inherent in a given community type. Some of these photos explicitly illustrate unusual and distinctive community variants. The community photo galleries are a work in progress that we will expand and improve in the future.