Open Bog

Definition

Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

Bogs are acidic, low nutrient, northern Wisconsin peatlands dominated by Sphagnum mosses that occur in deep layers and accumulate over time as peat. The bog surface is often uneven, with pronounced hummock and hollow microtopography. Hummocks formed by accumulating Sphagnum moss and leatherleaf often reach two feet or more in height relative to the adjacent hollows. In northern Wisconsin, bogs are frequently found in the kettle depressions of pitted outwash and morainal landforms. They also frequently occur on the borders of lakes that have low nutrient inputs. Vascular plant diversity is very low in the most acidic sites, but includes characteristic and distinctive specialists such as the narrow-leaved sedge species (Carex oligosperma and C. pauciflora), cotton-grasses (Eriophorum spp.), and ericaceous shrubs, especially leatherleaf (Chamaedaphne calyculata), bog laurel (Kalmia polifolia), bog rosemary (Andromeda polifolia), and small cranberry (Vaccinium oxycoccos). Trees are absent or stunted and achieve very low cover values.

In the strictest sense, bogs receive nutrients only from precipitation and limited internal runoff. The thick layers of Sphagnum isolate the bog from the influence of nutrient-enriched groundwater, and create an environment characterized by high acidity and low oxygen and nutrient levels that is inhabited by a limited number of highly specialized plants able to tolerate or thrive in the extreme conditions. Poor fen, open bog, and muskeg often occupy different parts of the same wetland basin, which may include one or more types of lowland coniferous forest as well. Each of these communities responds to slight differences in local site conditions.

Defining Characteristics and Similar Communities

Open bogs are distinguished by their strongly acidic peat soils isolated from the influence of mineral-rich groundwater by deep layers of Sphagnum and tall Sphagnum-ericad hummocks. They can be differentiated from poor fens by their lower pH, tall Sphagnum hummocks, a rooting zone isolated from surface and/or groundwater, and relatively low species diversity. Most "bogs" surrounding lakes in northern Wisconsin are better classified as poor fens, especially those with a diverse flora on floating mats. Open bogs may lie adjacent to black spruce swamps and muskegs, also known as treed bogs, but can be differentiated from these communities by typically having less than 10% cover of tree species.

Open bogs share some characteristics with central poor fens, like strongly acidic soils influenced by Sphagnum, but central poor fens lack the strong hummock-hollow microtopophraphy. In addition, central poor fens tend to occur in the Central Sand Plains where open bogs are uncommon to rare. Open bogs may seem superficially similar to bog relicts, which are usually minerotrophic rather than strongly acidic and are found in southeast Wisconsin. In fact, most "bogs" in southern Wisconsin are probably more correctly classified as bog relicts. Open bogs may also resemble patterned peatlands, especially the more acidic, Sphagnum-influenced ridges (strings), but they lack the minerotrophic hollows (flarks) and patterning usually evident on aerial photos.

Because Curtis's Vegetation of Wisconsin (1959) and related data did not focus on non-forested wetlands, early ecologists simply classified open peatlands as calcareous fens, sedge meadows, or open bogs, and the various types of communities recognized today were not differentiated. Thus, older data (and maps of open bog locations) need to be reevaluated using the current natural community classification.

Rare animals

Species of Greatest Conservation Need

The following Species of Greatest Conservation Need are listed according to their level of association with the Open Bog 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 Open Bog, 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 Open Bog in Ecological Landscapes with opportunities for protection, restoration, and/or management. For more information, see the Wildlife Action Plan.

Central Sand Hills

Hydrologic changes due to residential development and road building are an issue. Agricultural practices adjacent to this community can result in soil erosion and water quality degradation due to sedimentation and nutrient loading.

Central Sand Plains

Hydrologic changes due to drainage, dike construction, residential development, commercial cranberry operations, and road building have all impacted this community type. The Dewey Marsh in Portage County contains extensive tracts of open bog, poor fen and muskeg within a large, diverse wetland complex on managed and partially protected public land. Other examples of bog habitats occur on the Black River State Forest (Jackson County) and Meadow Valley Wildlife Area (Juneau County).

Forest Transition

Smaller open bogs associated with lakes are common. Residential and agricultural developments are concerns, as is habitat fragmentation. The community has been affected by changing site hydrology, wetland filling, and type conversion.

North Central Forest

Boggy habitats are widespread and common in this Ecological Landscape, usually associated with other wetland types. Increased pressure from motorized recreation is causing some impact (i.e., spread of invasive species such as purple loosestrife and phragmites).

Northeast Sands

This community type is usually found in association with smaller lakes in this Ecological Landscape. Population and road density are lower within this Ecological Landscape resulting in fewer impacts to this community. However, motorized recreation is on the increase and may enhance the spread of invasive species such as purple loosestrife. Best Management Practices and sustainable forest management should be used near this community.

Northern Highland

There is extensive representation of this community type in this Ecological Landscape, with numerous small and large open bogs and muskegs. The Powell Marsh and the vast peatlands along the Manitowish River (Vilas and Oneida Counties), and Thunder Marsh in Oneida County contain good representatives of this and related communities. These three areas are found mostly on public land. Road density in this Ecological Landscape is higher per square mile than in other northern Ecological Landscapes, and has impacted hydrology in several locations. Development adjacent to this community is causing some impacts to hydrology due to wetland filling and road construction. Commercial cranberry operations have altered some of this community. Increased pressure from motorized recreation is causing some impact (i.e., spread of invasive species such as purple loosestrife and phragmites). Best Management Practices and sustainable forest management adjacent to this community should be used.

Northwest Lowlands

The open bog complexes are large within this Ecological Landscape. Human populations and road densities are lower within this Ecological Landscape than many other places and have less impacts to this community type. Black Lake Bog, and the Empire and Belden Swamps (all in Douglas County) contain extensive bogs within large wetland complexes that are intact and well preserved. Increased pressure from motorized recreation is causing some impact (i.e., spread of invasive species such as purple loosestrife and phragmites).

Northwest Sands

This type is commonly found in the kettle depressions of pitted outwash landforms, often associated with lakes. Human populations and road densities are low but increasing in this Ecological Landscape, especially in the lake districts. Some small but high quality open bogs and poor fens exist and are now protected on the Brule River State Forest. There are some excellent kettle bogs in the Chequamegon-Nicolet National Forest (Douglas and Bayfield Counties).

Superior Coastal Plain

A complex ecosystem of open bog (though somewhat limited in size) within a wetland matrix of other peatland communities exists within the Apostle Islands archipelago. Some of this community in the archipelago is preserved in the National and State Park system and is being affected adversely by recreational uses. On the mainland, the Kakagon Sloughs on the Bad River Indian Reservation maintains smaller portions of an intricate open bog community in relation to the many quality wetland community types in the area. Though somewhat isolated from other open bog communities, it is well preserved. Sultz Swamp (Bayfield County) is one of the largest acid peatlands (with minimal disturbance) in the Lake Superior basin that contains an open bog community as part of the wetland complex. Though invasive plants may not be a serious problem for this type at the present time, there are scattered invasions of purple loosestrife, phragmites and reed canary grass. These invasives are usually present in areas that have been disturbed in some way.

Photos

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Open Bog 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.