"P Bog" Fen Site In Northern Maine

The P Bog Site is part of a large, calcareous northern white cedar swamp located in northern Maine, west of Caribou. It's part of a nature preserve that encompasses 156 acres and is drained by a small stream. The site's highly unusual calcium-rich wetlands have attracted botanical interest since 1939. The Nature Conservancy is protecting the botanical value of the site and monitoring the rare plant species which occur on the preserve.

P Bog belongs to a community type rarely found in Maine, the Northern New England Calcareous Seepage Swamp community. Unlike most Maine wetlands which are fairly acidic, P Bog is underlain by limestone which creates habitat hospitable to many rare calciphilic plants, including Valeriana uliginosa (marsh valerian), Cypripedium reginae (showy lady's slipper), Amerorchis rotundifolia (small round-leaved orchid), and Ranunculus lapponicus (Lapland buttercup).

P Bog Preserve lies in a lowland surrounded by forests and fallow farmland on the adjacent hillsides. The dominant vegetation of the preserve includes northern white cedar mixed with tamarack and black spruce, and groundcover consists mainly of mosses and liverworts. An exception to this is the beaver meadow, in the eastern section of the preserve, which is dominated by vegetation such as manna grass, bulrush, iris, and bur-reed.

Protection of this preserve is important due to the susceptibility of its rare plant community to damage from human activity and hydrological changes. The soils of the preserve's cedar swamp are soft, and the mossy groundcover cannot withstand repeated trampling without damage. Furthermore, hydrological changes brought on by human disturbance may adversely affect the soil pH and rare plant habitat.

Ecological Goals and Objectives

Maintain present habitat for existing stands of rare calciphilic plants by:

Ecological Summary

The water of most Maine wetlands are fairly acidic, P Bog is characterized by a basic pH due to underlying limestone formations. Calcium, dissolved in groundwater, from limestone deposits becomes available to the fen which, in turn, provides habitat to rare types of calciphilic plants. Calcareous fens, also referred to as rich or circumneutral fens, are similar to acidic bogs, however, the availablity of calcium rich groundwater is a unique situation. Circumneutral fens usually occur as a part of a larger peatland complex, and by definition, do not include forested areas.

Ecological Processes

The ecological model considers six potential disturbances that would directly effect the population size of the rare plants found at P Bog. Each disturbance has a varying degree of effect on each of the rare species.

These plants need the open moist calcareous conditions the fen provides. The plants are tolerant of filtered light, however, the natural succession of a fen leads to forest encroachment. As the forest encroaches the rare plants become too shaded and unable to compete with the woody vegetation and as a result the populations decline.

Disturbance may perpetuate the forest encroachment. The draining of the fen or surrounding water would drop the water table creating drier conditions more suitable to woody species. Such an event would hasten the forest encroachment and result in a population reduction.

Temporary flooding (e.g. a year of abnormanlly high rainfall) can reduce the woody vegetation, causing inceased light making conditions favorable for the rare plants and resulting in a population increase. Permenant flooding (e.g. beaver dams) would result in habitat loss in the area impacted, however, the surrounding area would have increased light and create suitable habitat for the rare plants.

The natural disturbance caused by blowdowns would create a more open fen favoring the plants, however, the results of soil disturbance associated with blowdowns are unknown. The perimeter of the blowdown would have an increase in light creating suitable habitat for the rare plants. The effects of disturbance to the forest and litter (e.g. fire) are unknown. This would exclude logging, except during winter months, as a means to reduce the canopy cover to maintain the population of rare plants. Logging while the ground is frozen would prevent sever disturbance of the litter and soil layers, and reduce woody vegetation favoring the rare plants.

R. lapponicus prefers heavily wooded sphagnum bogs. Disturbances such as forest encroachment that would adversely effect the other rare plants would favor Lapland buttercup.

At P Bog, R. lapponicus is found in the cedar forest surrounding the fen. As the cedar forest encroaches upon the fen additional habitat is created for Lapland buttercup. The reduction of the cedar within or surrounding the fen would reduce suitable habitat and result in a population decline. The effects of litter and soil disturbances are unknown.

Research Needs

The information of the biological and ecological processes of the rare plants found at P Bog is limited and management of these plants would beneifit from research in these areas. Below are some general and specific research needs for individual species. This is not an exclusive list.

General Needs

Valeriana uliginosa

Cypripedium reginae

Calypso bulbosa

Ranunculus lapponicus

Rare Plant Monitoring and Management

A management strategy for P Bog should address two potential problems: shading of rare plants and changing of hydrological conditions.

Although three of the four rare plants grow in the vicinity of forested canopy, the actual rare plant locations are in small, open patches or along old roads and trails. Valeriana grows only in full light. Cypripedium requires some sunlight. The healthiest Amerorchis stations were characterized by lush patches of Carex disperma and C. trisperma with only about 50% overstory cover. Ranunculus prefers the heavily wooded areas of the bog and the population would decline with a reduction in canopy cover.

The rare plants sensitive to shading should be monitored to determine whether shading is causing any decline. If so, trees or branches may need to be cut or pruned to maintain the existing light conditions. Natural blow-downs of trees may continue to provide appropriate light conditions for the rare elements.

Areas containing Ranunculus should be monitored for disturbance which would reduce the canopy cover making conditions unfavorable for this species. If the disturbance is reversible (e.g. removing a beaver dam) steps may need to be taken to maintain suitable light conditions.

The hydrology of the area may be critical to the continued existence of the rare plants for two possible reasons: First, if the stream, which enters the preserve from the east, is the primary source of calcium enriched groundwater for the soil and plants, then its flow may be necessary to maintain the calcium rich soils. And second, if too much water gets backed up in the preserve, the beaver meadow area may expand. However, the rare plants have been found only in the cedar swamp, away from the beaver meadow.

A simple survey of all known rare plant locations within the preserve is conducted annually along with a search for new locations. Each species is counted, concentrations of populations are mapped, and reproductive status is noted.

More Information

For more information contact Kyle Stockwell at kstockwell@tnc.org.