Beavers Disrupt Fen

by Hannah Ettema
MNA Intern

This past spring, it came to the attention of MNA that the new resident beavers of the Edwin and Margarita Palmer Memorial Sanctuary in Kalamazoo County were causing quite a problem. The sanctuary includes a prairie fen which is threatened due to the beavers. Prairie fens are rare plant communities declining across the landscape. Unlike pre-settlement times, southeast Michigan only has about 5,000 acres of prairie fen remaining today.

flooded fen

The flooded prairie fen

Fens are a type of wetland high in calcium and magnesium due to the fact that it is alkaline and fed by groundwater that picks up the elements via limestone. They are lower, however, in levels of nitrogen and phosphorus which leads to more evolved mechanisms in plants, such as the carnivorous sundew and pitcher plant which obtain their nutrients from insects. Fens are also botanically diverse due to presence of a wide array of microhabitats. For plant life to survive in fens, they require very specific water and nutrient levels which the beaver dam was disrupting.

Some but not all of the rare plants species that are under threat include the prairie Indian plantain, tussock sedge, purple fringe orchid, and sundew; all which have specific water requirements to flourish.

prairie indian plantain plant

The prairie indian plantain, photo Peter Gorman

The prairie indian plantain is not a particularly showy flower but its size is striking. With small flower heads and little noticeable scent, the plant is unique in shape and is an indicator of a high quality habitat. The plantain’s blooming period lasts about a month in early to mid summer and in the State of Michigan is listed as a species of special concern, which doesn’t grant them legal protection, it is carefully monitored because of its declining population in the state.

Tussock Sedge plant

Tussock sedge, photo Matt Schultz

Tussock sedge is a grass like plant that grows at or above water level. A good example of a microhabitat, the sedge’s hummock base acts as a wetland but the top of the hummock is more upland, leading different plants to grow at different places within each hummock. Typically growing in clumps of two feet by two feet, the sedge is a food source for a variety of animals including ducks, turkeys, deer, and our resident beavers. The sedge is also a great nesting site for birds.

purple fringed orchid plant

Purple fringed orchid

The purple fringed orchid is a tall one to two foot orchid blooming in July and August. The orchid is attractive to bees, butterflies, and birds and can grow anywhere from six to eighteen inches tall.

sundew plant

Sundew. photo John V. Freudenstein

The sundew plant is carnivorous. That alone should make it worth saving. On its leaves, a gel like substance is on the end of tendrils, appearing like morning dew all day long. In the sun especially, the glistening gel draws in insects for the plant to eat.  Sundew is also listed in the state of Michigan as a special concern.

beaver dam

The Beaver Dam, photo Matt Schultz

The beaver dam was blocking the drain of water from the prairie fen thus raising the water level to dangerous heights: 2 ½ to 3 feet above normal. For array of rare and unique plant species, including the ones listed above, an increase in water level could be detrimental.

MNA has many beaver dams in many properties around the state but none have ever caused such a severe problem to a habitat.

Initially, Andy Bacon, MNA Stewardship Coordinator and Matt Schultz, MNA Western Regional Stewardship Organizer, with the help of volunteers tried punching holes in the beaver dam to help drain the water from the flooding fen. However, within 2 days, each hole was plugged by the beaver because “they don’t have anything else better to do,” said Andy. More drastic measures needed to be taken to protect the prairie fen and its inhabitants.

Matt and Andy then worked to construct a beaver pond leveler. With the leveler, water from the flooded area is drained through a hole-drilled PVC pipe and carried through the beaver dam and out to the draining area. Around the hole-drilled end is a wire cage to block debris such as leaves and twigs from blocking the individual holes which drains the water.

Beaver Pond Leveler diagram

Beaver Pond Leveler

men working on leveler

Matt and Andy constructing the leveler, photo Matt Schultz

man with leveler in canoe

Andy about to canoe the leveler to the dam, photo Matt Schultz

On the day of installation this past August, Matt and Andy with the help of MNA volunteer steward Charles Goodrich canoed the leveler to the fen in pieces up the creek and to the flooded fen where it was constructed and installed past the beaver dam.

In order to fool the beavers, in addition to punching the necessary hole for the leveler, the guys also punched two additional holes in the dam so the beavers would repair the ‘fake’ holes and not the one being used by the PVC pipe.

Initially, the leveler was believed to have been a success by lowering the water level back to the it’s original state before the beavers arrived. However, after some time in the environment the water level is now 6 to 12 inches above the original level again.

beaver pond leveler in water

Where the leveler currently sits, photo Matt Schultz

Some steps are being taken to investigate and solve the water level problem. Schultz believes that the mesh cage of the leveler may be sticking too high out of the water causing the entire leveler to not drain properly. One idea is to push or sink the leveler further into the water for better drainage of the flooded fen.

Overall progress has been made. When the beavers leave and abandon their dam in the future, the leveler will be removed.

MNA would like to thank their members for making projects such as these possible to save such valuable sites such as the prairie fen in Edwin and Margarita Palmer Memorial Sanctuary.

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One thought on “Beavers Disrupt Fen

  1. Snohomish county in Wa state has seemed to design a cage/pipe system that lets water flow though. If you give me your email address I can forward you the design. We are looking at here in Black Diamond because we have SO many Beaver damns they are effecting the Oxygen level in our streams.

    Sincerely,
    Kristine Hanson

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