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Beavers and Dams


By Ranger Steve Mueller

Beavers became a commodity and fashion product. They were heavily trapped and numbers were greatly reduced. They brought business trade to what became Michigan. In prior centuries native people used the resource as part of a sustainable livelihood. The European beaver trapping industry became a boom and bust business. One might wonder how beavers change nature niches.

Beavers weigh 30-50 pounds and are the largest rodent in the area. Their natural history provides benefits but sometimes they are troublesome neighbors.

At the local Howard Christensen Nature Center (HCNC), a family of beavers moved into the outlet of Spring Lake in 1970s. They are better dam builders than most of us could hope to become. One wonders how a particular dam site is selected. Narrow sections of Spring Creek were ignored and a dam over two hundred feet long was constructed near the outlet of Spring Lake. It required lots of work but was successful. Two smaller dams were constructed down stream to create additional flood ponds.

Elevated pond water allowed beavers to swim to the upland shore for aspen trees without going far from shore. It is safer to stay in water. Water access to trees reduces danger from predators and makes it easier to move wood. That is the reason people used rivers to float logs to sawmills during the boom and bust era of Michigan logging. Current forestry practices encourage sustainable logging instead of boom and bust cycles. That practice helps maintain a sustainable community economy.

Beavers topple trees and gnaw branches for underwater storage. They eat meals as needed all summer but branches are hauled to flood ponds and stuck in mud that accumulates behind the dam. Branches provide food during the long winter when timber harvest is not possible.

A domed beaver lodge with an underwater entrance is constructed in the beaver pond. Beavers enter and come above water level to dry living quarters with no easy predator access. A family of beavers can live cozy and exit as needed during winter months to raid their refrigerator. They retrieve branches stored in the mud and feed on nutritious bark. Remaining inner wood is used for construction or discarded like we discard chicken bones or corncobs.

Beavers move to new areas after a few years when they have eaten themselves out of house and home. Their temporary residence activities provide valuable services. The area behind the dam traps sediments and reduces debris and soil in downstream areas. This helps some animals that need clear flowing water and also those that need ponds. Water flowing over dams picks up additional oxygen essential for fish and insects. Fishing generally improves but pond water can warm streams. Various plants are able to colonize the wetlands behind the dam. Willows and alders are colonizing shrubs. In such areas, animals like the Alder Flycatcher and the Acadian Hairstreak find living good.

A great many creatures benefit from the temporary residence of a beaver family. Beavers move in and move out but leave a life giving legacy for others that last for decades. We most notice water that floods roads or drowns trees we might desire survive. Beavers do not recognize our legal title to property so we remove them when their activities do not meet our approval.

Beaver benefits include raising water tables that keep wells flowing. They provide habitat for many wildlife like fish, ducks, and deer and many less noticed animals. During spring high water dams help reduce spring flooding along rivers and it is then when beavers search real estate for new homes and food. Maybe one will come your way and bring activities that improve nature niches in your area.



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One Response to “Beavers and Dams”

  1. I appreciate your pointing out that beavers benefit the streams in which they live. The dams provide richer soil and an increased invertebrate community which means the ponds become home for a greater density and diversity in fish population – which means an increase in all the birds and wildlife that eat fish!

    My city made a decision to live with beavers 8 years ago and installed a flow device to control pond height. Now because of our safe, beaver-tended wetlands we regularly see otter, steelhead, woodduck and even mink in our urban stream!

    Heidi Perryman
    Worth A Dam