A BEAVER DAM COULD TEST YOUR ENVIRONMENTAL CONSCIENCE

by Whit Gibbons

December 18, 2016

A walk in the woods near a stream has given me the opportunity to witness one of nature’s marvels that I have never seen before – the building of a beaver dam.

My first evidence of something unusual happening came in autumn after a month of no rain when I measured the water level. I do this at least once a week downstream from our cabin and was surprised to find that instead of dropping an inch or so, it had actually risen 2 inches. I attributed it to mismeasurement until I took my walk.

Beavers are unquestionably keystone species in a region with small to moderate-size streams. They not only modify the habitat but can also change the environment in ways that dramatically influence the lives of animals, including people, and plants.

Beaver activity can result in big trees dying from flooding and smaller ones being debarked for food or cut down for dam construction. A mile downstream from my incipient beaver dam a larger one has flooded several acres, leaving tall, lifeless sweetgum and pine trees that began life in a terrestrial habitat and cannot persist in an aquatic one.

Animals are affected, too. Large aquatic salamanders called sirens thrive and become more abundant in pools of a stream created by beaver dams. We once observed more than 500 sirens along the margins of a small stream when a dam was removed and the water level dropped.

Cottonmouths, watersnakes and turtles are more apparent, and maybe even more abundant, around beaver dams, which create areas for basking on sunny days. Waterfowl, such as wood ducks, are attracted to the pond created above the dam. Clearly, beavers and their dams set the tone of the neighborhood for many wildlife species.

Some facts about beavers speak to the impressiveness of these gigantic rodents. The historical geographic range for beavers is vast, extending from northern Florida and Mexico to Alaska and Newfoundland. Adult beavers can weigh more than 80 pounds, and their North American ancestors were even bigger, reaching the size of a full-grown black bear.

Beavers live 35 to 50 years in zoos and more than 20 years in the wild. The longest beaver dams, reported from Montana and from Alberta, Canada, are more than 2,000 feet long. Surely beavers across the continent are working feverishly to break the record. Beavers are usually nocturnal, but I saw one on top or our beaver dam during the day. Perhaps an OSHA dam safety inspector.

One of the conundrums with beavers is that their positive traits – being chubby, cute, industrious pioneers – aren’t always enough to outweigh less desirable traits. I know folks who have had beavers cut down a beautiful dogwood tree, flood an area intended for a garden not a fish pond and dismantle a wooden boathouse to build the beaver lodge. The predicament is how to keep beavers for outdoor show-and-tell yet not have them misbehave, from a human’s point of view.

An ecofriendly society will always face perplexing wildlife problems and environmental dilemmas. Entertaining, yet potentially destructive, beavers are a good example of the complexity inherent in environmental preservation, with no simple solution as to how to handle the issue. A range of responses are available for dealing with nuisance wildlife. Which solution people choose will depend in part on their environmental conscience.

A problem that too much of this beaver-dam building might cause on our stream is to make it more difficult to navigate up and down in a canoe or john boat. But carrying a small boat around the end of a beaver dam to get to the other side of the stream will not be much of an imposition in return for getting to experience a natural phenomenon that can change the character of the habitat and its wildlife. That is, as long as I don’t see part of our cabin being used to build that dam.

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