Wednesday, October 20, 2010

The Beaver: Our Slow Water Animal Ally

Us humans sure have an inflated sense of importance!  Since we are the ones who created pavement, rooftops, and channelized culverts, we think we are the only ones who can also work to slow down water with rain gardens, bioswales, and constructed wetlands.  It's time to face up to the truth.  There is another mammal who has been constructing wetlands and 'rain gardens' since long before humans even set foot in North America.  In truth, they do a better job of it than us, too.  Unfortunately, humans have done a good job of driving these animals away from much of the United States in the last 500 years.  The good news is that they are already on the comeback, and all they ask in return for their work is a little bit of space, tolerance, and some delicious aspen and willow to chew on.


This post will be a place to share a few observations and interesting facts about beavers, but please do further research if you are interested.  There are far too many amazing beaver facts to post them all here.

I've been doing some research on beavers in North America, known to science as (Castor canadensis) since I came to the eastern United States.  This includes some online research, but also examining every beaver dam I came across in the woods of Vermont and Pennsylvania.  I had in the past read that beavers are important parts of many if not most North American ecosystems, but until I came here I had no idea just how important they truly are.  Beavers don't just live in medium-sized creeks in the mountains.  They are found anywhere there is water and suitable trees (they don't eat conifers)...small seep areas, swamps and marshes (some of which they create or expand), enormous rivers (which they don't bother to dam or build lodges in - they just live in burrows instead), and even large lakes.  Most people know that beavers build dams, but they also build 'canals' so that they can drag trees around in the water.  This can vastly expand wetlands as water is routed to many new areas.  The huge 'beaver complexes' that form in suitable habitat are amazing, and fun to look at on aerial photos.  Here's a neat one near Bolton Notch in Vermont to check out.

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Beavers were extensively hunted for their pelts by fur trappers.  I hear they taste decent too but haven't tried Castor canadensis meat.  As a result, their range was drastically reduced after European colonization.  Since then, they have been reintroduced or allowed to expand back into much of their original range.  While beavers have been blamed for everything from increasing flood severity to decreasing fish abundance, in fact the opposite is true.  Beavers do a great job of building fish habitat, and the dams don't stop fish migration (there are many papers on this, I don't have space to link them all, but the wikipedia article links to quite a few).  Beaver-constructed wetlands also offer many of the benefits offered by human-constructed wetlands - and are constructed by beavers for free.  In fact, one amazing study in Washington found that reintroducing beavers could potentially store 650 TRILLION GALLONS of water from spring flood season, releasing it instead in the summer and fall.  In other words, beavers do the exact same things reservoirs do - retaining floodwater for release during drought - without any of the downsides of reservoirs, such as habitat loss, massive expense, and obstruction to fish.  It isn't that much of a stretch to imagine that the reason people 'needed' to build reservoirs in much of the country was only because beavers were expirpated.  Reintroducing beavers could be the key to removing some unnecessary dams while also improving habitat and dry season water flow.

(above: beaver pond on Nebraska Notch near Stowe, Vermont)

So, it's easy to see why I am so excited about beavers... they ARE the original Slow Water engineers!  Although they can't live in all urban environments, they DO have a place in urban, suburban, and rural ecology, albeit a less extensive one than in wild areas.  Places where beavers have been able to live include Centennial Woods near Burlington, Vermont; an urban stream in Martinez, California, and Lincoln Park in Chicago (where the beavers were not welcomed with open arms).  Beavers have been reported in Frick Park in Pittsburgh though they are not permanent residents.  I also have reason to believe that the site of Panther Hollow Reservoir may have once been a beaver meadow, though I can't find proof of that.  Even dry southern California may have had a history of beaver inhabitants, as in the book 'Ecology of Fear', Mike Davis mentions a historic account of beavers in Malibu Creek!  (I have not been able to find this source)...
It is true that beaver dams can cause localized flooding if built in undesirable locations, such as near culverts or downstream from farm fields, but this can often be controlled with an ingenious device known as a Beaver Deceiver.  Individual trees can be protected from beavers with wire netting.  Some areas will never be appropriate homes for beavers, but I do think that the potential for 'urban beavers' is greater than is currently recognized.

I've got a lot more thoughts about the role of beavers in 'slow water' but I am going to bring this post to a close, since it is already extremely long.  Please do feel free to share any thoughts about beavers here; I will also post more about them in the future.

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