Wednesday, January 16, 2013

Castor's New Year Resolution

Hi all,

This is Kelsey from Green Valleys Association.  I’ll do my best to keep you posted on the latest and greatest here at Welkinweir, home of Green Valleys Association, in 2013. 

Since it is January, the month of beginnings and New Year’s resolutions, I thought it might be appropriate to share what I believe to be the resolution of our resident beaver family.  But a bit of a backstory first:

Our family started out with just one beaver a few years ago.  Staff began to see its telltale tooth marks on pond-side trees and shrubs, and the beginnings of its additions to the dam at the east side of the Great Pond, right in front of the spillway underneath the bridge.  We named him (or her) Castor after the scientific name for the North American beaver (Castor canadensis).  Soon it became apparent that Castor had acquired a mate and was expanding his family – and his engineering exploits.  The beaver dam grew larger, as did the number of lodges (a beaver’s twiggy home; beavers don’t live in dams, building them instead to slow moving water and create ponds in which they live and forage for water plants).  You can see three beaver lodges to date on the southern banks of the Great Pond, along the Horseshoe Connector Trail: we think the smallest was Castor’s “bachelor pad”, before he had a family, and the other two larger ones were built to accommodate his mate and their babies.  Vacated beaver lodges eventually become home to other wildlife such as mink and muskrat.

Unfortunately, this past December we were forced to clear away Castor’s hard work from the dam spillway.  However, our plucky beaver family is undeterred and hard at work rebuilding their project for 2013.  While walking around the grounds last week I spied their latest efforts:

In case there was any doubt as to whose work this is!

A "Castor-eye" view of the beaver dam.

I think it’s clear to see what Castor’s New Year resolution is!  I also think it’s fascinating to see a beaver dam construction in progress.  Looking at the last photograph above, it appears that beavers install tree branches both perpendicular to, and parallel with, the flow of the water.  The first wall of the dam is reinforced with mud, while the branches behind the wall support it and brace against the force of oncoming water.  The beavers weave branches of all shapes and sizes together, which are anchored deep into the spillway’s muddy bottom either as part of the construction or over time from the force of water.  As someone who helped pull one apart can tell you, a beaver dam is a very sturdy and effective structure!  Last year I noticed that the mud “mortar” in the dam became colonized by wetland plants; in the wild, these dams must surely evolve into unique micro-habitats of their own.  For more information about beaver ecology and natural history, check out this link:

While this natural engineering project is interesting and entertaining to watch, the trees and shrubs along the pond’s shores definitely bear the brunt of Castor’s industry.  Beavers appear to favor alder (Alnus spp.) branches, judging from the contents of the spillway dam.  However, as the photo below shows, they aren’t afraid of attempting to bring down larger trees!  

As of this blog post, the ash tree (Fraxinus spp.) still stands.  Look for it on the south side of the Great Pond, along the Horseshoe Connector Trail (blue blaze) near the dam bridge.
More of Castor's work by the pond.
We are in the process of brainstorming ways of beaver-proofing some of the pond-side plants, in order to preserve as much of the riparian buffer as possible.  After all, the buffer is important for bank stabilization, stormwater filtration, and providing shelter for wildlife.  Perhaps we have an opportunity at Welkinweir to study beaver-human interactions?  Now that this keystone species is returning to Pennsylvania ponds and streams, we are sure to see more of them.  It will be important to learn how we can live alongside each other in the future.  Stay tuned for more updates on Castor and his projects in future blog posts and in GVA’s Streamlines newsletter.  And visit Welkinweir to check out the work of our beaver family!