New Article on Beaver for Maine Woods News and Forest Ecology Network

The Indispensable Castor Canadensis / N. American Beaver

For North America, beaver influenced watersheds are to the Earth as blood
capillaries and kidneys are to our own bodies. Imagine trying to function
with only 10% to 30% of your blood capillaries and kidney capacity working
to try to supply pure life blood to your various organs, extremities etc.!?
Beaver provide instead the proper flow and distribution of “lifeblood”/
water to the earth and thereby nurture the life forces throughout ensuring
the basic health of our ecology from which all our organisms evolve and
thrive! While insufficient planning and foresight has produced 200+ years of
human development and infrastructure that is often at odds with wetland
ecology and thereby presents a severe challenge to wetland restoration, it
is also true that these wetlands and, especially, beaver created cyclic
wetlands are crucial for restoring what should be some of the most
biologically productive ecosystems known to man!(1)

Unfortunately throughout the 220 years of modern human colonization of
North America much of these critical wetlands were converted and system-
atically drained for agricultural use and other development at the same
time that beaver were exterminated nearly to the point of extinction. The
result has been devastation to the biological and hydrological health of
the region as characterized by native fish population decline, wildlife
habitat degradation, water table and quality reduction and ecological
imbalances that have led to various insect and other pest population prob-
lems. These missing wetlands have also been a major factor in the continued
tremendous soil erosion on the continent and have exacerbated drought and
flood effects. The beaver’s role would be to recreate these diverse habitats
and hydrological benefits by opening forest canopies and diversifying and
slowing stream flows on the land to trigger explosions of biological
activity which begin entire food chains throughout these wetland systems.
They do this by allowing sunlight to stimulate the growth of algae and
aquatic plants which supports microscopic organisms in turn consumed by a
great variety of invertebrates which in turn attracts myriad amphibians,
reptiles, fish, birds and mammals.(2&3) Grasses, sedges, bushes and saplings
appear that provide food and cover for foraging animals and the deep pools
and sedimentation control provided by beaver damming increase salmon and
trout populations.(5)

These natural, bio-diverse ecosystems that are created by beaver through
their evolved role in nature should definitely not be confused with the
results produced by artificially maintained “wildlife openings” (as are
commonly promoted in our National Forests and other public lands) nor the
often touted value of clear-cutting or over-harvesting forests that are
conceived from a myopic view of extremely limited, valued species. This ra-
tionalization of what is usually extremely degenerate forestry practices
actually serves to increase biological imbalances and other deterioration
that lead to problems like tick infested Moose with brainworm disease and
other pestilent outcomes, and also contribute to excessive soil erosion
and surface water degradation. Beaver managed forest openings and wet-
land complexes act as natural sponges which store rainwater and slowly
release it, reducing downstream flooding and erosion and improve water
quality (4&6), by absorbing dissolved nutrients, processing organic wastes
and actually collecting and breaking down toxic runoff of heavy metals,
pesticides and fertilizers thereby serving as “earth kidneys”!
Beaver ponds and wetlands also recharge aquifers, stabilize the water table
and improve stream flow in the face of drought and are preventative for
uncontrolled wildfire, (none of which will ever be accomplished by anything
approaching a clear-cut or non-sustainable harvest!).

Unfortunately as the value of beaver has, in part, been realized and their
numbers have fractionally increased, there have also been increased conflicts
with the human footprint. Not only is the recent historic established
infrastructure blocking restoration, but also the continued expansion of
development and roads and trails for recreation and forest products are
highly problematic for beaver and ecological restoration due to poor
planning, lack of understanding and proper regulation. In the State of
Maine, beaver wetlands regulation and management is largely overseen by the
Dept. of Conservation, Inland Fisheries and Wildlife. This bureaucracy seems
to have as 1st priority the promotion and sale of hunting (& fishing) and
trapping licenses and things ecological are geared mostly toward that end.
The Department does not even have the funds to spare to actually monitor
beaver populations and certainly not their effective role in our ecology
(ironically, the role that would also be key to other game species health
as well!). In this unfortunate vacuum, decisions are made by calculation (or
perception?) from #’s of beavers trapped vs. “effort” (number of trapping
licenses sold?) and also the number of “nuisance” complaints so that the result
has become a greatly expanded trapping season, a proposed hunting season
and concessions to previously outlawed practices such as trapping on dams
and lodges and even permitted shooting of “nuisance” beavers. The commonly
heard sentiment from State wildlife managers is that beaver are at, near or be-
yond the “carrying capacity” or “tolerance” level and not enough trapping; yet
they have no statistical basis for these conclusions!**
This is a sad state of affairs which has resulted in the unregulated
trapping of beaver even where they would do the most good in non-conflicted
areas which along with conflicted site lethal removal has the real effect of
undermining all State efforts to improve and increase not only game animals
and birds but also ecological health and restoration in general, to the
detriment of both the public good and the effectiveness of public tax and
other dollars spent!

As part of my effort to counter and educate about this adverse trend, I am
trying to promote the use of engineered structures that can mitigate
conflicts between beaver and human activity. These engineered installations
such as “Beaver Deceivers”, “Flexible Pond Levelers”
and “Culvert Protective Fences” can be utilized to effectively and
economically prevent damages from culvert plugging and flooding of roads or
property. It should be stressed that the moderating effects of these
structures can be reliable, effective and economically viable for
protection, but also potentially degrade to a lesser or greater degree the
habitat that is also being (partially) accommodated. It would always be
preferable to maximize ecological benefits by using better design and
location of infrastructure where possible since we already are too far
behind with these lost ecosystems. Instead, we seem to have a rush to access
all remaining forests and wildlands with even more poorly designed and
located roads and trails for recreation and logging etc., creating excessive
and self-defeating conflicts. It is man that has saturated and degraded the
landscape, not beavers!

Most recently I was able to collaborate with Regional State Biologist, Scott
Lindsay and landowner, Bill Crain on a pond level control structure on
private property in Pownal, Maine. In order to protect the bordering public
road from possible flooding we installed a 20′ x 18″ dia. “flex-pipe”
polyethylene single wall culvert connected from a cylindrical 6′ enclosed 6
gauge wire mesh intake cage in the pond to a 1′ breach in the top of the
beaver dam near the road to lower the water level about 1′ at the road. The
1′ seems to be a good compromise that will protect the road from damage
during high flow rain and melt events, yet hopefully will maintain adequate
water level in the pond to facilitate continued beaver activity and the
ecological benefits as much as possible. So far so good, tho no real high
flow test since the Oct. 4 installation. In this case there was a long
history (maybe 20 years or so) of events that led to this hopeful
resolution. The landowners had been consistently adamant about protecting
the habitat on their property but problems with the road and culverts
persisted to the point that the Crain family finally consented to having
beaver relocated. This, however, went awry with the accidental drowning of a
beaver (only one of many ways in which relocation is usually not the best
option). After this incident a newly sympathetic, creative and resourceful
town road agent at that time, installed a stone barrier upstream of the road
to encourage future beaver damming activity away from road culverts. This
succeeded, but to a point that water level during high flow events could
deflect/detour across road causing significant erosion. This was mostly, but
not always, avoided by the diligence of the landowner manually lowering water
level by partially breaching top of dam ahead of oncoming storms etc.
Another simpler solution might have been to simply ditch &/or raise the road
bed just enough to give high water a path back to the ample road culverts
instead of across road, but it seems there was no flexibility in that direction
from the current town road officials.

So far the pond leveler seems likely to be successful and has eliminated the
stress and worry about damages and the work of continually monitoring and
controlling water level by the landowner; though we have yet to hear from
town officials. The State Biologist is hopeful that the installation is a
success and will serve as an example to be followed more often in future
conflict resolutions. He will also be attempting to secure a grant through
the Maine Outdoor Heritage Fund (they sell scratch tickets at local markets)
to help with funding some of this important work! Hopefully too, now the
Crains can relax and enjoy watching wildlife in their terrific wetland


“What Good Are Beavers” by Mike Callahan/; &
Heidi Perryman/ Worth A Dam (

(1) U.S. Environmental Protection Agency, Functions and Values of Wetlands,
EPA 843-F-01-002c, September 2001.

(2) Baker, B. W., and E.P.Hill, 2003. Beaver (Castor Canadensis).
Pages 228-310 in G.A.Feldhamer, B.C. Thompson, and J.A.Chapman, editors.
“Wild Mammals of North America: Biology, Management, and Conservation.
Second Edition. the Johns Hopkins University Press, Baltimore, Maryland,

(3) Cooke, H., Zack, S. (2008) Influence of beaver dam density on riparian
areas and riparian birds in shrub steppe of Wyoming. Western North American
Naturalist Vol (6) No.3. (3) P. Collen & R.J. Gibson
(2001) The General Ecology of Beavers. Reviews in Fish Biology and Fisheries

(4) Langcore,T., Rich,C. & Muller-Schwarze,D. (2006) Management by
Assertion: Beavers and Songbirds at Lake Skinner (Riverside County,
California) Environmental Management Vol.39 (4).

(5) Pollock,M., Pess,G. & Beechie,T. (2004) The Importance of Beaver Ponds
to Coho Salmon Production in the Stillaguamish River Basin,
Washington,U.S.A., North American Journal of Fisheries Management

(6) Terry,N. & Ban’uelos,G.S. (2000) Phytoremediation of contaminated soil
and water. CRC Press LLC

** regarding “carrying capacity”.

In the late 90’s and early 2000’s I heard the same arguments from MA DFW
biologists saying MA was at its “cultural carrying capacity” for beavers. They
stated it as if cultural carrying capacity was a fixed number that required the
beaver population to be decreased. What they didn’t anticipate was that
through education and effective flow devices the MA cultural carrying capacity
line they identified moved dramatically higher. Now it seems MA has many
more beavers but less complaints than we did back then. Cultural carrying
capacity is malleable. (submitted by Mike C. ;

See Also:

“Best Beaver Management Practices” DVD and more info from
(without which much of these successful technologies would
be unknown to me!)
Facebook; “Beaver Management Forum”;;
Beavers Wetlands Wildlife (; Unexpected Wildlife
Refuge (.org);; MSPCA Living with Wildlife Program, Boston, MA.; The Humane
Society of the United States, Washington,D.C.;


Nature: “Leave it to Beavers” (2014) (PBS / Netflix)


Check Out:

Wildlife and Habitat Protection petition;


“The Beaver, Natural History of a Wetlands Engineer”, by Dietland
Muller-Schwarze and Lixing Sun, 2003

“Beavers by the Mendenhall Glacier in Juneau, Alaska” by R.Armstrong and
M.Wilson, 2009

“The American Beaver: A Classic of Natural History and Ecology” by Lewis
Morgan. (written >125 years ago)

“Paddy: A Naturalist’s Story of an Orphaned Beaver” by R.D.Lawrence,
1977 (a personal favorite!)

“Lily Pond: Four Years with a Family of Beavers” by Hope Ryden, 1989

“Where Waters Run Beavers” by Paul Strong, 1997

“Beaversprite: My Years Building an Animal Sanctuary” by Dorothy Richards,

“Swampwalkers’s Journal” by David M. Carroll, 1999, Mariner Books,2001
(greatly insightful!)

“In Search of Swampland – A Wetland Sourcebook and Field Guide” By Ralph
Tiner, 1998

“Discovering The Unknown Landscape – A History of America’s Wetlands”
by Ann Vileisis, 1997 (“An excellant historical text of our nation’s
wetlands and how we got to where we are today.”)

“Wetlands: The Web of Life” by Paul Rezendes and Paulette Roy, 1996
(“Spectacular wetland photography and descriptive text combine…..”)

“Wildstream: A Natural History of the Free Flowing River” by Thomas Waters,
2000 (“…easy to read, in-depth…stream ecology.”)