Beavers have shown up a lot in the Estuary News Magazine. In fact it’s how I first met Lisa Owens Viani who used to be the editor and now runs the nonprofit Rats. It’s how I met Ann Riley and Joe Eaton and probably how I met many of the major estuary players. I asked her recently whether the magazine had ever written about beavers BEFORE Martinez, and she sent me to the archives because she couldn’t remember.
Turns out they did. Two very negative stories first in 2003 about how they destroy levees and another in 2004 about how they spread arundo. No mention of ecosystem services at all. Good thing Martinez came along to set the record straight!.
NOCTURNAL ENGINEERS
A century ago, wildlife officials proclaimed
that the Delta’s beavers had been trapped to
extinction. Most farmers responded with a
cry of “Good riddance!” Charismatic as they
are from a distance, beavers can be a major
nuisance: they weaken levees, in which they
love to build their lodges, cut down trees,
and (being obsessive dam builders) attempt
to inhibit the source flow of any water that
makes a sound, including irrigation and
drainage canals.
But the pronouncement was premature:
beaver numbers were on the rise again by
the 1920s. Today, there are probably more
than 27,000 of the long-toothed critters in
the Delta, according to Bill Grenfell, a retired
Fish & Game biologist, once responsible for
monitoring trapping in the state. That’s the
highest concentration in California and prob-
ably the highest ever in the Delta, which pro-
vides abundant human-made beaver habitat,
with no natural beaver predators.
These furry engineers try hard. Their
dens take a lot of work to build and main-
tain, but gusto is one thing they have more
than enough of. “If your average Joe Blow
worked as hard as a beaver, you could fire
half your crew,” says Nick Catrina, a profes-
sional trapper. “There are farmers on some
of the islands who have guys working all
day long taking apart the dams the beavers
just come and build again each night.”
Beaver dens range from the size of a
wheelbarrow to a pickup truck. The bigger
ones can cause levee failure, a serious mat-
ter in the Delta where flooding is a con-
stant and—as islands continue to subside—
growing threat. The cumulative weakening
of Delta levees could make a difference one
day if an earthquake shakes the levee sys-
tem hard enough to cause a chain reaction
of failures, according to Kent Nelson with
the Department of Water Resources.
When observed during the day, Delta
beavers belie their midnight industrious-
ness. Propelled by large scaly feet with
webbed toes, and steered by a rudder-like
tail, they cause almost no disturbance in the water. Unless, that is, they are fright-ened, in which case they smack a loudwarning “Pop!” with their tails and vanishunderwater, where they can remain for 10 minutes without taking a breath. GS
The scaly footed monsters lurk all across the delta just waiting to rip out levees and bother farmers. Gosh it’s a good thing we eradicated them once. I sure hope we can again.
California’s early Spanish settlers and its
contemporary beavers have something in
common—both discovered that Arundo
donax, an invasive bamboo-like reed, makes
fine construction material. In Shasta
County’s Stillwater Creek, beavers have
started using Arundo, as well as the usual
natives like willow, to build their dams.
But in so doing, the ecologically friendly
beavers are spreading the ecologically
damaging reed. 
In Southern California, Arundo now dom-
inates many riparian habitats, and it is rap-
idly becoming established in and along
Northern California creeks. In dense stands
that can grow up to four inches per day
and reach heights of 30 feet, this
“reed-on-steroids” crowds out
native plants. It sucks up vast
amounts of water, yet after it dies,
its dry stalks create a fire hazard.
Once touted as an erosion-control
plant, Arundo is now known to pro-
mote erosion. And during high-
water events, fallen clumps of
Arundo the size of school buses
sometimes clog river channels,
causing floods.
The problem with beavers and
Arundo mixing it up is that as the
industrious rodents drag the reed
to their dams, stem fragments are
released into creeks, then float
downstream and plant themselves
along the banks. The other prob-
lem is that beaver dams create shal-
low, slow-flowing water conditions
conducive to Arundo infestations.
Says Western Shasta Resource
Conservation District’s Valerie
Shaffer, “Arundo is found through-
out Stillwater Creek, but we always
find heavy concentrations near
beaver dams.”
Shaffer emphasizes that she
doesn’t want anyone to blame the
beavers. “Arundo would still spread
rapidly without the beavers’ help.
I’m more concerned about Arundo
impacting the beavers. Beavers
don’t eat Arundo, and it crowds out
the plants they do eat.”
Shaffer wants to raise public
awareness, so that landowners
know to remove Arundo right away.
She hopes to eliminate the plant
from the beavers’ habitat, so the
long-toothed critters can find plen-
ty of their favorite native plants to
chomp on—and build with.
