California: The Rebeavering

By Sara S. Moore

The California case for beaver reintroduction is picking up steam.

Specifically, the case is being made for the benefits of beaver dams and their ponds to California’s high Sierra, where a disappearing snowpack is threatening the state’s summer water supply—and overall economy.

Not all beavers build dams, and not every place beavers go is a suitable location for dams. However, where beaver ponds are found, there are higher water tables that benefit grazing animals like cattle, deep, cool ponds that benefit juvenile fish, and, when people are present, the aesthetic benefit of “watchable wildlife,” according to Brock Dolman, Director of the WATER Institute at the Occidental Arts and Ecology Center, and advocate for the strategic fostering of beaver populations in California.

California faces peculiar beaver-reintroduction barriers not faced by other western states where people are starting to think of beaver ponds as a landscape restoration and surface water retention tool, like Arizona, Colorado, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. And drought-plagued California might gain particular benefit from a new surface water retention tool. Hydrologist Suzanne Fouty, of the U.S. Forest Service in Oregon, said in the 2014 PBS Nature documentary “Leave it to Beavers:”

The bottom line is, [beavers are] your ace in the hole. […] If the snowpack’s coming off earlier and ranchers want water, then we’re going to have to figure out how to keep it on the landscape, because it’s no longer going to be stored as snow in the mountains, and what beaver do […] is they create these little savings accounts, […] no longer as snow, but as surface and groundwater.

Beavers? In California?

Joseph Grinnell (in a 1937 University Press publication) and then Donald Tappe (in a 1942 California Department of Natural Resources publication) brought in the idea that the mid-1800s “fur rush” had pared back a beaver population that was limited to inland valleys. Then, in 1988, evidence of ancient beaver dams was found in the high Sierras that carbon dated back to 580 CE (Novel physical evidence that beavers historically were native to the Sierra Nevada C. James and R. Lanman [2012]).

Further research, including a 2012 California Fish and Game piece by Lanman, Dolman and others, is showing evidence of beaver range extending across most of California, but what Dolman calls the “beaver blind spot” remains thanks to Tappe and Grinnell. Researchers working on the new maps of beaver range in California speculate that coastal and high Sierra beaver populations were smaller and easier to trap due to topography, so their populations were wiped out 100 years before Grinnell’s seminal work.

Before capitalizing on those precious “savings accounts” of water that high Sierra beaver could give California, the people of California have to buy the idea that beaver were here. They have to believe that supporting the expansion of their numbers and range is restoration instead of a new invasion, a la the 1946 experiment in Patagonia (Chile and Argentina), which has been an unmitigated disaster.


The second problem is the belief that beavers do more harm than good. The animal has been framed as vermin for 100 years. In some California counties there is no limit to the number of beavers you can kill in season. This is a public perception problem.

Beavers undoubtedly cause flooding where they build dams, and valuable property can suffer: orchards can suffer from both flooding and girdling by little teeth. Infrastructure can be put at risk if beaver populations are not managed. Advocates say there are remedies for most beaver/human conflicts. For example, it’s easy to protect valuable trees with fencing or painting the base with latex paint mixed with sand. The animal is tarred with stigma through the common name of Giardia: beaver fever. In fact, “it has never been demonstrated that the type of giardia beavers carry causes giardiasis in humans,” according to the Washington Department of Fish and Wildlife.

Although individual cases of conflict can be solved (as they did famously in Martinez, CA, now the home of an annual Beaver Festival), there is a lack of information in favor of beavers as a way to solve problems. There is a need for more data supporting the benefits of beaver dams to watersheds for surface water retention, water quantity and quality, and benefits to endangered species. There are loads of observations of these things, but a lack of rigorous research to support it. According to Dolman, scientists need to tease out the “beaver signal” between watersheds with and without beaver ponds.

In My Own Dam Backyard

A third problem specific to California is that beavers were introduced or reintroduced in a widespread, haphazard way as a way to combat erosion in the period after the Tappe report. Other western states also reintroduced beaver, including using parachutes, but they did it on the scale of 200-300 animals. Dolman says the exact figure is unknown, but it is believed that around 1,200 beaver were released in California in that period. Looking back, it appears to have been irresponsible rebeavering. It not only introduced non-native beaver species, but contributed to the confusion about what constituted native habitat for beaver and created conflicts with landowners.

So, What Next?

Besides publicizing the evidence that beavers are native to most of California, quantifying the benefits of beaver ponds for surface water retention (particularly interesting in the current historic California drought), changing public perception of beavers as vermin, and convincing people that beavers will not be parachuted into your backyard, wildlife managers need to get a fix on the current status of beavers in California.

A recent meeting between California Department of Fish and Wildlife (CDFW) staff and beaver advocates started with the staff asking the advocates how many beavers are in the state, according to Dolman. The last state-issued report on the matter was by Tappe: the current condition of the beaver in California is unknown. An online Beaver Mapper has been created to help with this problem.

The CDFW, the agency responsible for beaver population management in the state, is not about to start moving beavers around. But they also don’t want to ignore what beaver advocates are saying about their value for surface water retention and with the state’s old water retention system—snowpack—on its way out. Also, there’s legal liability to consider. It’s possible that in one hunting season, in a county where there is no limit on beavers killed for recreation, an entire beaver family maintaining a pond on which federally and state endangered species depend for survival could be lost. This would put the CDFW in the position of defending an “incidental take” of endangered species in a court of law.

So, the CDFW is cautiously showing interest in what the beaver believers have to say. There appears to be momentum behind locating and evaluating populations for possible increased protection. Sierra mountain meadows and their far-downstream neighbors, thirsty ranches and farms, may eventually see the benefits.

More information:

The Beaver Believers: A Film About Passion and Perseverance in an Era of Climate Change – the website for the film, scheduled for completion in November 2015, has useful background information and references.

Leave it to Beavers – a 53 min. video that premiered May 14, 2014, on PBS Nature, available streaming online. Besides giving a basic history of the animal in North America, it addresses the growing belief by scientists and environmentalists that beavers have been overlooked as a tool for reversing harm done by climate change. It illustrates how beavers have kept ranchers going through drought, as beaver ponds raise water tables on grazing lands.

The Martinez beaver story – a 14:50 video, by Heidi Perryman of “Worth a Dam.”

Beaver and Climate Change Adaptation in North America: A Simple, Cost-Effective Strategy – A 58-page report by scientists and advocates from the WildEarth Guardians, Grand Canyon Trust, and the Lands Council (2011).

Beaver and Climate Change Adaptation in North America: A Simple, Cost-Effective Strategy – A 58-page report by scientists and advocates from the WildEarth Guardians, Grand Canyon Trust, and the Lands Council (2011).