The industrious rodents can offer a range of benefits for California water supplies and habitats. But they’re still officially considered a pest
October 16th, 2015 by Alastair Bland ·
On California’s central coast, a region that usually receives drenching rainfall or fog for most of the year, some forests are now as arid as a desert. Streams that once ran at least at a trickle through summer have vanished in the ongoing drought, and environmentalists and fishermen fear that local salmon will disappear if climate conditions don’t improve. The landscape desperately needs rain. It could also use beavers, according to ecologists who say the near eradication of Castor canadensis from parts of the West in the 19th century has magnified the effects of California’s worst dry spell in history. “Beavers create shock absorption against drought,” says Brock Dolman, a scientist in Sonoma County who wants to repopulate coastal California with the big lumberjacking rodents. Beavers are a hated pest and a nuisance in the eyes of many landowners and developers, and the animals are regularly killed with depredation permits and by fur trappers. However, they are also a keystone species whose participation in the ecosystem creates benefits for almost all other flora and fauna, Dolman says. This is because of the way beavers’ hydro-engineering work affects the movement of water. “Beavers aren’t actually creating more water, but they are altering how it flows, which creates benefits through the ecosystem,” says Michael Pollock, an ecosystems analyst and beaver specialist at the National Marine Fisheries Service Northwest Science Center. By gnawing down trees and building dams, beavers create small reservoirs. What follows, scientists say, is a series of trickle-down benefits: The water that might otherwise have raced downstream to the sea, tearing apart creek gullies and washing away fish, instead gets holed up for months behind the jumbles of twigs and branches. In this cool, calm water, fish — like juvenile salmon — thrive. Meanwhile, the water percolates slowly into the ground, recharging near-surface aquifers and keeping soils hydrated through the dry season. Entire streamside meadows, Dolman says, may remain green all summer if beavers are at work nearby. Downstream of a beaver pond, some of the percolated water may eventually resurface, helping keep small streams flowing and fish alive. Dolman, co-founder of the Occidental Arts & Ecology Center in Sonoma County, says this water banking process could even, in theory, partially offset the worrying shrinkage of mountain snowpack, historically California’s most important water source. Dolman and his colleague Kate Lundquist, who are leading their organization’s “Bring Back the Beaver Campaign,” would like reintroduction of beavers from other regions to begin now as a measure for restoring salmon populations and building general drought resilience into the landscape.