Squirrel survival: Let forest burn

Cornell biologist Thomas Gavin indicates encroaching vegetation that isolates northern Idaho ground squirrels to small patches of habitat

May 13, 1999
Web posted at: 4:00 PM EDT

Scientists have found additional support for the federal government's "let 'em burn" wildfire policy in the form of a rare ground squirrel in Idaho.

Without lightning-sparked fires, which naturally occur every 10 to 12 years, a few non-native plant species have taken over the Payette forest of northern Idaho and populations of one species of ground squirrel are slowly starving, say biologists based at Cornell University and in Idaho.

"The non-native plants put all their energy into rapid vegetative growth rather than making nutritious seeds," said Thomas Gavin, a co-author of the study and researcher at Cornell's Department of Natural Resources. The squirrels depend on the fat-rich seeds of native bunch grass to sustain them through seven or eight months of hibernation.

Eric Yensen, a scientist at Albertson's College in Idaho, began studying the Spermophilus brunneus brunneus 14 years ago in the high-desert meadows of western Idaho. In 1984, there were about 1,000 of the ground squirrels on public and private lands around Payette National Forest. By 1998, that number had shrunk to about 600, and 12 of the 36 known populations were extinct.

"To make matters worse, when squirrels try to migrate in search of food or mates, their paths are blocked by dense stands of pine trees that thrive in the absence of fire. This means that groups can no longer mix when some populations expand and others drop because of disease, a hard winter or predators. Sometimes one hard winter and a little bad luck with hawks, badgers and other predators are all it takes to wipe out an isolated, local population. They cannot be rescued by dispersers from nearby populations that are doing well," says Gavin.

Squirrel populations as close as two miles apart are no longer mixing in the Payette forests.

The researchers are advocating the use of controlled, "cool" fires to burn off non-native vegetation and underbrush that blocks the ground squirrels' movement from one population patch to others. Unlike hot, uncontrolled wildfires, controlled burns don't usually destroy seeds of native plants, some of which actually need heat to germinate. Plus, the fires can be set while the squirrels are safely hibernating several feet underground.

"The Idaho ground squirrels are part of an ecosystem that functioned successfully for tens of thousands of years, and natural fires were a part of that system, too," Sherman said. "Perhaps by undoing some of mankind's tampering -- as well-meaning as it was -- and setting back the clock, we can encourage the re-establishment of native flora and fauna, especially the rodent variety, while saving the immense costs of fighting catastrophic fires every summer," says Paul Sherman, a Cornell biologist and co-author of the study.

The U.S. Fish and Wildlife Service has proposed listing the northern Idaho ground squirrels as "threatened," deserving of protection through the Endangered Species Act. The study was published in the current issue of Journal of Mammalogy.

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