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The Biological Cost of a Cabin in the Woods

By Jim Robbins

posted 4/30/02

Dreaming of a log cabin on 20 pristine acres in the mountains? Think again. Getting away from it all may pose the most serious threat to wildlife in the growth-plagued West, according to biologists who have been studying the ecological effects of rural residential development. New homes cause problems not only outside parks and wilderness areas, but inside as well.

The biological effects of sprawl have been suspected, but studies have been few. Now the science is beginning to gel. Andrew Hansen, for example, an associate professor of ecology at Montana State University, in Bozeman, has catalogued some of the effects of development on private land outside Yellowstone National Park, where the number of rural homes increased by 400 percent between 1970 and 1997.

Among the primary agents of change in rural development, says Hansen, are dog food and compost. Bears are drawn in by these goodies and may become comfortable enough to lose their fear of people. That leads to more human-bear encounters, which can result in the bear’s being put to death. Magpies and brown-headed cowbirds are also drawn to pet food and compost, and they flourish around rural houses. These "brood parasites" feed on the young of other birds, such as yellow warbler. In one of Hansen’s study areas, nearly half of the yellow warbler nests were raided by magpies or cowbirds, and abandoned by the warblers. Hansen found that American robins, which can better defend themselves, did not lose any nests to the brood parasites.

The problem is made worse by the fact that not all habitat is created equal. The same things that appeal to humans--deciduous trees, riparian areas, warmer temperatures, and lower elevation--make for ecological "hot spots" that are critical to wildlife. The human population along ecologically important forest fringes in Colorado, for example, grew 25 percent faster than in the rest of the state between 1990 and 2000.

Human dwellings affect wildlife indirectly as well as directly. Some western ecosystems, for instance, have evolved with frequent fires that burn out the thick undergrowth every 20 or 30 years, opening the forest to a broader range of species and higher numbers. "The presence of homes constrains fire regimes in these ecosystems," says David Theobald of the Natural Resource Ecology Laboratory at Colorado State University. No longer can a fire be allowed simply to burn itself out. "That has huge impacts and alters the function of these habitats."

Most federal land in the West is protected from development, but many biological hot spots are on private ground, and many species spend a disproportionate part of their time there. Around Glacier National Park, for example, 60 percent of the conflicts between bears and people occur on private land--which is just 17 percent of the land base. So the search is on for ways to make private land more compatible with the wilderness around it, everything from locking up the pet food to "cluster developments" that preserve some open space to conservation easements on critical habitat.

The recent research underscores the crucial role that private land plays in biodiversity and casts doubt on the assumption that species in Yellowstone and elsewhere are safe from the depredations of growth. And it raises a big question for managers of natural reserves. How do you protect habitat that is critical to species within a park, such as the yellow warbler or the grizzly bear, but that lies on private land outside the park? Research points to the need to mitigate the effects of development on private property--soon.

That’s where the science is headed, says Hansen. "It’s the same situation logging was in 20 years ago. All people had were strong personal beliefs. Then the science came on board, and it led to ways to log that minimize negative impacts."