Above, UC Davis researchers study a ski run made by clearing; below, they examine a graded run. A study led by ecologist Jennifer Burt suggests that that grading, compared to clearing, is worse for mountain ecosystems, reducing soil depth and fertility and promoting erosion. (Credit: Jennifer Burt/UC Davis)

UC DAVIS (US)—Building a new ski run by bulldozing a mountainside rather than only cutting its shrubs and trees is far more damaging ecologically, yet might offer only a week’s earlier start to the downhill season.

And even that extra week of revenue may be partly offset by higher summer maintenance costs, according to a new study by researchers at the University of California, Davis.

Jennifer Burt’s study of seven winter resorts in California and Nevada’s northern Sierra Nevada range found that ski slope grading, compared to clearing, is worse for plant abundance and diversity, reduces soil depth and fertility, and promotes erosion. Details were published in the December issue of the journal Ecological Applications.

graded_ski run2

“Most large downhill resorts in the United States are on lands managed for the public by the USDA Forest Service, which is supposed to encourage multiple uses while attempting to protect the ecosystem,” Burt says. “But ski areas are managed primarily for recreation, when they might be better managed to minimize negative impacts on water storage, nutrient cycling and biodiversity.”

“Cleared” runs are created by cutting and removing tall woody vegetation as needed to create open skiing and riding pathways, but leaving the top layers of soil and their existing seed bank largely intact. “Graded” runs are cleared—and then also machine-graded or leveled to remove tree stumps, boulders, and slope irregularities. The grading process disturbs or removes much of the topsoil and most of the vegetation, resulting in significant decreases in all measures of ecosystem function considered in the study.

In fact, Burt says she found that cleared ski runs were functionally more similar to adjacent forests than they were to graded ski runs in terms of plant community composition, diversity patterns, and soil characteristics.

“This begs the question as to why any downhill runs are graded,” Burt notes. “Resort managers told us that ski-run grading reduces surface depressions, hummocks, and boulders, which means that less snow—about 20 inches on average—is required to open a graded run than a comparable cleared run.”

At the Sierra resorts that Burt observed, graded runs opened about a week earlier than nearby cleared runs during the 2006-07 season. “However, managers also indicated that graded ski runs generally require more total summertime maintenance effort, due to erosion-control seeding and water-bar repairs,” Burt adds.

The research was funded by the National Science Foundation.

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