Browsing and Fire in Rocky Mountain's Shrublands: Why the Park Held Off Burning

A deer browsing in a montane shrubland. NPS-RMNP.

The question

Montane shrublands of bitterbrush, sagebrush and wax currant give food and shelter to several birds and small mammals in Rocky Mountain National Park, and elk and deer browse them heavily. The Estes Valley elk population had grown to a historic high of about 3,000, and its deer to an estimated 600. Meanwhile prescribed fire was being used along the Colorado Front Range to restore natural fire patterns and reduce fuels in lower montane forests and shrublands, often at the edge of towns, where wildfire is a special worry. Park managers wanted to know what heavy browsing and fire do to shrublands together.

The experiment

In 1995 researchers set up four sites in upland bitterbrush. Each had a fenced plot (no browsing) and an unfenced one (browsed), and half of each was burned, giving four treatments:

An earlier team collected data before fencing and burning and for two years after (analysed in 1997). In 2001 and 2002, Charles Olmstead and Kelly Nesvacil of the University of Northern Colorado gathered more post-fire data, measured how often deer and elk used the sites, and analysed the whole 1995–2002 record, seven years on.

A prescribed burn in the shrublands. NPS-RMNP.

The results

• Seven years after the burns, browsed plots had far less shrub biomass than unbrowsed ones: browsing was the main influence.
• Plots both browsed and burned fared worst.
• Plots neither browsed nor burned had grown so much that their canopy area and volume exceeded 1995 levels.

Heavy browsing alone is likely eroding these shrublands' value as food, habitat and cover for other wildlife, such as shrub-nesting birds, and adding fire makes it worse. So the park is not using fire in its montane shrublands for now, and will reconsider if managing the elk population reduces browsing.

This summary rests on reports available when it was written (September 2004, updated January 2008) and is not a statement of park policy or a definitive account of the research. More on the park's research: Continental Divide Research Learning Center.

Sources

• Judy Visty, "Effects of Browsing and Fire on Shrublands," National Park Service, Rocky Mountain National Park. https://www.nps.gov/articles/effects-of-browsing-and-fire-on-shrublands.htm