How softly do we really tread?

Brief by Central Staff

Outdoors – September 1997 – Colorado Central Magazine

Just how much does trail-based recreation affect wildlife on public lands?

Good question, and the Southern Rockies Ecosystem Project is looking for some answers.

Roz McClellan, who works for the project, says the main concerns at the moment are motorized and bicycle travelers in the woods, since those are the fastest-growing uses of public lands in Colorado.

The more participants, the greater the demand for trails, and the more dispersed recreation, which is a good thing all around, right?

Not necessarily. Trails can cause “habitat fragmentation” and “edge effects.”

To see how fragmentation works, assume an area 50 by 120 yards — 54,000 square feet, the size of a football field. Run a 5-foot-wide trail down the middle, and it doesn’t take that much land — 1,800 square feet out of 54,000 square feet.

So the theoretical area remains pretty much the same, but suppose the critters are afraid to cross that open trail because they fear predators. They can thus range only across 26,000 square feet, as opposed to 54,000 before.

Biologists have discovered that the effect extends farther into the woods — the constant passing of disturbances makes animals nest and forage away from the trail, further reducing habitat. Some have estimated that this “avoidance zone” can be 600 feet wide, which means no critters even near that football-field-sized chunk of habitat.

That’s a start on the “edge effect.” It also includes the introduction of new species, especially plants, which thrive in these disturbed areas. Seeds can arrive on hiking boots, pets, or tires, and they can push out native plants that the native wildlife relied on.

So should trails be outlawed? No. McClellan points out that they should be routed along existing corridors, and should avoid riparian areas along stream banks.

More study is needed, and the project is looking for volunteers to help with research — call 3034479409 for particulars.