Recreation and preservation of wildlife habitat aren't simply dual goals within the Pitkin County Open Space and Trails program. They may actually be conflicting goals.
Balancing human use and wildlife needs is, for example, at the heart of the winter closure of Sky Mountain Park, a conglomeration of open-space parcels near Snowmass Village, as well as the dog ban on much of the property. But locals who obey the regulations may not realize it's not just wintering elk they're protecting.
Nor do they likely realize the effect they have every time they walk on a trail.
Richard Knight, a conservation biologist at Colorado State University, has studied the impact of human presence on various species. He shared his findings with the county Open Space and Trails board of trustees Thursday during a board retreat at Avalanche Ranch, south of Carbondale.
"There is not an American who doesn't recreate on public lands, but all of us believe what we do on public lands is benign," Knight said.
Recreation, he said, affects biological diversity in ways the average hiker or mountain biker would not expect, and it's one of the main reasons that species wind up listed as threatened or endangered.
Knight, with the help of graduate students, has conducted various studies on how recreation affects wild animals. On open space in the city of Boulder and in Boulder County, his studies documented repressed numbers of certain songbirds near trails in both grasslands and in the forest. Nesting activities were also repressed near trails, compared to areas far from the paths.
The "edge effect," as Knight called it, extends beyond the trail itself, reaching 100 meters to either side.
"It's perfectly suitable habitat, but they won't use it. They can't use it," he said.
Knight estimated about one-third of the acreage on the open space lands he studied were rendered unsuitable for certain species by the extensive trail systems, compounded by the edge effect.
That sort of information could be an effective tool locally to help the public understand the need for trail restrictions and limitations on access, said Dale Will, county open space and trails director.
One of the bird species Knight studied was the Brewer's sparrow, a "sensitive species" that is present at Sky Mountain Park. The dog ban, along with limiting trails within the sparrow's habitat and restoration of sagebrush areas, are all measures that may protect and enhance the bird's habitat in the open space, said Gary Tennenbaum, land steward for the local open space program.
"The impact to the breeding population is much less when you have no dogs up there," he said.
The general perception among the public, Knight said, is that animals that are bothered by human presence will go elsewhere. It's not quite that simple.
"Suitable habitat is always already occupied," he said.
Knight has also delved into the impact of human presence on mule deer populations, documenting the increasing impact when someone leaves a trail, stays on the trail but has a dog on a leash, and leaves the trail with a dog on a leash.
A lone person walking on an open space trail had no impact on deer, according to the results of a study he conducted for the city of Boulder. But a dog, even on a leash, triggered a fear response in deer, according to Knight. The house pet is a potential predator in the deer's eyes, he said.
"They can't tell the difference between a coyote and a German shepherd," he explained.
Knight said his studies also show small mammals are as likely to be next to a trail as they are deep in the forest - if no dogs are allowed.
Future plans for Sky Mountain Park include the introduction of additional trails, but they will be routed to avoid large, unbroken areas of habitat, Will noted.
"There is a tradeoff every time you create a new edge," he conceded.
The need for closures and other trail regulations on open space is something the county's open space program could do a better job of explaining to the public, open space board members concluded Thursday.
"There's a cost to turning recreationists loose out there," said board member Hawk Greenway. "We've known this and we've tried to manage it."