As the number of people following the exhortation to "Go climb a rock" has skyrocketed over the last 2 decades, the effects of rock climbing on cliff ecosystems have gone largely unstudied. Now, the first comprehensive effort to measure the sport's impact on plant communities reveals that it dramatically alters cliff ecosystems.
Ecologists Michele McMillan and Douglas Larson of the University of Guelph in Ontario, Canada, examined the vegetation of the Niagara Escarpment in southern Ontario, a heavily used complex of limestone cliffs supporting the oldest forest east of the Rocky Mountains. The authors compared the types and numbers of plants growing on plateau, cliff face, and base sections of unclimbed cliffs and on areas where climbing routes were established. The contrasts were startling: Cliff faces used by climbers had 46% fewer vascular plants (trees and other flowering species) as did unclimbed faces, whereas the diversity of mosses and lichens in areas exposed to climbed was roughly 30% to 40% of that of unclimbed areas, the team reports in the April issue of Conservation Biology.
The most surprising finding, McMillan says, was that in climbed areas an average of 81% of the plants were alien--three times more than in unclimbed areas. Larson thinks the alien species are likely introduced by climbers, who inadvertently transport seeds and living plant fragments in their shoes and clothing. Once aliens gain footholds, they are nearly impossible to extricate, and the consequences for ecosystems can be devastating, Larson warns. The authors say that their findings should apply to other rock-climbing hot spots, because cliffs are biologically and physically similar worldwide. "Just as forest fires have similar effects regardless of location," Larson says, "feet, pitons, and ropes have comparable effects wherever climbers practice their sport."
"This work represents a real step forward" in evaluating how climbing disturbs cliff ecosystems, comments Gary Walker, an ecologist at Appalachian State University in Boone, North Carolina. The research, he argues, points to an "urgent need" for land managers to evaluate potential biological impact before opening new climbing routes.