A new study finds that all-terrain vehicles buzzing through the forest in Alaska cut a swath much larger than their tracks when it comes to how much habitat is available to moose.
The findings, which quantify exactly how much moose habitat the roads effectively eliminate, support what others have found for animals like elk, caribou and grizzly bears in other parts of the country and could give managers a tool to regulate the use of such vehicles.
Colin Shanley, who completed the work with Sanjay Pyare while at the University of Alaska, Fairbanks, worked in the community of Yakutat along Alaska's southeast coast. Many locals there rely on subsistence hunting for meat. Hunters have increasingly turned to ATVs to make their work easier.
"As more and more people started driving these, it became clear that there were all these ATV tracks all over the forest," Shanley said. "The people managing the forests started to have concern that it might be having an impact on the wildlife."
Shanley and Pyare used the wanderings of a group of GPS-collared moose combined with aerial views of ATV tracks through the forest and interviews with local hunters to gather information about trail use. This information allowed the pair to figure out how moose moved in response to ATV traffic, and how far-reaching the vehicles' influence was.
"We took what we learned about how these animals were affected and actually mapped out which areas were affected. We were actually able to quantify how much habitat was lost," Shanley said.
Shanley found that males avoided areas up to a third of a mile (500 meters) from the ATV tracks, and females avoided double that distance from tracks.
"We hypothesize that that is likely to do with female moose being a lot more vigilant to protect their calves," Shanley said. He and Pyare reported their results in Ecosphere.
Keeping road traffic to below an average of one vehicle every four days for every kilometer of road through a given square kilometer of forest was a threshold that would minimize the likelihood of disturbing moose in the area, the pair calculated.
"We can map out this disturbance threshold," Shanley said. "How much habitat are we likely losing here associated with this road network? If we pulled this road out, how much would we gain? If we put this road in, how much would we lose?"
Areas where traffic is above this threshold are effectively no longer suitable habitat. The authors determined that in the summer, 13 percent of the study area was effectively lost as habitat and 23.5 percent was lost in the fall. If road activity were to double on the roads, 30 percent of the habitat would exceed the disturbance threshold in fall, they reported.
"We're hoping this illustrates that we can get a lot more specific about where and how we manage access," Shanley said.
The findings are similar to what a team at the U.S. Forest Service in La Grande, Ore., found while studying elk and mule deer, said Marty Vavra of the Forest. His team monitored the effects of several types of disturbances including ATVs, mountain biking and horseback riding on tagged deer and elk in northeast Oregon.
"The ATVs were way out in front in terms of disturbance," Vavra said. "I don't know if it's the noise or the speed. I think it may be the speed. Mountain biking was rather disruptive as well."
"I think the implication is that managers need to weigh the effects of habitat reduction with the benefits of the road in any given area," Vavra said.
"I think there's always going to be trade-offs," Shanley agreed. "But I think the community of Yakutat, they want moose to stay around and they are supportive of management that ensures that they are going to conserve the resource as best as possible."
Vavra predicts increased regulation of such vehicles, which have previously been managed regionally. "I think now there will be national policy because use has become so tremendous," he said. "It's amazing how many people own these machines and how many get out on the public lands with them."