EDMONTON, Alberta, Aug. 14 (UPI) -- Expanding forests in the Canadian Rocky Mountains are slowly isolating groups of alpine butterflies from each other, which may lead to their extinction.

Jens Roland, a University of Alberta biologist, said the mountain's rising tree line is due to global warming, as well as a policy that avoids "prescribed burns" -- intentionally started, controlled fires -- to manage forest growth.

The result has created a tenuous situation for alpine Apollo butterflies (Parnassius) that inhabit open meadows because they need sunlight to generate enough body heat to fly. Forests are generally too shady for them and inhibit their ability to move.

"The risk of local extinction and inbreeding depression will increase as meadows shrink, the population sizes decrease and the populations become more isolated," Roland said. "The gene pool of this species is getting more and more fragmented, and gene flow is reduced, which means these populations are more vulnerable."

Roland is the lead author of a paper concerning the butterfly that appears in the current issue of the Proceedings of the National Academy of Sciences.