BILLINGS, Mont. (AP) — The U.S. Forest Service is attempting to grow whitebark pine that are resistant to blister rust as part of an effort to prevent the high-elevation tree from dying out in Montana, Idaho and Wyoming.

Workers have created a 15-acre nursery in the mountains south of Bozeman where seedlings resistant to blister rust are being grown.

Officials tell the Billings Gazette that limbs from older trees will be grafted onto the young trees to speed up seed production.

Jay Frederick of the Beaverhead-Deerlodge National Forest says the goal is to have the trees producing cones in four years.

Grizzly bears depend on whitebark pine that produce high-protein nuts in the fall and allow the bears to fatten up for hibernation.