Since the turn of the 21st century, whitebark pine of the Greater Yellowstone Ecosystem have been under assault. Due to a warmer climate, mountain pine beetles, which more habitually infest lower elevation lodgepole pine forests, have flourished at higher elevations. Whitebarks are apparently to their liking; in mixed stands of lodgepole and whitebark, beetles more often infest whitebarks, and grow bigger in the phloem of whitebarks than in lodgepoles. Weakened by years of drought, whitebarks succumb easily to the pests, which overwhelm the trees en masse.
In the summer, beetles fly through the forest searching for living whitebark pines. Finding one, they chew their way through the bark and lay new eggs in their tunnels, the eggs remaining under the bark all winter. During the spring, the larvae feed on the inner tree bark, or phloem, and grow into adult pine beetles. These new beetles leave the tree and the cycle continues. You can tell a whitebark that’s been recently attacked by mountain pine beetles by the pitch tubes dotting the bark — small, red mounds of sap and sawdust ringing the beetles’ bore holes.
In their jaws, beetles carry a fungus whose strangling fibers kill the trees’ cells that carry food and water. Also damaging to the tree are the hundreds of tunnels the beetles leave beneath the bark, called galleries, where they lay their eggs. Once beetles attack a whitebark pine, it dies quickly. A tree that has survived centuries on a frigid, blustery ridgeline can perish in a single summer. Over the next few years, its needles fade from green to yellow then red. When the red needles drop to the ground, the resultant gray, lifeless trees comprise “ghost forests.”
Also threatening the whitebarks of the GYE, and throughout the west, is blister rust. Accidentally brought to Vancouver, British Columbia in 1910, with a shipment of white pine seedlings from France, blister rust has gradually spread across the West, infecting a variety of pine species.
Blister rust takes the form of pouches, filled with orange spores, cracking and inflaming the bark of the whitebark pines. The spores infect the trees’ circulatory system, spreading from the needles to branches to the trunk. Young whitebarks, with narrow branches and trunks, are particularly susceptible.
There are 2.5 million acres of whitebark pine forests in the Greater Yellowstone Ecosystem. Some forests, in the Teton Wilderness and Gros Ventre Wilderness, have been utterly decimated. (Take a drive to Union Pass from Dubois, Wyo. to get a glimpse of such forests). Other ranges in the ecosystem, such as the Madison and Gravelly Ranges in Montana and Idaho, show up to 70 percent whitebark mortality.
Not surprisingly, stands of whitebark inhabiting the coldest, highest parts of the ecosystem, such as in the central highlands of Wyoming’s Wind River Range and on Montana’s Beartooth Plateau, seem the least susceptible to the beetle infestations.
By David Gonzales and Nancy Bockino, Grand Teton National Park ecologist.