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A Talk on the Wild Side.

Wyoming: ‘Perfect Storm’ Fuels Mountain Pine Beetle Epidemic

An extreme closeup of a mountain pine beetle
Triggered by a “perfect storm” of extended droughts, warm winters, and old, dense forests, mountain pine beetle populations have exploded across a landscape of lodgepole pine trees throughout Colorado and southeastern Wyoming. Photo: USDA Forest Service. Download.

Lodgepole pine forests in parts of Wyoming and other areas of the Intermountain West are being infested by the native mountain pine beetle – a voracious bug smaller than your little fingernail that is thriving in a warming climate.

Triggered by a “perfect storm” of extended droughts, warm winters, and old, dense forests, mountain pine beetle populations have exploded across a landscape of lodgepole pine trees throughout Colorado and southeastern Wyoming.

The mountain pine beetle is a true predator on many western pine trees because to successfully reproduce, the beetles must kill host trees. They typically kill trees already weakened by disease or old age, but even a healthy tree’s defensive mechanisms can be exhausted when beetle numbers are at epidemic levels. The beetle attacks pines in late summer, dispersing a chemical signal that attracts other beetles to mass-attack the tree. When the beetles bore through the bark of the tree, they introduce blue-stain fungus, which can work quickly to kill the tree. Trees stressed by drought and old-age are unable to produce sufficient defenses to fend off beetle attacks. The beetles form tunnels and lay eggs underneath the bark, which hatch into larvae. The larvae spend the winter underneath the bark and emerge as adults in the summer, beginning the cycle again.

A mountain against the sky plagued by patches of grey, dead trees
Attacked lodgepole pine trees cut a gray and brown swath through the Medicine Bow National Forest in southeastern Wyoming. Photo: National Agriculture Imagery Program. Download.

The U.S. Forest Service estimates that by 2012, the majority of lodgepole pines in northern Colorado and southern Wyoming will be killed by the beetle. Currently, there are four million acres of lodgepole pine trees on Forest Service land affected by mountain pine beetle infestation. Extensive beetle kill has resulted in ecosystem-wide impacts such as increased potential for wildfires and some loss of other tree species such as Douglas fir.

A woodpecker clinging to the side of a tree
Coniferous wildlife species, such as the three-toed woodpecker, breed and forage in lodgepole pine forests. Ongoing studies seek to understand what type of habitat coniferous wildlife species will select as mature lodgepole pine forests decline due to mountain pine beetle infestation. Photo: ressaure.

Lodgepole pine forests dominate the forested ecosystems of western North America and can provide breeding and foraging habitat for many coniferous wildlife species, including song birds, woodpeckers and red squirrels. To learn more about wildlife response to the mountain pine beetle epidemic in southeastern Wyoming, the Wyoming Cooperative Fish & Wildlife Research Unit at the University of Wyoming, in collaboration with the U.S. Fish and Wildlife Service and Wyoming Game and Fish Department, is currently conducting research on beetle impacts in the Medicine Bow National Forest.

The research team of students and staff is led by Anna D. Chalfoun, Ph.D., with the Cooperative Unit. Chalfoun said the research aims to determine which alternative stand types (for example, young previously harvested lodgepole and/or spruce-fir) may best support wildlife species until lodgepole stands can regenerate after the ongoing infestation.    

The lodgepole pines are not the only trees favored by the mountain pine beetle. The Fish and Wildlife Service is currently working on a listing determination for the entire range of whitebark pine, another western pine tree species heavily impacted by the insects.

“Because of warming temperatures, scientists are now seeing significant beetle impacts even in the high elevation sites occupied by whitebark pine,” said Amy Nicholas, a Service biologist in Rock Springs, Wyo.  “These sites are usually quite cold and unfavorable for epidemic levels of mountain pine beetle. That no longer seems to be the case.” 

The Service anticipates completing its review, which will determine whether the whitebark pine will become a candidate for ESA listing, in mid-July, Nicholas said.

 

Climate Change Focus: Adaptation, Engagement

Author: Anna D. Chalfoun, Ph.D., Wyoming Cooperative Fish & Wildlife Research Unit, University of Wyoming

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