Green, Brown and Gray: Climate change and bark beetle infestations in Colorado forests

Hayman, Waldo Canyon, Black Forest, Spring Creek and Cameron Peak—sound familiar? They were all infamous Colorado wildfires that consumed thousands of acres of forests. Every year, mountain communities are on edge when snowpack numbers are low and spring rains are sparse. Once beautiful green forests show ugly swaths of gray and brown, as heavy machinery and slash piles are evidence of the carnage wrought by bark beetles, no bigger than your fingernail. As average daily temperatures have increased in Colorado, due to climate change, there have been epidemic levels of bark beetle infestations, with the loss of hundreds of millions of trees.

What are these pests, and why have the combined forces of science and industry been unable to control them? Dr. Barbara Bentz, Research Entomologist with the US Forest Service’s Rocky Mountain Research Station, has a unique perspective on these issues, as well as thoughts for the future: “Bark beetles in the genera Dendroctonus and Ips that are causing tree mortality in Colorado are native to, and have evolved with, Colorado forests for eons. These disturbance agents, like fire disturbance, are important to ecosystem function. Recent climatic changes, including hot droughts, have altered their behavior”. Dr Bentz’s research is primarily aimed at understanding climatic changes that are influencing population outbreaks.

There are several species of bark beetles in Colorado which kill evergreen trees by burrowing under the bark, feeding on living tissues and “girdling” the tree, thereby interrupting the flow of vital nutrients. Trees affected include lodgepole, ponderosa, limber and piñon pines, as well as spruce and fir trees. Not even the venerable bristlecone pine is immune. Dr. Bentz and her fellow researchers found that tree size, forest density, drought and weather conditions all play a factor in how bark beetle infestations occur.

Dead trees are extremely dry, and once ignited, they are rapidly consumed by wildfire. What will kill these pests? Prolonged subzero temperatures may keep them in check, but with warmer winters, this effect has been blunted. There are pesticides and other chemical agents, including promising semiochemicals, that help trees resist beetle infestation, but they are most suitable for high value trees near campgrounds and other populated areas.

As average daily temperatures trend upward, it is critical that changes be made to try to reverse this. A reduced carbon footprint, and the increased use of green energy; such as solar, wind, and nuclear power may give some hope. In the meantime, remediation strategies, such as Firewise, can be helpful. As Dr. Bentz relates: “Increased awareness of spot initiations of bark beetle-killed trees by private landowners could help reduce surrounding tree mortality by removing or destroying the infested trees before adult beetles emerge.”