Western Forests Recovering from Mountain Pine Beetle Infestation

Published April 16, 2014

The mountain pine beetle infestation that has ravaged forests in the western United States and Canada in recent years appears to be losing its grip. Green saplings are rejuvenating previously declining stands of dying red and grey pines.

History of Epidemic
First observed in 1996, the mountain pine beetle epidemic spread rapidly, as the beetles swept through entire mountain ranges. The insects burrowed into large trees, depositing larvae and spreading a deadly fungus. More than 4 million acres of forest lands were affected in Colorado, Wyoming, and South Dakota alone. The fungus killed millions of trees from New Mexico to the Yukon Territory.

In a 2011 report, “Mountain Pine Beetle Epidemic,” the U.S. Forest Service (USFS) warned, “The imminent danger of falling trees pose[s] significant health and safety threats. Dead trees are falling at an ever-increasing rate; stands are beginning to fail; winds and soil moisture are influencing tree stability.”

“Fire hazard is high one to two years after trees are attacked, while red needles are still on the trees,” USFS observed.

Forests Emerge More Resilient
As severe as the infestation was, the direst predictions of ecological degradation, including soil nutrient degradation and rising streams, did not come true.

Brent Ewers, a botanist at the University of Wyoming, teamed up with Paul Brooks, a hydrologist at the University of Arizona, to study the ecological effects of the infestation, focusing their research on the Medicine Bow and Roosevelt national forests. The pair presented their findings at a December 2013 meeting of the American Geophysical Union in San Francisco. Their work centered on whether the abundance of dead trees would allow too much melted snow to flow into streams, and whether carbon and nitrogen released from dead trees would pollute streams and rivers.

When snow falls on healthy forests, it collects on needles, where some of it evaporates while the rest falls to the ground. The trees use some of the snow that reaches the ground, and the rest makes its way to groundwater, streams, rivers, lakes, and reservoirs. Some scientists feared the millions of dead trees, no longer absorbing water, would allow streams to rise to dangerous levels. The scientists also worried excess water would mix with carbon and nitrogen from dead trees, creating a polluting brew in streams that would be expensive to clean up.

The feared environmental harms never occurred. Snow fell in large open areas, evaporating and blowing away the same as if it had fallen on healthy pine needles. New trees and plants flourished without the large, older trees, taking in the excess water, Brooks explained. The remaining trees are absorbing the nitrogen, enabling the forest to grow faster than before, Ewers added.

The two researchers agree the long-term effects of the infestation require further study.

Other Examples of Infestation
The ferocious epidemic that struck Western pine forests is not unique. “Dutch elm disease—a fungus spread by insects—attacked American forests after World War II,” said William D. Balgord, Ph.D., president of Wisconsin-based Environmental & Research Technologies, Inc.

“Established plantings of gracefully arching elm trees shaded many small-town neighborhoods until the arrival of the pandemic that killed millions of elms,” Balgord explained. “Seventy years later, isolated American elms can be found in some rural settings. These resilient survivors have developed a resistance to the fungus.”

“A second invader, that’s now spread to more than a dozen states, attacks several species of ash,” Balgord added. “This exotic species, the emerald ash borer, is believed to have hitchhiked to North America in wood pallets aboard container ships arriving from Asia. In less than 10 years, the pest has spread from the port at Windsor, Ontario into Michigan, Illinois, Minnesota, Iowa, Wisconsin, Indiana, and Ohio.”

“As serious infestations of the beetle continue to affect forests in the Western States, global warming activists waste no time in blaming global warming as the culprits enabling the damage,” Balgord observed. “Entomologists and forest experts explain, to the contrary, that the beetle is fully capable of initiating attacks in either normal or abnormal weather conditions.”

Bonner R. Cohen, Ph. D., ([email protected]) is a senior fellow at the National Center for Public Policy Research.