Pine beetle outbreak buffers watersheds from nitrate pollution

University of Colorado-Boulder News: A research team involving several scientists from the University of Colorado Boulder has found an unexpected silver lining in the devastating pine beetle outbreaks ravaging the West: Such events do not harm water quality in adjacent streams as scientists had previously believed.

According to CU-Boulder team member Professor William Lewis, the new study shows that smaller trees and other vegetation that survive pine beetle invasions along waterways increase their uptake of nitrate, a common disturbance-related pollutant. While logging or damaging storms can drive stream nitrate concentrations up by 400 percent for multiple years, the team found no significant increase in the nitrate concentrations following extensive pine beetle tree mortality in a number of Colorado study areas.

“We found that the beetles do not disturb watersheds in the same way as logging and severe storms,” said Lewis, interim director of CU’s Cooperative Institute for Research in Environmental Sciences. “They leave behind smaller trees and other understory vegetation, which compensate for the loss of larger pine trees by taking up additional nitrate from the system. Beetle-kill conditions are a good benchmark for the protection of sub-canopy vegetation to preserve water quality during forest management activities.”

....“The U.S. Forest Service and other agencies have established harvesting practices that greatly mitigate damage to forests caused by logging, and they deserve credit for that,” said Lewis. “But this study shows just how important the survival of smaller trees and understory vegetation can be to stream water quality.”

In waterways adjacent to healthy pine forests, concentrations of nitrate is generally far lower than in rivers on the plains in the West like the South Platte, said Lewis. Nitrate pollution is caused by agricultural runoff from populated areas and by permitted discharges of treated effluent from water treatment facilities....

Fog at the treeline in Rocky Mountain State Park, shot by Michael Gäbler, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license

As climate warms, bark beetles march on high-elevation forests

Terry Devitt in the University of Wisconsin-Madison News: Trees and the insects that eat them wage constant war. Insects burrow and munch; trees deploy lethal and disruptive defenses in the form of chemicals. But in a warming world, where temperatures and seasonal change are in flux, the tide of battle may be shifting in some insects’ favor, according to a new study.

In a report published today (Dec. 31, 2012) in the Proceedings of the National Academy of Sciences, a team of scientists from the University of Wisconsin-Madison reports a rising threat to the whitebark pine forests of the northern Rocky Mountains as native mountain pine beetles climb ever higher, attacking trees that have not evolved strong defenses to stop them.

The whitebark pine forests of the western United States and Canada are the forest ecosystems that occur at the highest elevation that sustains trees. It is critical habitat for iconic species such as the grizzly bear and plays an important role in governing the hydrology of the mountain west by shading snow and regulating the flow of meltwater.

“Warming temperatures have allowed tree-killing beetles to thrive in areas that were historically too cold for them most years,” explains Ken Raffa, a UW-Madison professor of entomology and a senior author of the new report. “The tree species at these high elevations never evolved strong defenses.”

A warming world has not only made it easier for the mountain pine beetle to invade new and defenseless ecosystems, but also to better withstand winter weather that is milder and erupt in large outbreaks capable of killing entire stands of trees, no matter their composition....

A stand of aspens, with pines in the background, in the Rio Grande National Forest in southern Colorado, U.S. Department of Agriculture