The effects of global warming can be seen in the growing splotches of brown trees scattered throughout the otherwise green sheen of the Black Hills National Forest.

At least, that's the opinion of Matt McGovern, who leads the South Dakota campaign for energy-policy legislation in Congress. But it's an opinion that wasn't universally shared by those who heard McGovern speak last week during an energy conference at Mount Rushmore National Memorial.

"We've had the pine beetle outbreaks before," long-time Rapid City resident Jim Bell said. "I remember a real bad one, must have been 40 years or so, about."

McGovern contends, however, that the plague of mountain pine beetle infestations in forests across the American West is happening on a scale that is symptomatic of a world-wide climate-change problem. The beetles thrive in a warmer climate, which doesn't provide the degree of temperature lows needed to kill the bugs, he said.

"You're seeing more pine beetles throughout the region," McGovern said, adding that warming conditions and drought created a perfect environment for pine beetles.

An overwhelming majority of scientists agree that those environmental conditions are tied to a warming in the earth's atmosphere caused by increased carbon-dioxide emissions from a variety of man-made sources, including coal-fired electrical plants, McGovern said. The reform package pushed by President Obama, congressional Democratic leaders and the RePower American campaign would penalize carbon-producers such as coal plants and promote cleaner energy production such as wind and solar.

"This is really old technology we're dealing with," McGovern, director of Repower South Dakota, said of the coal industry.

Bell and other citizen skeptics at the conference, however, questioned whether the cause-and-effect chain in the environment is as clear-cut as McGovern contends. There's no dispute that pine beetle populations have exploded in the Black Hills and other national forests in recent years. And it is considered likely that multiple years of drought and warmer conditions were part of the cause.

But does that mean global warming caused today's pine-beetle outbreaks? Dave Thom, a natural resources specialist with the Black Hills National Forest, said the link between climate change and bark-beetle infestations isn't as clear as McGovern and others might suggest.

"It's more complicated than that," he said.

The complications include an increasingly dense forest with overgrowth of pine trees during the past 30 or 40 years, Thom said. Add that to the recent multi-year drought, and the forest is less able to defend itself against natural attacks, he said.

"As the trees get more dense, they are less able to resist bark-beetle infestations," Thom said. "When you take increasingly dense trees and add the drought, the intersection causes weakened trees that are more susceptible to beetle attack. That phenomenon can happen regardless of a few degrees of change in climate, measured on a global scale."

The drought has broken in most of western South Dakota. And cooler conditions came with moisture this year. That helped create a "way-below-normal occurrence of wildfires" in the Black Hills, Thom said.

It did not, however, reduce the need for the U.S. Forest Service to continue thinning the overly dense forest in the Black Hills, he said. Federal foresters normally award contracts for 20,000 acres of commercial tree thinning by private loggers each year in the Black Hills National Forest. Those acres hold commercially valuable trees for the timber industry.

But the BHNF officials also oversee about 10,000 acres of thinning through non-commercial contracts, taking out smaller trees that typically don't end up at sawmills.

That management work has a much clearer impact on the forest than the less-definable effects of climate change, Thom said.

"What we do on the national forest year to year has a greater effect than climate changes that occur over decades," he said.

Contact Kevin Woster at 394-8413 or kevin.woster@rapidcityjournal.com