Are pine beetles slowing down in Colorado high country?
Summit County correspondent
Aspen, CO Colorado
LAKEWOOD, Colo. ” A return to cooler winter temperatures the past few years may slow the spread of pine beetles in some parts of the Colorado high country, according to a veteran Forest Service researcher.
A spell of extraordinarily warm and dry weather from about 1997 through 2002 promoted the explosive spread of the bugs in the Colorado mountains by weakening trees that were already susceptible to attack and speeding the beetles’ life cycle, said entomologist Jeff Witcosky, who works at the agency’s regional office in Lakewood.
Climate researcher Klaus Wolter confirmed that winter temperatures in the northern Colorado mountains have dipped back toward historic averages during recent years, though he said summer temperatures have remained above average.
Past pine-beetle outbreaks were squelched by intense cold snaps, when the bugs froze to death.
The life cycle of the insects is key. At higher elevations and in cooler weather, it takes two years for the pine beetles to hatch, develop through the larval stage and spread to new host trees.
In warmer conditions, the cycle takes just one year, a huge factor in the exponential spread of the current epidemic.
Some recent anecdotal observations around Summit County ” an area hard hit by the beetles ” suggest that the insects haven’t spread as fast as they move into the higher elevations of the Upper Blue valley.
The bugs probably will still march through the area and kill large numbers of trees.
But at higher elevations and where lodgepole forests mingle with other trees, some of the pines may survive ” but how many?
“Summit County has been hammered. For the most part, we’ve been had. But there may be room for some successes on the margin,” said Jan Burke, lead forest scientist for the White River National Forest. The 2.3-million acre forest surrounds Aspen and Snowmass and the Roaring Fork Valley, and covers much of Summit County, as well as the Vail area.
Burke said even with colder winters, she fully expects that the beetles have already spread to most areas of susceptible, even-aged lodgepole stands in the county and have started to work their way farther south and west, toward Aspen.
She said some pockets may survive, based on specific geographic conditions, for example where trees sit in a small, cold pocket.
Witcosky said it’s too early to know for certain whether a return to cooler weather will have a significant effect on the beetles’ spread.
But a drop of just a few degrees could give land managers and property owners more time to protect some highly valued trees, for example around campgrounds and along ski area trails, with a combination of thinning and preventive treatments.
A new method of applying a well-known chemical shows some promise. California-based Forest Service researcher Nancy Gillette said spreading a common pheromone (a natural chemical attractant for pine beetles) with helicopters could be a cost-effective way to treat larger areas.
Combined with targeted removal of infested trees, the application could be used to protect limited areas.
During tests in the northern Rockies, this verbenone was used successfully to protect tree strips along ski area trails, Gillette said.
Burke said the White River has used verbenone in some very targeted applications at campgrounds, by hanging packets of the substance on individual trees. But aerial application on a larger scale hasn’t been tried in this area yet.
“We need to stay realistic and also stay open-minded. We’ve got nothing to lose,” Burke said. “I wouldn’t discourage it. It’s kind of like CPR. If someone has a stroke, you don’t just want to stand there with your hands in your pocket.”
Burke acknowledged that using verbenone is one of 15 to 20 options on the table as ski areas like Keystone develop long-term vegetation-management plans that will shape resort landscapes after the beetle invasion.
Based on the results of the Forest Service tests, it’s possible that an immediate and extensive application of verbenone might help save some trees in critical areas. But Burke said the real focus is on reforestation and encouraging species and age diversity in the “future forest.”
“We have to be pro-active and not just chasing beetles,” she said. “There’s a lot we can do, and it may not be hanging on to mature lodgepole pines. The best thing may be to cut out the dead and replant.”
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