Lake County sees incremental growth in its mountain pine beetle population, but scientists say more are coming
Aspen, CO Colorado
LEADVILLE, CO ” Scientists and foresters at a pine beetle informational meeting for local residents last month warned that Lake County has a forest ripe for a mountain pine beetle outbreak.
“They’ve eaten themselves out of house and home in Grand County and they’ve worked their way out of Summit, and unfortunately, we think they’re coming here,” said Leadville District Ranger Jon Morrissey.
“The conditions are here, at least host-wise,” agreed Colorado State Forest Service (CSFS) entomologist Dr. Ingrid Aguayo.
According to CSFS district forester Damon Lange, the mountain pine beetle epidemic continues to increase incrementally in Lake County, with the greatest population in the forest from Box Creek to Twin Lakes.
In northern Lake County, the greatest population is northwest of Turquoise Lake.
Morrissey noted, however, that the beetle appears to be moving across the lake, from west to east, and that there are substantial populations on the east side, particularly in and near the campgrounds.
As for new outbreaks, a recent aerial survey indicated that they are occurring in and around Tennessee Park, along Hwy 91 and on the west side of Leadville.
In other areas that have seen incremental growth, the population has suddenly exploded, usually with an environmental trigger that stresses the tress, such as drought or development.
Aguayo led the meeting off with an animated presentation about the year-long life cycle of the mountain pine beetle; the explanation shed some light on how and why the pine beetle has been so successful in Colorado.
The beetles move to new trees in the late summer, she explained: in mid-July the new beetles are ready to leave the trees that have fostered them. In mountain pine beetle culture, the females apparently make the decisions: they choose the trees, looking for those that are relatively healthy and large in diameter.
Boring in to start their home, the females encounter the trees’ main defense: pine pitch. If the tree has enough pitch, it can drown the beetles or kill them with the toxic chemicals in the pitch. However, a tree stressed by drought or other environmental impacts–or just overwhelmed by the number of beetles–may not be able to “pitch” the beetles.
The females releases pheromones to attract both males and other females of the same species, said Aguayo. Like a hotel, the tree will fill up with beetles attracted by the pheromone until the beetles living there decide it is full: at that point, they will begin releasing an anti-attractant.
The beetles mate and lay eggs in the cadmium layer of the tree, just below the bark. Larvae that are born from these eggs have an antifreeze that allows them to withstand Colorado’s freezing winters.
As for the mystery of why trees killed by the mountain pine beetle has a blue stain, Aguayo explained that the beetle carries spores of a blue-stain fungus with it. While the beetle is colonizing the cadmium layer, the fungus colonizes the xylem layer, further stressing the tree.
Although the mountain pine beetle has been known to attack many pines, including ponderosa, lodgepole, Scotch and limber pine, Aguayo said that, for reasons unclear to scientists, once the beetle starts colonizing a certain kind of pine, it tends to stay with that species until the food source runs out.
According to Aguayo, Colorado’s forests have provided perfect conditions for the pine beetle epidemic. A recent drought stressed many of the trees, warm winters have helped keep the beetle populations alive even during winter, and thick forests filled with trees that are all about 80 years old make for prime mountain pine beetle territory. Such trees are already stressed by competition for water and sunlight and may be unlikely to successfully pitch the beetles. Moreover, since beetles prefer old, thick trees, a forest full of mature trees is akin to a grocery store full of their favorite food.
Showing Grand County slides of whole valleys of brown trees with a few pockets of green, Aguayo explained that the green pockets were areas of forest that had been clear-cut and thus had younger trees. The beetles had left those younger, less attractive trees alone.
Aguayo cautioned people not to underestimate Mother Nature, which has her own defenses. In addition to the trees’ ability to pitch out the insects, woodpeckers–who love the mountain pine beetle larvae–provide some natural predation. Several other insect predators exist, said Aguayo, and their populations tend to increase as mountain pine beetle populations increase, with a slight lag between the two.
Although she pointed out that spraying the trees with a chemical repellant is an option, she cautioned that the insecticides are broad-spectrum and will kill both the beetles and their natural predators. She also noted that spraying is expensive–and she recommended that landowners use the technique only for the trees they really want to save. Spraying should be done before the beetles fly, or June at the latest, said Aguayo.
Bark peeling is another option, said Aguayo. Once exposed to the elements, the larvae will likely either dehydrate or run out of food.
There is also a synthetic version of the beetle’s anti-attractant that is available commercially. However, Aguayo cautioned that it doesn’t work as well when there are high populations of beetles and so should be used in addition to other strategies.
Several of the representatives cautioned people not to move cut beetle-kill wood into untouched areas, as doing so can lead to an infestation of the healthy trees.
Morrissey noted that the Leadville Ranger Office is spraying about 1,000 trees a year at Twin Lakes and Turquoise. They’re also trying to cut the dead trees in those areas, and remove them, as fast as they can. Proactively, they’re trying to thin the forest before the beetles come: a chainsaw crew will begin cutting this summer, as soon as the snow is gone, said Morrissey.
However, State and National Forest Service representatives also emphasized that the pine beetle epidemic is part of the natural process of forest renewal. If managed correctly, they argued, the epidemic could result in a healthier forest.
The experts present Thursday night suggested that, in essence, the mountain pine beetle’s success is the result of poor forest management. For 75 years, said Morrissey, the USFS put out every fire it could get its hands on–resulting in a forest of over-mature and over-thick trees. Fires, landslides, beetles or avalanches are the four ways that Colorado forests renew themselves, said Aguayo–and eventually one of them will be successful.
“We cannot stop the beetle–it’s a natural part of our ecosystem,” she said.
If the beetles do take many of the trees in Lake County, said Morrissey, the forest could look dramatically different in twenty years.
For one thing, the natural event is allowing new species to come in–sometimes aided by the forest service. For example, as forest rangers have cut and removed dead lodgepole pines at Twin Lakes and Turquoise, said Morrissey, they’ve noticed aspens moving in. In other places, forest service employees are planting Ponderosa pine or Douglas firs. They’re not planting lodgepole on the assumption that those pines will come back on their own, said Morrissey.
Lange used Grand County, which is on the downside of its epidemic, as an example of the positive aftermath of a pine beetle epidemic: “Every time we go to Grand County, it’s amazing to see a carpet of pine from the trees that were first killed.”
– Popcorn-shaped masses of resin on the trunk where the tree is trying to “pitch” the beetle out.
– Boring dust in bark crevices and on the ground immediately adjacent to the tree base
– Evidence–such as removed bark–of woodpeckers feeding on the trees.
– Foliage turning yellowish to reddish throughout the entire crown. Brown needles usually appear eight to ten months after a successful pine beetle attack.
– Presence of live mountain pine beetle and/or their galleries. Galleries are the living space that beetles create by chewing in characteristic patterns under the tree bark. Use a hatchet to remove the bark and check the trees.
– Bluestained sapwood.
Source: Colorado State University “Trees and Shrubs” pamphlet, created in cooperation with the Colorado State Forest Service. For more information, visit http://csfs.colostate.edu or call the Colorado State Forest Service at 719-539-2579. For a $30 charge, state foresters will come to your property for an individual consultation.
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