SAN LUIS VALLEY—The infestation of spruce bark and mountain pine beetles in Colorado’s forests continues to grow, in what forestry experts are calling an epidemic.

 In the Rio Grande National Forest alone, at least 144,000 forested acres have been infested by the spruce bark beetle since 1996, according to Public Information Officer Mike Blakeman.

A forest health survey released on Friday and taken from an aerial survey indicated 36,000 acres of new infestation in the Rio Grande National Forest last year. Blakeman said that, because the results of beetle kill are not visible in the forests for at least a year, the 36,000-acre figure is probably low.

In the past, the epidemic has struck primarily larger older spruce trees but as the beetles continue to propagate and search for new areas of food, smaller trees are also under attack, Blakeman explained.

“We are seeing them investing down to 5 inches in diameter,” he said. In the past, the beetles targeted trees 14 inches in diameter or larger.

Much of the beetle kill in this part of the state in the past has occurred in the Weminuche Wilderness Area and south of the Rio Grande above Creede, but Blakeman said the beetle infestation has now spread onto the other side of the river, north of the Rio Grande.

“We are seeing it continue to move, continue to spread.”

Blakeman said that, while some preventive measures can be completed in areas not yet infected by the beetles, not much can be done to treat the already-affected areas.

“This is a landscape level epidemic,” he said. “Because of the size of this, there’s really not anything we can do to stop this kind of thing.”

According to Blakeman, the forest generally cycles through a dramatic change or “disturbance” such as this every 300 years, but it appears the bug infestations occur as frequently as every 200 years. The natural disturbance must run its course before the forest can begin to rebuild, he explained.

“We have a lot of old forests and these are natural events,” he said. “We just happen to be around to watch this disturbance occur.”

In the case of the beetle epidemic all of the conditions in the forest came together for the “perfect storm,” Blakeman explained. The drought of 2001-2002 stressed the trees so they were not able to produce as much sap to defend themselves against the beetles, and the winters have not been cold enough to kill the beetles out.

Blakeman said the spruce beetles are native to this forest and are always around, but do not generally take over as much as they have in recent years.

He said the spruce beetle will often attack a forest in an area where trees have blown down. One prevention method is to clear out those trees. That is the tactic the National Forest will take with a blow-down area on Del Norte Peak where logging is expected this summer to clear the trees. The spruce beetles have not infected that area much, Blakeman said, and foresters hope to keep it that way.

In addition to the spruce bark beetle, the forests are now under attack from the spruce budworm, moth larvae that feed on new needles and buds of trees. Not appropriately named, spruce budworms actually prefer true firs and Douglas firs but they will also eat spruce trees, Blakeman explained.

These bugs do not kill the trees outright but defoliate them, Blakeman said. Generally the spruce budworms stick around for a couple of years before they experience a population crash.

If the bugs stay longer, the trees die.

“We have seen that,” Blakeman said.

The available data shows 37,000 acres infected by the spruce budworms in 2008 and 78,000 acres in 2009, a more than double growth.

One of the most obvious infested areas is visible from Highway 160 before the tunnel on Wolf Creek Pass.

A press conference on Friday to announce the results of the 2009 forest health aerial survey primarily focused on areas in the northern part of the state and southern Wyoming infested by mountain pine beetles.

Greater resources are being directed to that area because of the threat to watersheds, recreation, infrastructure and public safety.

The San Luis Valley and surrounding mountainous areas have not seen the infestations by the mountain pine beetles as the northern part of the state because this part of the state does not provide much of the mountain pine beetles’ preferred food source, lodge pole pines.

Blakeman said most of the mountain pine beetles in this area have been found in ponderosa pine stands in the Saguache area, although some infestation has occurred in stands of lodge pole pines in the area near Cochetopa Pass. Blakeman said this region has not experienced growth from year to year with the mountain pine beetle population, with a total of about 35,000 acres affected.

 The threats of falling trees are more prevalent up north where there are more lodge pole pines, Blakeman explained, because lodge pole pines tend to have shallower root systems and are more likely to fall over while the beetle-infested trees in this region die but are not as likely to topple.

Fires among the dead trees are also threats, but again those are not as likely in this region as up north, Blakeman explained. Although this region can experience a big fire, as evidenced by the Million Fire several years ago, people should not be fearful that, just because there are dead trees, the forests will be raging with fires.

U.S. Forest Service Regional Forester Rick Cables, one of the spokesmen during the Friday press conference, said the beetle infestation in the Rio Grande National Forest is a concern because of the potential damage to the Rio Grande headwaters. He said the biggest threat to water is often the fire that can occur as a result of beetle kill.

One mitigation method to prevent devastating fires, he said, is to conduct prescribed burns to remove fuels.

“That’s what we will be looking for significantly in that part of the world as well as northern Colorado,” Cables said.

He and other spokesmen said the southern and western parts of the state might receive a portion of $40 million allocated by the secretary of agriculture to combat the beetle epidemic and promote forest health but the largest percentage of that funding would go to the hardest hit mountain pine beetle area in northern Colorado where populations are denser and threats greater.

The money will also assist efforts in nearby states. Spokesmen said this is not a regional problem but a national one that continues to spread each year.

They added that an elite national incident management team authorized in December to mitigate the cause in the next two years would not be managing beetle kill in the southern or western parts of the Colorado because the team is designed for short duration high intensity operations and could not address all of the affected areas, which would be like trying to stretch a quilt over too large of an area.