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.





   

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