Montrose - Daily Press

MONTROSE — Aspen stands afflicted by a progressive decline appear to continue spiraling down, even with an increase in moisture brought by spring.

This is one of several observations from ongoing studies of sudden aspen decline (SAD) in forests surrounding Montrose.

Canker fungi and wood boring beetles, some of the organisms implicated in SAD, have life cycles lasting several years, causing declines to persist even though there's more soil moisture, said entomologist Roy Mask, Forest Service Forest Health Management in Gunnison.

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"It's probably too early to tell (what the effect of moisture is). What we suspect is if indeed these stands are weakened by drought, then we would expect that if we returned to a more reasonable moisture regime that things would eventually improve," said Mask.

Impacted stands would not be able to heal right away just because they are taking on more moisture, he said. "The decline they're experiencing is already at play. What might play out is if we have several years of improved conditions then we might see it taper off. We might see those organisms complete their life cycles and we might see aspen return to a better condition."

Severe drought, especially what occurred in 2002, is suspected of triggering the sudden aspen decline, and creating stressful conditions which leave trees vulnerable to insects and diseases.

SAD has shown up in large areas in the San Juan, Grand Mesa, Uncompahgre and Gunnison National Forests (GMUG).

A fairly extensive outbreak is visible in the Terror Creek area near Paonia.

In 2007, substantial new areas of mortality were seen on the GMUG and the affected area statewide more than doubled, affecting about 13 percent of the aspen acreage.

Aerial surveys conducted in 2006 showed 138,000 acres of aspen forest were affected, the USDA Forest Service reported. In some stands, more than 60 percent of the mature trees died between 2003 and 2006.

The crew that's been deployed to survey the local forests saw a lot of trees that did not re-foliate or break bud this past spring, Mask said.

"They will often break bud but then the leaves don't ever develop," he said. "So, we're seeing a lot of trees that have certain energy reserve that basically died about the times the buds flushed. What we see with those trees is they're scattered among trees that are otherwise looking pretty good, breaking buds (and) growing leaves."

Researchers have found five organisms that consistently occurred in various combinations on these two sites: two bark beetles, two wood-boring beetles and a canker fungus. Mask said surveys continue to provide more evidence of the existence of these organisms, in various combinations, in SAD-afflicted aspen.

"They may not all be there but there's always some mix of those five. In many cases, there are all five present," he said. Healthier aspen stands continue to be seen at higher elevations, suggesting SAD ails stands in the lower, warmer elevations.

Researchers are continuing studies initiated in 2007. In that project, plots of healthy and SAD influenced stands are being paired in an effort to make comparisons to better understand why the decline affects some areas and not others, Mask said.

Crews survey forest areas about six to seven months out of the year, and cover hundreds of thousands of acres in a field season.

"We are working with a number of resource managers to address SAD on private property," Mask said. "There's an awful lot of people providing an awful lot of focus to this particular effort right now ... everyone's focus is to provide some more understanding of what's going on, how long it might last."

For the most part, aspen mortality happens when trees reach 80 to 100 years old. What concerns scientists and managers is the sudden and expansive nature of recent declines. A Forest Service report noted the current phenomenon has increased dramatically over a few years, as opposed to typical changes seen over decades.

Contact Lisa Huynh via email at lisah@montrosepress.com

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