Sudden aspen rebound
Regional aspen tree infestation starts to stabilize

A healthy stand of aspen trees awaits spring north of Durango. The spread of Sudden Aspen Decline, a mysterious infestation that hit many of Southwest Colorado’s lower elevations, appears to be have stopped. The area west of Durango was especially hard hit by SAD and will see increased logging as a result./Photo by Stephen Eginoire

by Will Sands

Southwest Colorado is finally getting some good news on the forest front. The spread of Sudden Aspen Decline, an epidemic that has afflicted many aspen stands in the region, appears to have stopped. Foresters are hoping that a combination of regeneration and harvest will restore health to groves of one of Southwest Colorado’s trademark trees.

Sudden Aspen Decline, or SAD, has struck and killed large stands of aspen trees all over Colorado and hit Southwest Colorado especially hard. SAD really came into its own late in 2008, when visitors to Colorado’s forests started noticing fewer yellow aspen displays. In their place, leaf lookers found more and more stands of dead and dying aspen.

Since its recent appearance, SAD has grown exponentially in size and severity, threatening current and future aspen forests as well as wildlife habitat and viewsheds. Sudden Aspen Decline was first noted by land managers on the San Juan National Forest in 2006. At that time, an aerial flyover found that nearly 17,000 acres had been afflicted by the phenomenon. In 2008 the Forest Service conducted a second flyover, discovering that the number of dead and dying stands had more than doubled to a total of nearly 40,000 affected acres. With only 300,000 total acres of aspen stands on the San Juan National Forest, local land managers were concerned.

SAD has shown up elsewhere in the state as well. The Grand Mesa, Uncompahgre and Gunnison National Forests saw their aspen forests go into deep decline and experienced massive die-off virtually overnight. Northern Colorado has also taken a hit, with aspen groves near Craig in some of the worst shape of all. However, the spread of SAD appears to have slowed. Foresters have noted fewer outbreaks, and they’re hoping infected aspen groves are on the path to regeneration.

“I’d say it’s stabilized,” said Mark Krabath, supervisory forester with San Juan Public Lands. “It seems like Sudden Aspen Decline has already hit the stands that it’s going to hit. I think we’ve seen the worst of it.”

The cause of Sudden Aspen Decline remains somewhat mysterious. Researchers believe that widespread and severe drought conditions earlier this decade stressed the trees. That stress weakened4 mature and low-elevation stands of aspen in particular, making them more susceptible to infection and insect infestation.

“The stands that are most likely to be affected are on lower elevations and southeast and west slopes,” Krabath said. “These were areas that were most likely to be drought affected, and the drought set these areas up to be infested by a host of beetles and other insects.”

The conservation group Colorado Wild has been keeping tabs on Sudden Aspen Decline since the spread began. Executive Director Ryan Demmy Bidwell commented that he hopes that the infestation has run its natural course and that the San Juan National Forest has dodged a major crisis.

“As best as we understand it, the Sudden Aspen Decline phenomenon was caused by drought and climate change,” Bidwell said. “We expected the impact at the lowest elevations, and I’m not surprised that it’s trailing off. Hopefully, Sudden Aspen Decline will be limited to these areas and not spread to higher elevations.”

Researchers have reported that weakness in the trees gave aspen borers, bark beetles, canker and other ailments an added advantage. But unlike past cases of aspen mortality, SAD appears to be hitting stands harder by striking at the roots, or clones, and preventing future regeneration. That said, new aspen shoots in areas like Missionary Ridge have shown strong resistance to SAD. One conclusion that land managers have reached is that aspen need adverse conditions to thrive. Over time, disturbance leads to regeneration of aspen and has ultimately created the healthiest stands of trees.

“People may assume that because we’ve had such a big winter everything will be fine,” Krabath said. “I do think the moisture will help healthy stands. But we’ll still need to go in and cut those areas that are in decline.”

Krabath noted that SAD has wreaked the most damage from Mancos Hill west to Haycamp Mesa. In response, the Forest Service has ramped up the timber offer of SAD aspen to the Mancos-based Western Excelsior lumber mill. In addition, prescribed fire is often the only viable management tool for afflicted trees. More than two-thirds of the San Juan National Forest’s aspen groves are located inside roadless areas and designated wilderness.

However, Bidwell and Colorado Wild suspect that management may do more harm than good in Southwest Colorado. Now that Sudden Aspen Decline appears to be in decline itself, he advocated taking a hands-off approach and letting the infestation run its course.

“The Forest Service has been trying to figure out whether or not logging or prescribed burning can regenerate aspen, and they’ve seen mixed success,” Bidwell said. “The fact is that we may have missed that window of opportunity on Sudden Aspen Decline. At this point, I’m not sure there’s a need to go out there and thin and burn to address the problem.”

Bidwell added that there’s often a danger of unintended consequences in forest management. Efforts to help situations can often lead to erosion, the spread of noxious weeds and damage to existing stands of aspen.

“Unfortunately, I don’t know if there’s anything we can do to maintain aspen groves,” Bidwell said. “The best we can do is take care of those lands and encourage healthy forests and vegetation. Doing more good than harm on the ground will be crucial as we go forward.”

Nonetheless, the Forest Service will continue to work to restore forests to a more natural condition. Whether they’ll succeed in areas stricken by SAD and whether the infestation is indeed on the run both remain unknown.

“It’s too early to say,” Krabath concluded. “We’re all hoping that it’s out turns out OK.” •