Forests feel relief from sudden aspen decline
Sudden aspen decline in Southwest Colorado is facing a decline of its own, according to studies completed by the U.S. Forest Service.
Aerial surveys, as well as landscape analysis and survey data, have shown a decrease in the momentum of the phenomenon first noticed in aspen groves in 2004.
“The flights and the on-the-ground observations would indicate that sudden aspen decline has really run its course,” said Mark Krabath, supervisory forester at the Dolores Public Lands Office. “It certainly has not infected many or any new stands.”
A report released by the forest service in February stated there has been no notable increase in the size of the area affected by sudden aspen decline since 2008 when the affected area was estimated at more than 553,000 acres, roughly 17 percent of the overall aspen acreage.
Sudden aspen decline is described as “a widespread, severe, rapid dieback and mortality” of aspen groves, according to the February report. A number of factors have been found to contribute to the impact on aspen groves, among which are predisposing factors, such as low elevations, open stands, and south to west aspects; inciting factors, primarily drought conditions of 2002 and 2003; and contributing factors, such as secondary insects and diseases that damage or kill trees already distressed.
“The stands that were most susceptible were the ones at lower elevations on south and west aspects,” Krabath said. “Those were hit first and the hardest, and the rest of the aspen on the forest seem to be doing rather well.”
While sudden aspen decline seems to have not spread in the past few years, stands hit early on still face devastating consequences.
Because of the interconnective nature of aspen roots and the tendency of sudden aspen decline to damage root systems, natural regeneration has not occurred in many stands with noticeable decline. The forest service has worked to encourage regeneration in many stands through clearing and wood recovery, Krabath said.
“We have sponsored four aspen sales in the area in the past five years to try to salvage the logs from these sudden aspen decline stands and help regenerate those stands,” he said.
Mancos-based Western Excelsior has been the recipient of the sales, and Krabath said it is an excellent example of private industry working with the forest service to reach land management goals.
Surveys have been completed on some of the stands that contributed logs to the timber sales, and the results have been promising.
“We’ve gone through a round of first-year surveys on some of those sites from last year, and now this year and it seems that we are getting sufficient regeneration to keep aspen on those sites,” Krabath said. “So that is a little silver lining.”
With time, financial and workforce constraints, the forest service has not managed every aspen stand affected by sudden aspen decline. Krabath said analysis has noted that some unmanaged stands are recovering, while others seem to be unregenerate.
Forest service research cited in the February report has linked sudden aspen decline to climate change, noting “the inciting drought was called a ‘global-change-type drought’ because it was both unusually hot and dry.” The report goes on to say that two-thirds of the aspen-suitable area in Colorado is projected to become unsuitable by 2060 due to climate change.
Krabath said it is a given that the presence of sudden aspen decline in the state will lead to an overall loss of trees but other factors may turn the tides and counteract predictions.
“I think due to sudden aspen decline we will see a loss of aspen in Colorado but other disturbent factors, such as fire, may bring us back into balance,” Krabath said. “I hate to wish for that occurrence, but you just never know what the next year is going to bring in terms of ecosystem health.”
For more information, visit http://www.aspensite.org/pdf/sad_faqs_2011-02-01.pdf.
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