A walk through golden aspens in the mountains is a favorite autumn pastime of many Northern New Mexicans.

But those golden days could be in jeopardy from a deadly condition scientists call SAD — sudden aspen decline. It's a condition they are still struggling to understand even as thousands of acres of aspens in the West succumb.

Now the Carson National Forest is worried some of its aspen stands near Hopewell Lake are showing SAD signs. "I have a great deal of concern that the mortality we're seeing above Tierra Amarilla on that west slope could be SAD," said Kendall Clark, Carson National Forest supervisor.

There are few signs of SAD in Santa Fe National Forest aspens currently, though some spots are showing decline from an undetermined cause, according to staff. Last year, scientist William M. Ciesla of Forest Health Management International took aerial shots of three aspen stands near Jemez Springs showing tree mortality that could also be because of SAD.

Aspen stands suffering from SAD have brown leaves and blistering trunks one year, and the following year the trees fail to leaf out. Drought, age and pests all contribute to SAD, scientists say. But they're concerned about the rapid pace of mortality in entire aspen stands.

Aspens, known also as quaking aspen trees, are distributed widely across the West, thriving in higher altitudes and moister spots. A single aspen seedling sends out an extensive root system as it matures. Those roots like a little catastrophe such as fire, earthquake, avalanche or landslide to stimulate baby aspen shoots. Most of Northern New Mexico's aspen stands began in the late 1800s following large wildfires, Clark said.

The root suckers give rise to genetic clones of the original tree. "Aspens are like our hair. You can cut them, and they come back. The clone will keep sending up new trees," Clark said.

Usually there are a lot of clones — 20,000 to 30,000 in less than half a square mile. "In stands with SAD, we're lucky to see 2,000 to 3,000 clones," Clark said.

Aspen, on average, live only about 110 to 120 years, but the new clones usually re-establish healthy stands as old ones die off. Instead, scientists are seeing die-offs of whole stands, both mature trees and seedlings, especially on southern and western slopes at lower altitudes.

The drought in much of the West between 2002 and 2005 probably contributed to the aspen distress by weakening trees, scientists believe. Then pathogens sweep in. Cytospora cankers, poplar borers and other pests finish off the trees. But so far, scientists aren't sure what's causing mortality in clones and root systems.

SAD has swept through Utah, Nevada, Colorado, and parts of Arizona and Wyoming in the last few years.

In a 2008 SAD meeting of foresters and entomologists in Colorado, silviculturist Wayne D. Shepperd, retired from the Rocky Mountain Research Station, estimated aspen die-offs around the state had increased from 30,000 acres in 2005 to 553,000 acres in 2008, based on aerial surveys. The total die-off represented 17 percent of Colorado's aspen stands.

Aspens are not only beautiful in their golden autumn hues, "they are a big deal for wildlife," Clark said. Elk and deer calve in the stands. Neotropical birds rest in the trees. And the leaves from the trees help create a sponge for holding moisture and cooling the soil. "In the face of warmer days, warmer nights and warmer times, that's pretty important for water," Clark said.

Scientists are still trying to understand how SAD works. In the meantime, they are testing methods for helping aspen stands survive. Some of those methods won't be popular with the public.

Aspen stands thrive when the surface trees are periodically taken down. Fire works, but it takes a really hot fire to burn aspen, and that risks burning other trees around the stands, Clark said.

Clear-cutting the trees might be another way to stimulate clone growth.

Clark is waiting for scientists to confirm if the aspen stands in the Carson are suffering from SAD. If they are, it may take something drastic to save them, she said.

"We really need the public's support. The tools we need to use are the tools the public doesn't trust us with anymore. Clear-cutting is a dirty word. But it is one way to restart the aspen groves," Clark said.

Clark, forest supervisor for the Carson National Forest, will talk about SAD and the future of aspens during the Wednesday public meeting of Santa Fe's Native Plant Society at the REI community room in the Santa Fe Railyard.

Contact Staci Matlock at 986-3055 or smatlock@sfnewmexican.com.

IF YOU GO

What: A talk by Carson National Forest supervisor Kendall Clark about SAD (sudden aspen decline), a set of pathogens killing off aspen groves in the Rocky Mountains.
When: 6:30 p.m. Wednesday
Where: REI community room, 100 Market Street
Hosted by: Santa Fe Chapter of the Native Plant Society
For more information: www.aspensite.org/index.html