A scenic drive through Hart Prairie Road provides a closer look at the colors of the leaves changing and the outbreak of the aspens dying off. Jennifer Hilderbrand / The Lumberjack

In the Kaibab and Coconino forests near Flagstaff, 60 to 90 percent of the aspen trees are dying.

Biologists named the occurrence Sudden Aspen Decline, or SAD, and are avidly working to discover the cause behind this problem as well as a solution to it.

Aspen leaves are known for their bright colors, most notably in the fall and the trees have a key role in the ecosystem. Many animals depend on them, and a multitude of other plants can survive underneath them.

SAD has been shown to affect other areas in America centered mostly in the West. Margaret Moore, a forestry professor at NAU, said it has been more of an issue in Flagstaff during the past 15 years than ever before.

“Aspen trees decline naturally as part of forest succession over 100 years or so, as conifer trees encroach and as fires are suppressed,” Moore said. “But the decline disease is a more rapid phenomenon and occurs quickly over a period of five to 10 years.”

A trunk of an aspen tree within the Kaibab Forest. Jennifer Hilderbrand / The Lumberjack

Currently, the Kaibab National Forest, the NAU School of Forestry and the Ecological Restoration Institute are working together to look for a solution.

Tom Zegler, a forestry graduate student, is involved in the efforts to combat SAD in Flagstaff. He said while SAD may not be a dire issue at the moment, because many of the aspen groves people visit are located at higher elevations, it could become much more critical in the future.

“If SAD continues, and long-term decline continues, even on the peaks, then future residents and Flagstaff students may find it harder to visit aspen [forests],” Zegler said.

Zegler said the cause of SAD is a vague concept, although biologists have some potential ideas as to what is causing the aspen to die so quickly.

“As of yet, we have discovered nothing groundbreaking,” Zegler said. “The forces at work driving aspen mortality in northern Arizona are not novel; they have been observed and reported elsewhere.”

In Western America, factors such as changes in climate, plant succession rate and site characteristics have been identified as possible causes.

“However, preliminary observations suggest that pathogens and disease such as fungi, cankers and root decay are playing less of a role in northern Arizona than elsewhere, while browsing and damage by ungulates [elk] and insect pests are playing more of a role,” Zegler said.

Moore said researchers plan to inventory the aspen in the Kaibab forest and make more observations concerning SAD.

“We will also reconstruct the stand history of the site…past to determine how variation in climate, drought, fire occurrence, domestic and wild ungulate populations, and insect or disease may have affected aspen regeneration and stand structure,” Moore said.

Katie Ireland is another forestry graduate student from NAU researching SAD.

“Many aspen stands are dependent upon fire to open up the overstory and promote sprouting and regeneration from roots,” Ireland said. “Lack of fire prevents this regeneration and allows slower growing, shade-tolerant conifers to eventually out-compete the aspen.”

Zegler said students can become involved in the search for an answer to the problem.

“Students can become more aware of the ecological role fire should, and did, play in the forests around Flagstaff,” Zegler said. “Aspen are dependent upon fire and cannot expect to remain healthy with continued fire suppression.”

Leaves are beginning to change color in the valley off of Hart Prairie Road. Jennifer Hilderbrand / The Lumberjack