Spring 2009 Perspectives Magazine

Perspectives: Research and Creative Activities at SIUC, Spring 2009

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BEAUTY AND THE BEAST

There are few species of trees in Southern Illinois forests as beloved as the dogwood. But an invading fungus now threatens the flowering tree's future, not just here but across its range.

Researchers at SIUC who are assessing the extent of the damage say the situation appears to be another argument for using fire as a forest management tool. Eric Holzmueller, assistant professor of forestry, and David Gibson, professor of plant biology, received a $2,000 grant from the Illinois Department of Natural Resources to conduct the study.

The fungus, known as anthracnose, is an invading exotic organism that first appeared in the United States in 1978. It subsequently spread through the Appalachian Mountain range and then west, appearing in Fayette County, Ill., in 1995.

Spread by wildlife, contact, and spores, the fungus targets only dogwood trees, killing them by first attacking leaves and interfering with their ability to photosynthesize, Holzmueller says. Eventually, it spreads to twigs and trunks, where it develops cankers that can "girdle" the tree, cutting off all nutrients and killing it. Researchers estimate that up to 95 percent of infected trees eventually die.

"It's attacking these flowering dogwoods, which is a very charismatic species everyone loves," says Gibson, who has done previous work on dogwoods. "Not only that, but dogwoods also have this nice red fruit in the winter that serves as a food source for wildlife. We're looking at a potentially big impact on forests. It compares to Dutch Elm disease or chestnut blight."

Holzmueller, who previously studied the fungus's impact on dogwood trees in the Great Smoky Mountains National Park in Tennessee and North Carolina, found that areas that burned 20 or 30 years ago had more and healthier dogwood trees than areas that had not. He theorized that fire helped open the forest canopy, letting more sunlight in and making the area drier and less hospitable to the fungus, resulting in a better habitat for the dogwoods.

For the current study, Holzmueller and Gibson are examining dogwood plots established in 1991 in the La Rue Pine Hills area of the Shawnee National Forest, in Union County. Forest workers burned the area in 1991 and again in 1993, making it similar to the dogwood stands Holzmueller studied in the Smokies. Holzmueller expects to see similar findings in these quarter-acre plots, where he, Gibson, and Paul Suchecki, a biology teacher from nearby Johnston City High School, measured every tree and took readings on the lay of the land, including its slope, aspect, and soil chemistry.

Holzmueller and Gibson are still analyzing the data, but preliminary findings suggest the disease is present and having a devastating effect on seedlings as well as larger trees. Every tree showed signs of infection to one degree or another, Holzmueller says, but the team is still looking at what effect the earlier prescribed burns may have had on the stand.

Most likely, the research will show that prescribed fire is an important tool for maintaining dogwood and oak/hickory forest stands. The open canopy caused by fires helps discourage the development of the anthracnose fungus attacking dogwoods and also allows more sunlight for oak and hickory seedlings.

"Fire is an important tool if you want to maintain these types of forests," Holzmueller says.

As for that favorite dogwood tree in your backyard, as long as the area is relatively dry and open to sunshine, there is less chance of the fungus thriving in that area, Holzmueller says. And if it does show up, there are a few things you can do to combat it.

"You can prune infected branches and water it, and there might be a few fungicides out there you can use," he says. "Basically, you want to relieve other stresses on the tree so that it can live a longer life."

—Tim Crosby