UF Researchers: Fire May Help Combat Fatal Dogwood Epidemic

August 4, 2003

GAINESVILLE, Fla. — There may be hope for that embattled Southern icon, the dogwood tree, say University of Florida researchers.

Most dogwoods in the Great Smoky Mountains National Park have died in recent years, the victims of an epidemic devastating dogwoods up and down the East Coast. So Mike Jenkins, a park ecologist, was surprised to discover in a recent survey of parklands that dogwoods in a few spots had not only survived the fungal disease, but flourished. The common thread: The three plots, part of land set aside for research, had all been part of an area burned in a forest fire more than two decades ago.

In a follow-up study, Jenkins and Shibu Jose, an assistant professor in the University of Florida’s School of Forest Resources and Conservation, are testing the obvious hypothesis: that fire may impede the onslaught of the fatal disease, dogwood anthracnose.

If true, that may suggest a way to save at least some dogwoods from an otherwise bleak fate. “If it turns out that fire can prevent anthracnose or reduce its impact, it would give parks and other large landowners a method for fighting the disease – prescribed burning,” said Erich Holzmueller, a doctoral student working on the project.

The team will present the research and preliminary findings at the 2003 Ecological Society of America annual meeting beginning today in Savannah, Ga.

Dogwood anthracnose is a disease caused by a fungus, Discula destructiva. Although its origin is unclear, it is thought to have originated in Asia . Since first striking dogwoods on the East Coast in New York in the late 1970s, the disease has marched steadily south, killing more than 90 percent of the dogwoods in some eastern hardwood stands of forest.

Today, the disease threatens dogwoods from Maine to central Georgia and from British Columbia to Washington and Oregon on the West Coast. The leaves of infected trees develop large holes and often fall off. Anthracnose kills dogwoods either by defoliating them, which prevents their leaves’ abilities to photosynthesize, or by causing cankers in their stems.

The dogwood plague has been a high profile news event in the South, where dogwoods are an important part of the cultural iconography. The dogwood is Virginia’s state tree and its characteristic

white flower is North Carolina’s state flower. Knoxville and Atlanta are among several Southern cities that hold dogwood festivals annually.

Jenkins said anthracnose has killed between 70 percent and 94 percent of the dogwoods in the Great Smoky National Park since it arrived there in the late 1980s. However, in the three plots that burned in the forest fire in the late 1970s, dogwoods had increased 200 percent. Although that may seem like impressive evidence, “three plots don’t give you an awful lot of statistical power,” Jenkins said.

As a result, Jenkins and Jose received $48,000 from the National Park Service’s regional office in Atlanta to study the matter more comprehensively. Holzmueller, who is in the second year of his field research on the project for his doctoral degree in forest ecology, currently is counting dogwoods and collecting data on other attributes of the forest in 60 one-tenth-acre plots – 30 in previously burned forest and 30 in unburned forest.

Although his findings are preliminary, it appears previously burned plots in areas dominated by oaks and hickories appear to support more and healthier dogwoods than unburned plots. The likely explanation, according to Jose: The fire removes some of the tree canopy, which in turn, increases light, heat and the flow of air — just the opposite of the cool, moist conditions preferred by most fungi.

“Fire basically opens up the forest and dries it out, and there may also be a short term impact of fire killing the fungus,” Jenkins said.

Jose and Jenkins agree that dogwoods, besides being a favorite tree for people, are an integral component of the ecosystem. The trees act as a “calcium pump”, drawing calcium from the deeper soil and returning the mineral to forest floor through their calcium rich foliage, Jose said. When dogwood leaves fall on the forest floor, they make the calcium more readily available to land snails and other organisms that rely on it for growth and sustenance. That in turn increases the availability of these organisms as prey to birds or other animals. Dogwood berries, which are high in protein, also are an important food source for birds, Jenkins said.

“We’ve found that what replaces dogwood in the park is hemlock, which is not a food source for birds, although it is a good habitat for some,” he said. “The problem is that hemlock is currently being attacked by an exotic insect.”

Jose and Jenkins are planning to team up with researchers from the University of Tennessee, Yale University and the Forest Service to examine the role of fire in controlling dogwood anthracnose in a regional study that includes several states and federal and private forests across the eastern United States. Jose said the research will help the efforts of natural resource agencies in adding prescribed burning as a powerful tool in their arsenal to fight anthracnose.