What Difference Does the Dogwood Make?
As dogwood blight sweeps through 19 states, experts worry about food supplies for woodland wildlife
The crisp, rolling landscape of Virginia Tech's campus is vibrant with the sounds of cicadas and students, but tree doctor Jay Stipes notices nothing but ailing patients as he strides the grounds. Yellowing pin oaks starved for iron, elm trees kept alive with periodic injections, various species with lightning scars or lawn-mower cankers-and his current obsession, the blight ravaging that jewel of the Appalachian woodlands, the flowering dogwood.
"This one is loaded with it," says Stipes, stopping at a sick dogwood perhaps a foot in diameter. Though still topped by a resplendent crown, the tree is losing its lower leaves and branches, which are mottled and withering. "Here's your dogwood anthracnose," Stipes says as he pulls off a leaf covered with brown spots. "And you can see how it's moving back into the branches. But it will probably never kill this tree. It's just too hot and sunny here."
Would that Stipes could say the same for the millions of dogwoods in the nation's forests under siege from the killer fungus. Since it first appeared nearly simultaneously in the Northeast and Northwest about 16 years ago, dogwood anthracnose has savaged its host species with a speed unmatched since the outbreaks of chestnut blight and Dutch elm disease earlier this century. The new disease attacks several native species, including both wild and cultivated trees of the widespread species known simply as the flowering dogwood. In a broad swath of woodlands stretching from Maine to Alabama, the flowering dogwood is literally vanishing.
The good news is that, unlike chestnut blight or Dutch elm disease, the curse striking dogwoods is fatal only under certain conditions. It flourishes in moist, cool mountain environments. In the warmer, drier flatlands, it attacks trees but generally does not kill them. "It's been in Atlanta now for about four years," say Robert Anderson, a plant pathologist with the U.S. Forest Service. "So far, it's disfigured the trees, but not taken them out completely."
Though dogwoods in hot, sunny spots will survive, the species will soon be only a memory in many forests, where it is an important food source for wildlife. Rabbits, deer, squirrels and a remarkable variety of game birds and song birds rely on the dogwood to build up energy reserves to survive the winter. No studies have been made yet of the disease's long-term impact on wildlife-but clearly, the change will not be good. "From a wildlife standpoint, there really isn't anything to replace the flowering dogwood," says Robert Whitmore, professor of wildlife
ecology at West Virginia University.
"We don't know how animals are going to adapt when they're ready for a heavy dose of dogwood fruit and there isn't any."
That is particularly the case in the South, where the flowering dogwood-one of some 60 species of dogwood worldwide-grows abundantly. There are dogwood festivals and dogwood boulevards and dazzling spring displays along popular venues such as the Blue Ridge Parkway. Postcards in gift shops explain the local folklore of the flower, with the stained tips of its blossoms said to represent the wounds of the crucified Christ and the jumble of angular central flowers his crown of thorns. The tree's year-round beauty and food value for wildlife has made the flowering dogwood perhaps the most-planted ornamental tree in the eastern United States.
Dogwood anthracnose first appeared on a western species of dogwood in Washington State in 1976. Shortly thereafter the fungus struck its eastern cousin in Connecticut and New York. But not until the early 1980s was the disease recognized as some kind of new fungus. And not until 1991 did pathologists finally isolate the anthracnose organism.
"Most anthracnose will cause lesions on branches and leaves, then the plant's natural resistance will stop it," says Stipes, who's been teaching and researching tree biology at Virginia Tech for 25 years. "This one is unique; it's lethal to the whole tree. It's like a cancer that gets in your lymph system and just keeps moving and moving."
Significantly, the blight has not proven fatal to related species such as the Chinese dogwood. This is one of the factors that led Stipes and other plant pathologists to conclude that the disease is an import, brought here unwittingly on the Chinese dogwood or some other ex-otic that long ago developed a tolerance for the fungus.
Once the fungus arrived, it spread down the East Coast; maps showing the disease's progression trace almost perfectly the spine of the Appalachian mountains. There conditions are the best for the fungus-shady, wet and cool. It's carried by the wind, wind-driven rain and birds. The sweep from north to south suggests that many migratory birds play a key role in spreading the fungus. At lower elevations, the blight seems less deadly. "I don't think it will ever be a big problem in tidewater areas," says Stipes. "It just can't take the heat."
Stipes is back in his lab, talking amid a jumble of microscopes, refrigerators, petri dishes and other equipment when Kyle Thornham, who runs Virginia Tech's electron-microscopy facility, walks in and reminds him of another factor helping the disease along-acid rain. Stipes digs out a slide showing the acidity in East Coast rain and snow. The image forms a near-perfect match with the disease map, the highest acidity framing the worst infection.
"I don't think this is entirely an acid-rain problem," Thornham says, pulling out a greatly enlarged photo of a dogwood leaf. Acid has definitely damaged the leaf surface, and in addition, fungus spores are invading. "Somehow it's very easy for this to happen."
While research continues on a micro level, the macro picture grows gloomier every year. The number of states invaded by the disease is now up to 19. It's in every county in West Virginia, and officials in Pennsylvania estimate they've lost more than half of their flowering dogwoods. Individual study plots reveal equally devastating effects. In Catoctin Mountain Park in Maryland, for example, plots surveyed in 1984 contained an average of 276 dogwoods per acre; by 1986, they had only 32 per acre. By 1988, not a single dogwood in the plots could be classified as "apparently healthy."
Surveys of seven southern states (Virginia, North and South Carolina, Georgia, Alabama, Tennessee and Kentucky) compiled by Robert Anderson show a dramatic increase in the number of acres infected by the dogwood blight, which jumped from 500,000 in 1988 to 9.1 million by the end of 1991. Worse, sites stripped of dogwoods show no sign of regeneration. "Young trees come up, but they're killed very quickly," Anderson says. "I went back recently to the first place I saw the disease, in the Chattahoochee National Forest in 1988, and there isn't a single dogwood left."
No flowering dogwoods means no dogwood fruit in the fall, a time when a number of animals-in particular migratory and overwintering birds-depend on it. Dogwood fruit has one of the highest fat contents of any food in the forest-nearly 18 percent. That's important to both songbirds bulking up for a trans-Gulf migration and game birds such as turkey and grouse putting on layers of fat for the winter. Dogwood fruit is also high in calcium, the major component of eggshells.
"We've documented over 40 species of birds that use dogwood fruit as a rood item," says Robert Whitmore. "It's even been linked to the late breeding and fall migration of cedar waxwings, which eat dogwood berries quite a bit."
What's likely to happen once dogwood fruit is gone from the mountains?
"Birds will have to forage in a wider pattern, which means they'll need _more energy to get as much food as they did before," says Whitmore. "Because of what you might call increased foraging costs, the individual animal will likely have lower fat reserves, which could mean it won't be able to fly as far south, or can't make it at all, or makes it in such lousy condition that it can't compete. The other thing birds can do is eat something else. The trouble is, there's not a lot of something else available at that time."
For bird populations already beset on other fronts, the food loss could be severe. "There're so many other contributing factors already knocking migratory songbird populations down," notes Craig Tufts from the National Wildlife Federation's urban wildlife programs. "We have habitat fragmentation on this end, loss of tropical forests where they over-winter, and fewer and fewer rich food-bearing open spaces where they can stop and recharge in between. I'm afraid of what the impact of losing a significant food resource will be."
Dogwood anthracnose is not unstoppable. Homeowners can control it by pruning dead twigs and branches,mulching, improving air circulation and, if necessary, spraying trees with fungicides. But such measures are obviously impractical in the forest. Flowering dogwoods are vanishing, at least until some naturally disease-resistant form spreads or the disease itself dies down. Neither process will occur in our lifetime. "It'll be 500 to 1,000 years before you see dogwoods in the woods again," Stipes predicts.
Except for the hardy few that survive the blight. University of Tennessee's Mark Windham and Stipes are currently studying a pair of trees found near Camp David, the presidential retreat in Maryland. Survivors are being culled by other plant pathologists as well, who are hoping that one of the trees holds a natural resistance to dogwood anthracnose in its genetic makeup that can be identified and eventually reproduced. "We feel we have a good propagation system-if we ever find a resistant tree," says Anderson.
Trees are much more likely to have survived because of a chance placement in open sun or on an airy, well-drained hillside than because of genetic resistance. Finding a lone survivor somewhere in the woodlands which can tip the forces of natural selection back in favor of the flowering dogwood is considered by scientists to be a long shot at best.
But at this point, it's the only one that we have.
Writer Frank Kuznik finds plenty of dogwoods to worry about near his home in Washington, D.C.