Dogwoods Feeling the Burn
Anyone who grew up in the northeastern suburbs will tell you that dogwood trees are among the true highlights of spring, their riotous white flowers as spirited a seasonal cheerleader as any neon-yellow forsythia or ruffled cherry blossom. Generally lost on the suburban aesthete is the fact that dogwoods also play a starring role in forests: The trees take up calcium from deep in the soil and store it in high concentrations in their leaves and fruit. Fifty species of migratory bird depend on dogwood berries for their food, and on its calcium for producing strong eggshells. Calcium-rich dogwood leaf litter is also important because it greatly enriches topsoil.
So when an exotic fungus deadly to the flowering dogwood, or Cornus florida, was first spotted in New York in 1978, there was alarm in the forestry world. Ten years later, dogwood anthracnose had decimated trees from Massachusetts to Virginia; by 1992, on its way to completely colonizing the Midwest, the pathogen had reached west to Tennessee and south to Georgia. The fungus, Discula destructiva, thrives ideally in wet, shady, cold environments, which explains why the cove and alluvial forests of the Great Smoky Mountains National Park lost between 92 and 94 percent of their dogwoods. (In contrast, the forest’s drier, airier, oak-pine areas suffered a relatively low 69 percent loss.)
Desperate to find a remedy for the scourge, the park’s resident ecologist, Michael Jenkins, hunkered down in the attic at headquarters and began sifting through years of records. What he discovered, to his surprise, was that three lone plots had increased in dogwood density over recent years and had in common a single thing: they had all been exposed to fire.
Dogwood trees have thin bark and so are normally fire-intolerant, but as Jenkins and his colleagues Eric Holzmueller and Shibu Jose explained in Forest Ecology and Management last March, a controlled landscape burn every 10 years might allow more of the trees to survive by opening the understory to fungus-discouraging sunlight. In the absence of the anthracnose fungus, says Jenkins, now a forestry professor at Purdue University, dogwood doesn’t benefit from regular burning. "But this disease has shifted the ideal disturbance regime for the species."
Controlled burning is a limited solution, restricted to those ecosystems that are dry enough to support fire, and the fungus will never be eradicated completely. But Jenkins says that burning could function like a treatment for chronic illness. At least dogwood won’t disappear entirely from the landscape, and it’s possible, adds Jenkins, that those trees that do survive will build up resistance they can then pass on to future generations. An outcome with which foresters and northeastern suburban aesthetes would be equally pleased.