Giant Hemlocks Face Predator.
GATLINBURG, TENN.--In a park where trees are protected from the logger's ax, some of the largest and oldest hemlock trees in the world now face a more sinister threat: an alien insect transported from Asia will reduce these old-growth trees to bare trunks if it enters the lush hemlock groves found only in Great Smoky Mountains National Park.
The hemlock wooly adelgid feeds exclusively on hemlock trees by inserting its sword-shaped mouth into the base of the trees' needles and draining them of vital fluids. Needles fall prematurely from the branches, leaving the trees dead within a few years. Most of the hemlocks in the park have been growing undisturbed for more than 400 years and are the only eastern trees left that predate European settlement. When the hemlock adelgid enters the park, most if not all 4,000 acres of colossal hemlocks could be killed, a loss that will jeopardize the survival of a multitude of forest creatures. Great Smoky Mountains National Park protects the largest concentration of plant and animal biodiversity remaining on the East Coast of the United States.
"We've lost so many trees here to exotic pests--chestnuts, Dutch elms, dogwoods, beech, firs, and now potentially the hemlocks. It's a real tragedy," says Charles Parker, an entomologist in Great Smoky Mountains National Park.
Most likely the adelgid arrived in the eastern United States in the 1950s via trees imported from Asia. Unchecked by natural predators, the non-native adelgid spread quickly up and down the forested coast. The insect travels on wind currents or in the fur and feathers of animals and birds. Currently rampant in central North Carolina, the insect has already killed trees in 11 states. A close cousin of the hemlock adelgid, the balsam woolly adelgid has consumed 90 percent of the red-spruce Fraser fir trees found in the southern Appalachian Mountains, including those in Shenandoah National Park. The trail to Clingman's Dome--the highest peak in the Great Smokies--bears testimony to the insects' rapacious appetite for firs. Hundreds of dead trees, ashen gray and bare, stand in stark contrast against the otherwise verdant forest canopy.
Biologists have been working since 1992 to find an effective enemy of the adelgid. Dr. Mark McClure, with the Connecticut Agricultural Experiment Station, found a minute beetle--a member of the ladybug family--in Japan and is now evaluating its effectiveness against the adelgid in eastern North America. So far, the beetle has been released and tested in forests of Connecticut and Virginia, killing 45 to 90 percent of the adelgids at five test sites during the year of release. If the beetle can successfully reproduce and spread throughout the 521,000-acre park, the ancient hemlocks stand a chance for survival.
"Although the beetle has significantly reduced adelgid numbers during the year of release," says McClure, "studies during the next two years will determine if the beetle can control adelgids from year to year and be a lasting solution to the problem."