War below the canopy: Park Service managers throughout the East are finding new ways to fend off the hemlock woolly adelgid.
A pinhead-sized beetle encounters a tiny ball of fluff on a hemlock branch. Like an attack dog, the beetle bites and shakes its head, shredding the woolly cocoon. Within moments it devours half a dozen orange eggs and munches the mother as well. Still ravenous, the assassin scuttles along the branch, ripping more sacs and slurping delicious eggs.
Nutrients in these eggs send the beetles into sexual overdrive. Within days, egg-laden females tuck their spawn into crevices on the hemlock branches. In two months, well-fed beetles can double in number.
Rapid reproduction of forest insects and disease vectors usually signals trouble. A decade ago, sudden oak death made the journey from Europe to California via nursery stock, spreading to Muir Woods National Monument, Golden Gate National Recreation Area, and Point Reyes National Seashore. White pine blister rust--a fungal pathogen accidentally introduced from Asia--now attacks whitebark, sugar, and white pines at Crater Lake National Park in Oregon. And mountain pine beetles create epidemic infestations, killing ponderosa, lodgepole, and limber pines throughout the Rocky Mountains.
But the murderous melodrama taking place in the Great Smokies is a little different. The parks' resource managers are actually hoping that Sasajiscymnus tsugae--predator beetles wearing shiny black shells--can defeat hemlock woolly adelgids, which hide under white shrouds.
Both combatants hail from the forests of Japan, where trees similar to eastern and Carolina hemlocks grow. The cause of all the troubles, woolly adelgids (pronounced "ah-DEL-jidz") do little harm to Asian trees, but in 1951 they were discovered near Richmond, Virginia, delivered via nursery plants. With no natural predators, the pests' numbers increased exponentially. One adelgid can produce enough offspring to kill a hemlock tree in five years. Hiding in potted plants, hitching rides on migrating birds, and sailing on strong winds, they've spread from Maine to Georgia. Ghost forests of dead hemlocks, such as those at Delaware Water Gap National Recreation Area and Shenandoah National Park, mark their wake.
Perhaps the saddest demise is Shenandoah's Limberlost, a magnificent stand of hemlocks with trees as old as 350 years. In their prime, the beautiful, ancient trees mirrored the look of the Pacific Northwest, according to Shenandoah biologist Rolf Gubler.
Gubler began working at Shenandoah in 1988, the same year hemlock woolly adelgids appeared in the park. While Shenandoah's forest health team was busy battling gypsy moths--another invasive species whose caterpillars defoliate oaks--adelgids slipped unchecked into pristine hemlock sites including Rapidan Camp, Hemlock Springs, and the Limberlost. By the mid-1990s, hemlocks were dying. Resource technicians began the only treatment available, spraying horticultural oil or insecticidal soap on selected trees. These garden-safe substances, made from fatty acids, kill existing adelgids but cannot prevent new invasions.
Workers reached as many infested hemlocks as they could from the park's administrative roads. Treatments were effective, but there was no budget to conduct further work on a frequent basis, so reinfestation from trees in adjacent areas was pervasive, according to Gubler. Because cold winters inhibited the spread of hemlock woolly adelgids and Limberlost's 3,500-foot elevation made it one of the cooler areas of the park, there was hope the altitude would protect the trees. Indeed, Limberlost was one of the last remaining hemlock stands, but droughts in 2000, 2002, and 2003 provided a "knock-out punch" for the shallow-rooted sentinels.
Dead hemlocks are messy--branches fall, chunks drop from their tops, and trunks shatter, posing a costly maintenance challenge. Hemlock forests generally resist exotic invasive plants because they create such dense shade, but after adelgids denuded the branches, invaders including garlic mustard, Asian lady's thumb, tree-of-heaven, and Paulownia sprouted alongside native black birch, tulip poplar, and red maple. Environmentally sensitive large purple-fringed orchids that once thrived in the shade struggled to compete. Preliminary surveys suggest conifer-dwelling birds--including breathtaking Blackburnian warblers and tiny winter wrens--have all but disappeared, replaced by robins and goldfinches.
About 1,200 chemically treated hemlocks survive at Shenandoah. "People may wonder why resource managers didn't do more to save the hemlocks, but back then we didn't know what worked well," says Gubler. "Our techniques, access, and budget were limited, and biocontrols weren't available. What happened at Shenandoah is a shame, but it served as an important early warning for others."
And it's not just the sprawling natural parks that heeded the warning. Forestry technician Irene Van Hoff discovered the pests on hemlocks at Carl Sandburg Home National Historic Site in western North Carolina in 2001. The park unit preserves a 263-acre farm owned by the noted writer, including graceful hemlocks along the entrance road and behind the plantation house. "The park's grounds without hemlocks would be like the Sandburg Home without books--the void would be immense," says Superintendent Connie Backlund. "We're dedicated to doing everything possible to keep that from happening."
Resource personnel donned Tyvek safety suits and employed a special pumping system and platform lift to coat the tall trees with insecticidal soap. The hemlocks' location along the main visitor walkway and around the historic home posed several challenges, and ongoing maintenance required the skills of half of the small park's staff. Even though the pests were temporarily vanquished, there is no ongoing funding for hemlock woolly adelgid control of this magnitude.
Fortunately, Van Hoff consulted nearby Forest Service experts and obtained emergency funds to inject an insecticide into the soil, which is then absorbed into the trees' twigs and needles. Adelgid nymphs the size and color of black pepper flakes generally crawl to areas of new needle growth, attach themselves to the tree, and suck the life from their hosts; if hemlocks are treated with insecticide, adelgids ingest it and die.
Residual insecticides persist at least two years, making soil injection less costly than repeated foliar spraying. For a thousand dollars' worth of chemicals and several weeks of her time, Van Hoff can treat half the park's 800 hemlocks annually, keeping adelgids at bay. As she strolls through the allee of trees that Lilian Sandburg planted decades ago, she is encouraged by healthy new growth. Personnel at the Sandburg home also provide expertise to those who live adjacent to the park, fielding hundreds of phone calls, demonstrating techniques to private-property managers, and organizing workshops so community residents are better able to preserve their hemlocks.
Meanwhile, 100 miles away in the Great Smoky Mountains of Tennessee, hemlocks blanket some 4,000 acres of the largest wilderness in the eastern United States. Virgin hemlocks include the national champion--165 feet tall--and numerous behemoths exceeding 400 years old. Here, hemlocks grow quite widely, along cool streams as well as mountain slopes, creating a stable forest ecosystem. Little light penetrates mature trees, and decades of decomposing needles produce acidic soils. Certain specialized plants, including pink lady's slipper orchids, downy rattlesnake plantain, and polypody ferns, survive well in these conditions. Distinctive songs of scarlet tanagers, black-throated green warblers, and solitary vireos reverberate in the cathedral-like forests. Smoky shrews, southern red-backed voles, hoary bats, and several species of salamanders also dwell there.
More than a decade ago, Smokies resource managers realized that hemlock woolly adelgids would eventually assault the park. They began collecting baseline data on healthy forests, preparing to meet the enemy head-on. When adelgids appeared in 2002, they were met by an emergency response team with backpack sprayers ready to fend off the threat. Within months, workers upgraded to motorized rigs, spraying accessible trees at Cades Cove, Elkmont, and along roadsides. As expected, adelgids continued to stream into the park from surrounding forests and private property. Most hemlocks are now under siege. In 2006, the park spent nearly $850,000 to keep hemlock woolly adelgids in check.
"Foliar treatments are very effective," says Smokies forester Tom Remaley. "The spray kills every adelgid it reaches. And soil drenches work great on old-growth trees: We dig a shallow trench, pour in the proper amount of insecticide, and cover it. Effectiveness depends upon individual tree health, rainfall, and soil condition, so we monitor annually." Most trees drenched three years ago are still protected. As of August 2006, some 40,000 hemlocks have been treated.
Managers learned from the Limberlost incident and want to keep Smokies hemlocks alive for aesthetic as well as practical reasons. It costs $19 to drench a mature hemlock, versus $150 to clear it when dead. Biologically, it's imperative to keep old-growth hemlock forests intact. Irreplaceable trees in Albright Grove, Ramsey Cascades, Greenbriar Pinnacle, and Boogerman Loop have been doctored. In the past decade, the Forest Service and several universities have tested the impact of the release of predatory beetles from Japan and the Pacific Northwest, revealing no unwanted side effects, and reduced hemlock woolly adelgid populations in Virginia and Connecticut. Nearly 175,000 shiny black Sasajiscymnus tsugae predator beetles have been unleashed in Great Smokies hemlock stands; Laricobius beetles, another promising predator, are also being tested.
"We'll be living with hemlock woolly adelgids forever," says Remaley. "We want to keep the backcountry trees alive until beetles reach them. Our goal is to limit tree mortality as predators come into equilibrium with adelgids. Research shows positive results from biocontrols, but we need a lot more beetles."
Funding from the Park Service, Forest Service, and Friends of the Smokies supports a beneficial insect lab at the University of Tennessee, where predators are raised. On the retail market, these tiny creatures are worth more than their weight in gold. Even so, private landowners are purchasing the few available beetles to release in their own hemlock groves. Some Appalachian residents are old enough to remember the demise of the American chestnut, and many fear losing another important component of the Eastern forests.
For anyone who loves hemlock-shaded mountainsides where orchids, trilliums, ferns, and salamanders flourish, where the sweet song of the winter wren splashes down mossy streams, the loss of eastern and Carolina hemlocks is unthinkable. Thus we pin our hopes on tiny beetles, hungrily seeking adelgids, and try to keep enough trees alive to achieve the natural balance required for hemlock ecosystems to survive.
BY CONNIE TOOPS
Illustration by Diane Fester
Former park ranger Connie Toops lives in forestland near Marshall, North Carolina, where she recently released predator beetles to combat hemlock woolly adelgids on her own property.
|Printer friendly Cite/link Email Feedback|
|Date:||Jan 1, 2007|
|Previous Article:||The refuge: the National Elk Refuge--in the shadow of Grand Teton and Yellowstone National Parks--may be doing more to harm elk than anyone would...|
|Next Article:||Open to interpretation: the National Park Service is making a concerted effort to share all of the nation's treasures with all of America--including...|