Survivors for more than three centuries, the towering hemlocks in Swallow Falls State Park are a remnant of the primeval forests that once blanketed much of Maryland before European settlers arrived.
But after evading loggers' saws, storms and fires through the years, these evergreens now face a new threat — the hemlock woolly adelgid. A tiny insect from Japan no bigger than a pencil point, it coats hemlock twigs with a snowy waxy substance and slowly sucks the life out of the tree.
Determined to save the largest stand of virgin forest left in Maryland, a small army of state workers and volunteers fanned out Wednesday in the Garrett County park in a bid to hold at bay this exotic pest, which has devastated hemlock stands elsewhere in Maryland and throughout the East.
"Hemlock woods are just a special place," said Biff Thompson, a forest technician with the Maryland Department of Agriculture overseeing the effort. Their sheltering boughs cool the ground and water around them, he explained, and they're home to upwards of 900 different species of insects, flies and other organisms. "There's just a richness of life."
Besides their ecological role, the stately hemlocks at Swallow Falls also draw 250,000 visitors a year. Tourists stroll along rocky paths among trees reaching up to 200 feet tall on their way to view the roaring waterfalls along Muddy Run and the Youghiogheny River.
Unless the woolly adelgids are held at bay, said Park Ranger Eric Savage, "it could change the whole landscape."
Native to Japan, hemlock woolly adelgids were first discovered in Virginia in 1951. They apparently hitchhiked aboard a shipment of Japanese hemlocks imported by an arboretum near Richmond, said Brad Onken, with the U.S. Forest Service, assisting the state in its fight to control the adelgid invasion.
Since then, the sapsucking pests have spread from Georgia to Maine. They were found in landscape hemlocks in the Baltimore and Washington areas in the 1980s, reaching Garrett County a decade ago. In the process, they've wreaked havoc in most of the state's remaining 42,000 acres of hemlock forests, including a grove near Prettyboy Reservoir in Baltimore County and another stand at Broad Creek in Harford County.
With 478 acres of hemlocks, Swallow Falls is the largest such tract in the state, and foresters say 37 acres of it along the Youghiogheny have never been logged, though the timber industry had cut over virtually every corner of western Maryland by the beginning of the 20th century. State workers called the area the "crown jewel" of Maryland's forests.
"The mission is to protect the park," Thompson said. "The priority right now is to protect the old-growth timber."
More than 60 staff members of the state departments of agriculture and natural resources have been working for the past week in the park to inoculate as many hemlocks as they can against the insects. They're using insecticides with an active ingredient of imidacloprid.
Five-member crews spread out through the forest to inject the ground around the trees — and in some cases the trees themselves to kill any adelgids infesting the branches 30 or more feet above the ground.
To help scout for the insects, Potomac Edison lent a bucket truck and a crew to look for the telltale white wool on some trees. On his first try, lineman Eli Green found some spittle bugs lurking on one branch, but no adelgids. The crew intended to check at least one other spot accessible to the truck.
Mary Ellen Setting, deputy secretary of agriculture, said the campaign to protect Swallow Falls was a "perfect example" of teamwork involving state and federal governments and a private company. While her agency has experts on pests and pesticides, she said, her staff of 15 is not enough to treat many trees.
Maryland Conservation Corps members, who spend a year in paid service at state parks and forests across Maryland, provided much of the muscle. By Wednesday, the corps and staffers had injected 1,200 trees, about 700 of them in a single day.
Andrea Warren, 20, of Frederick paused while pumping insecticide into the ground around one hefty hemlock to say the work was "one of the most rewarding things we've done. It's a beautiful place."
While the insecticide is effective at killing the insects, state officials say, it's laborious to treat every individual tree, particularly those near water, where the insecticide could kill aquatic bugs if it leaked out. For that reason, trees within 50 feet of water are injected directly, rather than getting dosed in the ground through their roots.
Each crew can treat the soil around 150 trees in a day, but the painstaking process of drilling holes in riverside trees to pump in the pesticide means they can only do 25 or so. And there are roughly 4,000 trees just in the patch of virgin hemlocks, with thousands more in the rest of the forest. Officials say they're concentrating on the virgin hemlocks, which number up to 4,000, and the park's entrance now. It may take them up to five years to complete the treatment of the entire stand. An estimated $122,000 a year for two years in state and federal funds is dedicated for the statewide effort.
Before long, officials hope to supplant the chemical treatment with a natural predator for the adelgids, a tiny black beetle no bigger than a pinhead that they call "Lari." That's short for its scientific name, Laricobius nigrinus. The beetle is common in the Northwest and appears to feed only on adelgids, officials say.
State and federal technicians have collected and bred them, and have been releasing them in infested hemlock stands in other parts of the state. So far, the beetles have taken hold in seven of 10 spots.
Swallow Falls isn't ready for what officials call "biocontrol" because it doesn't appear that infested yet, and the state is still waiting for its colonies of pest-eating beetles to grow.
"We're using pesticides now to hold on until we can get biocontrol up and running," said Bob Tatman, head of the agriculture department's forest pest management program.
For those hemlock stands elsewhere that have been destroyed by the adelgids, state officials say there's little to be done but knock down the pest populations and try to restore the trees.
Chad Baker, 24, another conservation corps member from Frederick, said he helped plant 100 pre-treated hemlocks on Earth Day at Cunningham Falls State Park, where the adelgids have killed off the vast majority of what was once a majestic hemlock stand. But it'll likely be a half-century or more before the new slow-growing trees reach the height of those found at Swallow Falls, he added.
"Anytime you can be pre-emptive and save trees before what's coming comes," said Baker, "it's much better than being reactive."