Decades ago, several hundred hemlock trees stood in a section of Patapsco Valley State Park around Cascade Falls along the Patapsco River near Elkridge. Today they barely number 100.
Similar losses have hit forests from Georgia to Maine in recent decades as an invasive insect has feasted on hemlock sap. The thinning numbers are a significant loss for the ecosystem because the towering evergreens provide habitat for nearly 1,000 types of creatures — hundreds more than other trees do — from birds to microscopic invertebrates.
But an effort to restore hemlock groves in Maryland is under way. More than 200 hemlock seedlings will be planted in the Patapsco Valley this month, along with another 280 in Western Maryland. Hundreds more will come over the next several years through a serendipitous partnership with Pennsylvania.
Conservationists are working to move past the invasion of the hemlock woolly adelgid, a tiny insect from Japan blamed for the hemlock decline, now that they know how to protect the trees by treating them with pesticides and unleashing beetles that prey upon the adelgids.
The adelgids first appeared in the eastern United States in Virginia in the 1950s, spreading to states up and down the Appalachian Mountains in the following decades. In many areas, they devastated populations of eastern and Carolina hemlocks, with losses of as much as 80 percent to 90 percent in Western Maryland, said Biff Thompson, a forest health technician for the Maryland Department of Agriculture.
The adelgids have no native predator here, but since the early 2000s conservationists have been battling them with beetles the width of a toothpick, imported from China, Japan and the Pacific Coast of the U.S.
Maryland officials have spread 50,000 beetles from five difference species. In many sites, their populations have taken hold and are counteracting the adelgids with no apparent effect on other creatures.
The beetles, combined with pesticides that target the adelgids, appear to keep the adelgids at bay.
"I think we're proving this is a viable means," Thompson said. "It's not a silver bullet."
Progress has prompted Maryland officials to begin the slow process of rebuilding the hemlock forests that have been lost.
"It's bottom-of-the-food-chain stuff we're trying to protect here," Thompson said. "We need to hang onto what's going on here, and what we've lost, we need to restore."
Several hundred hemlock seedlings were planted around Cunningham Falls in Frederick County in 2010 through a tree-planting program of the beverage company Odwalla, at a cost of nearly $100,000.
The state Department of Natural Resources tried to grow hemlock at its nursery on the Eastern Shore, but the trees are more inclined to grow in rocky soil near streams and the seedlings did not thrive.
By happenstance, though, Thompson learned late last year that a Pennsylvania nursery had 1,500 hemlock seedlings it didn't know what to do with. He called it "pure dumb luck."
Environmental officials from the two states struck a deal. In exchange for Pennsylvania's hemlocks, Maryland will provide beetles gathered from its forests to guard restoration projects on the other side of the Mason-Dixon Line.
Within a few years, Pennsylvania will provide hemlocks grown from seeds gathered from Maryland trees' cones.
"Cooperation between states dealing with the impacts of the hemlock woolly adelgid is essential to our efforts," said Don Eggen, forest health manager with the Pennsylvania Department of Conservation and Natural Resources, in a statement.
Maryland's first 500 seedlings will be divided among Patapsco Valley, Cunningham Falls and Big Run state parks. More are expected over the next few years.
Mature hemlocks are marked by sturdy trunks covered with scaly bark, and spindle-like branches bearing short, soft needles. They tend to grow slowly in the shade but can sprout rapidly in sunlight, with their trunks reaching a thickness of 10 to 14 inches and heights of 60 to 80 feet within half a century.
Members of the Maryland Conservation Corps, a natural resource management initiative that is part of the public service AmeriCorps program, planted a dozen hemlocks Tuesday along a stream flowing into the Patapsco. The seedlings, resembling bunches of rosemary, are placed in wide, shallow holes — along with tablets of pesticides that will protect them for at least the next five years. Cylindrical metal cages are placed around them to keep hungry deer away.
Corps members said they have learned what the species likes — the rocky soil of slopes lining stream and river valleys.
"It's incredible how resilient they are," said Cinthia Myers, who recalled seeing a hemlock thriving on a rocky cliff at Swallow Falls in Garrett County.
Volunteers are scheduled to plant the rest of the trees on May 14. Groups such as Patapsco Heritage Greenway are eager to protect endangered trees after seeing the effect of an invasion of an insect known as the emerald ash borer on local ash tree populations in recent years. They hope to prevent devastation like that experienced by American chestnut trees in the early 1900s.
"Any time you have native trees, we're always concerned about it whenever some kind of blight or insects are attacking them," said Betsy McMillion, the group's director of environmental programs. "Once they're gone, it's just really hard to restore them again."
Historically hemlock trees have been valued for the tannic acid their bark contains, used in treating leather, and for their lumber, said Todd Berman, president of the Maryland Forests Association.
"It's important to preserve that for future generations," he said.
While state officials estimate Maryland has about 42,000 acres of hemlock forest habitat, in some forests they represent less than 1 percent of trees. However, the species is not valued as much for its footprint as for its impact.
Hemlocks can be home to some 970 species of organisms, compared to about 460 species in the white pine, the tree with the second-most diversity, Thompson said.
"They help feed the rest of the area with the diversity they have in them," he said.
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