The grave of John McCaskey rests on a Pennsylvania ridge top, overlooking the hemlocks he fought to protect. In the early 20th century, McCaskey helped save the stand of majestic, old growth trees from harvest. In 1973, it became a National Natural Landmark.

But the fight to save these hemlocks is not over.

The trees grow in the Hemlock Natural Area of the Tuscarora State Forest and are under attack by a small but deadly insect: the hemlock woolly adelgid. Many of the hemlocks in the natural area — some hundreds of years old — have become standing skeletons. Others lie toppled on slopes and across Patterson Run, in a slow surrender to moss and decay.

The section with the most damage was once known for the dramatic atmosphere under the hemlocks’ heavy boughs.

“At one time, it was deep and dark, pretty much pure hemlock,” said Steve Wacker, assistant manager for Tuscarora State Forest. “It was called the cathedral, with a big high canopy and open space below it.”

Now, the sun fills the sky against the peaks of scattered living hemlocks and the gray spikes of dead trees. The forest floor is crowded with the fluttering leaves of wispy birch saplings that will soon replace the hemlocks. They mix with fallen branches, ferns, brambles and other low growth that has clogged the trail and made footing unsteady.

“Nothing here looks the way it did 15 years ago,” Wacker said.

The woolly adelgid (pronounced a-DEL-jid) is an aphid-like insect from Asia that has been destroying hemlocks throughout the Eastern United States. It was discovered in Virginia in 1951 and has spread from Maine to Georgia.

The most visible sign of the tiny insect is an abundance of white masses resembling cotton, where the female shelters and lays eggs. There are 50–60 eggs in each batch, and she lays them three times a year.

The woolly adelgid feeds only on hemlocks, attaching to new growth and sucking juices from the base of its needles. While feeding, the adelgids inject a toxin that weakens the tree and stunts its growth. Left untreated, most infected hemlocks will die within four to 10 years.

The pest has destroyed trees throughout its range, turning large patches of landscape from green to gray.

“In some places, you can stand back and look at a mountainside and all the hemlocks there are gone,” Wacker said.

The damage has reached hemlocks along headwater streams of the Chesapeake Bay in Pennsylvania, Maryland, Virginia and West Virginia, and the loss could have deep impacts on the ecosystem.

“Hemlocks are what we call a foundation species,” said Donald Eggen, forest health manager for the Pennsylvania Department of Conservation and Natural Resources. “That means it’s the dominant life form in the habitat. Everything else is there because the hemlocks are there.”

Hemlocks are slow-growing trees that usually take root along streams and cast very dense shade. This keeps the water cool, which is important for fish and the tiny aquatic organisms they feed on —especially native brook trout.

The Chesapeake Bay Program, a regional partnership to restore the Bay and its rivers, considers brook trout an indicator of a healthy headwater stream.

“Why do we have good trout streams in Pennsylvania? It’s the hemlock shade. Hemlocks and trout go hand in hand,” Eggen said.

Hemlocks do more than cool the water. The trees have high water content, so their network of roots along a stream can impact water flow and nutrient filtering.

Hemlocks also define the flora and fauna in their immediate area. Their needles fall and collect in streams, sustaining different types of macroinvertebrates than do forests filled with leaf-bearing trees. This impacts stream life from the base of the food chain. Streams lined by hemlocks have a wider variety of species than those lined by hardwoods.

Hemlocks increase the vertical structure of the forest, providing warmth and forage for wildlife. And most plants (other than hemlocks) can’t grow in their shade, so they provide a niche habitat for songbirds and animals that use them. More than 120 vertebrate species make use of mature stands, including 90 species of birds.

Although the woolly adelgid has been on the East Coast for more than 60 years, forest managers weren’t aware of its destructive capacity until about 30 years ago, when damage in Connecticut became apparent.

The woolly adelgid began sweeping Pennsylvania in the 1990s. Stands in the Baltimore-Washington area were infested by 1990, and then the adelgid moved west. The large tracts of hemlock in far western Maryland were hit by 2001. Those in Cunningham Falls State Park, along the Potomac’s headwaters, were devastated about 10 years ago.

Ninety percent of the hemlocks in Shenandoah National Park, VA, have died, including the popular Limberlost Trail — originally preserved by Addie Pollack in 1920 to save the hemlocks from logging.

West Virginia has lost thousands of hemlocks in the Eastern Panhandle and is now fighting the adelgid in Cathedral State Park, where the trees are 400–600 years old, up to 90 feet high, and 21 feet in girth.

And yet, despite the damage taking place, some hemlocks survive.

“It’s not all doom and gloom,” said Christopher Asaro, a forest health manager with the Virginia Department of Forestry. “There are lots of places where the adelgid has been for many years and some trees seem to be hanging on. They don’t look so good, but they don’t die.”

Researchers are investigating whether genetics may help some hemlocks resist the adelgid so that the best trees could be propagated.

Cold weather helps by knocking back the adelgid population, and recent winters have delivered. But the overall long-term trend toward warmer winters has helped the adelgid spread vigorously.

In most cases, hemlocks surviving on public land are the result of research and treatment.

“Over time, we’ve learned a lot about the hemlock woolly adelgid and its interaction with the host trees,” said Noel Schneeberger, forest health program leader for the U.S. Department of Agriculture Forest Service Northeastern Area. “We’ve got very good insecticides for protecting individual trees but we’re still looking for a landscape-wide solution.”

Imidacloprid can be injected into the trunks of the trees or the soil directly at its base in a carefully measured dosage.

Imidacloprid has become a concern for its impact on honey bees, but Schneeberger emphasized that the insecticide is injected, not sprayed, and hemlocks are pollinated by wind, not bees. “The risk to honey bees is extremely low,” he said.

Imidacloprid works its way up the tree, but it can take two years for it to reach the crown. Protection typically lasts for to five years, and sometimes longer. As an alternative, dinotefuran can be applied at the base of the tree. It takes effect more quickly but must be reapplied every two years.

Homeowners can purchase and apply these treatments too, usually as a “soil drench,” which involves mixing the solution with water, as prescribed on the package, and pouring it around the base of the tree.

This can save special trees. It also works in forests, but becomes challenging in large areas because the insecticide must be applied to each tree —by hand. On Pennsylvania’s state land, this has amounted to more than 30,000 applications since 2005, applied by foresters and park staff working tree-by-tree. Hemlocks are prioritized for treatment in places where they are especially valuable to the stream system or have a big aesthetic impact.

Maryland has tackled the treatment challenge with help from the Maryland Conservation Corps, an AmeriCorps program that employs young adults in natural resource conservation projects.

The partnership was formed when park service superintendent Nita Settina met with Robert Tatman of the Maryland Department of Agriculture and asked how to fight the adelgid. Tatman said there was a pesticide available. They had been applying it since 2004, but they didn’t have enough manpower to make headway.

Settina suggested the Maryland Conservation Corps, whose work is coordinated by the Department of Natural Resources.

A team of 35 young adults in the corps has been treating hemlocks every spring and fall since 2010. “We go from tree to tree, and we’ve been doing it long enough that we are going to start re-treating trees,” Settina said. “And it works. The trees survive.”

Together with staff from the Departments of Natural Resources and Agriculture, more than 53,000 treatments have been applied on state land in Maryland.

However, insecticides are a short-term answer. Hand-applied treatments are not practical or affordable for large landscapes or places that are hard to access. “We need a more sustainable solution,” Settina said.

That solution may already be flitting about in some of the region’s forests.

The Laricobious osakensis beetle, a native of Japan, has been the focus of Scott Salom’s research since 2006. Salom, a professor of entomology at Virginia Tech, reared the beetles in a laboratory until they were deemed safe for release in the wild.

“These are tiny beetles that just eat the hemlock woolly adelgids,” Salom said. “They can probably supplement themselves with other adelgid species, but they can’t successfully develop on anything else.”

Rearing the beetles in a lab is tricky, painstaking work. They need a supply of woolly adelgids, and they go dormant in the spring. The beetles must be released soon after they emerge in the fall, because they only live for one year. “You only get one shot,” Salom said.

Since 2013, Salom’s research team has released the beetles into test sites in Virginia, West Virginia, Maryland and Pennsylvania. It’s too soon to evaluate their impact and it will take years for their population to build up, but researchers and forest managers are hopeful.

“I’m optimistic, but I’m not making any claims yet,” Salom said.

Schneeberger of the U.S. Forest Service hopes that insecticides will knock back the adelgids until the beetles take hold and eventually maintain a lower population of adelgids without significant damage to the trees.

Research continues on several other adelgid predators to increase the chance of success.

“It’s all about creating balance in the hemlock ecosystem, where currently there is no balance at all,” Schneeberger said.

When Wacker surveyed the hemlocks in Tuscarora State Forest with Paul Weiss, who coordinates all hemlock treatments on Pennsylvania state land, the benefits of treatment were obvious.

The ravaged section was infected for several years before treatments began. Small-scale, experimental treatments began in 2003 and 2004, and the program ramped up as research confirmed success. Hemlocks in the upper section of the ravine were treated before the woolly adelgid became aggressive there. Some trees are dead or stressed, but many are still standing.

But with hope on the horizon, the future of the former “cathedral” is unclear. The damage is done. How will the forest change? How will streams and brook trout feel the results? Beech is filling in all gaps, swarming the base of the remaining hemlocks.

Weiss is troubled, but notes that forests are always changing, in ways and on time scales that escape our control. “The question is, what will replace the beech?” Weiss asked.

“Hemlock, is my hope,” Wacker said.

To read about a hike through healthy hemlocks, see “Hemlock Gorge hike / Riverside ramble offers cool retreat,” in the June 2015 Bay Journeys insert or visit www.bayjourneys.com.