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Preservation effort planned for trees threatened by insect at Flight 93 site

Mary Pickels
| Thursday, Nov. 7, 2013, 12:05 a.m.

Over the next three years, National Park Service staff, partners and local contractors will work to preserve a grove of “witness trees” at the Flight 93 National Memorial, which are threatened by a nonnative, invasive insect.

When United Flight 93 barreled from the sky and crashed in a Somerset County field on Sept. 11, 2001, the aircraft plowed into a hemlock grove.

Referred to as witness trees, the grove contains the remains of the 40 passengers and crew, who died after terrorists wrested control of the plane. It crashed in Stonycreek Township instead of hitting a target in Washington.

Those trees are under attack by the hemlock woolly adelgid, park service officials said Wednesday. The staff discovered the insects' presence by their egg sacs, which resemble small tufts of cotton clinging to the underside of hemlock branches.

Infected hemlocks can change from a healthy green color to a grayish-green.

In a news release, officials said the park service and U.S. Forest Service scientists this week began a project to suppress the insect population's spread and preserve the hemlock grove.

Workers will treat 1,351 selected mature trees, along with many seedlings and saplings.

A combination of soil-buried tablets, soil injection, low-pressure tree injection, bark spray and horticultural oil spray are among treatment methods.

“We hope that these treatment methods will protect the hemlock trees and help us preserve the crash scene,” said Jeff Reinbold, superintendent of the National Parks of Western Pennsylvania.

The hemlock woolly adelgid was accidentally introduced to North America from Asia in 1924, according to the park service.

Its earliest record in Pennsylvania was in 1967, and it has become established in 19 eastern states from Georgia to Maine. As of 2007, 50 percent of the geographic range of eastern hemlock has been impacted by the insect, park officials said.

What remains of the grove in Stonycreek Township, which was damaged as the plane exploded, includes a gap where those trees were removed. A boulder at the base of the grove marks the impact site, considered a sacred burial ground.

When family members visit the memorial, and on annual 9/11 observations, they are escorted to the site to privately pay their respects.

Mary Pickels is a staff writer for Trib Total Media. She can be reached at 724-836-5401 or

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