Historic trees. Growth rings in old hemlocks can provide insights into past climates and forest changes.

Richard Webb/IPM Images

Saving the Past in Dying Trees

A "dust of snow from a hemlock tree" once gave the poet Robert Frost "a change of mood" that saved his day. Now, researchers are hoping tree lovers will pay it forward, by helping to preserve the trees' legacy: They are asking scientists and students to collect tree ring data from these handsome, long-lived evergreens before they succumb to a rapidly invading insect and climate change.

"It's a bit of a race against time—we don't want to lose this natural archive of information about past climate and ecosystem change," says Amy Hessl, a tree ring researcher at West Virginia University in Morgantown. She's one of the founders of the new Hemlock Legacy Project (HeLP), a volunteer effort unveiled last week in the journal Progress in Physical Geography.

HeLP originated, in part, in Hessl's backyard. For years, she had heard talk of how eastern hemlocks, which are found from Georgia to Canada, were being killed by an invasive sap-sucking insect called the woolly adelgid (Adelges tsugae). It has spread extensively since arriving from Asia in 1951, wiping out hemlock stands along a widening front. Many fear that the insect, plus a warming climate, will end the eastern hemlock's days as an important part of forest ecosystems. But Hessl didn't fully grasp the gravity of the situation until a few years ago, when the adelgid quickly killed some hemlocks growing behind her Morgantown house. "The threat really hit home, as it were," she says.

Hessl wasn't worried just about the hemlock's future; she also recognized a danger to a unique trove of information about the past. Hemlocks are widespread and can live a long time—500 years or more—so their growth rings provide a useful record of past droughts and forest changes. Indeed, hemlocks provide "arguably the most important natural archive of annually resolved paleoenvironmental data across eastern North America," write Hessl and forest ecologist Neil Pederson of the Lamont-Doherty Earth Observatory at Columbia University.

To save that archive, however, researchers will need to move fast. Many stands of ancient hemlocks are already gone, and the remaining giants are often in rugged and remote terrain. HeLP has identified at least 29 areas, for instance, where it suspects old hemlocks still grow. The project's name is appropriate; to get samples from those trees, says Hessl, "we realized that we are going to need a lot of help," especially because little funding is available for such efforts. So she and colleagues are asking academics, students, and even private citizens involved in forestry and forest research to use some standard techniques identified by HeLP to assist them in collecting tree-ring data. For instance, they can use a corer to extract a thin cylinder of wood (without hurting the tree), or use a saw to take a slice of a branch. The ring measurements and other information would then be shared by researchers through online collections, such as the International Tree-Ring Data Bank maintained by the U.S. government.

"It's a good idea; none too soon, that's for sure," says David Stahle, director of the Tree-Ring Laboratory at the University of Arkansas, Fayetteville. "What's happening to hemlocks is a complete disaster," he adds, "and there doesn't seem to be any way to stop it. So anything we can collect now will surely be appreciated in the future."

HeLP has already preserved one rare find, Hessl and Pederson report: A West Virginia hemlock that appears to be at least 515 years old, with growth rings that record changes between 1707 and 2007. Other such trees likely hold "secrets yet to be discovered by a new generation of scientists," they write—if current researchers can get to the trees before they disappear.