GardenDesignOnline: Saving Hemlocks

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As most of you readers already know, the wooly adelgid that attacks our native hemlock trees has been moving north at a rapid pace, threatening to wipe out the trees that remain in our Eastern forests. Hemlocks native to western states are not affected by the beetle.

Now, two entomologists at the University of Massachusetts, Amherst, are conducting experiments with a natural adelgid predator -- the Laricobius nigrinus beetle from the Rocky Mountains -- in hopes that our remaining hemlock forests might be saved. Two years ago, researcher David Mausel began releasing the predatory beetle in hemlock study plots in Pennsylvania, New York, Maine, Massachusetts and New Hampshire. He returns to the sites later this year to find out whether the beetles are still there and whether they've slowed the damage to hemlock trees and reduced the wooly adelgid population.

According to team member Joseph Elkinton, if they can get the beetles established in northern forests, the adelgid population may become simply "innocuous." Elkinton says the battle to save the eastern hemlock is important because "they're one of the few evergreens whose loss affects stream temperatures, for example, so trout and other fish species are lost. When the hardwoods move in, many characteristic birds of the hemlock forest are gone, too. Losing the hemlock has an ecosystem-level impact."

The hemlock wooly adelgid is native to Japan and accidentally was introduced to Virginia in 1953. Since then, it has wiped out millions of native hemlocks, particularly in southern states, where winter temperatures are not cold enough to stop it. Adelgids drill into a tree's circulatory system through the bark and suck out its natural sugars. Once the insect multiplies, the tree likely dies within a few years.

Mausel's experiments using the native beetle predator are the most promising so far in the effort to save eastern hemlocks, says Elkinton, but he adds that no one else is anywhere near being able to test another natural adelgid predator. If the current experiment does not work, our northern hemlocks could disappear completely.