Magazine article American Forests

Ghost Moths & Dead Spruce

Magazine article American Forests

Ghost Moths & Dead Spruce

Article excerpt

This elusive insect, abitted by acid rain, may be pushing some forests over the edge.

Armed with carrots, plastic party cups, and antifreeze, Dave Wagner and his crew hike three miles in the freezing Vermont rain on a blustery day in june to the top of Camel's Hump Mountain. From there, they move off the Burrows Trail several hundred yards and begin bushwhacking back down through the soggy conifer forest. Stopping at every 200-meter (650-foot) drop in elevation, the rain-suited researchers bury carrots under the pine- and fir-needle litter. They also dig holes, half-fill several party cups with antifreeze, and place the cups in the holes so that the rims are flush with the forest floor. In the dank cold, swirling fog, and stinging wind, it takes six hours for the group to complete its task.

In this first field experiment of the season, Wagner, an assistant research professor in the Plant and Soil Sciences Department at the University of Vermont (UVM), hoped his antifreeze cocktails and carrot bait would trap larvae of the conifer swift moth. The larvae were supposed to stumble along and fall into the cups, where they would be killed and preserved by the antifreeze. As for the carrots, well: Once a swift-moth larva finds something as delectable as a carrot, it's not likely to move on until that carrot's gone," says Wagner.

Wagner's quarry, a nondescript, drab brown moth virtually unstudied until a few years ago, may be helping to kill trees in the high-elevation forests of northeastern America. The trees, principally red spruce, have been dying in distressing numbers for years, and the experts don't know why.

Foresters first became aware of the steady and ubiquitous decline of the high-elevation conifer forests in the late 1970s. "That was when we realized we were losing red spruce at an astonishing rate," says Hubb Vogelmann. Vogelmann, chairman of the Botany Department at UVM, has tracked the declining tree populations on Camel's Hump since 1979.

What's happening on Camel's Hump, however, is representative of a much larger picture. High-elevation stands of red spruce are in trouble throughout the Appalachian range, from Mt. Mitchell in North Carolina to the slopes of the Adirondacks, Green Mountains, White Mountains, the mountains of Maine, and on up into Canada.

Wagner and his colleagues find the conifer swift moth living in forests ranging from the highest peaks of the southern Appalachians north to Labrador and west to Alberta, including all areas where foresters have identified red spruce as declining. Although the larvae will eat a wide variety of plants, they consider red spruce roots a delicacy and are most abundant in red spruce stands. Wagner's average count of 10 larvae per quarter square meter translates to an estimated 160,000 larvae per acre; he has observed as many as 40 larvae per quarter square meter. Pale, squirmy, and voracious, a mature larva can reach 11/2 inches in length.

In laboratory experiments, the researchers find that a single larva can kill a red spruce seedling. In the field, young larvae essentially girdle saplings. Older larvae gouge wounds down the length of the roots of mature trees. In the areas of high larval densities often corresponding to the areas of most severe decline-feeding wounds pepper the roots of the trees.

In some forests, more than half of the standing red spruce have died. The rest show various signs of ill health. Much of the blame is placed on air pollution, particularly the phenomenon known as acid rain. Although most scientists do not dispute that acid rain can destroy ponds and lakes, the jury is still out on whether acid rain can, in fact, kill trees.

"Pollutants are playing a role," asserts Jerry Hertel, manager of the Spruce-fir Research Cooperative, a program set up by the U.S. Forest Service to fund research on spruce and fir decline. Just which ones and how they might be playing a role is still open to debate. …

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