Forest ThreatNet
Researchers Track "Gray Ghosts" Across the Southern Appalachians
People living in the Appalachian Mountains of the eastern United States have long enjoyed a rich culture of storytelling. Often rooted in a deep connection to the natural world, stories from Appalachian folklore serve to entertain as well as to educate; sometimes, important life lessons emerge, especially from tales of demise. A present-day ghost story has captured the attention of Eastern Threat Center researchers who are using high-tech tools to follow the footprints of lost life.
The ghosts in this story are eastern and Carolina hemlock trees being killed in increasing numbers by an exotic invasive insect, the hemlock woolly adelgid. Often called gray ghosts because of their pale, skeleton-like appearance, the dead hemlocks are obvious across the mountain landscape. Using the satellite-based ForWarn forest monitoring tool, scientists are able to see just how devastating the hemlock losses have become across the southern Appalachians, where the hemlock woolly adelgid thrives in the warmer temperatures and is killing trees much more quickly than in the more northern areas of the hemlocks’ range.
Above: Gray ghosts are a common sight in the southern Appalachians. Photo by Steve Norman, Eastern Threat Center. (Click to enlarge.)
ForWarn delivers weekly maps showing levels of U.S. forest vegetation greenness and can distinguish deciduous and evergreen vegetation. Because hemlocks are evergreen, their decline and death are most noticeable during the winter months. In locations where losses from dead and dying hemlocks are extensive, ForWarn maps show an overall greenness decline during the growing season as well.
“What’s truly staggering is how rapidly southern Appalachian forests are changing due to the losses of these trees,” says Center research ecologist Bill Hargrove. “While these rapid losses make it difficult for land managers to protect hemlocks in all areas, ForWarn can reveal where trees are declining so that managers can make informed decisions about prioritizing areas for on-the-ground monitoring and management.”
As researchers and land managers focus on the casualties of the hemlock woolly adelgid, something can be learned from this ghost story. “Perhaps the widespread damage caused by the hemlock woolly adelgid example serves as a cautionary tale: everyone must play a part in preventing the introduction and spread of destructive invasive species,” says Hargrove.
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