To save the hemlock, scientists turn to genetics and natural predators
Then, starting in the 1970s, a tiny aphid-like insect known as hemlock woolly adelgid, originally from Japan, unleashed the tree version of a pandemic in American hemlock forests. The adelgid, recognizable by cotton-like fuzz it produces while feeding on hemlock needles, has killed millions of trees and upended ecosystems throughout the eastern United States. Having turned much of Appalachia and New England into tree graveyards, the insect reached the Eastern Shore of Lake Michigan by 2016 and threatens to continue its death march through the upper Midwest.
Many scientists and foresters wrote off the hemlock as a lost cause. But a few wondered whether rare combinations of adelgid-resistance genes might lurk in the trees. Those scientists sought, propagated and planted cuttings from trees that remained green when their neighbors had become gray ghosts.
When hemlocks started dying in large numbers in the late 1970s and early 1980s, forest experts knew they had a problem. The tree hosts dozens of insects and birds such as the blue-headed vireo and hermit thrush, and its year-round shade keeps mountain streams cool enough for trout. Scientists started looking for ways to keep hemlocks around.
One strategy involved looking for rare hemlocks that appeared to tolerate the adelgid. In the mid-2000s, a New Jersey state entomologist surveying near Delaware Water Gap found a stand of lush, green hemlocks amid gray skeletons. University scientists cloned some cuttings from what they called “bulletproof” trees and, in 2015, planted them in test plots near other hemlocks that were infested with adelgids. Four years ...
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