While the era of cutting hemlock for the tanning industry is over, there continues to be use of the tree for fiber and construction, and commercial forest owners have something to lose with the demise of the hemlock. But far more important, as the hemlocks expire they take an ecosystem down as they fall.
In cool hollows and along shady mountain streams the hemlock has grown for millennia where other trees wouldn't thrive: a quiet giant soaring to over 150 feet. With a range from Alabama along the Appalachians into the Canadian Maritimes, its shaggy crown creates a blueish green haven unmistakable to turkeys and deer (and hunters): a thick understory of duff, deep with shade that accentuates the black furrows of the hemlock's tannin-rich bark.
In winter, chickadees eat the small seed cones of the hemlock and they are only one species of many that depend on the hemlock not just for food but for the architecture of their world. Some warblers only nest in hemlocks and the mountain fish depend on the trees to keep streams cool.
"See all this white growth?" Costa says in his UVM lab, tracing his finger above the soft flat needles. "That's mycelium and likely as not there are spores at the end of each of those." To the untrained eye, the fungus he and Grassano are growing looks much like the pest they hope it will fight. Hiding on the underside of hemlock branches, the pest produces a white woolly tuft that gives it its name. The fungus looks white and woolly too. But the subtle difference may mean life or death for the eastern hemlock.