Lethal Stowaways

Lethal Stowaways


Discomfort Zone

by Rikki Hall

If you have never figured out which trees are hemlocks, it is getting easier to recognize them. They are the dead ones.

Hemlocks are conifers, evergreen trees that produce cones rather than nuts or fruits. Like most conifers, their shape is simple: a stout, central trunk with a regular branching pattern. Hemlock needles are short and flat, growing in neat rows on lacy twigs, and their cones are small and more delicate than those of pines. They are common in campgrounds and along waterways. If you have been in an Appalachian forest, you have seen them, but the next generation may not be able to say that as confidently.

An Asian insect is killing eastern hemlocks. Western and Asian hemlock species have natural resistance to the tiny sap suckers, but the two eastern species do not, and both eastern and Carolina hemlocks are suffering major die-offs. Likely introduced by a tree collector near Richmond, Va. half a century ago, hemlock woolly adelgids crept northward, reaching outbreak proportions in the northern Appalachians in the 1980s and 1990s before spreading back south in massive numbers. They hit our forests about five years ago, and their impact is now apparent.

Adelgids will probably not drive hemlocks to extinction. Like the once dominant chestnuts, they will persist and may eventually recover, but on time scales you and I care about, hemlocks are doomed. If you have a few growing in your yard, an arborist can protect them with periodic insecticide treatments, but there is no way to rescue hemlock forests from the devastation.

Natural predators of the adelgid are being reared in the Lindsay Young Beneficial Insect Lab at the University of Tennessee and released into public forests, but if these tiny, predatory beetles have any effect, it will be in slowing future outbreaks. It is too late to stop the current invasion.

For now, prominent trees are being treated, and selected stands in the backcountry are being protected. These stands get experimentally treated with insecticides, soap sprays, beetle releases and combinations thereof, and they are monitored in hopes of finding effective strategies to fight the invading insect. Adelgids are related to aphids and attack plants in a similar fashion.

Will Blozan, co-founder of the Eastern Native Tree Society, has been exploring ancient trees and old-growth forests in the southern Appalachians for the past 15 years. He has climbed and measured dozens of hemlocks, including the tallest (173.1 feet) and most voluminous (1,601 cubic feet). His top-15 lists for height and wood volume are now littered with the stark annotation â“Dead.â” The remaining champions are infested and will soon join their brethren.

Blozan and his colleague Jess Riddle have spent much of the past two years trying to assemble a snapshot of hemlocks in Great Smoky Mountains National Park, funded in part by a grant from the Park, but primarily by Appalachian Arborists, Willâ’s tree care company. Photographs Blozan sent from a recent outing make it clear the battle against the adelgid has been lost. Though taken in summer, the pictures look like a bare, winter forest, except the bare trees are hemlocks that would be green even in winter.

Hemlocks once provided shade all year, cooling mountain streams and keeping soils from drying out. Populations of native trout and smaller fishes may decline as their waters warm. Small songbirds like kinglets, wrens and warblers build nests in hemlocks and forage for insects in their branches, and they will have to adapt to other trees. Many species of spiders and insects depend on hemlocks for food or habitat. Their absence from our forests will have broad ecological impacts.

It is sad to know the biggest and tallest hemlocks are dead and dying, but the big trees are not always the oldest ones. Cores taken from otherwise unremarkable hemlocks have shown them to be over 400 years old. The oldest hemlocks were likely growing when the first Europeans crossed the Atlantic Ocean. Now they are dying because of a fuzzy, white stowaway on an exotic hemlock some collector had shipped across the Pacific.

Rikki Hall is managing editor and publisher of Hellbender Press , a non-profit environmental education journal.


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