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Urban Naturalist: A tall cool one


story by bernard brown | photo by flickr user nicholas tI often feel hemlock trees around me before I look up and identify them. I’ll be hacking my way through the woods, sweating in summer heat. Then the underbrush opens, the light dims and a slow, refreshing breeze washes over me. I’m under the tight canopy of a hemlock standing alongside a stream. I love that dark, cool atmosphere on a hot day, and so do the wildlife—in particular, stream denizens such as trout that rely on cold water.

Hemlocks keep it cool, and they take their time. They grow slowly, sometimes taking a couple hundred years to reach maturity, and then living upwards of 800 years.

The Wissahickon Valley is a great place to check out some hemlocks (named for their scent, which is similar to that of the poisonous plant that killed Socrates). There are shrubby examples along the trails and some real giants presiding over the creek. This time of year, when few other trees have any leaves, it’s easy to spot the evergreens with the short, flat needles. My wife Jen and I walked along Rex Avenue, and I inspected the trees we passed. (Want to weird out your neighbors? Walk really slowly and fondle the trees.)

I was looking for the tiny pest killing the trees: the hemlock woolly adelgid (pronounced a-DEL-jid). Starting in late autumn, these itty-bitty insects with a bewilderingly complex life cycle make themselves easy to spot by producing cottony white balls to protect their eggs in between the needles, which looks sort of like the trees got a pedicure.

It might take four years, or it might take 10, but those little white balls spell death for the tree. The adelgids slowly suck the life from the hemlocks, killing them branch by branch. On a vacation to Western North Carolina, we visited a waterfall in Pisgah National Forest. Death was slowly sweeping up the creek valley, the deep green of intact trees upstream fading to the sickly tan of dead ones downstream.
Our hemlocks are dying, but not quite that fast. Kelli Holland, an entomology professor at Penn State explains, “the impact is greater the further south you go.” New England hemlocks have been spared the worst of the blight so far. Pennsylvania is in the middle, with particularly high mortality in our region, the warmest corner of the state.

The sinister woolly adelgids (it’s hard to think of something “woolly” as sinister, but trust me) hail from East Asia and arrived in eastern North America with no predators, except out West, to keep them in check. Insecticides can control the adelgids on a small scale—say in a garden—but in a forest, the best chance may be the adelgid’s natural enemies, including tiny adelgid-egg-eating beetles from China.

Holland’s lab is working to test these beetles and figure out how to deploy them on a large scale. Other labs are studying other predators, some of which have already been released. “We’re going to need a guild of predators,” Holland says, and indeed the U.S. Forest Service has been funding work with a wide range of adelgid enemies.

Losing hemlocks means more than just losing a beautiful tree. The cascade of effects on our forests and waterways is terrible to contemplate, but in 1931 the Pennsylvania legislature chose the hemlock as our state tree. If there’s any place to take a stand for hemlocks, it’s here.

Bernard Brown is an amateur field herper, part-time bureaucrat and director of the PB&J Campaign (, a movement focused on the benefits of eating lower on the food chain. Read about his forays into the natural world at

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