Speaking of Nature: The eastern hemlock
Bill Danielson photo
Hemlocks intercept and hold a lot of snow, providing shelter below their crowns.
Bill Danielson photo
The cottony-white egg cases of the woolly adelgid are a sign of invasion.
In 1860, at age 23, John Burroughs went on his very first camping trip. The Catskill Mountains had been Burroughs’ home for his entire life, but he had never walked into the woods on those mountains for an extended stay. In 1868, Burroughs returned to the same spot for a second camping trip and the adventure made such an impression on him that he used it as the subject of one of his most famous essays, “Birch Browsings.” If you have never read it, you should.
In the first paragraph, he describes the mountains and the trees that live on their slopes:
“They are the natural home of the black and yellow birch, which grow here to unusual size. On their sides beech and maple abound; while mantling their lower slopes and darkening the valleys, hemlock formerly enticed the lumberman and tanner. Except in remote or inaccessible localities, the latter tree is now almost never found. In Shandanken and along the Esopus, it is about the only product the country ever yielded, or is likely to yield. Tanneries by the score have arisen and flourished upon the bark, and some of them still remain. Passing through that region in the present season, I saw that the few patches of hemlock that still lingered high upon the sides of the mountains were being felled and peeled, the fresh white boles of the trees, just stripped of their bark, being visible a long distance.”
These words summarize humanity’s relationship with nature fairly well. Sometimes we destroyed intentionally, as with the bison or the passenger pigeon. Other times we destroyed by accident, as with the American Chestnut and the American Elm. But life is resilient and living things often find a way to survive. Such is the story of the eastern hemlock.
I was born in 1968, 100 years after Burroughs wrote “Birch Browsings,” a time when the landscape was still recovering from the terrible impact of conquest. I had no idea of the past, but I was quite familiar with the hemlock. In South Amherst, where I grew up, the trees once again grow in thick stands along the lower slopes of the Holyoke Range. Their green “mantle” gives any area a deep, dark, mysterious quality.
When I was a boy, my family used to visit a camp in the Adirondacks and there, along the shores of a gorgeous lake, hemlocks thrive. Every family canoe trip included a pass along the eastern edge of this lake where the shoreline was steep and rocky. The limbs of hemlocks growing at the water’s edge reached out over its glassy surface, drooping toward the water as they reached farther and farther. We would all take our canoes through the magical green tunnels that resulted. My heart breaks just thinking about it.
In the spring of 1988, I took my first forestry classes at UMass-Amherst and one of them was Forest Botany. This class gave me my first serious look at the world of trees and I learned that hemlock trees were conifers, but they were definitely not pine trees. I had to identify trees by sight and provide the proper scientific name for each species. The name for the eastern hemlock — Tsuga canadensis — remains my all-time favorite scientific name of any organism on Earth.
The hemlock is a shade-tolerant species, which means it can take root and linger in the gloomy understory of a mature forest for decades while still remaining quite small. These trees patiently wait for an opportunity, which usually takes place when one of the dominant trees in a forest finally dies and leaves a large opening in the canopy.
Once such a chance presents itself, the small trees can quickly capitalize on the opening. They race skyward and, as they grow, their increasingly large shadows can remove competitors. Given enough time and the proper conditions, hemlocks can grow to be very old and quite large.
Ideal conditions in our area can be found anywhere there are cool, damp hillsides and ravines with well-drained soils. Pure sand is not conducive to hemlock growth, but sandy soils are. Thus, the northern sides of mountains are especially good places to look. Hiking in the lower portions of the Holyoke Range, or the northern slopes of Mount Toby, you will see hemlock in abundance.
In such places, you can expect to find hemlocks approaching 100 feet in height. Trees of this size can be 100 of years old, which means they were somehow spared the fate of the tanner’s ax. Acids in the bark of the hemlock (known as tannins) were prized for their ability to preserve animal hides and this multi-million dollar industry claimed many trees. Trees were cut down and peeled, the wood being left to rot. Today, the largest hemlock in existence (about 168 feet tall) is found in a remote corner of the Appalachians.
The hemlock has survived an assault by human industry, but there is a relatively new threat to the survival of this species. The hemlock woolly adelgid is an invasive insect brought to the U.S. from Asia in 1924. It is a small “true bug” that makes a living by sucking the fluids from the branches of hemlock trees. Sadly, our eastern hemlock doesn’t seem to tolerate this very well. The hemlock that formerly held the record for maximum height (171 feet) was killed by adelgids.
The presence of woolly adelgid is easily determined by discovering their white, cottony egg cases on the lower surfaces of hemlock branches. Any time I see a hemlock, I take a quick peek to see if such egg cases are present and last spring I very sadly located some on trees enshrouding the lower slopes of Mount Toby.
Sad as this is, however, I choose to remain optimistic when it comes to hemlocks. Scientists have been working diligently to defeat the adelgid and progress is being made. Adelgid diseases have been isolated and predators identified. It is my great hope that with the best side of our ingenuity brought to bear on this problem, we never lose this most beautiful of our native trees.
Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. To contact Bill, or to learn more about his writing, visit