A Short History of the Eastern Hemlock I

About 16,000 years ago, glaciation from the last ice age finally began to retreat after millennia of occupation. As the glaciers melted and filled scrapes in the landscape with fresh water, the animals and plants followed, once only able to live in the temperate climes of southern North America.

The eastern hemlock (Tsuga canadenis) was one of these pioneers, albeit a slow, steady one. Spreading north at about 100 - 400 meters per year (incidentally about the same rate of large ungulates like elk), the hemlocks wouldn't reach the extent of their expansion, around the glacier-crafted Great Lakes, until about 2,000 years ago.

Over the Thanksgiving break, I finally got a chance to do a little exploring. I took the fam up to Laurel Hill State Park in Western PA to hike through the remnants of an old growth eastern hemlock forest set aside for environmental education.

It's tough to find old growth forests anywhere in the eastern US nowadays, especially old growth areas dominated by hemlock. Laurel Hill has a small but beautiful remnant of the tree's unique habitat.

Hemlocks typically grow on cool, moist, north-facing slopes along streams. The density of these trees tends to diminish as you progress up slope.

Laurel Hill Creek runs through the hemlock stand in the valley bottom.

Notice the hardwood forest beyond the hemlock stand. Hardwoods like red maple prefer the drier conditions of higher altitudes.

Hemlocks are conifers, but produce small cones relative to the height/breadth of a mature tree. They are a long-lived species, maturing in 300 years, able to reproduce for 450; the oldest recorded hemlock was 988 years old.

In Laurel Hill, most of the hemlocks were young, especially around the periphery, but once you reached the center of the forest, there stood the remnants of an old stand, trees reaching 100+ ft., alive since William Penn roamed what would become Pennsylvania.

These trees in the center of the stand are over 300 years old.

Hemlocks are a part and sometimes a progenitor of a very special understory habitat and support a variety of other organisms. Next post I'll talk about some more of the ecology of the eastern hemlocks, including what are called "ecotones," the animal and plant species hemlocks support and why it is essential to protect and preserve these ancient conifers.

More like this

In Part I we looked at the eastern hemlock's northwestern progression after the last ice age, and the frequency of the hemlock along a slope-oriented moisture gradient: The distribution pictured above is almost exactly the case in the Laurel Hill old growth stand. The hemlocks are dense at the…
Walking through a streamside copse of eastern hemlock in the ancient Appalachians is revealing for several reasons. First, the sheer size and age of these virgin stands can be humbling - at 45+ meters high, one tree may have been alive for more than 600 years. Second, a closer look at the forest's…
Whispers from the Ghosting Trees A guest post by Gail Zawacki, who blogs at Wit's End. While we hustle busily through the necessities of our lives, wrapped up in our daily preoccupations - our obligations to our families, our jobs, and our dreams - at the same time all around the world, trees are…
In the story of climate change, humans and the carbon dioxide we pump into the atmosphere are the villains of the piece. Now, it seems that we have an accomplice and a most unexpected one at that. It lives in the pine forests of North America and even though it measures just 5 millimetres in length…

Hemlocks are a really nice tree. We have a bunch of stands of it in southeast/central Ohio. The Hocking Hills area (just southeast of Lancaster) has a bunch of 150 foot gorges, so it stays cool enough and moist enough for the hemlocks to thrive. In Hocking Hills there is even a "Cedar Falls," so-named because the settlers didn't know the difference (they are of course really hemlocks).

Another place with really large old growth hemlocks is Ramsey's Draft National Wilderness Area, near Staunton, VA. Some of those trees are just enormous (like the one in your picture).

I thought we were in danger of losing most of them though, from the woolly adilgid, yet another imported pest. We've lost the elm to dutch elm disease and the chestnut to the chestnut blight, and we're losing the ash to the green ash borer. And now this.

You know, if we are going to lose a whole plant species, how come there's never a poison ivy blight? Now that's one I could get behind (and its ecological niche could be filled by virginia creeper with no problem).

Huston Woods State Park, which is also in southeast Ohio, hosts what they claim is the last old-growth beech forest in the eastern US. Most of the park is typically dense secondary growth, but then you hike in a short ways and it suddenly opens up into a real forest with a real canopy, and these great smooth grey trunks rising up to the sky. Hiking there made me wish I was an ecologist and not just some guy saying "Wow."

Interesting stuff and nice shots. My wife has actually worked quite a bit with the Hemlock Woolly Adelgid and Hemlock Scale, and indeed it's hard to find a try without one or both on it somewhere.