Jeremy Bruno is a tech writer who blogs about ecology, evolution, conservation and culture at The Voltage Gate. Visit the 
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 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.
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.
Comments
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).
Posted by: Ahcuah | October 29, 2007 1:20 PM
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."
Posted by: HP | October 29, 2007 2:25 PM
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.
Posted by: Laelaps | October 31, 2007 12:00 PM