A dead hemlock at Coweeta

In Part 1, I reflected on whole-watershed-sized forest science experiments that have informed present-day management practices and understanding of water cycling through forests. But what happens when a factor beyond our control changes the forest ecosystem, creating a quasi-experiment of its own? That’s what is happening right now in the southeast U.S. due to an aggressive non-native insect.

Traveling through the hills of North Carolina, it was hard not to see the impact of the hemlock woolly adelgid. This miniscule leafsucking insect came from Asia and was first detected at the Coweeta Hydrologic Laboratory about 10 years ago. Because the hemlock woolly adelgid has no natural predators here in the U.S. and because eastern hemlocks have low natural resistance to it, it is pretty much sucking its way through the eastern hemlock range. Nearly all the eastern hemlocks I saw on my trip were either dead or dying.
hemlock woolly adelgid: Photo from invasive.org

For the record, we have hemlock woolly adelgids here in Oregon also, but they don’t cause much harm to Oregon’s two native hemlock species, western hemlock and mountain hemlock. The scientist who led our tour at Coweeta described why, tossing around fancy terms I haven’t uttered much since graduate school such as stylet, petiole and parenchyma. Basically what it boils down to is that the insects cannot penetrate the leaf structure of our west coast hemlock species very easily.

But back east, the hemlock woolly adelgid is leading to the loss of an entire component of the forest ecosystem throughout the Appalachian region. What is the impact when a tree species is lost from the landscape? Many scientists are trying to answer that question, looking at everything from soil chemistry to aquatic habitat to understory species composition.

Dead hemlocks in North Carolina. Photo from invasive.org

Unfortunately the hemlock woolly adelgid is not the only non-native insect to create such widespread impact. While on a family trip to Wisconsin last summer, I heard a lot about the emerald ash borer, another invader from Asia which is killing ash trees throughout the midwest. Unlike the hemlock woolly adelgid, the emerald ash borer hasn’t shown up on the west coast yet (that we know of). If it arrived, would it wipe out our Oregon ash trees? I hope we don’t have to find out.

Print Friendly, PDF & Email

Comments are closed.