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Weeping hemlock

Anne Dalke's picture

I’m realizing that—since I’m not on campus Friday-Monday—it’s going to be very hard for me to find time to sit under my weeping hemlock tree (since all of you were complaining this weekend about the cold, this may be just as well…). So this week, as substitute for a “site sit,” I took inspiration from the proposal The Unknown wrote for her first web-event—tracing the history of a plant—to do some research on the tree I’ve selected to shelter me this semester.

Turns out my shelter is the result of all sorts of migration—of words, the tree, and its pests. The name “Tsuga Canadensis” (Canadian hemlock) is derived from the Japanese (!?) word tsuga 栂 (ツガ), which is used to identify a genus of conifers in the pine family Pinaceae. It’s called “hemlock” because its crushed foliage smells like that of the poison hemlock (though the Tsuga species are not poisonous).

The tree is native to eastern North America, and dates back to the early Holocene (c. 16,000 BP). It began growing in the southeastern US, then expanded rapidly and successfully—but experienced a pronounced decline approximately 5,500 BP, which lasted for about 1,000 years. The decline may have been the result of pathogens, insects, and/or climatic change. The eastern hemlock increased again after this period, but was no longer a dominant species.

It is now the state tree of Pennsylvania (who knew?!); the oldest living specimen, in northwest Pennsylvania, is over 500 years old. The lumber from the tree is used for general construction and crates, and “because of its unusual power of holding spikes” (these details are rather bizarre…), it is also used for railroad ties. The species is currently threatened by the hemlock wooly adelgid  (Adelges tsugae), a sap-sucking bug accidentally introduced to the U.S. from East Asia in 1924. Thousands of hectares of hemlocks in the southern Appalachian Mountains have died from this infestation within the last two to three years.

My own particular version of the Canadian hemlock is a “pendula,” or weeping form. Can’t wait to get under it next week, and check for possible infestation….