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Results from a Long-term Study of Hemlock Loss

Tuesday, March 12, 2013
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hemlock Harvard Forest

Eastern hemlock, a foundation species common in many local forest stands, is disappearing from the southern New England landscape. Its loss is due in part to the invasive hemlock woolly adelgid, and in part to pre-emptive logging. A large-scale experiment at the Harvard Forest has tracked the ecosystem impacts of adelgid invasion (simulated by tree girdling) and commercial logging in hemlock stands since 2005.

New results from the experiment--published in the journal PeerJ by David Orwig, Audrey Barker-Plotkin, Eric Davidson, Heidi Lux, Kathleen Savage, and Aaron Ellison--document the dramatic changes in vegetation structure, downed/standing dead wood, and literfall in both girdled and logged plots. Logging led to abrupt, rapid changes in these factors, whereas girdling (and by inference, the adelgid itself) caused slower responses of similar magnitude several years later. Invasive plant species are now found in girdled plots, but not logged plots. The authors note it may take decades for changes in soil nitrogen, carbon, and pH to become apparent.

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