A Hemlock in the Town Square

Throughout the eastern U.S., the invasive hemlock woolly adelgid is decimating hemlock populations. In nursery experiments on young trees, high levels of sunlight reduced the number of adelgids.

Researchers are testing that hypothesis in the forest. If the experiment has positive effects, thinning the canopy could supplement other methods like pesticides and biocontrol.

The experiment measures how the health of a hemlock tree changes when additional sunlight is introduced. For some of the hemlocks, all of the surrounding trees that shaded it were cut down. In other cases, trees were girdled—a strip of bark was removed from around the tree. Sunlight was added gradually as the girdled trees slowly died.

Every component of an ecosystem has connections to many other components, and the function of the whole depends on almost every one of its parts.

The method could be an alternative to other methods which have different trade-offs. Forest managers could select a combination of treatments that would conserve the most hemlocks at the least possible cost.

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