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When Minus 29°F Feels Good

Hemlock woolly adelgid infestation. USDA Forest Service

Next time Saranac Lake makes news as the coldest place in the nation, rejoice. Occasional dips to minus 29°F are what make us different, sorting the locals from the snowbirds. In addition to building character, temperature also sorts natives from newcomers that could kill them.

A month ago, hemlock woolly adelgid (uh-DEL-jid) was discovered in Schenectady, near the southern edge of the Adirondack Park. The aphid-like insect has been moving gradually north. It appears to have leapt in our direction after last year’s mild winter. Long cold winters keep the tiny invasive at bay.

Believed to have been accidentally imported to Virginia from Asia around 1950, hemlock woolly adelgid feeds on hemlocks, nearly eradicating the tree in Shenandoah National Park, southern Connecticut and other parts of its North American range. Biologists believe the forests of northern New England and northern New York will face the same fate by the end of the century. Because hemlock is more prevalent in the Northeast, the impact here is likely to be more severe, according to a 2008 study published in the journal Mitigation and Adaptation Strategies for Global Change.

Rarely is the correlation between global warming and invasive species placed so clearly on our doorstep. Several studies find that hemlock woolly adelgid die when temperatures reach around –29°F, even if only for a few hours. Prolonged cold can be just as important as extreme cold: the 2008 study found that a stretch of winter below 23°F can also kill the pest.

Entomologist Annie Paradis and her three co-authors wrote, “Our results suggest that it is unlikely that new towns will become infested during a winter with at least 77 days in which the average daily minimum temperature is below −10°C [14°F], or when winter temperature falls below an absolute daily minimum of −34°C [–29°F], or below an average daily mean temperature of −5°C [23°F].”

The pattern of previous Adirondack winters would appear to provide protection. With 1980–2010 U.S. Historical Climatology Network data, Curt Stager, professor of natural sciences at Paul Smith’s College, calculated a mean daily temperature of 17.8°F for Lake Placid; the average of Lake Placid, Dannemora, Chazy, and Indian Lake combined was 18.8°F. Stager cautions that these measures do not tell how many days are above or below a certain temperature. “This kind of thing would require going through the weather records day by day and counting the number of cold/warm threshold days,” he said.

Of course, USHCN records also show a steady rise in local temperatures since 1980. And greenhouse gas emissions are on pace with extreme climate model scenarios, which Paradis concludes would open all of the Northeast to infestation by hemlock woolly adelgid by the end of this century. By her calculations, the best case scenario would be infestation of only half of the Northeast if greenhouse gas emissions are quickly and rapidly decreased. In the meantime, natural resource managers are experimenting with biological control, introducing Asian beetles that feed on the adelgid.

Hemlocks were once the foundation of the Adirondack tanning industry, but they are no longer important to loggers. However, the trees are widespread and inhabit a unique ecological niche, shading streams and growing to great age and size. Last week I hiked under giant hemlocks in Pisgah State Park in southern New Hampshire. Signs along the trail showed photographs of white fuzz (source of the name “woolly”) at the base of short, green conifer needles and asked visitors to report sightings. You don’t have to travel so far to enter adelgid country anymore. Geographically it’s close. Climatologically, it’s getting closer.

Meanwhile, other invasives are slouching towards the Adirondacks. Making news last week were emerald ash borer, which were detected for the first time in Tioga County. (Last year it was found in Albany County, which is closer to the Adirondacks.) The insect is expected to wipe out the state’s ash trees regardless of temperature. Hydrilla, an aggressive aquatic weed, was reported in the Erie Canal north of Buffalo; now it will encroach from the west as well as the south.

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