Deep winter freezes a blessing for hemlocks
Time to cheer, tree huggers!
The hemlock woolly adelgid — the scourge of one of the state’s most consequential trees — may be frozen out of Connecticut, a victim of successive blasts from the Polar Vortex.
It’s one of the few good things climate change may bring to the state.
“That is absolutely thrilling news,” said Patrick Comins, executive director of the Connecticut Audubon Society. “It’s some of the best environmental news I’ve heard in a long time.”
Carole Cheah, an agricultural scientist with the Connecticut Agricultural Experiment Station, is the state expert on hemlock woolly adelgids — tiny insects that kill the trees by sucking sap from their branches. They may have arrived in the state in 1986, carried here by the winds of Hurricane Gloria.
Although a southern import, they’ve killed thousands of hemlocks in the state.
“People used to go out on Candlewood Lake and used to say ‘Look at the beautiful pine trees,’” said Cathy Hagadorn, director of the Connecticut Audubon Society’s Deer Pond Farm nature center in Sherman. “Then, they went out a few years later, and those trees were all dying.”
But Cheah, studying the woolly adelgids over the years, has learned the mightiest foe of the insects is a serious blast of subzero cold.
We’ve had that, she said, in four out of the past five years, especially in the St. Valentine’s Day massacre cold snap of 2016.
As a result, Cheah said, when she went looking for woolly adelgids in the state this year — from the Northwest Corner to the state’s coastline — she
could hardly find any.
“Ninety percent of the time when I looked, there was nothing there,” she said.
The few populations she did find, she said, were much diminished.
“It is pretty amazing,” Cheah said.
Cheah thinks cold air from the Polar Vortex — bringer of frigid temperatures that freeze your nose, freeze your fingers, freeze any part of your body not covered by at least three layers — may be responsible for this good news.
Bill Jacquemin, senior meteorologist at the Connecticut Weather Center in Danbury, said the vortex is nothing new — it’s a trough of low pressure that’s been in place for millennia.
“In the summer, it sits over Hudson Bay and the polar region,” he said. “In the winter it migrates south.”
If the northern jet stream lets it set up shop over the Great Lakes, Jacquemin said, it cools off southern New England, while still allowing moisture to get to the state from the south.
“If you like snowy winters, that’s what you want,” Jacquemin said.
However, he said, when the vortex settles over the state it blocks those coastal storms, and all we get is a block of hard, cold, dry winter weather.
Cheah said what climate researchers now think is that the vortex is becoming less stable because of climate change. Global warming is bringing us colder winters.
In 2017, researchers published a paper in the Bulletin of the American Meteorological Society showing why this might be happening.
Researchers know Arctic sea ice is melting at a fast pace, warming the polar region. That creates less of a contrast between the vortex and the northern jet steam that ordinarily blocks it from heading south.
That’s bringing longer periods of very cold weather south in the United States.
Looking at temperature
While we may curse the cold, it’s saving the Eastern hemlocks — one of the most important native evergreens in the state.
records for December and January from 1975 to 2015, the researchers found cold spells which lasted an average of 5.3 days in the beginning years of the study had expanded to 14.1 days by its end.
So while we may curse the cold, it’s saving the Eastern hemlocks — one of the most important native evergreens in the state.
Hemlocks grow on hillsides and rocky slopes. They are shade tolerant and grow in acid soils. As a result, they often thrive in habitat others trees can’t tolerate.
They cool the soil. If they grow close to streams, they shade and cool the water as well.
“They have a big effect
on aquatic life,” Comins said.
There are certain birds, he said, — blue-headed vireo, blue-throated green warblers, and Acadian flycatchers — that favor hemlock stands.
“But they’re really important for wintering birds and migrating birds as well,” Comins said of their thick protective groves.
Hagadorn said if Cheah’s research holds true, it could bring back a native species that in some spots, had truly died off.
“This has consequences,” she said. “People could start planting hemlocks again.”