Scientists are enrolling trees in a wet bark contest to understand the effects of ice storms

Making the perfect ice storm.
Icicles on branches.
Frozen branches part of a study to determine the effects of ice storms on forests. Lindsey Rustad
Icicles on branches.
Frozen branches part of a study to determine the effects of ice storms on forests. Lindsey Rustad

Lindsey Rustad is an ice sculptor. But she doesn’t make the swans you see at weddings or corporate events. She makes ice storms in forests. Her designs, like those in nature, glisten and evoke wonder. But they also foretell danger. With increasing evidence that climate change is driving more frequent and severe weather events, likely including ice storms, she wants to find out what that means for the health of the forest.

Ice storms can be immensely destructive. Frozen limbs, dragged down by the weight of ice, can break, landing on cars, power lines, homes and people. In the United States, such storms cause an estimated 60 percent of winter storm losses, and — here and in Canada — billions of dollars in damage. In January 1998, a massive ice storm devastated parts of northern New England, northern New York and southeast Canada, and a 2008 ice storm in China killed 129 people.

But scientists still don’t know the long-term impact of ice storms on forests. “Our forests are tremendously resilient,” said Rustad, an ecologist with USDA’s Forest Service. “We think they can recover from a light icing, but extreme icing or repeat icing might exceed their capacity to recover.”

USDA Forest Service ecologist Lindsey Rustad in the forest
USDA Forest Service ecologist Lindsey Rustad creates ice storms to study their effects on forests. Lindsey Rustad

Forests are very valuable in the fight against climate change. An intact forest acts as a carbon “sink,” absorbing huge amounts of carbon from the atmosphere. But when trees are crippled by a severe ice storm — and branches topple — the damage depletes carbon stores, and makes it more difficult for the trees to take in carbon. It also hampers the trees’ ability to repair themselves. “Trees can’t take up as much carbon and they lose what they have stored,” Rustad said. “The impact of these extreme events reduces the vigor of trees, threatens their mortality, and weakens their effectiveness as a carbon sink.”

Rustad, a team leader at the 8,000-acre USDA Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, has been manipulating forests for several decades, testing other effects of climate change in the forest’s controlled setting. She’s acidified them and subjected them to other chemical disturbances to measure their resiliency. “I like to poke forest ecosystems to see how they respond,” she said. After a spate of ice storms in New England in the winter of 2008–2009, she and her collaborators decided to add ice storms to the list. “We thought we might have to spend six months being ice storm chasers, then realized that was ridiculous,” Rustad said.

In ongoing experiments that first began in 2009, she and her team used firefighting pumps and hoses — drawing water from the nearby streams — to create several levels of ice storms on a series of forest plots, each the size of a basketball court. The spraying varied in degree from a light icing to more extreme coatings, including repeat icings to simulate potential back-to-back events. They are studying the effects, including comparing the frozen areas to undisturbed forests, looking at soil nutrient recycling, forest regrowth and wildlife.

Man thaws a firefighting pump
Ian Halm, Hubbard Brook Site Manager, thaws the firefighting pump used to spray the trees. Joe Klementovitch

While the research has another year to go, Rustad already has some preliminary thoughts about what they are seeing. “A light icing can actually have beneficial effects,” she said. “It can thin out some of the diseased branches and increase air circulation, and open up the canopy to light. Because trees have stored carbon, that can help them recover and refoliate. But if they are then subjected to more extreme or more frequent icing, they will be in trouble, and not be able to recover, because they won’t have food, having depleted their carbon stores. So we think a light icing is okay— but only one.”

She worked with more than a half-dozen interdisciplinary collaborators from the Forest Service and academia, including atmospheric scientist Katharine Hayhoe, director of the climate science center at Texas Tech University. Hayhoe and her colleagues are using computational and statistical techniques to analyze historical atmospheric characteristics to gain a more accurate picture of past ice storm records, which she calls “woefully incomplete.”

Using these data and global climate models, Hayhoe’s team is designing algorithms that will generate more information on future ice storm frequencies and intensities. “Stay tuned,” Hayhoe said, adding: “We are particularly excited about this work because ice storms are not isolated to the central and northeastern U.S. They occur across the southern and central United States, Europe and even China. As our algorithms can be applied to different parts of the globe, we hope this project will go a long way towards tackling the question of how ice storms might be affected by climate change in many different places around the world.”

Rustad calls the project “the most difficult” she has ever undertaken. At the same time, “it’s being a weather-maker, which is the most amazing feeling,” she added.

How did it work? In one of the more recent field experiments, which took place during the winter of 2016, the team waited for temperatures to dip into the 20s (Fahrenheit) for several days. More than two dozen people then drove snowmobiles up three miles of snow-covered roads into the forest, starting at about 4 p.m. Warmly clothed and wearing reflector vests, equipped with sprayers and hoses, headlamps and LED lights, they sprayed all night, four hours a plot, two plots a night. It took four nights.

Then they did it again last January.

“The hoses spray water 100 feet into the air, and we adjust the nozzles to control the size of the droplets,” she explained. “It goes way up over the trees. If you do this when it is very cold and the surfaces are frozen, it freezes on contact. You want it to come down as a very fine mist so it lands on the branch surface and doesn’t drip off. You move the nozzle to layer the branches. That’s when it becomes sculpting. You control how much ice builds up. That makes all the difference. That way, we control a suite of perfect ice storms.”

Rustad’s team of scientists conduct icy tree experiments in New Hampshire.
Rustad’s team of scientists conduct icy tree experiments in New Hampshire. Lindsey Rustad

The team, in the dark and the cold, shared a sense of awe at the sight — before branches began to topple. “In the reflected light, it was absolutely beautiful, and glistening and looked like crystal,” Rustad said. “You could hear a tinkling sound as the branches rub against each other. We were all looking up, ooh-ing and ah-ing.”

To be sure, the plots with extreme icing also posed a potential danger. But the team stayed safe. “It was scary when they reached their tipping point, and started cracking and breaking,” she said. “There was this terrifying sense of this impending disaster when the treetops started bending over.”

Nevertheless, “we’ve accomplished something that no one else has done in creating this particular type of extreme weather event,” Rustad said. “We could imagine what it [would be] like if [it were actually] happening in the whole forest. We are purposely trying to run the risk now in finding that tipping point. We are seeing already that local weather is being pushed outside historic norms. If the climate projections are close to being right, we need to understand the impact of these storms before they happen — not after.”

Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.