New Hampshire scientists unveiled a landmark study Friday of how ice storms affect northern forests.
The first-of-its-kind research, from the Hubbard Brook Experimental Forest in North Woodstock, could help landowners and emergency managers plan for future disasters.
Researchers at the forest studied the effects of the catastrophic ice storm that cost the Northeast billions of dollars in 1998 – and created their own experimental ice storms in the forest in 2016 and 2017.
They sprayed water onto sections of the forest on cold nights, building up different thicknesses of ice in different areas to study how they damaged the trees. Part of the experiment was repeated the next year to gauge the effect of back-to-back storms.
Federal researcher John Campbell says they found that ice accumulations above half an inch do the most serious damage to trees.
The National Weather Service issues ice storm warnings at a half inch of accumulation in New England. Researchers say ice storms are already likely dangerous -- to people, infrastructure and the environment -- when those warnings come. They suggested the level should be reconsidered.
Campbell says they found the damage also has long-term effects. It thins tree canopies and makes forests less resilient in subsequent years, especially with repeat storms.
"That's important for forest ecology,” he says, “but it's also potentially important for infrastructure, because if those trees bend down and there's a power line there, that's a big problem.”
Utility arborists, meteorologists and state emergency managers were among the stakeholders who came to hear the research discussed in Concord Friday.
Vanesa Urango is the public assistance coordinator for the state division of homeland security and emergency management. She says the findings will help her office work with the Federal Emergency Management Agency in responding to different kinds of ice storms.
“Although they are a rare occurrence, they do cause a significant amount of damage and have a high dollar value,” Urango says. “So we’re definitely interested in learning about how specific thicknesses of ice or certain setups can cause certain kinds of damages.”
Severe ice storms occur once every 35 to 85 years in New England, with moderate storms every 5 to 10 years. Nationwide, ice storms account for about 60 percent of economic losses from winter weather.
Urango was also interested in the long-term implications of ice storms for New Hampshire’s high-value timber industry. Timberland owners who were affected by the 1998 storm also came to hear about the research Friday.
The study found that New Hampshire's forests are still recovering from that storm.
It also found that forests are now responding differently to ice storms than they did in 1998, at least in one way: in how much nitrogen affected trees can process.
After the 1998 ice storm, scientists say they saw a spike in nitrogen in soil and water – indicating the damaged trees were less effective at fixing it.
Researcher Peter Groffman says they did not see the same spike in the more recent experimental ice storms.
He says it could be due to warmer winters and longer growing seasons, making it easier for trees to process nitrogen even after taking ice damage. The ecosystem is also recovering from decades of acid rain damage, he says.
More nitrogen fixing is good for soil and water quality, he says, but could also make trees less effective at sequestering carbon dioxide.
"If the world is changing around us, then we have to constantly question those ideas about sustainability and resilience,” Groffman says.
Ice storms are expected to occur with roughly the same frequency as the climate warms, but will likely become more intense, scientists say.
Researchers will keep monitoring the ice-damaged forests to gauge more delayed effects. They could conduct another experimental storm many years from now to see if the past damage made the forest less resilient in the long-term.
