Jonathan Lesage / Getty Images
It may seem paradoxical, but sugar maples need snow to keep warm and grow.
Every winter, a deep blanket of snow – 8 inches deep or more – covers about 65 percent of north-eastern sugar maples. Without this insulating snow, the ground freezes deeper and longer, damaging the shallow roots of the trees.
A study published last week in Global Change Biology warns that without the snowpack it is expected that the maples will grow 40 percent slower. Given that climate change reduces the amount of deep snow in New England, the study says this creates problems for trees – and for humans – because trees not only give us syrup, but also eat a piece of carbon pollution.
"If temperatures continue to rise and the snowpack continues to shrink, it suggests that our maple forests will not grow so much and will not sequester so much carbon," says Pamela Templer, a biology professor at Boston University and senior author of the study.
Templer says that forests in the United States extract carbon dioxide from the air and store it in trees, plants and soil, can offset between 5 and 30% of carbon dioxide emissions in America.
Damage to the growth of the maple tree, he says, also has more immediate economic consequences.
"Many people in the northeastern United States rely on sugar maples to live," says Templer. "And if these forests do not grow so much, they will probably influence the livelihoods of people who rely on this tree species."
"This paper is a big problem," says Peter Groffman, a biogeochemist at the Cary Institute of Ecosystem Studies in New York, who has worked with Templer in the past, but was not involved in the current study. "When you talk to the forest people in New England, the number one question people ask is: What's going to happen to sugar maples?" This is very pertinent to this question. "
While scientists They have known for years that the deeply frozen soil damages the roots of sugar maples, says Groffman, it is unclear whether this damage has influenced the growth of trees.
"This is what makes this study so exciting," says Groffman. "Show – using very meticulous and very accurate methods – that, in fact, manipulating snow to induce soil freezing reduces long-term tree growth."
The researchers also found that the amount of north-eastern forest with snow cover could fall by 95% by the end of the century, from 33,000 square miles to just 2,000, in the worst-case scenario. It is shrinking from a larger area of Maine to half the size of Connecticut. Even under a scenario of lower emissions, the area covered by the snowpack could still decrease by 49 percent, up to 16,500 square miles, says study author Andrew Reinmann, forest ecologist at the City University of New York .
"So if you like skiing, go now," he says.
Research leading to the study of maple trees began ten years ago. For five winters, from 2008 to 2012, Templer and his team wiped out the first four weeks of winter snow from forest patches in Hubbard Brook's 8,000-acre experimental forest in New Hampshire. This approximated the diminished snowfall of New England by the end of the century. (They left the first few inches of snow in place, so they would not accidentally push the dirt later.) After four weeks of clearing, they allowed the snow to naturally accumulate for the rest of the winter.
After five winters and then a year off to see if the trees would recover, the researchers took core samples of sugar maples and examined their growth rings. The growth of sugar maples has slowed by about 40 percent after the first two years of the experiment.
Reinmann says it is unclear whether the trees will return to their normal growth after a few more years with normal snow, or if the damage is permanent.
"Whether or not this means that sugar maples will die or simply lose a competitive edge is not clear enough," he says.
Researchers observe that warmer winters can have some benefits, such as lower heating bills and longer growth seasons. And, adds Templer, maple sugar production has been able to keep up with climate change so far.
"They can still extract the sap and produce delicious maple syrup," says Templer. "The concern is that in the long run, we may not have maple syrup simply because the conditions required for production [it] could disappear."  This history comes to us from a member station WBUR in Boston.