Plant ecologist Kristina Stinson at the University of Massachusetts Amherst and Joshua Rapp, a Bullard Fellow at Harvard Forest in Massachusetts, are both involved in a study to find out the impact that climate change has on the quality and quantity of sugar maple sap.
At stake is an industry that was worth $117 million in the U.S. in 2014. Sugar maple sap only flows when the temperature during the day rises above freezing and drops below freezing at night. The temperature difference creates enough pressure to force the sap out of the tree, a miracle of nature.
The research team received a two-year grant of $148,000 in what they believe is the first study on sugar maples and the impacts of man-made climate change on the sap quality, sugar content and chemistry, as opposed to only sap flow and volume. “We’re looking at the flow of sap and its sugar content,” said Rapp. “We want to see how those two things vary with climate across the sugar maples’ range,” reports WTTW Chicago.
Stinson explains that maple sap is mainly sugar and water. However, there are compounds called phytochemicals that are naturally occurring that give maple sap its distinctive flavor. Rapp adds that any sap containing sugar could be boiled down to syrup, but maple has an unique taste all its own.
People have been known to tap birch, walnut, or hickory trees to get their sap, Phys.org points out, but the syrups produced have a different flavor and are too labor intensive and have less sugar to be profitable. Stinson notes, “Phytochemicals are what give sap from the different species their particular flavors.”
The sugar content and secondary chemistry are what determines the quality of the sap. Rapp says, “Sap sugar content determines how much syrup can be made from a given volume of sap; all syrup sold commercially has a consistent density of sugar, about 66 to 68 percent.”
With stands of maple trees ranging from Canada and on down to Virginia, the researchers are using volunteers and students at six sites who tap 15 to 20 trees at each site, ranging from one at Harvard Forest in Petersham, Mass., one near Dartmouth in New Hampshire, two managed by a scientist at the University of Virginia’s College at Wise, one led by a researcher at the University of Québec Chicoutimi and one at Indiana Dunes National Lakeshore.
Climate change is already having an impact on the natural production of maple sap. It is most noticeable in the shift of the maple season over the past 40 years. Winters have been warming at about 1°F (0.6°C) per decade across much of the Northeast since 1970.
While the research is ongoing, Rapp points to the decreasing range of sugar maples in the U.S. shown on the USDA Forest Service’s Climate Change Atlas. Current estimates say that by 2100, the current habitats for sugar maples will be unsuitable, with all of them being found in Canada, along with maple syrup production.
Charles Cannon is the director of the Center for Tree Science at the Morton Arboretum, and he says, “Climate change is a much harder thing to deal with for people who grow trees versus other things. You can’t just mow down last year’s harvest and start over if it was a bad year.”