For decades, maple syrup producers have eyed the weather to help understand spring sugar yields. But new research in the journal Forest Ecology and Management reveals a more valuable metric for understanding — and even predicting — syrup production: how many seed helicopters rained down from the trees the year before?
“Weather affects how much sap will flow out of the tree, but sap volume is only one piece of the puzzle,” said Josh Rapp, who as a postdoctoral fellow with Elizabeth Crone, associate professor of biology at Tufts University and senior author on the paper, analyzed the factors influencing 17 years of maple syrup production at 28 sites in Vermont.
What really matters to maple syrup producers, Rapp explains, is the amount of sugar in the sap: “Sugar maple sap is 2 to 3 percent sugar. The rest is just water to boil off. Sweeter sap is more profitable. If you start with sap that’s 3 percent sugar, it takes a third less sap to make a gallon of syrup.”
So, what predicts how much sugar is in the sap? “Not weather,” says Rapp. “Weather alone was a surprisingly bad predictor of how much sugar came out of the taps over those 17 years.” “That tells us there is something else at play.”
For several years, Rapp and Crone have been studying “mast” seeding events — years when trees collectively produce far more seeds than usual — at the Harvard Forest in Massachusetts. In sugar maples, mast seeding tends to occur every 2 to 5 years.
Recent mast seeding events occurred in Vermont in 2000, 2006 and 2011. Rapp’s research shows that in Vermont, syrup production declined following every mast seed year.
“Both seeds and sugar are made from carbohydrates stored in trees,” explains Crone. “When a tree produces a lot of seeds one summer, then the next spring, the carbohydrate bank account is low for making sugar. It’s a matter of budgeting resources.”
This article appears in the January 2015 issue of Acres U.S.A.