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News Article

Study identifies new method of predicting syrup yield

Researchers hope findings will help producers plan ahead

For a number of years, maple syrup producers have paid close attention to the weather in order to help understand spring sugar yields.  However, a recent study has identified a useful metric for understanding and predicting syrup production – by the amount of seed helicopters that fall from the trees during the previous year. 

“Weather affects how much sap will flow out of the tree, but sap volume is only one piece of the puzzle” said study author and postdoctoral fellow, Joshua Rapp.  Rapp, with his colleague Elizabeth Crone from Tufts University, analysed the factors influencing 17 years of maple syrup production across 28 different sites in Vermont. 

The quantity of sugar in the sap is important to maple syrup producers.  But what is it that predicts how much sugar is in the sap?  Rapp says it’s not the weather, “weather alone was a surprisingly bad predictor of how much sugar came out of the taps over those 17 years.  That tells us something else is at play.”

Rapp and Crone studied ‘mast’ seeding events, when trees collectively produce more seeds than usual.  In sugar maples, mast seeding tends to occur every 2-5 years.  Mast seeding events in Vermont took place in 2000, 2006 and 2011.  The research showed that 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.”

Looking forward to next year’s harvest, Rapp predicts that “at the Harvard Forest and likely throughout the northeast, the seed crop was small this year, suggesting the 2015 maple syrup harvest should be a good one.”

According to Rapp, “the best way to predict syrup production is actually a combination of factors: proportion of trees with seeds, minimum and maximum March temperatures and maximum April temperature.  Those factors together explained 79% of the variation in syrup production in Vermont from 1998 to 2014.”

Because seeds develop a full six months before the syrup harvest, Rapp and Crone hope that this study will give syrup producers a window into the upcoming season.


Joshua M. Rapp, Elizabeth E. Crone. Maple syrup production declines following mastingForest Ecology and Management, 2015; 335: 249 DOI:10.1016/j.foreco.2014.09.041


Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 04 December 2014
  • Source
  • Harvard University
  • Subject(s)
  • Forest products