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Maple Syrup

Maple syrup bottles sit on a shelf.
Toby Talbot
Maple syrup bottles sit on a shelf.

Spring is here, the time when the sap in trees is rising. So, let’s think about the making of maple syrup!

The sugar in maple tree sap is created through the process of photosynthesis, which converts sunlight energy into sugar. When temperatures drop in the fall, trees convert that sugar into starch, which they store in their trunks and roots.

As winter’s grip loosens, the tree converts that starch back into sugar, which passes into the xylem, the part of the tree's transport system that carries water and dissolved materials upward. Boring a hole into a tree severs the sap-carrying wood fibers, so the sap drips out of the tree and into a waiting bucket — becoming part of the United States’ $150 million-dollar maple syrup industry.

One of my students, Max, grew up in Wisconsin, where he and his siblings would stir big vats of sap, guess the yield of each tree and griddle up stacks of pancakes for the first run of the season.

Sap collection methods have evolved from the early hand-collecting from individual trees and using horse-drawn carts into more mechanized operations. Max’s family now uses plastic tubing and gas-powered pumps to deliver sap directly to the heating vats that transform the watery sap to the gooey goodness we pour on our pancakes.

But this delightful symbiosis between people and trees is becoming endangered, due to climate change. As summer temperatures warm, a tree’s rate of respiration increases faster than its rate of photosynthesis, which decreases the sugar content for the following year’s harvest. And decreasing snowpacks make the soil more likely to freeze, leading to increased death of tree roots, which can reduce tree growth by as much as 40%.

Sugar producers are now working on climate adaptation actions such as shifting the tapping season and thinning the density of sugarbush trees to ensure that pancake-eaters will be able to enjoy those dollops of converted sunlight far into the future.

Dr. Nalini Nadkarni is an emeritus professor of both The Evergreen State College and the University of Utah, one of the world’s leading ecologists and a popular science communicator. Dr. Nadkarni’s research and public engagement work is supported by the National Geographic Society and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. @nalininadkarni
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