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The Migrating MapleWhy you're eating Canuck syrup.

By Constance CaseyPosted Monday, April 2, 2007, at 2:30 PM ET

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Still, it was a pretty good idea for 18^th- and 19^th-century New England. Randall notes that Americans in those early days commonly drank as many as 15 cups of tea per day, and they liked it sweet. Jefferson believed that Vermont could produce enough maple sugar to meet domestic needs and even export some, competing with British sugar. Jefferson rarely missed an opportunity to annoy the British.

Here's why Jefferson's maple sugar trees didn't produce well in the 19^th century, and why 21^st century American maple-sugar makers are losing out. The movement of the sap up the tree and out of the spout and into the pail (or, more recently, into plastic tubing) depends on temperatures that move back and forth across the freezing point in a delicate dance. The best sap flows occur when night temperatures are in the 20s and day temperatures are in the 40s. This normally happens for four to six weeks as the northeastern winter thaws into spring.

With the cold night, the tree absorbs moisture from the ground. When the tree warms up during the day, internal pressure builds and the sap will flow from a tap or even from a broken twig. This productive balance between cold and warm used to occur in Vermont and New Hampshire around the first Tuesday in March. Over the past decade, the right temperature mix has occurred on the average earlier and, more crucially for the economic health of the industry, for a shorter time. The season is over when the nights no longer freeze.

Not only are those crucial times becoming shorter, but sugar maples are moving north. The trees do not get up and walk to Quebec or Ontario when they sense that winters are getting warmer. The existing trees die off; their seeds germinate and do well only in a cooler place. The maple population in general will adjust its range and we'll see a very slow shift in the mix of northeastern trees.

Like Jefferson, we have a pleasing fantasy of the yeoman maple-tapper—a sturdy New Englander right off the picture on the syrup tin, in red and black plaid, driving his horse-drawn sled. (And not speaking French with a Quebec accent.) He's very patient, our ideal maple producer, because it takes 20 to 40 gallons of sap to yield one gallon of syrup. To produce 30 gallons of syrup you need the output of 65 mature trees, according to the Cornell Sugar Maple Research and Extension Program.

As spring comes ever earlier, it's getting harder to keep those mature sugar maples happy. The tree atlas of the U.S. Forest Service predicts that oaks and other trees tolerant of a wider range of temperatures will replace sugar maples as the dominant New England forest tree. Autumn foliage may be a monkish dark brown instead of the breathtaking red and orange and yellow of the sugar maple.

Toward the end of his trip, circling back to Philadelphia, Jefferson shopped for trees at a nursery in Flushing, N.Y. Undaunted, he bought 60 maples for Monticello. They died.

We never did get over our love of cane sugar, but Jefferson would have been pleased to see that for most of the 20^th century, the Northeast produced 80 percent of the maple syrup in the world. Now the figure is 20 percent. We're losing our sugar orchards and, Jefferson would say, we have failed to secure the independence of our country.

There is an International Maple Syrup Institute, a nonprofit group of Canadian and American producers. Any day I bet it will be dominated by those darned Canadians, flaunting their maple leaf flag. The syrup institute will begin to behave like OPEC, threatening to bring us to our knees. Soon we'll be dependent on foreign syrup.

Note: It's not widely appreciated that sugar maples have a yellow-green finely textured flower that comes before the leaves. Should you live in or visit the Northeast in March and April, you'll see a mist of chartreuse in the forest. Appreciate it while the trees are still on U.S. soil.