In the predawn darkness of Putney's maple-studded hills, Don Harlow begins his mornings by coaxing his truck down a rutted forest path. At the end is a cylindrical tank twice his height into which hundreds of gallons of sweet maple sap have flowed, siphoned through 11,000 taps and 40 miles of plastic tubing.
Mr. Harlow carts the sap up to his sugaring house to boil it down to syrup. It's a ritual Harlow loves, and one his family has performed for more than 100 years - albeit with horses and metal buckets in earlier days.
Despite having one of the most coveted labels in the industry - "pure Vermont maple syrup" - on their products, Harlow and other sugarmakers in the state are struggling to compete with Canada, where maple syrup production has more than tripled since the 1970s.
While much of Canada's syrup boom can be attributed to generous subsidies from the government, as well as its aggressive promotion of maple products, some researchers believe another factor may be coming into play: climate change.
As temperatures rise and weather patterns become more erratic, New England's maple trees are facing growing threats that may eventually force syrup aficionados and leaf-peepers out of the region and into Canada.
When Harlow took over the farm in the 1950s, the US produced 80 percent of the world's maple syrup, with Canada supplying the remaining 20 percent. Now the countries' market shares have flip-flopped, with Quebec alone providing over three-quarters of the global supply.
"Due to changes in both sap collection technology ... and climate ... the maple syrup industry is migrating from New England into Canada," concluded the New England Regional Assessment Group in a 2001 report. The study, spearheaded by University of New Hampshire researchers, also predicted that if current climate projections hold true, New England forests will be dominated by oak and hickory trees - not maples - by the end of the century.
Admittedly, maple trees won't flock northward one spring like Canada geese. Rather, the transformation of New England forests will come by a gradual change in the competitive balance of one species over another, says Timothy Perkins, who is nearing completion of a research project on the impact of global change on the maple sugar industry.
A projected rise in temperature of 6 to 10 degrees F. over the next century could heighten drought conditions, air pollution, and pests - stress factors that affect maples more than oaks or hickories.
But it's difficult to tell the degree to which climate change is affecting New England maples at the moment, says Dr. Perkins, director of the University of Vermont's Proctor Maple Research Center.
But a change that does present an immediate threat to the industry, he says, is a temperature-driven trend toward shorter sugaring seasons in New England but not in Canada.
At Morse Farm in Montpelier, Vt., that meant the sap "crop" was only one-third its usual size this year. The season started late, but winter morphed into spring practically overnight, reducing the number of freeze-thaw cycles that propel sap flow.
Just as air whistles out of a pierced car tire, sap flows out of a tree because the pressure on the inside of the tree is greater than the pressure outside the tree.
When the air temperature drops below freezing, a maple acts as a giant suction system, bringing the sap out of its branches and back down to its roots.
When the temperature rises above freezing, the action is reversed, sending sap surging through the branches - and out of any "wound" in the tree, such as the holes drilled for taps.
Traditionally, northern New England's climate has provided the optimal freeze-thaw patterns for sugaring. But in recent years, the transition from winter to spring has accelerated, leaving fewer days for the mercury to hopscotch across Vermont thermometers' 32-degree F. mark.
In Canada, however, warmer daytime temperatures have increased the number of freeze-thaw cycles there.
Technological improvements have also changed the season's timing in both countries. Back in the day of metal buckets, sugarmakers were wary of tapping their trees too early, when temperatures were liable to drop significantly below freezing for long periods.
"If [the sap] freezes hard, it can bust your bucket," explains fifth-generation sugarmaker Rick Marsh.
But now, with plastic tubing, sugarmakers can tap weeks earlier and get more out of their taps. This is especially true for those who have installed vacuum systems that draw more sap than would drip into a bucket. In Canada, tubing has facilitated greater sap collection in areas where deep snows make it difficult to reach individual trees for daily collection.
In recent years, Canada's booming syrup production flooded the global market, driving prices down and putting the squeeze on US sugarmakers. Five years ago, Harlow ended the season $30,000 in the red, but couldn't raise his prices to cover costs because of the low prices of Canadian syrup.
Jacques Couture, president of the Vermont Maple Sugar Makers' Association, has found himself in a similar position. But he notes that as someone who makes his living off sugaring, "It's pretty hard for me to criticize someone from another country who's doing the same thing."
"To the Canadians' credit, they've put a lot of effort into developing markets - not just in Canada, but in the world," notes Mr. Couture, who has mail-order customers in China, Japan, and Europe.
Back in Putney, Harlow's jovial tone turns somber as he acknowledges his biggest competition comes from Canada.
Is he worried? "Oh no, we can sell Vermont syrup anytime," says the fourth-generation sugarmaker. "The worst Vermont syrup I ever had was fantastic."