Warmer world puts squeeze on U.S. maple syrup

By Scott Malone

LUDLOW, Vermont (Reuters) - In the seasonal rhythm of New England, March marks the start of sugar season, when farmers tap thawing maple trees for their sap. But some worry that a warming climate is endangering their future.

Long skeptical of claims that the planet is warming as a result of human activity -- the release of greenhouse gases through the burning of fossil fuels -- syrup-maker Doug Rose said he's started to wonder.

"I've always been, 'Oh, global warming, I don't know about that.' But now I do think we need to start thinking about it, because we are seeing changes," Rose said in an interview at Green Mountain Sugar House in Ludlow, a rustic Vermont town settled in 1761.

"We're seeing production go down, we really are."

His concerns, shared by several syrup-makers around the state, were piqued by a study by the Proctor Maple Research Center at the University of Vermont, which showed that the month-long season has gotten about three days shorter over the past four decades.

"What we're seeing is about a 10 percent reduction in the season," said Timothy Perkins, the center's director.

If that trend continues, it could mean that one day sugaring -- the process of boiling the sap down to sweet, aromatic, amber maple syrup -- would no longer be economically feasible in the region.

Perkins is currently working on a study on how climate change could change maple production in the region over the next half-century.

"You don't need to get to the point where you have zero (sap production) before people stop making maple syrup," Perkins said. "They're going to stop doing it when the economics of it no longer work."

Vermont last year was the largest producer of maple syrup in the United States, supplying 32 percent of the country's 1.4 million gallon (5.3 million liter) total output, according to Agriculture Department data. In 2005, the most recent year for which data is available, U.S. farmers produced $37.1 million worth of maple syrup.

MODERNIZATION OF MAPLE

The traditional way of making maple syrup was labor-intensive. Farmers bored holes about 1.5 inches deep into maple trees, inserted taps, hung buckets on the side of the trees and waited for the sap to start to run. Then they would return each day to empty the buckets and carry the sap back to a "sugar house," where they boiled it down to syrup.

Sap flow is stimulated by swings in temperature. At night, when the temperature drops to around 20 degrees Fahrenheit (-6.66C), the trees suck up water from soil, which they convert into sap. During the day, as the tree warms to about 40 degrees Fahrenheit (4.44C), the sap expands and runs out the hole.

Once the temperature stops dropping below freezing overnight and the trees start to produce buds, the sap starts to taste more bitter and the syrup season ends.

While the tree's role in the process remains the same, almost everything else has changed. Today most syrup-makers use plastic tubing to collect the sap, which saves daily trips to each tree.