Scientists say earlier maple sugaring seasons part of climate change trend

Editor’s note: This story is by Carly Brown, a graduate student in the Field Naturalist Program at the University of Vermont.

Steam escaping from the sugar shack at Bragg Farm in East Montpelier.

With temperatures as high as 45°F in January it is easy to assume this maple sugar season is doomed. In fact, it is too early to predict what the season will bring, says Tim Perkins at the Proctor Maple Research Center. Sap flow in trees, and therefore the maple syrup production, is almost entirely dependent on the weather that occurs during the actual maple sugar season in the spring.

So while the warmer weather has left many of us in tee shirts and mud boots, maple trees are still holding on to their starch. Starch is the carbohydrate that plants use to store the sugars produced in the summer. In the fall, the trees will convert many of these sugars into starch to store them for the winter when they are not needed. They convert the starch back to simple sugars, the sweet sap we collect, in the spring in preparation for budding.

Perkins cited research that showed that sugar maple trees now release their sap approximately 8.2 days earlier and stop producing usable sap 11.4 days earlier than they did 40 years ago. This translates to an approximate 10 percent loss in the duration of the season. These trends coincide with regional climate changes recorded in the last 50 years.

Maple sugarers are not the only ones noting a change in the seasons. The USDA recently released an updated 2012 Plant Hardiness Zone Map that guides gardeners by mapping the country by zones, which reflects the average annual extreme minimum temperatures from 1976-2005. Plants can be classified according to the zone in which they thrive. Much of Chittenden County jumped up a half of a zone as compared to the 1990 map; a potential leap of 5 degrees Fahrenheit. The same warming trends that drove the change in the zones could affect the long-term health of sugar maple populations by altering their range, as modeled by the USDA Forest Service.

The seasonal shifts can affect maple syrup producers in several ways. A shorter maple season can decrease maple production over the season, as there are fewer days of sap flow, Perkins says. Surprisingly, he continued, there has not been an overall decrease in the volume of maple syrup produced thus far which is attributed to evolving technology that has allowed for double the yield per tap. In addition, the maple syrup economy is favorable, triggering producers to expand their operations.

Shifts in the start of the season can lead to producers tapping their trees too early or too late. Producers traditionally used historical dates that sap flow began to determine when they would tap their trees. They optimize their maple syrup yield by tapping the trees just before the sap flows. As the sap flow trend changes, predicting the start of the flow becomes more difficult.

Tapping the trees too early may lead to “drying out”. Drying out refers to the tree reacting to microorganisms by plugging the tap hole. Tapping a tree exposes the unprotected tree tissues to the environment. The earlier in the season a tree is tapped, the longer they are exposed to potential microorganisms. Producers that tap their trees after the season has started are missing out on valuable collection time.

Brad Lewis, who manages the sugar operation at Johnson Farm Teats and Taps in Williston, installed 1,000 taps just before Valentines Day. In the past, Lewis said, Vermonters used to follow the guideline “tap by Town Meeting Day.” Lewis says they are tapping earlier for two reasons: to capture some of the sap from the increasingly early thaws that periodically take place in January and February, and because advancements in equipment have allowed them to tap earlier without the taps “drying out”. Tapping too early in the season could mean damage to his maple sugaring equipment if the sap freezes.

What does this all mean for the sugar maple tree that stretches its branches over my front yard? In the short-term, not much. Producers will still tap their trees this year, though maybe a bit earlier than 40 years ago, and the sap will still flow. Scientists predict changes in the geographic range of sugar maples as the climate changes.