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On a raw late-winter afternoon in March, 10 Dartmouth students participating in an immersion program sponsored by the Sustainability Office trudged up a steep hill and into the woods, navigating an icy, rocky trail and a thin layer of fresh snow. 

Members of the Sugar Crew headed for the 5-acre sugarbush across Route 10 from the , part of a larger forest used as a kind of living laboratory for research. Conditions for sugaring—daytime temperatures in the 40 degree range, nights below freezing—had been good. 

Leading the group was , a Guarini School of �鶹��Ƶ and Advanced Studies PhD student in the who is researching the science, culture, and history of maple sugaring.

The students watched Sigman going from maple to maple, taking down small plastic containers of clear sap that will be tested for such contaminants as PFAS “forever chemicals” and heavy metals, like lead. Lead occurs naturally in many soils, typically in amounts small enough that they are not thought to pose a risk to human health. However, in other areas, soil lead can be much higher as a result of industrial land use or from flaking lead paint on older houses. 

High soil lead levels pose a risk to human health, particularly for children, and complicate activities such as urban farming. Sigman also removed control containers filled with “ultrapure water” that is known to be PFAS-free. If the latter contain contaminants, then she knows that the sap was not the source. 

Wearing disposable gloves to prevent cross-contamination, Sigman enlisted the help of the students, who also donned disposable gloves to hand her equipment as she removed the bottles from the trees.

The Dartmouth sugarbush is one of 10 sites in Connecticut, Massachusetts, Vermont, and New Hampshire where Sigman is collecting both sap and soil samples from sugar, red, and Norway maples. 

Eight of the sites are in areas where she expects to find contamination, which is not where most sugaring takes place. That includes a hillside near the ChemFab factory in North Bennington, Vt., a former automotive scrap yard in the Upper Valley, and a Superfund site where chemical dumping used to take place.

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A red maple in the Dartmouth sugarbush. (Photo by Katie Lenhart)

Sigman is also sampling from backyards, tree belts, and parks around different neighborhoods in her old stomping grounds in New Haven—a city with a long history of industrial activity that left behind significant contamination. The Dartmouth site and the Yale-Myers Forest in Connecticut serve as control sites because they have no known history of contamination, she says. Sigman brings all her samples to the Connecticut Agricultural Experiment Station in New Haven for testing. 

A Colorado native and Yale undergraduate, Sigman took a class about maple syrup at Yale, when she was studying towards dual master’s degrees in forestry and public policy. The course was taught by Yale’s director of forest and agricultural operations, Joseph Orefice, who now serves as co-principal investigator on the project. Orefice had mentioned that it was possible to tap Norway maples, which are common in urban and suburban environments and often considered an invasive species, but aren’t necessarily thought of as sugaring maples.

Already active in urban agriculture, Sigman turned to sugaring during the COVID-19 pandemic, when she tapped Norway maples in the backyard of her New Haven house. The syrup was excellent, she says, and “it’s a good way to make use of a much maligned tree that a lot of people look at and think doesn’t have a lot of uses.” 

At first, she thought she was the only person making maple syrup in New Haven, a city of 135,000 on Long Island Sound. That wasn’t the case. 

“It turned out there were quite a few people making syrup from trees in New Haven,” she says, sometimes as part of longstanding communal projects that brought people together.

Thrilled to make her own syrup, Sigman gave a small bottle to someone who asked her whether they had to worry about lead in the syrup, given the prevalence of lead residue in post-industrial urban sites—one of which happened to be across the street from Sigman’s house. “That gave me pause,” she says. 

As a test, Sigman brought her homemade syrup from New Haven to the agricultural experiment station, which found that it contained “significant concentrations of lead.” She strained her syrup through a low-cost felt filter, retested the syrup, and found it was safe to use. 

That initial question, and her own experiences, led to her long-term research. She was drawn to Dartmouth both for the interdisciplinary EEES program, and because of Dartmouth’s location in what she calls “maple country.”

To make syrup, sugarmakers boil the sap to evaporate the water and concentrate the sugar. The rough ratio is 40 gallons of sap from a sugar maple yields one gallon of syrup, though for Norway and other maples with lower sugar content, 60 or more gallons of sap might be required.

Sigman’s immediate objective, she says, is “to understand if trees growing in contaminated soils also have contamination in their sap. If the trees do have contamination in their sap, then we want to understand what happens to that contamination as the sap is boiled into syrup and if there is anything you can do to remove the contamination through filtering.” 

Her long-term goal is to “come up with a protocol that an urban maple producer—or any maple producer who is concerned about contamination—would be able to follow at home to understand whether and how they can safely tap their trees.”

Many larger-scale producers use filter presses as a routine part of their operations, but such equipment is generally too large and cost-prohibitive for community-scale sugaring, especially in lower income areas. “If we do find contamination,” Sigman says “we want to also identify low-cost, relatively simple solutions for people to mitigate the problem.”

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Sigman’s dog Toly came along for the expedition in mid-March with the Sugar Crew. (Photo by Katie Lenhart)

The study is not evaluating sap or syrup from producers who use professional-grade equipment and filters, and Sigman is only sampling in areas with known contamination. 

There’s no reason to believe that maple syrup bought in a store contains unsafe levels of contaminants, Sigman stresses. “Most maple producers are very aware of food safety issues,” she adds. “Our study is really about understanding the unique challenges and opportunities for sugaring in nontraditional landscapes, like cities, or other areas with histories of contamination.”

, an assistant professor in the and EEES, is Sigman’s adviser. Greenleaf tends to work with students doing environmental anthropology or political ecology research. Sigman’s project calls not only on these fields of study, Greenleaf says, but also on ecological research. 

“It is a great example of interdisciplinary work and an innovative project that connects Dartmouth with the people around us,” Greenleaf says.

The Dartmouth sugarbush taps around 125 trees, which yield annually about 15 gallons of syrup, says Jack Walker ’22, the Organic Farm program coordinator in the . 

In the Dartmouth sugarhouse, Sigman talked to the Sugar Crew about how she got into tapping, and what she gets out of it. “I found it so life affirming and wonderful,” she tells them. The challenge with urban agriculture, Sigman says, is “systemic toxicity and these legacies that are so much bigger in time and scale than the individual little plot of land that you are trying to make maple syrup, or grow tomatoes, on.”

In a larger sense, Sigman is interested not only in the “how-to” of maple syrup, but also in the longstanding history of and culture around sugaring, which can be traced back to the tapping of maples by Indigenous peoples in the northern woodlands of North America.

Manu Gupta ’27, a captain in the Sugar Crew, grew up in the San Francisco Bay area but his mother is originally from Quebec City. She encouraged him to become involved in the Sugar Crew. “I wanted to learn more about the process and wanted to know the community more,” Gupta says.

Trevor Gittes Taplin ’25, who is originally from Miami, says the workshop was great. “I’ve been learning about New England forests and indigenous history,” he says.

As she goes forward, Sigman plans to incorporate social science research methods. “It’s really fascinating to be immersed in so much maple culture here in the Upper Valley, and I want to understand more about what underpins that culture,” she says. “So much land and knowledge is required to make maple syrup. Who has access to that land and that knowledge? What does maple mean to them? What keeps people going back to the sugarhouse, year after year? And what sorts of barriers might be preventing people from being able to participate in this tradition? Sugaring is such a special experience—and it makes me wonder what the world could be like if more people had access to it.”