University of Vermont

Abby van den Berg Taps the Science Behind How Trees Produce Sap

Alum profile

Abby van den Berg pours sap at Proctor Maple Research Center.
Abby van den Berg pours sap at Proctor Maple Research Center.

Research Assistant Professor Abby van den Berg (FOR ‘99; MS-FOR ’00; PhD-UVM ‘06) is a plant physiologist in the University of Vermont’s Plant Biology Department in the College of Agriculture and Life Sciences.  She specializes in the eco-physiology behind how trees, in particular maples, produce sap and how maple sugar makers produce their products.

At UVM’s Proctor Maple Research Center (PMRC) in Underhill, Vermont, Abby studies how to increase productivity and profit of maple operations.  She discovers ways for maple producers to attain better sap yields using sustainable practices that maintain the health and longevity of maple trees in the Northern Forest.

Fascinated early in life with science, biology, and trees, Abby earned all three of her college degrees in forestry and botany at the UVM.  As an undergraduate, she began her study of the chemistry behind development of fall foliage color in sugar maple for her honors thesis with Professor John “Doc” Donnelly. Her undergraduate work transitioned into her master’s research with Doc and then advanced to her doctoral research with Professor Tim Perkins on the physiological and chemical processes that affect anthocyanin pigment production and light absorption in juvenile and senescing maple leaves.

She began working at the PMRC as a research technician after completing her master’s degree in 2001.  With completion of her doctoral degree in 2006, she became a research associate until achieving her current position as a research assistant professor.

With Northeastern States Research Cooperative (NSRC) funding in 2010, Abby, in collaboration with her colleagues at the PMRC, regional extension agents, and sugar makers’ organizations, looked more closely at sustainable tapping guidelines for modern maple syrup production. They wanted to learn if existing, older tapping guidelines are still appropriate for modern sap collection practices, such as the use of higher levels of vacuum, which enable producers to collect more sap.

“The maple industry has about doubled the amount of sap harvested annually per tree since these guidelines were established,” explains Abby.  “With this larger portion of the trees’ carbohydrate reserves being removed, do maple trees still have sufficient growth rates to enable them to replace the non-conductive wood generated annually by each tap hole when existing tapping guidelines are followed?”

Abby and her colleagues measured the growth rates of trees tapped with today’s high yield practices and developed a computer model of the tapping zone of an individual sugar maple. By incorporating multiple factors, such as tree diameter and annual radial growth, the model calculates the amount of conductive wood in the tapping zone of a tree.  The model accounts for an individual producer’s practices (such as tapping depth and number of taps) and estimates whether wood growth will remain at or above sustainable levels over time.

Using the model, Abby discovered that for healthy, overstory maple trees 10 to 12 inches in diameter or greater and growing on good quality sites, the existing, conservative guidelines are likely still sustainable with today’s high volume sugaring practices.  For trees growing on questionable or poor quality sites, she recommends that producers check tree growth rates.

The tool is available for use by maple producers on the PMRC website at www.uvm.edu/~pmrc/.

“Abby's work on sustainability of tapping guidelines is very timely based on the evolution from the older traditional ways of harvesting maple sap in generations past to the new technology that is being applied in the sugar bushes today,” acknowledges Jacques Couture, Chair of the Vermont Maple Sugar Makers Association Board of Directors.  “We are harvesting much larger quantities of sap per tap, so it is very important for our industry to know whether or not what we are doing is having any possible negative effects on our trees. Abby's work will go a long way in helping us figure that out.”

A second NSRC award enabled Abby and her colleagues to discover ways to increase maple producers’ profits by expanding to include possible production of syrup from birch trees.  In Scandinavia and Eastern Europe, inhabitants have collected birch syrup far longer than maple syrup has been produced.  They traditionally drank the sap and made a fermented beverage to preserve it. In Canada and Alaska, birch sap is commonly made into syrup.

Birch syrup is highly valuable and in demand by retail consumers and chefs desiring natural, locally-produced sweeteners and food ingredients. Many Northern Forest sugar bushes have a plentiful source of birch trees, producers already have the equipment, and birch sap flows at the end of the maple season, so producers could extend their season and add to their profits.

To confirm this, Abby tapped paper birch trees at the PMRC during two sap flow seasons and determined that on average 0.14 gallons or 18.3 ounces of syrup can be produced annually from a paper birch tree tapped using modern equipment and practices. With consultation from Glenn Rogers, a retired UVM Extension agent, Abby conducted the financial analysis and confirmed that these yields could be sufficient to result in a net profit when added to an existing maple operation.

“Maple producers in the region face increasing challenges to maintain profitable operations while keeping syrup prices affordable due to rising costs of production,” states Abby. “Adding birch syrup production may be a practical and ecologically-sustainable way for producers to increase revenues and, thus, the profitability, of maple operations.”

“Dr. van den Berg has been doing important work at the Proctor Maple Research Center to the benefit of all the maple industry,” shares David Marvin, owner of Butternut Mountain Farm in Morrisville, Vermont. “Whether it’s analyzing the impacts of technology, looking for opportunities to expand the production base, or looking at influences on the health of maple trees, her work contributes to science-based decision making by sugar makers.”

Abby continues her research on fall foliage color and the impacts of climate change.  She is also involved in a 10-plus year study on long-term effects of tapping on tree growth and a study of the chemistry of maple syrup and how processing practices impact quality and flavor.

She lives in South Burlington with her fiancé Chris Driscoll, an accountant. When she isn’t working in the lab or the woods, Abby can be found tapping into her musical talents and interests by playing the piano or attending musical events.