Last summer, tent caterpillars infested the sugar bush at Umbrella Hill Maple in Hyde Park, Vermont, causing almost complete defoliation in some areas of the forest.

Despite the severity of the devastation, only a small percentage of the infested trees were the red maples and sugar maples that sugarmaker Arnold Piper has been tapping for five seasons. The reason: The sugar bush is filled with multiple tree species, including beech, white ash, yellow birch and cherry that helped take the pest pressure off the maples, preserving their health.

“Having a diversity of species has really paid off for me,” Piper said.

Maintaining a diverse species mix is just one of the sustainable practices Piper employs at the Vermont-based farm. In addition to responsible tapping to protect the maple trees, he also focuses on timber stand improvement through selective thinning, removal of dead or diseased trees and reducing invasive species that can prevent seedlings from sprouting.

“We are definitely in the business of land use management,” he said.

For producers, success lies in preserving forest resources. Maple syrup might be one of the oldest agricultural crops but, without careful attention and proper care, sugar bushes will experience declines in health and productivity, reducing profitability for sugarmakers. Sustainable forest management is a key element for ensuring the long-term viability of maple syrup production.

“People assume that tapping trees is sustainable because it’s been done for so long, but it’s important to get data on a practice to see what kind of impact it’s having, which is where research comes in,” said Mark Isselhardt, maple specialist with the Proctor Maple Research Center at the University of Vermont.

Sweet research

Most of the current research being done on maple production involves assessing the impact of high vacuum extraction on maple trees.

“Modern sugaring doesn’t appear to cause acute stress, but we’ve only been using high vacuum extraction for 10 to 20 years, so we need to be vigilant about how new technology could be affecting a very traditional crop,” Isselhardt said.

At the Proctor Maple Research Center, researchers have found that four years into a 10-year project that compares previously untapped trees to trees tapped with traditional gravity extraction and high vacuum extraction, the modern methods have no apparent impact on tree growth.

Additional research conducted at the center found that current conservative industry tapping guidelines did not damage a greater volume of wood that could be replaced with annual radial growth or remove enough carbohydrates to impact the growth rate or the replenishment of functional wood, further supporting the notion that sustainable forest management and modern sap collection technology can coexist.

“Even with advances in technology, these are hardy, long-lived perennial plants, and there is no anecdotal or investigative evidence of sugaring being the cause of tree death or decline,” said Isselhardt. “But there is low-level chronic stress.”

Maple trees also face seasonal pressures such as pests and severe weather events that cause cumulative stress, making it more difficult to recover from tap wounds. Over time, if the trees aren’t growing well, producers will hit brown wood each time a new tap is inserted, which Isselhardt noted, will have a direct impact on production and profits for sugarmakers.

“It can be tempting to think, ‘There are zero documented cases of tapping alone causing trees to die,’ but we don’t want that to be the standard of sustainable sugar making,” he explained.

What Is Sustainable Tapping?

The Proctor Maple Research Center at the University of Vermont developed guidelines for sustainable sap collection to help ensure that the volume of nonconductive — brown — wood created by tapping is less than the volume that can be replaced during annual growth.

Their recommendations for healthy trees with dominant or co-dominant canopy positions include four basic guidelines for tapping:

  1. A minimum of 12 inches in diameter at breast height
  2. A minimum dropline length of 30 inches
  3. A maximum tapping depth of 1.5 inches
  4. A spout size of 5/16 inch

The guidelines also advise a conservative approach to adding a second tap, choosing only healthy trees with excellent growth rates and a diameter greater than 18 inches at breast height. Continually hitting brown wood with a second tap is a sign that tapping intensity should be reduced.

Taking a sustainable approach to tapping helps prevent sap extraction from compromising tree health, ensuring the long-term sustainability of the sugar bush.

Tapping the experts

At Bascom Maple Farms in Alstead, New Hampshire, sustainable forest management has been an essential part of the operation since the 1960s, but the farm did not formalize its efforts until 2012 when second-generation sugarmaker Bruce Bascom created a written management plan.

“Our grandfathers knew how to manage a stand of trees but we’ve gotten away from that,” Bascom said. “Current sugarmakers are spending a lot less time in the woods and it’s impacting the forests.”

Modern extraction methods might make tapping easier but losing the connection with the forest – or not understanding what can impact its health – could cause production (and producers) to suffer.

Climate change has increased the numbers of invasive species and altered deer populations, leading to more deer browsing on saplings and impairing their growth. To encourage resilience to environmental stresses, sustainable forest management is more important than ever.

Although data on the number of producers with forest management plans is scant, an older survey by the Department of Natural Resources and Cornell University found that just 8 percent to 13 percent of producers had written plans; producers with fewer than 99 taps were just as likely to have written management plans as producers with more than 2,000 taps.

Of producers with written plans, the survey found that fewer than 17 percent of those plans were prepared with the support of a professional forester. Perhaps even more worrisome: Fewer than 29 percent of producers with written plans used the information to guide their decisions in the forest.

“Sugarmakers have to do active management and have a plan to guide them,” Isselhardt said.

Bascom worked with the local forester to craft the plan for Bascom Maple Farms, which spans 3,000 acres and includes 92,000 trees. As part of the plan, he thins the forest each season, removing underperforming trees to support their stronger neighbors.

“When nature takes its course, the forest gets crowded. If you leave all the trees, it stunts their growth,” he explained. “You can’t increase the growth rate of trees but thinning out the competition increases the health of the trees that remain and stronger trees have higher sugar content. There isn’t a single year that we don’t cut trees.”

Bascom avoids working in areas of the forest that are under stress from pests or natural disaster to give those trees a chance to bounce back and solicits the advice of his forester as conditions change.

“We’ve thinned out areas or cut stands of trees in a different order than we planned based on his recommendations, he said.”

Umbrella Hill Maple also relied on a team of experts to help craft its sustainable forest management plan. In addition to input from the Lamoille County forester, Piper sought out advice from the U.S. Department of Agriculture’s Natural Resources Conservation Service and Audubon Society. He is also active in state and county sugarmakers associations to learn about best practices.

“There are great state and federal programs to support sustainable forest management,” Piper said.

The resulting plan, which Piper consults when making decisions about forest management, includes strategies for thinning the forest and maintaining native underbrush and snag trees, which provide nesting sites for birds that eat caterpillars and other pests.

Like other producers, Piper and Bascom follow conventional tapping guidelines, only placing taps in healthy trees that are at least 12 inches in diameter and limiting the use of two taps to trees that are 20 inches (or more) in diameter.

Producers using vacuum extraction may also have an edge when it comes to forest management. Vacuum pumps minimize the number of tap holes in trees and the tubing allows producers to maintain a more diverse and lush underbrush.

The less time producers spend walking from tree to tree for sap collection, the less they compact the soil or disturb nesting sites.

Although tapping is not likely to cause the demise of a sugar bush, poor forest management practices can turn a thriving sugaring operation to one that is all tapped out.

“We want to manage our forests in the most sustainable ways possible to preserve them for future generations and increase the value of the land,” Piper said. “When you take care of what you have, you get more out of it.”