by Emily Carey
As the maple industry has evolved, sugarmakers have had to adjust their operations to adopt new knowledge and research. Sustainable tapping practices help to conserve this industry and provide a bright future for producers.
Abby van den Berg of the UVM Proctor Maple Research Center provided insight on sustainability in maple production during her presentation, “Sustainable Tapping Guidelines for Modern Maple Sap Collection Practices,” at the Northern Hardwood Conference.
Each year, when a tree is tapped for sap collection, an area directly above and below the tap becomes permanently non-conductive wood. This non-conductive wood does not allow for the collection of water or sap if someone were to tap into that area of the tree. With each tap that creates non-conductive wood, the tree also loses some of its carbohydrate reserves. However, as van den Berg explained, each year, radial growth adds conductive wood and replaces some lost carbohydrates.
This understanding of conductive and non-conductive wood and tree growth plays an important role in defining sustainable sap collection.
Although the term sustainable is defined differently by each person, van den Berg said generally, for tapping to be sustainable, it must not generate more non-conductive wood than can be replaced with annual radial growth and it must not remove an amount of carbohydrate resources large enough to impact growth rate or health (replacement of conductive wood).
“If we’re looking at and defining sustainability in that very simplistic way, one thing that kind of rises to the surface and is very apparent is that tree radial growth rates underlie the sustainability of any of our tapping practices,” van den Berg said.
This addition of new conductive wood not only contributes to the sustainability and health of the tree, but it also works to increase the yield of sap collected.
“If tap holes are drilled into nonconductive wood, the sap yields will be very, very low,” she explained. “By maintaining a high level of conductive wood, particularly in the tapping zone of a tree, that is going to result in sustainable sap yield over the long term from the perspective of the main producer.”
Tapping guidelines help ensure that conditions of sustainability are met. “Basically, these are just a set of voluntary, informal best practices that exist within the maple production industry that specify practices like the minimum tree diameter for tapping, the minimum length of the sap drop line… also things like the maximum tap hold or spout size and its maximum depth,” van den Berg said.
A problem facing the sustainable maple industry is that although there are many variations of the tapping guidelines, these guidelines are based off tapping practices and guidelines from the 1900s, when buckets and gravity used to be the main method of production. The technology and methods have improved, and the tapping guidelines need to move to meet them.
“We’ve had pretty radical improvements in equipment and technology and practices that have allowed us to basically double or more the amount of carbohydrate reserves we are able to extract from trees each year,” van den Berg said. “We’ve gone from two-tenths of a gallon equivalent per tree to anywhere from a half gallon syrup equivalent or more using these modern practices. The question becomes, what tapping practices are appropriate and sustainable for use with these current sap collection practices? Are the tapping guidelines that we’re already using good enough?”
Sustainability comes back to the radial growth. The importance of the tree’s radial growth was a point that van den Berg kept prioritizing.
During a research project examining tree cores to study the conductivity and non-conductivity, her team was able to calculate average annual growth rates for trees and created a set of equations that estimated the amount of conductive and non-conductive wood in the tapping zone of trees over a set of time. Dubbed the “Tapping Zone Model,” these equations were used to estimate the minimum growth rates required to reach sustainability.
“The average growth rates for trees that have been tapped with these high yield practices were generally higher than the estimated minimum,” she said. “This looked reassuring that the growth rates of trees that we were tapping with these practices were generally acceptable and maintained a sustainable level of conductive wood when we were following the existing tapping practices … in the industry at the time.”
The research focused on three groups of collection practices: untapped trees, gravity and vacuum. Since the research started in 2013, there have been no significant differences in the growth rates of any of the trees. Although, looking closely at the percentage of growth, the trees in the vacuum group grew 1% less than the other groups.
However, these results were averaged. Across the board there were mixed results, as it is impossible to control the conditions facing every tree. Between 27% and 41% of individual trees had growth rates below the estimated minimums with standard tapping practices.
This study will continue to be looked at and evaluated over time to gauge whether these small fluctuations will change or remain constant.
“Radial growth is the linchpin of sustainability; however, the tapping method that producers choose also impact sustainability,” van den Berg said.
The tree size and tapping practices determine the total volume of the tapping zone. The amount of conductive wood available in the tapping zone is determined by the dropline length, tapping depth and tree circumference. The practice of tapping each producer chooses to use directly plays a role in what the total volume of non-conductive wood is added annually to the tree proportional to the size of the taphole.
“For example, by simply increasing the length of the dropline that we used, we reduced the number of trees with growth rates below the minimum rate to 8% from 27%,” van den Berg explained. “Simply increasing the total volume of the tapping zone and giving us more potential conductive wood to work with increases the likelihood of sustainability of these practices quite substantially.”
Additionally, increasing the dropline length and reducing the tapping depth further reduces the number of trees below the growth rates below the minimum. These results show that changing tapping practices improves sustainability.
To increase sustainability, producers need to select tapping practices that can and need to be adjusted to result in long-term sustainable outcomes. Practices should be selected based on radial growth rates, tree health and pre-existing non-conductive wood. Future recommendations will integrate results of experiments on long-term sap collection impacts on radial growth.
Van den Berg stated, “What this means for maple production is that appropriate forest management to manage the growth rates for crop trees is essentially the starting place for all the sustainability for maple production.”