University of Vermont

Proctor Maple Research Center - Underhill Center - Vermont

Proctor Center Research Center Staff

Proctor Maple Research Center Staff


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Dr. Timothy Perkins, Director
Dr. Abby van den Berg, Research Assistant Professor
Brian Stowe, Research Technician
Mark Isselhardt, UVM Extension Maple Specialist
Miriam Pendleton, VMC Site Operator


Timothy PerkinsTimothy Perkins, Director
Ph.D. Botany 1991, University of Vermont
Telephone: (802) 899-9926  Email:

Department of Plant Biology Faculty Research Profile

    As Director of the Proctor Center, I determine the type and course of scientific studies conducted here.  My primary role, aside from conducting my own research, is to ensure that the PMRC staff has adequate resources to conduct their work, and that the research is pertinant to the PMRC mission, funding, and interesting to the maple industry.  To this end, I am responsible for writing and managing grant proposals, reporting our progress to funding agencies, and serving as budget manager and overall station supervisor.
    My personal research interests involve long-term monitoring of forest health, and the relationships among tree health, growth, stress, and nutrition.  I am currently investigating the effects of air pollution and global change on forests,, as well as several other projects aimed at improving sap and syrup production. I have also been involved in the Camels Hump Vegetation Survey, a project to monitor the long-term health of forest communities.

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Abby van den Berg, Research Assistant Professor
Ph.D. Botany 2006, University of Vermont
M.S. Forestry 2000, University of Vermont
B.S. Forest biology 1999, University of Vermont
Telephone: (802) 899-9926   Email:

Much of my research focuses on the ecophysiology of maple sugaring, including the effects of tapping and carbohydrate extraction on tree growth and health, the physiology of stem pressure and carbohydrates in xylem sap, and ultimately on helping to develop management practices and tapping guidelines to ensure the long-term sustainability of maple syrup production. Recently, my work has expanded to include studying the physiology of stem pressure development in birch trees, and investigating sap yields and the potential profitability of adding birch syrup production to existing maple operations in the Northeastern US.

Maple syrup is Vermont’s signature agrifood product, and another area of my research is focused on the chemical composition and flavor of maple syrup, particularly on gaining a better understanding of the compounds important to its flavor profile, and on how factors such as the environment, processing technologies, and management practices might affect its composition and flavor. Most recently, we have studied the impacts of modern sap processing technologies, such as reverse osmosis, on the composition and flavor of the maple syrup produced.

I also study the ecophysiology of anthocyanin pigments, particularly the potential effects of climate change on the development of the anthocyanin pigments in autumn senescing leaves that are responsible for the highly-prized display of autumn coloration in Vermont.

Selected publications

van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2012. Maple syrup production with sap concentrated to high levels by membrane separation: effects on syrup chemical composition and flavor. International Sugar Journal 114:572-576.

van den Berg, A.K. 2012. Defining modern, sustainable tapping guidelines for maple syrup production. Northeastern States Research Cooperative, 22p.

van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2011. Effects of producing maple syrup from concentrated and reconstituted sap of different sugar concentrations. International Sugar Journal 113:35-44.

van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2009. Air injection into concentrated maple sap during processing: impact on syrup composition and flavor. Journal of the Science of Food and Agriculture 89:1770-1774.

van den Berg, A.K., Vogelmann, T.C. and Perkins, T.D. 2009. Anthocyanin influence on light absorption within juvenile and senescing sugar maple leaves – do anthocyanins function as photoprotective visible light screens? Functional Plant Biology 36:793-800.

Perkins, T.D. and van den Berg, A.K. 2009. Maple syrup – production, composition, chemistry, and sensory characteristics. In Advances in Food and Nutrition Research (Ed. S.L. Taylor), 56:103-144. Academic Press, San Diego, CA, USA.

van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2009. Effects of air injection during sap processing on maple syrup color, chemical composition and flavor volatiles. International Sugar Journal 111(1321):37-42.

van den Berg, A.K. and Perkins, T.D. 2007. Contribution of anthocyanins to the antioxidant capacity of juvenile and senescing sugar maple (Acer saccharum) leaves. Functional Plant Biology 34:714-719.

Perkins, T.D., Morselli, M.F., van den Berg, A.K. and Wilmot, T.R. 2006. Maple chemistry and quality. In North American Maple Syrup Producers Manual (R.B. Heiligmann, M.R. Koelling, T.D. Perkins, Eds.) pp 294-300. The Ohio State University, Columbus, OH.

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Brian Stowe, Woodlands & Sugaring Operations Manager
B.S. Forestry 1985, University of Vermont
Telephone: (802) 899-4923  Email:

    I am the woodlands and sugaring operations manager at the Proctor Maple Research Center.  My position emphasizes sugarbush management, maple tubing layout, upgrades, repairs, and the annual production of maple syrup.  I am also involved in designing, building, and maintaining various studies centered around maple sap collection and maple syrup production techniques and assisting in many of the studies on forest growth, health, and nutrition.
   The Proctor Center is in a unique situation in that we have a state of the art research facility smack dab in the middle of a production sugarbush. This allows the rapid transfer of theory and new techniques between maple production and pure science.  Running a sugarbush allows us to encounter the same problems and issues that other sugarmakers are dealing with.  In this way, we can relate to the maple community and better serve their needs.
    I encourage everyone to come pay us a visit.

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Mark Isselhardt, UVM Extension Maple Specialist
M.S. Plant Biology 2012, University of Vermont
Telephone: (802) 899-9926  Email:

My research interests include the dynamics of nonstructural carbohydrate in sugar maple (Acer saccharum Marsh.), how modern production methods impact flavor and chemistry of maple syrup improving the efficiency of sap collection equipment. As a research associate at the Proctor Maple Research Center my duties include the design and execution of experiments related to the practice of maple syrup production. I am also involved with experiments related to white birch (Betula papyrifera Marsh.) syrup production.

I have published articles and technical pamphlets related to my work, presented to professional maple groups in the US and Canada and fielded sugaring related questions from preschoolers on up.

I work closely with Drs. Tim Perkins and. Abby van den Berg on experiments related to the long term sustainability of syrup production, maintaining high yields of sap collection and how modern processing technology impacts the quality of pure maple syrup.

Selected Publications

Isselhardt, M.L., van den Berg, A.K., and Perkins, T.D. Chemical Composition of Scale in Maple Syrup Evaporators, Maple Syrup Digest, December 2012 (pp. 23-28).

Isselhardt, M.L., Carbohydrate reserves and growth response in Sugar Maple (Acer saccharum Marsh.) under two levels of spring xylem sap extraction. October, 2012. M.S. Thesis, University of Vermont, Burlington Vermont.

van den Berg A.K., Perkins, T., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2011. Effects of producing maple syrup from concentrated and reconstituted sap of different sugar concentrations. Int. Sugar J. 113: 35 44.

Isselhardt, M.L. 2011. Estimating Twig Starch Content in Sugar Maple (Acer saccharum Marsh.): Evaluation of the Visual Technique. Maple Syrup Digest (pp. 13-17).

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Miriam Pendleton, VMC Technician
B.A. Art 1978,
University of Vermont
Telephone: (802) 899-9926  Email:
Mim Pendleton

    I'm the Vermont Monitoring Cooperative  (VMC) site operator. My responsibilities include collecting samples, field analysis and preparation of samples for shipment, and maintenance of the equipment. 
There are two VMC sites at PMRC; one is an air quality (A.Q.) site and the other is a forest canopy tower. The tower site is being reconstructed after some intense winds tipped it from its base last winter. The tower had been the site of some first-ever mercury flux measurements with Eric Miller of Ecosystems Research Group, LTD as principle investigator. A grant through the EPA and administered by VMC is funding the study. Eric’s mercury research continues at the A.Q. site. We are measuring reactive gaseous mercury, particulate mercury and gaseous elemental mercury, using Tekran analytical equipment. This is the latest generation of analytical equipment for measuring trace mercury, a potent neurotoxin that is concentrated as it moves up the food web
 There are two other programs at the A.Q. site that also deal with how much mercury deposition Vermont receives; the first is the longest continually running mercury monitoring program in the world. It is in co-operation with the University of Michigan’s School of Public Health Air Quality Lab.   Mercury Project .   The second is the NADP/ Mercury Deposition Network.

    We are relatively new members of this national network,(LINK to NADP/MDN) but we also have two long running NADP programs at the, NADP/NTN National Atmospheric Deposition Program and NADP/AIRMoN.  Atmospheric Integrated Research Monitoring Network  Both of these programs have in common a concern with acid precipitation, although NADP and AIRMoN also look at individual pollutants as part of the enforcement of the Clean Air Act. The State of Vermont is also represented with the Vermont Acid Precipitation Monitoring Program VAPMP is run by the Vermont Agency of Natural Resources Dept of Environmental Conservation. Acid precipitation has been monitored at the A.Q. site since 1981.

    The USDA is represented at the A.Q. site as well.  USDA UVB Monitoring Program.   This instrument cluster measures the kind of ultraviolet radiation that causes skin cancer and cataracts in humans, for example; and tissue damage resulting in stunted growth in plants. The USDA /UV-B network has provided agricultural researchers data to determine the impact of solar UV-B damage on crops, livestock and forests since 1994. Our participation in this network dates from 1996.

    The Air Quality site also has a meteorological array that includes temperature, relative humidity, wind speed and direction, barometric pressure and precipitation. Data from this array are archived by the VMC and are available to researchers and other interested parties.

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Timothy Wilmot, Retired
M.S. Botany 1987, University of Vermont

    My position with UVM Extension combines research with outreach and education. As one of two Extension Maple Specialists, I work closely with UVM Extension Maple Specialist George Cook to plan and facilitate educational events for sugarmakers, such as the January Vermont Maple Conferences. Another of my responsibilities is writing and talking about maple research, both my own and that of my colleagues at the Proctor Maple Research Center; as well as reporting on successful methods, innovations, and discoveries by other sugarmakers.
    One of my principal research interests is the sap flow mechanism in sugar maple, and the interactions among temperature, sap pressure, and sap flow rate. During the sugaring season I conduct experiments related to these phenomena, (a portion of which can be seen on our webpage “TREEMET”) as well as on related issues, such as the effects of vacuum on sap flow, and optimal timing of tapping for sugarmakers.

    A second research interest is forest nutrition and relationships among soil and foliar chemistry, tree growth and vigor, and sap sugar production in maple stands. Additionally, the efficacy of fertilizing maple stands, a topic of considerable interest to many forest managers in the northeast, has been the subject of several of my experiments.

Several of my recent publications, on topics such as sugarbush fertilization, vacuum system maintenance, and lead abatement, can be found elsewhere on this website.

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This document was created by E.M. Murphy, Proctor Maple Research Center. 01/03/08 

Last modified January 25 2016 04:09 PM

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