Technical Publications
Perkins, T.D., van den Berg, A.K., Isselhardt, M.L., Haynes, B.M., Bosley, W.T., Abair, S. 2025. When to Add a Second Tap Under Vacuum? - Part 2. The Maple Digest 64(2): 22-27.
Perkins, T.D., van den Berg, A.K., Isselhardt, M.L., Haynes, B.M., Bosley, W.T., Abair, S. 2025. When to Add a Second Tap Under Vacuum? - Part 1. The Maple Digest 64(2): 13-17.
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Boutin, J., Bosley, W.T., et Haynes, B.M. 2023. Pratiques d’entaillage pour maximiser les rendements a long-terme. La Technique CDL (3) 24-25. https://tinyurl.com/3b5cc2vr
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Boutin, J., Bosley, W.T., and Haynes, B.M. 2023. Tapping practices to maximize yields over the long-term. CDL’s Way Spring 2023 (3) 24-25. https://www.cdlusa.com/wp-content/uploads/2023/04/2023_CDLs_Way-USA.pdf
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Haynes, B.M., and Bosley, W.T. Nonconductive wood associated with taphole wounds in sugar maple. Maple Digest 63(3): 5-15. https://www.maplesyrupdigest.org/?m=202309
Perkins, T.D. and A.K. van den Berg. 2022. Ask Proctor: Why does the sap stop running after a few days if it doesn’t freeze again? The Maple Digest 63(2): 33-34. https://mapleresearch.org/wp-content/uploads/md0323sapstop.pdf
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Haynes, B.M., and Bosley, W.T. 2022. Total yields from red maple trees. CDL’s Way Spring 2022 (2) 22-23. https://tinyurl.com/vdBergRedMaple
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Haynes, B.M., and Bosley, W.T. 2022. Rendement total des érables rouges. La Technique CDL (2) 22-23.
https://www.cdlinc.ca/wp-content/uploads/2022/05/La_Technique_Edition2.pdf
Perkins, T.D., Bosley, W.T., van den Berg, A.K., and Abair, S.J. 2022. Early spout deployment doesn’t impact sap yield. The Maple News July 2022: 10.
Stockie, J.M., van den Berg, A.K., Perkins, T.D., and Wilmot, T.R. 2022. Exudation pressure in maple trees: Comparing simulations with experiments. The Maple Digest 61(2): 9-17.
Perkins, T.D., Heiligmann, R.B., Koelling, M.R. and van den Berg, A.K. (Editors). 2022. North American Maple Syrup Producers Manual. Third Edition. University of Vermont and the North American Maple Syrup Council, Burlington, VT. 434 p. https://mapleresearch.org/pub/manual/
Chapters in the North American Maple Syrup Producers Manual:
van den Berg, A.K., Boutin, J., and Perkins, T.D. 2022. Chapter 7: Sap and Syrup Processing.
Hopkins, K., Graham, G., Bailey, P., van den Berg, A.K., and Wightman, A. 2022. Food Safety for maple Producers.
Perkins, T.D., van den Berg, A.K., Boutin, J., Childs, S., Wilmot, T.W. 2022. Chapter 6: Sap Collection.
Isselhardt, M.L., Marckres, H., Perkins, T.D., and van den Berg, A.K. 2022. Chapter 8: Syrup Filtration and Grading.
Smallidge, P.J., Isselhardt, M.L., D’Amato, A., Graham, G., Heiligmann, R.B., and Perkins, T.D., and van den Berg, A.K. 2022. Chapter 5: Sugarbush Management for Syrup Production and Forest Health.
Perkins, T.D. and A.K. van den Berg. 2021. Ask Proctor – Defoamer. The Maple Digest 60(3): 36. https://mapleresearch.org/wp-content/uploads/ask0921.pdf
van den Berg, A.K., Perkins, T.D., Larsen, M.D., Bosley, W.T., and Haynes, B.M. 2021.
Yields from early tapping and taphole “rejuvenation” strategies. The Maple Digest 60(4): 13-26. https://mapleresearch.org/pub/yields-from-early-tapping-and-taphole-rejuvenation-strategies/
Perkins, T.D., van den Berg, A.K., and Bosley, W.T. 2021. Timing of spout and dropline deployment has no effect on sap yield. The Maple Digest 60(3): 9-12. https://mapleresearch.org/wp-content/uploads/timing0921.pdf
van den Berg, A.K., Perkins, T.D., Bosley, W.T., Haynes, B.M., and Isselhardt, M.L. 2021. Wound response to taphole rejuvenation practices. The Maple Digest 60(2): 9-17. https://mapleresearch.org/wp-content/uploads/wound0621.pdf
Perkins, T.D., van den Berg, A.K., and Haynes, B.M. 2021. Why the sap may not always flow well in the early season. The Maple News May: 6-7. https://mapleresearch.org/wp-content/uploads/mn2021earlyflow.pdf
Perkins, T.D., van den Berg, A.K., and Bosley, W.T. 2021. Effects of tapping depth on sap volume, sap sugar content, and syrup yield under high vacuum. The Maple Digest 60(1): 8-12. https://mapleresearch.org/wp-content/uploads/depth0321.pdf
Cannella, M., Isselhardt, M., van den Berg, A.K., D’Amato, A., and Lindgren, C. 2021. The Northeast Maple Economy: Crop Distribution and Outlook. The Maple Digest 60(1): 19-26.
van den Berg, A.K., Isselhardt, M.L., and D’Amato, A. 2021. Red maple as crop trees for maple syrup production. Web resource: https://blog.uvm.edu/farmvia/files/2021/01/Red-maple-as-crop-trees-for-maple-production.pdf
Perkins, T.D., van den Berg, A.K., and Isselhardt, M.L. 2021. Sap flow, wounding and compartmentalization in maple compartmentalization in maple The Maple News 20(3): 10-11. https://mapleresearch.org/wp-content/uploads/mn2021wound.pdf
Perkins, T.D. and van den Berg, A.K. 2020. Taking care of the woods. Leader Evaporator 2021 Catalog.
Perkins, T.D., van den Berg, A.K., and Bosley, W.T. 2020. Sap sugar within, between seasons at UVM PMRC. The Maple News 19(10): 25. https://mapleresearch.org/wp-content/uploads/mn2020sapsugar.pdf
Perkins, T.D. and van den Berg, A.K. 2020. Quick Tips to Achieve High Sap Yield. The Maple News 19(8): 8. https://mapleresearch.org/wp-content/uploads/mn2020yieldtips.pdf
Perkins, T.D., van den Berg, A.K., and Isselhardt, M.L. 2020. UVM PMRC & Extension Update. Vermont Maple Sugar Makers Association Newsletter. August 2020.
van den Berg, A.K. and Perkins, T.D. 2020. Identifying an Effective Defoamer for Certified Organic Maple Production. The Maple Digest 59(1): 8-23. https://mapleresearch.org/wp-content/uploads/0220defoamer.pdf
Perkins, T.D. and van den Berg, A.K. 2019. Sanitation, Clogging, or Both: A Comparison Study of 3/16” and 5/16” Maple Tubing. The Maple Digest 58(4): 8-13.
https://mapleresearch.org/wp-content/uploads/1219tubing.pdf
Perkins, T.D. and van den Berg, A.K. 2019. Ask Proctor: The North American Maple Syrup Producers Manual. The Maple Digest 58(3): 26.
Perkins, T.D., van den Berg, A.K., and Childs, S.L. 2019. A Decade of Spout and Tubing Sanitation Research Summarized. The Maple Digest 58(3): 8-15. https://mapleresearch.org/wp-content/uploads/1019sanitation.pdf
Perkins, T.D. and van den Berg, A.K. 2019. Comparison of 3/16” and 5/16” tubing sanitation. The Maple News 18(10): 1,24-25.
https://mapleresearch.org/wp-content/uploads/tubingsani2020.pdf
Perkins, T.D., Bosley, W.T., and van den Berg, A.K. 2019. The Goldilocks Touch – Overdriving Spouts Reduces Sap Yield. The Maple News 18(9): 1, 29.
https://mapleresearch.org/wp-content/uploads/overdrive2020.pdf
Perkins, T.D. and van den Berg, A.K. 2019. Effect of spout diameter on sap yield. The Maple News August: 5. https://mapleresearch.org/wp-content/uploads/spoutdia2020.pdf
Perkins, T.D., van den Berg, A.K., and Childs, S.L. 2018. Assessing strategies for spout and drop sanitation in 5/16” tubing: Sap yield, cost, and net profit. The Maple Digest 57(3): 9-13. https://mapleresearch.org/wp-content/uploads/1018sanitation.pdf
Isselhardt, M.L., Perkins, T.D., and van den Berg, A.K. 2018. Tree size and maple production. New England Soc. Amer. Foresters News Quarterly 79(2): 5-6. https://mapleresearch.org/wp-content/uploads/treesize.pdf
Perkins, T.D., van den Berg, A.K., Stowe, B., and Bosely, W. 2018. Check-Valve Spouts vs Standard Clear Spouts: A Multi-Year Comparison of Yield in 5/16” Tubing. The Maple News Aug-Sept: 10-11. https://mapleresearch.org/wp-content/uploads/checkvalvesaug18.pdf
Perkins, T.D., van den Berg, A.K., Stowe, B., and Bosely, W.T. 2018. High brix syrup processing – first two seasons with Lapierre HyperBrix. Maple Syrup Digest 57(2):8-13. https://mapleresearch.org/wp-content/uploads/0618highbrix.pdf
Perkins, T.D., van den Berg, A.K., Isselhardt, M.L., Stowe, B., and Bosely, W. 2018. Does color matter? The Maple News June-July: 9. https://mapleresearch.org/wp-content/uploads/spoutcolor.pdf
Perkins, T.D. and van den Berg, A.K. 2018. Relationship between slope position, vacuum, and potential yield in 3/16” tubing systems. The Maple News March: 20-21. https://mapleresearch.org/wp-content/uploads/slope2018.pdf
Isselhardt, M.L., Perkins, T.D., and van den Berg, A.K. 2018. Tree size matters. Maple Syrup Digest 57(1):36-38. https://mapleresearch.org/wp-content/uploads/0218treesize.pdf
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., and Wilmot, T.R. 2017. Growth rates of maple trees tapped with high-yield practices – are existing tapping guidelines sustainable? In: Proceedings of the 8th Eastern CANUSA Forest Science Conference: Understanding and Managing ECANUSA Forests in a Changing Environment. Pontius, J., Schaberg, P. and J. Duncan (Eds.) September 30-October 1, 2016. Burlington, VT. Forest Ecosystem Monitoring Cooperative. pp 113-114.
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2017. Understanding the relationship between tree size and yield. The Maple News 16(9):1,36. https://mapleresearch.org/wp-content/uploads/treesizeyield.pdf
van den Berg, A.K., Perkins, T.D., and Isselhardt, M.L. 2017. Reverse osmosis and maple syrup flavor. The Pipeline 1:4-5.
van den Berg, A.K. and Perkins, T.D. 2017. Assessment of the flavor of syrup produced with High-Brix RO systems. Maple Syrup Digest 56(4):8-13. https://mapleresearch.org/wp-content/uploads/1217highbrix.pdf
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2016. Is tapping below the lateral line a good idea? Maple Syrup Digest 55(4):9-16. https://mapleresearch.org/wp-content/uploads/1216belowlateral.pdf
Perkins, T.D. and van den Berg, A.K. 2016. Sap collection from small-diameter trees. Maple Syrup Digest 55(3):29-36. https://mapleresearch.org/wp-content/uploads/1016smalldiametersap.pdf
Perkins, T.D., van den Berg, A.K., Hopkins, K., Marckres, H., Roberge, S., Childs, S., Graham, G., and Farrell, M. 2016. Do not use isopropyl alcohol as a maple sanitizer in the U.S. Maple Syrup Digest 55(1):25-26.
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A., and Lloyd, S.W. 2015. Effects of sap concentration with reverse osmosis on syrup composition and flavor – a summary of experiments conducted at the University of Vermont Proctor Maple Research Center. Maple Syrup Digest 54(3):11-33. https://mapleresearch.org/wp-content/uploads/1015reverseosmosisflavor.pdf
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2015. Recent trends in the maple industry IV – Bulk syrup prices. The Maple News 14(9):34. https://mapleresearch.org/wp-content/uploads/mn1215bulk.pdf
van den Berg, A.K. and Perkins, T.D. 2015. Spreadsheet to estimate profitability of adding birch syrup production to a maple operation. https://mapleresearch.org/wp-content/uploads/PMRCbirch.xlsx
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2015. Recent trends in the maple industry III – Changes in sap yield. The Maple News 14(8):11. https://mapleresearch.org/wp-content/uploads/mn1215yield.pdf
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2015. Recent trends in the maple industry II: U.S. expansion. The Maple News 14(7):10.
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2015. Six top-producing states accounted for nearly 3 million increase in taps from 2007-2012. The Maple News 14(6):1.
Perkins, T.D., Isselhardt, M.L., and van den Berg, A.K. 2015. Tech helped boost yields in last decades. The Maple News 14(5):10. https://mapleresearch.org/wp-content/uploads/mn415tech.pdf
Perkins, T.D., van den Berg, A.K., and Isselhardt, M.L. 2015. Off-flavors in maple syrup: metabolism. The Maple News 14(4):1, 32.
van den Berg, A.K., Perkins, T.D., and Isselhardt, M.L. 2015. Birch syrup production in maple operations. The Maple News 14(3):19. https://mapleresearch.org/wp-content/uploads/mn315birch.pdf
Perkins, T.D., van den Berg, A.K., and Isselhardt, M.L. 2015. Maple water – A first look. The Maple News 14(3):1, 36.
van den Berg, A.K., Perkins, T.D., and Isselhardt, M.L. 2015. Chemical composition of five standard grades of pure maple syrup. Maple Syrup Digest 53(1):7-13. https://mapleresearch.org/wp-content/uploads/0215chemicalcomposition.pdf
Isselhardt, M.L., Perkins, T.D., and van den Berg, A.K. 2014. Does sugar removal impact trees? Maple Syrup Digest 26A(3):6-9. https://mapleresearch.org/wp-content/uploads/1014tappingimpacttrees.pdf
van den Berg, A.K. and Perkins, T.D. 2014. A model of the tapping zone. Maple Syrup Digest 26A(1):18-27. https://mapleresearch.org/wp-content/uploads/0214tappingzonemodel.pdf
van den Berg, A.K. 2013. Birch syrup production to increase the economic sustainability of maple syrup production in the Northern Forest. Northeastern States Research Cooperative, www.nsrcforest.org. 27p.
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., and Wilmot, T.R. 2013. Growth rates of trees tapped with high-yield sap collection practices – Are Conservative Tapping Guidelines sustainable? Maple Syrup Digest 25A(4):27-34. https://mapleresearch.org/wp-content/uploads/1213treegrowthrate.pdf
van den Berg, A.K. and Perkins, T.D. 2013. Interactive tapping zone model. https://mapleresearch.org/pub/tzspreadsheet/; https://mapleresearch.org/wp-content/uploads/tapzonemodel.pdf
van den Berg, A.K. 2012. Defining modern, sustainable tapping guidelines for maple syrup production. Northeastern States Research Cooperative, www.nsrcforest.org. 22p.
Isselhardt, M.L., van den Berg, A.K., and Perkins, T.D. 2012. Chemical composition of scale in maple syrup evaporators. Maple Syrup Digest 24A(4):23-28. https://mapleresearch.org/wp-content/uploads/1212chemicalcomposition.pdf
Perkins, T.D. and van den Berg, A.K. 2012. Tubing cleaning – methods used in the U.S. Maple Syrup Digest 24A(3):11-18. https://mapleresearch.org/wp-content/uploads/1012tubingcleaning.pdf
Perkins, T.D. and van den Berg, A.K. 2012. Relationships between tubing system component age and sap yield. Maple Syrup Digest 24A(1):11-16. https://mapleresearch.org/wp-content/uploads/0212tubingagesapyield.pdf
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2009. Metabolism off-flavor in maple syrup Part II: Remediation of metabolism off-flavor in maple syrup. Maple Syrup Digest 21A(3):11-18. https://mapleresearch.org/wp-content/uploads/1009metabolismoffflavorpart2.pdf
Martin, N., Perkins, T.D., Ramacieri, P., and van den Berg, A.K. 2009. Technical position paper on air injection. Maple Syrup Digest 21A(2):23-31. https://mapleresearch.org/wp-content/uploads/0609airinjectionpositionpaper.pdf
van den Berg, A.K., Perkins, T.D., Godshall, M.A., Lloyd, S.W., and Isselhardt, M.L. 2009. Metabolism off-flavor in maple syrup Part I: Identification of the compound responsible for metabolism off-flavor. Maple Syrup Digest 21A(1):15-80. https://mapleresearch.org/pub/m0209metabolismoffflavorpart1/
Godshall, M.A., van den Berg, A.K., Lloyd, S.L., Perkins, T.D., and Isselhardt, M.L. 2008. The influence of processing factors on maple syrup volatiles. Proceedings of the 2008 Conference on Sugar Processing Research, “Diversifying Research in Sugar Processing”, Delray Beach, FL, USA, September 28-October 1, 2008.
Isselhardt, M.L., van den Berg, A.K., and Perkins, T.D. 2007. Temperature patterns within an oil-fired maple evaporator. Maple Syrup Digest 19A(3):20-25. https://mapleresearch.org/wp-content/uploads/1007temperaturepatternsoilevaporator.pdf
Wilmot, T.R., Perkins, T.D., and van den Berg, A.K. 2007. Vacuum sap collection: how high or low should you go? Maple Syrup Digest 19A(3):27-32. https://mapleresearch.org/wp-content/uploads/1007sapcollectionvacuumlevel.pdf
Wilmot, T.R., Perkins, T.D., Stowe, B., and van den Berg, A.K. 2007. Comparison of the ‘small’ spout with the traditional 7/16″ spout. Maple Syrup Digest 19:20-26. https://mapleresearch.org/wp-content/uploads/0607smallvstraditionalspout.pdf
van den Berg, A.K., Perkins, T.D., and Isselhardt, M.L. 2006. Sugar profiles of maple syrup grades. Maple Syrup Digest 18:12-13. https://mapleresearch.org/wp-content/uploads/1206sugarprofilessyrupgrades.pdf
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.
van den Berg, A.K., Perkins, T.D., and Marckres, H.J. 2005. Chemical safety in sugaring operations. University of Vermont, Agricultural Experiment Station and Extension Miscellaneous Publication, Burlington, Vermont. 12p.
Murakami, P.F., Turner, M.R., van den Berg, A.K., and Schaberg, P.G. 2005. An instructional guide for leaf color analysis using digital imaging software. Gen. Tech. Rep. NE-327. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 33p.
Peer-Reviewed Publications
Robinson, J.A., Rennie, M., van den Berg, A.K., Clearwater, M., Holland, D.J., and Watson, M. 2025. MicroCT imaging of fibre water uptake in sugar maple (Acer saccharum) in response to freezing. Micron 196-197. https://doi.org/10.1016/j.micron.2025.103869
Zarrinderakht, M., Konrad, I., Wilmot, T.R., Perkins, T.D., van den Berg, A.K., and Stockie, J.M. 2024. Experimental and computational comparison of freeze-thaw induced pressure generation in red and sugar maple. Tree Physiology 44(4). https://doi.org/10.1093/treephys/tpae006
Driller, T., Robinson, J.A., Clearwater, M., Holland, D.J., van den Berg, A.K., and Watson, M. 2023. Quantitative anatomy of the juvenile sugar maple xylem. PLOS One 18(20). https://doi.org/10.1371/journal.pone.0292526
Robinson, J.A., Holland, D.J., Watson, M., Clearwater, M., van den Berg, A.K., and Rennie, M. 2023. Examination of embolisms in maple and birch saplings utilising microCT Micron 168(4). https://doi.org/10.1016/j.micron.2023.103438
van den Berg, A.K., Perkins, T.D., and Isselhardt, M.L. 2019. Composition and properties of maple sap, concentrate, and permeate. Agricultural Sciences 10:32-45. https://www.scirp.org/pdf/AS_2019010916110298.pdf
van den Berg, A.K., Isselhardt, M.L., and Perkins, T.D. 2018. Identifying sustainable practices for tapping and sap collection from birch trees. Agricultural Sciences 9:237-246. https://www.scirp.org/pdf/AS_2018030515015914.pdf
van den Berg, A.K. and Perkins, T.D. 2017. Do anthocyanins function as photoprotective light screens in senescing sugar maple leaves? Journal of Plant Science: Current Research 1:2-5. http://dx.doi.org/10.24966/PSCR-3743/100002
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L. and Wilmot, T.R. 2016. Growth rates of sugar maple trees tapped for maple syrup production using high-yield sap collection practices. Forest Science 62:107–114. https://mapleresearch.org/wp-content/uploads/highyieldgrowth.pdf
Isselhardt, M.L., Perkins, T.D., Schaberg, P.G. and van den Berg, A.K. 2016. Preliminary results of sugar maple carbohydrate and growth response under vacuum and gravity sap extraction. Forest Science 62:125-128. https://mapleresearch.org/wp-content/uploads/nrs_2016_isselhardt_001.pdf
van den Berg, A.K., Perkins, T.D., Isselhardt, M.L., Godshall, M.A. and Lloyd, S.W. 2014. Effects of membrane separation on maple syrup composition and flavor. International Sugar Journal 116:656-665.
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., 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 111:37-42.
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.
van den Berg, A.K. and Perkins, T.D. 2005. Nondestructive estimation of anthocyanin content in autumn sugar maple leaves. HortScience 40:685-686.
van den Berg, A.K. and Perkins, T.D. 2004. Evaluation of a portable chlorophyll meter to estimate chlorophyll and nitrogen contents in sugar maple (Acer saccharum Marsh.) leaves. Forest Ecology and Management 200:113-117.
Schaberg, P.G., van den Berg, A.K., Murakami, P.F., Shane, J.B. and Donnelly, J.R. 2003. Factors influencing red expression in autumn foliage of sugar maple. Tree Physiology 23:325-333.