Date of Award

Spring 2026

Abstract

Maple (Acer spp.) syrup production is a culturally and economically important activity in North America, and other types of trees are economically important (or show potential to become more economically important) for their syrup as well. For both established and novel syrup-producing trees, questions remain about tapping sustainability and the physiological mechanisms that underpin winter-dormant-season stem-pressurization cycles, which create the pressures necessary for sap harvesting. I investigated aspects of tapping sustainability related to two important xylem functions, storage and transport. I measured nonstructural carbohydrate concentrations and radial growth of tapped and untapped sugar maples (Acer saccharum) and found a weak negative effect of tapping on carbohydrate storage and no effect of tapping on radial growth. I also investigated the tradeoff between radial growth and losses in hydraulic conductivity due to tapping in seven different syrup-producing or potential-syrup-producing species. Many study species, including sugar maple, paper birch (Betula papyrifera), American beech (Fagus grandifolia), American sycamore (Platanus occidentalis), and American basswood (Tilia americana), generally met the sustainability condition that radial growth must outpace losses in hydraulic conductivity due to tapping, but study species with very low radial growth rates, like American hophornbeam (Ostrya virginiana), did not meet this condition, suggesting that more conservative tapping practices would be required for the sustainable syrup production. Additionally, I used wood-temperature and stem-pressure sensors deployed throughout the winter-dormant period at different axial positions in the same seven study species to identify patterns and drivers of stem-pressure generation. These data generally confirmed existing theories about stem-pressure generation in maples and birches and provided new insights into stem-pressure generation for the other study species. Overall, my results generally indicate that tapping is sustainable, particularly when tapping guidelines (where they exist) are followed, and that stem pressure is generated in response to temperatures and changes in temperature. Future work focusing on cellular and subcellular physiology will improve our understanding of how tapping affects carbohydrate storage, compartmentalization, and stem-pressurization mechanisms.

Document Type

Dissertation

First Advisor

Heidi Asbjornsen

Second Advisor

Matthew Vadeboncoeur

Third Advisor

Jeff Garnas

Department or Program

Natural Resources and Environmental Studies

Degree Name

Doctor of Philosophy

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