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Isselhardt, Mark Louis

Plant Biology

2012

MS

Sugar maple (Acer saccharum Marsh.) is an important species in forests of the northeastern United States and eastern Canada. The ecological and economic importance of this species comes from its broad distribution and varied commercial uses such as lumber, maple syrup production, and its importance in fall foliage displays. The annual production of maple syrup takes advantage of a unique phenomenon whereby sucrose-enriched xylem sap (from stored nonstructural carbohydrates-NSC) is extracted and concentrated. Maple syrup appears to have been produced in North America since before the first European settlers arrived. Perhaps owing to this long history, combined with the absence of clear evidence to the contrary, syrup production has been considered a sustainable agricultural practice causing little or no impact to the tree beyond the small stem wound created by tapping. However, recent technological advancements have greatly increased the yield of sap attainable (and therefore the amount of NSC) that can be extracted from a tree each production season. Direct evidence is almost completely lacking related to the potential impacts of such increased sap extraction on the growth of sugar maple.
The present study investigates the impacts of high-yield versus traditional sap extraction on sugar maple radial stem growth, twig growth and residual NSC concentrations in stem and twig xylem tissue. Results show the use of vacuum extraction methods translate to a significant increase in NSC removal (and corresponding sap volumes) as compared with traditional extraction methods. The results do not indicate a treatment effect on residual twig or stem xylem NSC concentration (starch or soluble sugars) from increased sap extraction. Radial stem growth in the year following sap extraction appears to not be affected by increased rates of sap extraction.
The visual method for estimating root starch concentrations was adapted and evaluated for use with spring sugar maple twig tissue. The method of iodine-staining starch contained in xylem tissue was compared with starch detennined with the chemical method. There was little agreement between the two methods detennination of starch content. The highly dynamic nature of spring starch concentrations could help explain the result. Overall, the results of this work reveal no substantial threat to sugar maple growth or stored carbohydrates due to modem vacuum sap extraction and corresponding increases in NSC removal.