the Answer:
Maple syrup is produced from the sap of maple trees, which is collected from late winter through early spring. The collected sap is clear and only slightly sweet; to produce syrup and sugar, the sap must be concentrated through evaporation (boiling) or reverse osmosis.
During the growing season, maple trees store starch in their sapwood (an outer layer of wood within the tree’s trunk). When the temperature of the wood reaches approximately 40°F, the starches are converted into sugars, which pass into the sap. When a tap hole is drilled, the sap-carrying vessels are severed, allowing the sap to flow out for collection (1). Sap flow is heavily weather-dependent, with temperature fluctuations creating pressure within the tree to move the sap. Among maple producers, it is well-known that spring temperatures must fall below freezing (usually at night) and rise above freezing (usually during the day), for sap to flow. After a freeze-thaw event, sap can continue to flow for 30-72 hours. The season typically lasts 4-6 weeks and ends when temperatures remain above freezing and buds begin to break dormancy (2). Under ideal conditions, a single tap hole can yield 40-80 gallons of sap in a season, although a more typical average is between 5-15 gallons (1). The sugar content of the sap varies widely among individual trees but generally averages 2-3%; thus, it takes approximately 40 gallons of sap to yield one gallon of maple syrup (3, 1). Sugar maple (Acer saccharum) is the primary species targeted, but red maple (Acer rubrum) and other maples also produce sugary sap.
In 2017, maple syrup production was a $147 million industry in the United States, with 4.27 million gallons produced from approximately 13.3 million taps. In the United States, maple production primarily occurs in New England and the Midwest. Vermont, New York, and Maine are the top-producing states currently (4), while Michigan, Pennsylvania, and other states have an even larger amount of potential maple resources that could be tapped (5). Due to the weather-dependent nature of sap flow, climate change is likely to have significant impacts on the maple industry. These impacts will be geographically dependent; some areas will see a loss inability to produce any appreciable quantity of syrup, while other areas will see increases in sap flow and overall yield (3, 6, 7, 8, 9, 10).
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