Is Global Warming Affecting Sugar Maples?

Reduced Growing Range

• The growing range for sugar maples is reducing, at least in the United States. If sugar maples are able to grow elsewhere, they may retreat to areas more hospitable to their needs. Those areas may include the upper elevations of northern Maine. Forests can shift ranges over long periods of time, however, and climate change may occur at a rate untenable to the current sugar maple population. Sugar maples on the southern edge of their current growing range already may show signs of distress.

Reduced Sugar

• About 50 or 60 years ago, the sap from a sugar maple tree had 2.5 to 3 percent sugar content. Now the sugar content reportedly ranges from about 1 to 2.5 percent, which means it takes many more gallons of sap than in the past to produce 1 gallon of maple syrup. Previously, 32 to 35 gallons of sap were needed to make 1 gallon of syrup, but now nearly 45 to 50 gallons are needed. Because more sap is required, the cost of maple syrup production increased, making syrup more expensive for consumers.

Earlier, Shorter Cycle

• Sugar maples require several weeks in below-freezing temperatures in order for sap to develop. The cold weather should be followed by a period with very cold nights and warmer days. Sap flows best when nighttime temperatures reach about 25 degrees Fahrenheit and daytime temperatures are about 40 degrees Fahrenheit. The daily cycle of freezing then thawing is when sap extraction occurs. Because the cycle happens earlier in the season than it used to, the people involved in sap removal must begin earlier in the season. Because the cycle also is becoming shorter, the period during which sap can be removed is reduced.

Reduced Leaf Color

• The autumn leaves of sugar maples have become more muted. The chemical that creates the red color in fall leaves is called anthocyanin, and reduction of this chemical reduces the reds and oranges in leaves during fall. The chemical's reduction is related to the reduction in the sugar content in sugar maples. A lack of early frosts due to a longer growing season also affects leaf color display. Peak leaf color periods occur later than they did previously.