Maple syrup has been an important agricultural crop in America since before Native Americans taught colonists how to tap trees. Currently, global warming threatens the maple syrup industry. On June 4, 2007, Timothy D. Perkins Ph.D., director of the Proctor Maple Research Center at the University of Vermont, testified before Congress that warming trends have begun to shorten the syrup collecting season. Perkins says the long-term effects of global warming may lead to a shift in forest composition and the maple-beech-birch range will begin migrating northward to cooler areas (See References 1, page 4).
Sugar Maple Characteristics
Sugar maple trees are a unique species that thrive in narrow ranges. It takes 40 to 50 years before a maple tree is large enough to produce enough sap for sugaring. Sap flows between late February and early March, depending on location and weather. Good sap flows depend on freeze-thaw periods that occur in late winter. Ideal temperatures for sap production are 25 degrees Fahrenheit at night and temperatures of at least 40 degrees Fahrenheit in the day time. Perkins says, as of 2007, the syrup collecting period in New England and New York begins 8.2 days earlier than it did 40 years ago and ends 11.4 days earlier (See References 1, page 5).
One of the causes (and effects) of global warming is air quality. Summer air pollution is often severe, and in many areas, this produces acid rain. Researchers at the Hubbard Brook Research Foundation's Experimental Forest have found that rain contains lower levels of acid since the 1960s, yet it still has pH levels that are 10 times lower than ideal (See References 2). Soils with high amounts of acid provide poor growing conditions for trees and plants, and dissolved aluminum depositions hinder maples from getting enough essential nutrients and water for sap production. Acid precipitation has led to sugar maple deaths in Pennsylvania because it has combined with insect defoliation and drought.
Uncharacteristic Weather Phenomena
One aspect of global warming is increased incidences of extreme weather, such as droughts, ice storms and systems that produce high winds. These events limit production and damage trees. Drought decreases root starch in maple trees, which in turn lowers the sugar content in the sap. Since 1916, temperatures in maple sugar production areas have increased steadily. Sugar maple trees cannot be sustained if summer temperatures are consistently above 77 degrees Fahrenheit over a long period. (See References 3, page 10).
Global warming often produces insect infestations. Pear thrips and forest tent caterpillars present the highest insect threat for sugar maples. The insects eat maple leaves in the spring and summer, decreasing the tree's abilities to produce photosynthesis, which means less stored sugars in the stems and roots. Less stored sugars mean lower sugar content in the sap. Insects do not survive during freezing temperatures, but global warming produces more days above freezing, and this promotes more harmful insects (See References 3, page 10).
Robin Odach has been a technical writer specializing in consumer services since 1987. She publishes online in the areas of gardening, family and a variety of subjects related to community life. Odach frequently contributes to various websites. She received a Bachelor of Arts in sociology at the State University of New York, Fredonia, and a Master of Social Work from Fordham University.
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