March 24, 2011

Think Maple!

By Margaret Gillespie, Illustration by Cheryl Johnson

I grew up in Canada surrounded by sugar maples – even the Canadian flag features the maple leaf! At the Ward’s farm near our house in the Laurentian Mountains north of Montreal, maple sugaring was an annual late winter ritual – a celebration, gathering of friends, source of income, and incidentally, lots of hard work. At that time, sap dripped out of spigots in trees into pails and was collected by hand. The best part was emptying the buckets into a huge collecting container drawn by two black Percheron draft horses. I can still see in my mind’s eye the dark of the horses against the white snow, the gray trunks of maples in rocky terrain outlined against the clear blue Laurentian sky. Warming up later in the sugar house, we watched the sap foam as it boiled and we sipped hot sweet “maple tea” which is sap on its way to becoming syrup.

For those who like mystery, there is still some intrigue involved in understanding exactly how and why maple sap flows. During the spring and summer, maple leaves are actively involved in photosynthesis – the process whereby leaves absorb sunlight, take in carbon dioxide from the air, and use water to make their own food (a sugar called glucose). In fall this glucose is stored as starch in the wood of the maple. As the weather warms in late winter, the starch changes to sugar and moves into the xylem or transporting vessels in the sapwood or outer area of tree trunk. Sap flows in the xylem in direct relationship to pressure within the tree. Pressure during the daytime comes from carbon dioxide in tree cells and in sap as this gas moves into the spaces between tree cells. Additional pressure results from osmosis where the high concentration of sugar in the sap draws water into the roots. When the tree is tapped, this pressurized sap drips out. Freezing temperatures at night are essential because pressure in the tree becomes less than the air surrounding the tree. As a result of the decrease in pressure, sap stops running and water moves into the tree from the roots, recharging the tree. Ideal conditions for sap flow are day temperatures are around 40 degrees Fahrenheit with night temperatures dropping to the low 20’s Fahrenheit. In good circumstances, the maple season can last for six weeks. During this amazing process, maple buds get the sugar they need to grow into leaves and people share in the bounty!

Sugar maples (Acer saccharum) have a life beyond syrup even though the species name “saccharum” means sugar. “Acer” refers to trees having winged fruit and as children, I am sure many of us have made descending helicopters of the double winged maple seeds or samara. Then up come the myriad of tiny maples reaching for a place in the sun. Over the summer, mature maples shade our lawns and houses and make nesting spots for birds like orioles and robins. In autumn comes the season of splendor as maples turn our hillsides into rolling waves of yellow, orange and red. These sugar maples are a specialized feature of the eastern Canada and United States region, a gem found only in this part of the world, with just the right climatic conditions. As maples age, woodpeckers drum territorial rhythms on dead branches and owls nest in holes along the trunk. Inside our own homes, the dense hard wood of maples has been transformed into sturdy furniture and flooring or provides gentle warmth from our wood stoves. It is truly a tree for all seasons!

Sugar maples can also play the role of the canary in the coal mine, telling us about safe environmental conditions. These magnificent trees have been showing signs of stress for a number of reasons and now may be the time to listen to the trees. One major change affecting trees in general is global warming but sugar maples are specifically tied to the alternating freezing night temperatures with day temperatures in the vicinity of 40 degrees Fahrenheit for the movement of sugary sap in their systems. Researchers at the University of Vermont’s Proctor Maple Research Center studied the effects of global warming on the timing of sap production in the northeast and found that “the sugaring season is starting significantly earlier than 40 years ago and the duration has decreased by an average of 10%.” A warming climate could make New Hampshire less hospitable to sugar maples and change the face of the forest with more oaks, hickory and southern pines dominating the forest landscape. Air pollution, particularly chemicals from burning coal for energy and pollutants from cars, produces acid rain, having an impact on sugar maples in insidious ways. Acid rain can change soil chemistry, affecting the intake of nutrients and water by trees. In addition, organisms like mycorrhiza (fungus) and other microscopic decomposers can die affecting absorption and recycling of nutrients. Weakened sugar maples become more susceptible to additional stresses like insect infestations, soil compaction, and road salt.

Chief Seattle said in 1855, “All things are connected like the blood that unites us. We did not weave the web of life. We are merely a strand in it. Whatever we do to the web we do to ourselves.” As we look up into the spreading branches of a huge maple tree, being linked to our environment is both a challenge and a privilege. Our blood circulates; its sap flows. Finding our own roots and connection to a sugar maple could be a very healthy pursuit.

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