Maples not so sweet
Michael J. Caduto
As a farmer’s daughter in rural Maryland, Martha Carlson worked the land and developed a keen eye for nature. She now lives on Range View Farm in Center Sandwich, N.H. -- 65-acres of field and forest that have been in her husband’s family since the Great Depression.
Over time, Carlson has worked as a journalist, market gardener and co-founder of the Sandwich Community School -- an environmental college-prep for teens.
While engaging students in the Forest Watch Program at the University of New Hampshire in Durham, Carlson met Barrett Rock, a professor of natural resources and world-renowned climate change ecological researcher. Carlson is now a doctorate candidate working with Rock to conduct groundbreaking research that gauges the response of forests and sugar maples to climate change.
Last weekend in the family sugarhouse -- while ladling sap, stoking the evaporator with wood and watching the syrup’s progress -- Carlson shared some striking early research findings: evidence indicating that acid rain, climate change and other sources of stress in our forests are the probable cause of a significant drop in the sugar content of maple sap during the past 35 to 40 years.
U.S. Climatological Network Data reveals that the mean annual temperature has increased by 3.8 degrees since 1835, but that 70 percent of this rise in temperature has occurred since 1970. Carlson’s research charts a parallel trend between warming temperatures and the decreasing sugar content of maple sap.
Carlson is researching, organizing and analyzing records kept by a dozen farm families throughout New Hampshire that have run maple sugaring operations in the same sugarbushes for a century or more. Proprietors of the Hunter Farm in Tuftonboro, for instance, have been producing maple syrup for seven generations. Carlson averaged the records of sugar levels over time and graphed a dramatic drop in the sugar content of sap.
"In my research of old agricultural records and sugarmaker journals," she says, "I am finding that, in the 1970s it took 25 to 30 gallons of sap to make 1 gallon of syrup, and the sugar content of sap averaged 3.0 percent. Today it takes 45 to 50 gallons of sap to make 1 gallon of syrup and, in 2010, sap contained an average of 2.2 percent sugar. That’s a drop of nearly 30 percent."
Although modern technologies, like reverse osmosis and vacuum pumps, have enabled maple sugarers to increase the volume of syrup produced, the sap-to-syrup ratio has declined. There is less sugar flowing through the tap lines, so sugarers must boil away significantly more gallons of raw sap to make each gallon of syrup.
"The stress caused to the trees by acid rain has been there from about World War II to the present," Carlson observes. "Acid deposition has contributed to dieback in the crowns of maple trees. Climate change is one more stress on top of all the stresses the trees encounter."
In addition to expanding the work of Barrett Rock at UNH, Carlson is building upon the pioneering research on maples and sugaring conducted by the late Dr. Mariafranca Morselli at the University of Vermont’s Proctor Maple Research Center -- work that continues under the current director, Dr. Timothy Perkins. Decades ago, Dr. Morselli predicted that stress experienced by sugar maples would begin to affect foliage and flavor.
Carlson asks farmers to collect samples of sap for chemical analysis, then she measures sugar levels and electronegativity to search for signals of distress in trees. Stress affects more than just the sweetness of sap. "When sugar levels are lower, I wonder if the tree’s ability to deal with stress is lower. A repeatedly stressed tree might be killed by one violent storm or one long dry spell."
Hot, dry stretches of summer weather, plus severe storms and rain events due to climate change, have reduced the number of days that leaves can photosynthesize efficiently -- the process by which leaves convert the sun’s energy into vital nutrients that feed a tree’s growth and sustain its health. Carlson uses spectral analysis to measure the levels of chlorophyll and water in maple leaves, noting that, "A stressed tree will still make good buds, so if bud growth is impaired then a tree is really stressed. All of the leaves in 2008 were water-stressed. Healthier trees kept their leaves into the fall but stressed trees lost leaves when they dried up."
"My concern is for the tree. Trees are now producing about two-thirds of the amount of sugar they used to produce to grow leaves and buds to make wood and roots. What is the impact on longterm health of losing 30 percent of their normal sugar? Will they be able to respond to climate change stresses as well as all the normal stresses they experience if they have less sugar to make protective pigments, phenols and lignins? Such a change means less sugar for building wood, growing large leafy canopies, producing buds and managing a biochemical system that can repel insects, deal with acid rain and withstand more hot summer days. Sugar is health for the maple."
Although 2011 looks like a strong sugaring year, and we could still have some nice sugaring seasons, evidence points to the overall trend that maples will be damaged, if not extirpated in some regions.
"You think about the possibility of the collapse of the forest," says Carlson. "It’s a combination of many stressesŠand then one final straw. The forest will be going along -- then the collapse will not be gradual. Like a tiny frog in a Costa Rican rainforest. someone suddenly says, ‘Where did they go?’ That’s going to affect our kids, grandchildren and the trees."
Still, she is hopeful, "Maples are resilient. Those growing on north slopes, and on cooler mountain slopes are more protected. These places may retain their maples."
Carlson wants to involve foresters, farmers, maple sugar producers and others who know the forests well. "How do you start a conversation to engage those people who are close to nature, and those who are in their sugar houses?"
"I’m also looking for indicators that sugarers can see and measure to note the stress levels of trees. I want people to be able to look out the window and see how climate change is affecting plants and animals in their own backyards."
Michael J. Caduto is an ecologist, educator and author of 18 books on the environment, including the recent Catch the Wind, Harness the Sun: 22 Super-Charged Science Projects for Kids (Storey Publishing). His Website is: www.p-e-a-c-e.net.
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