Researchers: Maple trees in dire straits

The tree responsible for the most vibrant hues in New Hampshire's fall foliage season — as well as the state's maple syrup industry — may be on the decline in the Granite State and the rest of New England, according to some researchers.

Barrett Rock, a botanist and forestry professor at the University of New Hampshire's Complex Systems Research Center in Durham, has been studying spectral satellite imagery of New England's forests for decades, and said he's seen a pattern of maple tree decline.

Maple trees are being affected by climate change, which over the last 100 years has been unnaturally accelerated by human activity, he said. (Right: maple fall foliage)

One way in which the changes he's seeing via satellite imagery are beginning to manifest to the naked eye is that foliage seasons are more often becoming less spectacular, he said.

Scientists have expected the northward migration of trees susceptible to temperature ranges. Unfortunately, maple tree migration is now occurring faster than was anticipated – a journey in time and space marked by a loss of autumn maple foliage colors; colors that once ran to deep, true reds but are now confined to the red-gold range (left). This change has been documented by three year’s worth of spectral analysis of satellite photos, and is virtually irrefutable.

The sweetness of the maple sap has also declined from about three percent (the average nationwide is about 2.5 percent, though 7.4 percent is not unheard of) to one percent.

Global warming in New Hampshire also has meant warmer springs, a time that is typically the height of maple sugaring season, with March of 2010 being the warmest in recent memory.

The New Hampshire Division of Travel and Tourism Development estimated some 7.7 million visitors came to the Granite State during foliage season this year and spent roughly $1.1 billion. According to the New Hampshire Maple Producers Association, some 90,000 gallons of maple syrup are produced annually, bringing more than $3 million to the state.

Rock said his ongoing research is focused on long-term changes, not yearly variations, though he said the last three years have shown how unpredictable the weather caused by rapid climate change can be and how it has affected the foliage season.

In particular, the red and crimson hues of the maple tree have been dimmer during the past three autumns, Rock said. He said 2008 and 2009 both had wet, cool and rainy summers and this summer was hot and dry for the most part. "All three were atypical summers," Rock said.

He said a good foliage season starts with a rainy spring. "But there is such a thing as too much water," Rock said. Likewise, a too-dry spring is also not good for trees. If rain comes too late in summer, at the end of July or in August, "it's water the trees can't use," Rock said.

So the foliage seasons of 2008 and 2009 were not as spectacular because of too much rain either in the spring or too late in the season.

"Because of the summer we had this year, we expected nice foliage, but the colors were muted and the season was late," Rock said. He said the 2010 foliage season was late due to the summer's warm weather extending into mid-November.

"In order to have a spectacular foliage season, the area needs a hard frost by the middle or end of September," Rock said.

The declining sugar content of maple leaves also has affected recent foliage seasons. "In order to get the brilliant reds and burnt orange colors, you need high sugar content in the leaves," Rock said. The low sugar content may be due to a few different causes, Rock said, though more research is needed in this area.

One cause is because certain types of fungus are growing on leaves, depleting their sugar. "These fungal spores are more plentiful because of shorter, warmer winters," Rock said, adding that, during typical cold winter, the fungus wouldn't be able to survive. A fungal infection, in addition to other environmental stressors, such as too much or too little water, can affect a tree's health and its foliage, Rock said.

The low sugar content in leaves not only affects foliage, it affects another beloved time of the New England year — maple sugaring season, when the sap of maple trees is collected, boiled down to its syrupy, amber essence and sold to consumers the world over.

One person researching the declining sugar content of maple leaves is one of Rock's former students and a current doctoral candidate, Martha Carlson of Sandwich.

Carlson, a former teacher and journalist, owns Range View Farm in Sandwich, which includes a stand, or "sugarbush," of maple trees. A sugarbush or stand of maple trees are often connected with a network of plastic tubing (at right). The sap flows to collecting tanks where it is transferred to the evaporator which boils away 40 gallons of water to produce one gallon of maple syrup.

Carlson said when she learned from research by the U.S. Forest Service and Rock that maple trees have been declining in New England for past 40 years, she decided to do something about it, so she went back to college and is on her way to earning a doctoral degree in the university's Natural Resources and Earth Systems Science Program.

"I wanted to learn how I, as a land owner and maple syrup producer, determine if my trees were stressed," she said, adding that she began by looking at changes in the size of the leaves on her maple trees, before moving on to study the sap.

What she has learned is that less-healthy or environmentally stressed trees produce smaller leaves, with less vibrant colors and they fall off quicker, Carlson said. However, maple trees are resilient in that, despite their quickly falling leaves, they continue to grow healthy leaf buds into October.

Carlson said that, in studying the sap produced by her maple trees, she's noticed a change in sugar content and color over the last few years.

"They are producing less-sweet sap, so it takes more sap to make the same amount of syrup," Carlson said, adding that her sap research is ongoing, aided by the New Hampshire Maple Producers Association.

Members of the association have been sending her leaf and sap samples for the past year or so, she said.

Making Maple Syrup
Courtesy of Growing Things

Maple sugaring season typically lasts six weeks, between mid-February and early April. But a balance of freezing nighttime temperatures and above-freezing daytime temperatures is needed for the sap to run.

Optimum syrup-making weather is when night temperatures are in the 20s and day temperatures are in the 40s. Yet during the latest sugaring season, the state had its warmest March in recent memory, with temperatures in the 50s and 60s during many days.

"The 2010 sugaring season was not a good one. It was short and the quality of syrup produced wasn't as good," Rock said.

Warmer winters, longer growing seasons and odd rain patterns are all part of global warming, Rock said, adding that different climate models suggest the region will continue to see more wild variations in weather.

"So it's anyone's guess as to what the maple sugar season of 2010-2011 will be like," Rock added.

Carlson concurred with Rock. "I don't have a crystal ball," she said.

Rock said the acceleration of global warming, which began in the early 1900s, became "more aggressive" from the 1970s on. He said all the warmest years on record have occurred within the last 12. (Right: sugar maples in summer)

He added that, going into the second decade of the 2000s, people are seeing weather changes that had previously been predicted to occur much later on in the century.

"The maple is on the edge," Rock said. Yet he said it's hard to know if the maple species will disappear from New England.

"We don't have climate models to predict what will happen that far out," Rock said, noting that, during the Earth's life, the land we now call New Hampshire once had miles and miles of ice over it.

Gradual changes, over thousands of years, produced the heavily forested land encountered by the area's first human inhabitants. "But those changes happened gradually," Rock said. "The rapid warming is what is affecting maples now."

Rock said if he had to give a prediction, he'd say if more isn't done to slow the pace of global warming, the maple species will be in dire straits. "In New Hampshire, 100 years from now, we'll have a lot of old, dying maple trees and no new maple trees," Rock said.

Source:
The Citizen of Laconia, "Researchers: Maple trees in dire straits", accessed December 14, 2010
Green Change, "Climate change harms sugar maples, and dims the splendors of autumn", accessed December 14, 2010
Celaius, "Climate Change Signal No.10 - Sugar Maples in Decline", accessed December 14, 2010
Growing Wisdom, "Quick Tips: Making Maple Syrup", accessed December 14, 2010