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  • Staff photo by Bob Hammerstrom

    An old maple tree outside Mac's Apples in Londonderry.

  • Staff photo by Bob Hammerstrom

    An old maple tree outside Mac's Apples in Londonderry.

  • Chart by Barrett Rock

    This chart quantifies the fact that 2005's leaf-peeping season was less vibrant that the years before, based on spectrometer analysis of leaf color from satellite photos.
  • Illustration courtesy Dr. Barrett Rock

    These satellite photos show how "leaf peeping" season looks from space, and how the 2005 season was much less vibrant than the 2003 season at the same time of year.
Saturday, November 6, 2010

Expert: Climate change harming sugar maples

There may not be any species more central to the New Hampshire advantage – our history, our image and our surroundings, especially at this time of year – than the sugar maple tree. Which explains why Barrett Rock is so bothered by the results of his own research and research from a graduate student.

“I think there’s a general sense within the forest community that we’re seeing the beginning of the loss … of sugar maples,” said Rock, a professor of forestry and botany at the University of New Hampshire, who has studied New England’s woodlands for decades.

He attributes the maple trees’ problems largely to the effects of climate change that is worsened by human activity and says it is was predicted years ago but is occurring faster than expected.

That loss is most obviously seen, Rock says, by a dimming in the brilliance of the sugar maple’s fall foliage over the past three years. The key point is that he means “seen” in a scientific sense, based on three years of data about such things as foliage color measured by spectral analysis of satellite photos.

“This isn’t my saying so, because I think they look good, this is the numbers saying so,” he said.

Some of those numbers are prompted by work of Martha Carlson, a Ph.D. candidate under Rock who, with her husband, owns a Center Sandwich farm that has a 60-acre “sugarbush” operation.

Carlson, a former journalist and teacher, enrolled at UNH because she was worried about the condition of maples on her farm and elsewhere, including a decline in sweetness of the sap.

Sugar levels of 3 percent used to be not uncommon, she says. Now, similar trees have sugar levels around 1 percent.

“Imagine if you have 3 percent something in your blood and it drops to 1 percent – you’d probably be in the hospital,” she said.

“This seems to be a real phenomenon that I don’t know that anyone has documented before,” Rock said.

The drop in sugar levels is directly connected to a loss in autumn brilliance, causing a decline in anthocyanin – a chemical that creates the color red. Less sugar leads to less anthocyanin, which means less red to combine with yellow to create orange.

Different colors reflect different wavelengths of light. Measuring those wavelengths, doing spectral analysis, turns subjective opinions about “leaf-peeping” pleasure into objective data. That data, says Rock, tells the story of how one of the region’s premier moments is being diluted.

“You get numbers that tell you how red the foliage is, how orange the foliage is,” he said. “Since 2003, we just haven’t had a typical fall color display. They’ve been muted, they’ve been delayed.”

As far as what’s going on inside the trees, Carlson’s main work is to find and calibrate easily measurable items – “four or five thermometers, if you will, to measure the health of sugar maples,” as Rock puts it.

“I want to see if I could see the decline of the maples and also help teachers and sugar producers, ordinary citizens, to learn how we see if climate change is here and what it’s doing to our forest,” Carlson said.

“We are working to develop some very simple measurements of things that anybody can see, like timing of when the leaves open – called bud burst – and leaf size and leaf retention, how long do they stay on the tree … and the quality of the sap season,” she said.

Carlson is less certain than Rock that human-accelerated climate change is the root cause of the trees’ problems, although she agrees that it’s a factor.

She also is less pessimistic about the effect of a decline in sugar maple brilliance because other species, such as red maple and aspens, still change each fall.

“New England’s still going to have spectacular foliage. … I don’t think the bus tour companies have to worry,” she said.

As a researcher, however, she knows that good data is needed in order to make judgments.

A dozen members of the New Hampshire Maple Producers Association are helping out, gathering samples of sap to be chemically tested. They’re interested because the decline in sap sweetness means sugar shacks have to boil many more gallons of sap to produce the same amount of syrup.

Overall syrup production hasn’t declined because its price has been high, due largely to the situation in Quebec, which makes 80 percent of the world’s maple syrup. It means more trees are being tapped and more aggressive methods are being used, including vacuums to pull out sap. But this just adds pressure to the region’s sugar maples.

All in all, Rock is worried.

“What this (data) is telling me is that the sugar maples are on the edge. It all relates back to the climate; milder winters, lack of frosts, mean more fungal spores are over-wintering … leading to fungal diseases associated with color change,” he said.

Rock, who’s been studying the science of climate change for many years, is an advocate of changes in energy usage and land development patterns to combat it. He was part of an eye-opening UNH report issued almost a decade ago that was the first public prediction of how New Hampshire was going to change as temperatures rose, growing seasons shifted and weather patterns changed.

Part of that prediction involved how our forests would change over the years, including a decline in sugar maples.

So to some extent, this data is no surprise to him. Only the timing is a shock, he adds.

“Back in 2001, we thought we’d see this 20 years out. The fact that we’re seeing it happen in less than a decade is sobering,” he said.

David Brooks can be reached at 594-5831 or