Tourists, soothsayers & scientists try to predict peak Fall foliage color

But new study sheds light on what makes leaves turn red

Groundhog behavior is supposedly a harbinger of spring.

Wooly Bear Caterpillars are a possible portent of the severity of winter.

But who knows when the Vermont forests will blaze with autumnal gold, orange and scarlet?

Not the weather forecasters, not the almanacs, not some octogenarian recluse Vermonter. Leave that to the scientists.

Here in Vermont where one out of four of the forests’ trees are maples, predicting peak leaf color is important business. Maples are those trees whose brilliant yellow, orange and red foliage most responsible for making the landscape look like a giant spilled his whole bowl of Trix cereal across the Green Mountains in October.

Tourists spent more than $710 million dollars in Vermont last fall, making 1.5 million trips to the state, according to information gathered by the University of Vermont’s Department of Community Development and Applied Economics, published last month.

So Vermont monitors the changes in its forests as carefully as a tourist on Vermont’s Route 100 studies a road map.

Now scientists at the University of Vermont and US Forest Service who track forest color feel they may have unraveled one of the mysteries concerning leaf color.

While color development is affected by a number of factors, “one common thread may be stress,” according to Abby van den Berg research technician at UVM’s Proctor Maple Research Center, who’s spent the last four years studying foliage in Vermont forests. She and a team of University of Vermont and US Forest Service scientists used the data from her master’s thesis research to evaluate potential environmental and chemical triggers of fall color development.

“This data has been a source for deeper understanding and a new hypothesis about the connection between stress and red pigmentation in autumn leaves.” says Paul Schaberg, UVM adjunct faculty, US Forest Service scientist and the study’s lead author. He says that their study, soon to be published in the journal Tree Physiology, concludes that “nutrient stress, particularly low nitrogen, can instigate early and more intense red color in maples.” Others contributing to the research are: Program Chair of Forest Ecology John Shane, Professor Emeritus John Donnelly and UVM alumni Paula Murakami who is also with the US Forest Service.

“We’re developing new clues about what affects the timing and quality of fall coloration. Very little of this kind of work has ever been done before,” van den Berg says.

Researchers tested the chemical composition of thousands of leaves from 16 maple trees, providing important information about various indicators of red fall-color development. They used state-of-the-art computer imaging technology to measure the percentage of color in each leaf throughout the seasonal cycle.

In addition to nitrogen, many other factors – potential climate, drought, pollution and others – could affect color, but it will take years of further study to uncover the many mysteries of autumnal color displays.

Scientists do know that cold temperatures and less daylight trigger the breakdown of green chlorophyll from leaves to reveal the yellow that exist hidden beneath all summer. “Then the leaves can also produce red. But why would a tree make red in a leaf that’s about to die?” asks Schaberg. “That’s one of the fundamental questions that we seek to answer.”

An abstract of the soon-to-be published study suggests that a primary function of red pigments is to protect trees from photoxidative damage and thereby enhance nutrient recovery during leaf senescence. That means “the trees probably turn red because it’s a helpful coping response to stress,” says Schaberg. “One theory is that red is like a sunscreen that allows the leaf to linger long enough for the tree to absorb more nutrients.”

But even scientist Schaberg isn’t a soothsayer. In early September he predicted that due to the stress of last summer’s shortage of rainfall, New England would enjoy an early autumn. Alas, a warm September doused by excess rain from two tropical storms, led to an early October with forests still decked in green leaves.

“We’ve had a warm, wet autumn so far,” says van den Berg “so trees are a bit late in losing their green, but it all could change practically overnight. Vibrant fall color is going to happen, I can guarantee it.”