This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
View from Rabun Bald peak on the GA/NC border. Elevation of 4,696 feet. Photo courtesy: Robynne Boyd
It was time to get away. Remove myself from the city and head to the Appalachian Mountains to watch its warm-weather greens turn to the auburns, tangerines and rusts of autumn.
First thing I noticed on arriving at the mountain cabin in the southwestern part of the state, just outside Highlands, NC, was the pressing quiet. No hum from engines. No cars. No pedestrian traffic. Just the shuffling of millions of leaves as they dosey-doed with the wind.
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I had come to watch this colorful dance, despite concerns that summer's heat and drought might diminish the show. It didn't seem to, but many agreed that this was not a great year for fall color in North Carolina. If I had visited any later, the spectacle would have been cut short by Hurricane Sandy’s gusts that swept the entire east coast. Today, the peaks are covered with snow. But, last week, the timing was right.
Leaf season peaked around that time. Trees above 3,000 feet had already begun to drop leaves and were mostly showing up gold and ginger. But, those in the middle elevations on the eastern slopes were brilliant and assorted with the intense red that marks the season.
According to the website North Carolina Natural, "the most varied fall color, as well as the longest lasting, occurs in areas such as the southern Appalachians, where a dozen or more kinds of trees may change color at slightly different times over the longer fall season."
There was a desynchronization in leaf color changes, added Howard Neufeld over the phone, a leaf specialist and professor of biology at Appalachian State University, known for his annual fall color report. For example, Sourwoods turned colorful early this year, while other trees were still very green. Dogwoods and some Maples also began to change in late August. Oaks, on the other hand, only turned a deep burgundy towards the middle and end of October.
The speckled scheduling of color among tree species seems to be genetic, explains USDA's Forest Service website. Trees of the same species turn in unison whether on high or low if located within the same latitude.
The mechanism at work? Temperature and precipitation. "Conditions leading up to the fall were ripe for good fall color (sunny, cool, no severe drought), but they didn't develop," said Neufeld via email. "I don't know why that is."
Though heat and drought hit the Appalachian mountains this past summer, it wasn't dry enough for the USGS to declare it a drought. And some people even think a little drought is good for leaf color. Whether or not that's true, the heat isn't believed to be the cause for muted foliage in the southern Appalachians since this area hasn't displayed a warming or precipitation trend since the 1930's.
"The lack of warming is thought to be due to the production of volatile organic compounds (VOCs) which are produced by trees," said Neufeld via email. "These are the familiar smells we associate with pine or spruce or fir trees, and these small molecules reflect radiation from the sun back into space, preventing that radiation from heating up the area."
The trees VOC armor will not stay strong forever. It will weaken as the climate warms, and will one day demonstrate the same higher temperatures as most rest of the country, which have already seen significant increases. The forests surrounding Ithaca, NY, are an early example of this. The summer's persistent heat and lack of water are to blame for a particularly lackluster leaf season.
"Because plants are cooled by water evaporating from their leaves, many tree leaves were damaged as a result of the inability of root systems to supply sufficient water to leaves that experienced high temperatures," emailed Karl Niklas, a professor of plant biology at Cornell University. "The damage to leaves earlier in the season meant that many leaves could not color up or simply died while still attached."
Before heading to the southern Appalachians in search of color and solace, I didn't know the science behind foliage color. I didn't know the regions climate stats, and I was unaware that I would be visiting a cooler climate island within warmer seas. I was merely going as a witness, one who wanted to view millions of trees bid farewell to summer. It's a sendoff I'd like to witness for decades to come in all its tints and shades.
