Fall colors are on display across the land. Here's how it works.
By JOE FOX AND LAUREN TIERNEY | The Washington Post | Published: October 21, 2019
As the East Coast sweated through record October heat, parts of the Rockies were buried under wildly early snow. Late heat and early cold can stifle some of the most photo-worthy foliage, but soon enough, large swaths of the country will be engulfed in the brilliant yellows, oranges and reds that herald an approaching winter. "Leaf peepers" and "color spotters" will swarm, cameras in hand, in search of peak fall glory.
Forested areas in the United States host a variety of tree species. The evergreens shed leaves gradually, as promised in their name. The leaves of deciduous varieties change from green to yellow, orange or red before letting go entirely. Using USDA forest species data, we mapped the thickets of fall colors you may encounter in the densely wooded parts of the country.
During the summer, trees produce chlorophyll, the pigment that turns leaves green and allows trees to harvest light to make food sugars. At the same time, trees manufacture carotenoid, a yellow to orange pigment that is masked by the green chlorophyll during the summer months. When the production of chlorophyll slows with the onset of fall, the carotenoid's bright color can emerge. This yellow pigment also helps the leaf absorb different wavelengths of light that the green chlorophyll cannot.
Certain species begin to produce another pigment, anthocyanin, when the seasons begin to change. That is what turns forests red and orange. Anthocyanin is also responsible for the red, purple, black and blue colors in certain foods high in antioxidants, — think raspberries, purple cauliflower and black rice. This crimson pigment allows trees to continue storing just a little more sugar and nitrogen to have on hand for the next year, according to Paul Schaberg, a research plant physiologist with the U.S. Forest Service.
Some areas of the country are more likely to experience those bright red and orange leaves than others. New England is a perennial fall destination because of its abundance of tree species contributing bright colors.
Schaberg points out that the best color displays occur in forests that have a diversity of species — and trees that have the tendency to turn red.
The progression of fall creates a wave of color across the country, with grassy plains and farmlands in the Midwest drying up, and the trees of the East Coast rolling from green to yellow/orange/red to brown. Descartes Labs collected and analyzed 10 years of satellite imagery to develop this cloud-free animation of fall in the eastern United States.
NASA's two MODIS satellite instruments collected all of the imagery that made the map you see, taking a picture of every part of the Lower 48 states twice a day. This is the equivalent of 500 iPhone snapshots, or 2.2 gigabytes of imagery, per day. Descartes Labs experts brought together all images from 2009 to 2018 to create this composite of the magic of fall, visible from space.
Back on Earth, the leaf peepers prowl different parts of the country to find their own special spots for the best fall colors. For Massachusetts resident Jeff "Foliage" Folger, who runs a New England fall foliage blog, his annual photo-foraging is "like a Christmas present. I run around New England, unwrapping all these presents," he said.
In an exploration of fall from space, Descartes Labs curated satellite imagery of locations from Alaska to the southern United States that highlight spectacular fall colors — both common and uncommon.
Dazzling colors can be seen in plenty of regions outside New England. Wisconsin, Michigan and Minnesota are great places to go, with forests that blend bright yellow birch, beech and aspen with red maple. Farther south, a mix of oak and hickory forests in Arkansas provides stunning views, especially at higher elevations where there is less development.
Even as far south as New Mexico, yellow oaks can be seen on mountainsides, along with sporadic flashes of red maples. Near Bosque Peak, in the Manzano Mountains just south of Albuquerque, New Mexico, bright red foliage can be seen in the foothills amongst dense green forest and brush.
Moving west, yellow dominates. Western U.S. forests are predominantly evergreen, where species of juniper, spruce and fir are better adapted to the more extreme temperature and moisture shifts. The deciduous trees in the West, including aspens, tend to display strong yellows. But in some places, such as near Provo, Utah, the aspens are known to show red and orange leaves as well. This could be because of a few different factors. Sometimes, carotenoid pigments can at times appear orange (think carrots). But all deciduous trees have the ability to produce anthocyanins that create a red color, and trees that are typically known to have yellow leaves in the fall can begin producing anthocyanin if the trees are experiencing more stress and find it physiologically beneficial to produce the pigment.
"There are pockets of beautiful color all over the West," says John Poimiroo, who runs a fall color blog focused primarily on spotting colors in California, "but there aren't a lot of people there." So the majesty can go unseen in some places.
To find vivid color shows, Poimiroo recommends looking in high-elevation areas in the Sierra Nevada and near Mount Shasta in northern California, where pockets of deciduous trees thrive. Along Interstate 5 between the towns of Black Butte and Mount Shasta, oak trees with orange leaves and yellow aspen dot the outskirts of the two towns.
Across Alaska, yellows and some reds begin to appear as summer comes to an end, lighting up mountain sides with bright colors. In the Chugach Mountains just east of Anchorage, Alaska, birch and cottonwood trees, along with low-lying vegetation, electrify the slopes. Yellows and oranges also color the forested spaces throughout the city, from Far North Bicentennial Park all the way to Elmendorf Air Force Base.
When it comes to tracking down those optimal fall colors, some years can be good, and some years can be bad. The stochastic, which is scientist-speak for random, nature of when fall colors occur "makes it a more interesting challenge if you're trying to do leaf-peeping," according to Schaberg.
Moderate stress, such as changing seasonal temperatures and the amount of daylight, helps induce the onset of leaf-color change, but more severe stress can mute the vibrancy of autumn's palette. Drought causes tree leaves to close up their pores to retain water, limiting their ability to produce sugars and leading the tree to jettison the leaves. Too much water can promote fungal pathogens that can infect leaves, which can also lead to early leaf drop.
Folger can tick off a few years that were very disappointing for fall colors in New England in particular.
"2005. 2011. 2017," Folger recalls without pause. "It's almost cyclic."
The first two years he cites were ruined by Hurricanes Katrina and Irene and the excessive moisture they brought to New England.
But this season is going to be lit, both Poimiroo and Folger predict, on both coasts. This week the Eastern Sierras will continue to turn, followed by color shows in Northern California, Southern California and the urban forests, Poimiroo says. In New England, low evening temperatures have helped jump-start the fall colors, according to Folger. This will eventually wave down the eastern United States, down through Appalachia and beyond.