Joe Fox & Lauren Tierney
THE WASHINGTON POST – This is starting out as a complicated season for leaf peepers.
As the United States (US) 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 ‘colour spotters’ will swarm, cameras in hand, in search of peak fall glory.
Forested areas in the US 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 colours 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 colour 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 colours 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 US 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 colours.
Schaberg points out that the best colour 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 colour 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.
Back on Earth, the leaf peepers prowl different parts of the country to find their own special spots for the best fall colours.
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 US that highlight spectacular fall colours – both common and uncommon.
Dazzling colours 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 US 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 colour, 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 colour all over the West,” said John Poimiroo, who runs a fall colour blog focussed primarily on spotting colours in California, “but there aren’t a lot of people there.”
So the majesty can go unseen in some places.
To find vivid colour 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 colours.
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 colour 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 colours, some years can be good, and some years can be bad.
The stochastic, which is scientist-speak for random, nature of when fall colours 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-colour 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 colours in New England in particular.
“2005. 2011. 2017,” Folger recalled 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 colour shows in Northern California, Southern California and the urban forests, Poimiroo said.
In New England, low evening temperatures have helped jump-start the fall colours, according to Folger.
This will eventually wave down the eastern United States, down through Appalachia and beyond.