Fall color explained

Gary Hart Photography: Autumn Morning, El Capitan Reflected in the Merced River, Yosemite

Autumn Morning, El Capitan Reflected in the Merced River, Yosemite
Sony a7R II
Sony/Zeiss 16-35 f4
2 seconds
F/16
ISO 50

Like most photographers in the Northern Hemisphere, my fall color season is about finished. But things are just ramping up along the streets near my home in California’s Central Valley (where winter doesn’t really begin until December, and spring’s first blooms start to pop up at the end of January—sorry). While there’s not a lot for me to photograph in my neighborhood, the opportunity to partake of the visual feast without a camera in my hands is refreshing.

I’m also harvesting the fruits the most intense autumn workshop/travel schedule of my photography life, and appreciating all over again how much I enjoy fall photography. Browsing my autumn images, I’m reminded of the need to understand my subjects. That goes double for the why and when of fall color, a blend of science and myth so intertwined that casual observers often resort to memory, anecdote, and lore to fill knowledge voids with partial truth and downright falsehood.

Innkeeper logic

Show up at at the fall color spot that guy in your camera club said was peaking at this time last year, you might find the same trees displaying lime green mixed with just hints of yellow and orange. Ask the old guy behind the desk at the inn, and you’ll get a head shake and confident explanation that, “The color’s late this year—it hasn’t gotten cold enough yet.” Check into the same inn on the same weekend next year, you might find just a handful of leaves clinging to exposed branches—this time, as the old guy hands you the key, he proclaims, “That hot summer got everything started early—you should have been here last week.”

While “expert” testimony like this sounds like objective truth, it only perpetuates the myths surrounding fall color. Fortunately, science has provided a pretty good understanding of the fall color process to all who want to understand.

It’s all about the sunlight

The leaves of deciduous trees contain a mix of green, yellow, and orange pigments. During the spring and summer growing season, the green chlorophyl pigment overpowers the orange and yellow pigments, keeping the trees green. While this chlorophyl is quickly broken down by sunlight, the photosynthesis that turns sunlight into nutrients that nourish the tree, warmth and long days provide the energy to sustain chlorophyl creation through the summer.

As the days shrink toward autumn, things begin to break down. Cells at the “abscission layer” at the base of the leaves’ stem (the knot where the leaf connects to the branch) begin a thickening process that blocks the transfer of carbohydrates from the leaves to the rest of the tree. Meanwhile, movement of nutrients to the leaves is inhibited as well—without these minerals, the leaves’ chlorophyl production dwindles and finally stops. No longer masked by the chlorophyl’s green, it’s time for the tree’s yellow and orange pigments to shine: Color!

Sunlight and weather

Contrary to popular belief, the timing of the onset of this fall color chain reaction is much more daylight-dependent than temperature- and weather-dependent—triggered by a genetically programmed day/night-duration threshold; contrary to innkeeper-logic, the trees in any given region will commence their transition from green to color at about the same time each year (when the day length drops to a certain point).

Nevertheless, though it doesn’t trigger the process, weather does play a significant part in the intensity, duration, and demise of the color season. Because sunlight breaks down the green chlorophyl, cloudy days after the suspension of chlorophyl creation will slow the coloring process. And while the yellow and orange pigments are present and pretty much just hanging out, waiting all summer for the chlorophyl to relinquish control of the tree’s color, the red and purple pigments are manufactured from sugar stored in the leaves—the more sugar, the more vivid their color. Ample moisture, warm days, and cool (but not freezing) nights after chlorophyl replacement has stopped are most conducive to the creation and retention of the sugars that form the vivid red and purple pigments.

On the other hand, freezing temperatures destroy the color pigments, bringing a premature end to the color display. Drought can stress trees so much that they drop their leaves before the color has a chance to manifest. And wind and rain can wreak havoc with the fall display—go to bed one night beneath a canopy of red and gold, wake the next morning to find the trees bare and the ground blanketed with color.

Of course all these weather factors come in an infinite number of variations that make this year’s color timing and intensity a little different from last year’s and next’s. Despite my need to understand nature’s mysteries, it’s this (perceived) randomness, the impossibility of ever knowing for sure what I’ll encounter, that draws me back.


About this image

Yosemite isn’t an inherently great sunrise location. With most of its views facing east, toward shaded subjects beneath the brightest part of the sunrise sky, sunrise light is difficult here. And without clouds, more the the rule than the exception in California, Yosemite sunrises can be rather bland. But Yosemite’s bland sunrises are more than compensated by the first direct sunlight light visible Yosemite Valley, which starts on the highest points a few minutes after the “official” (flat horizon) sunrise, and progresses over the next hour or so until the valley floor is bathed in sunlight. El Capitan is among the first of Yosemite’s prominent features to benefit from this early light.

I have a mental list of go-to El Capitan views for photographing its first light. Among them is a quiet bend in the river, known affectionately (and unofficially) to photographers as “Tahiti Beach,” with views of Cathedral Rocks, El Capitan, and the Three Brothers. Additionally, the river widens and slows here, providing some of Yosemite Valley’s best reflection opportunities as well.

One morning in the first of this year’s two Yosemite fall color workshops, I guided my group to Tahiti Beach for El Capitan’s first light. Clouds ruled the sky as the first light window opened, but fleeting patches of blue gave me hope. And with the deciduous trees across the river displaying their finest golds and oranges, we weren’t lacking for opportunities in the meantime.

The sun broke through suddenly, spotlighting a thin slice of granite near El Capitan’s summit. Unsure how long the opportunity would last, I moved quickly to compose this wide, vertical frame that emphasized the reflection  juxtaposed with a thin veneer of colorful leaves floating at my feet. I reminded myself to heed the frequent admonition I issue my workshop groups: the focal point for a reflection is the focus point for the reflective subject, not the reflective surface. In other words, while the leaves floated in water that was just a few feet from my lens, their focus point was much closer than the infinity focus point of the reflection in the same water. I focused on the leaves, confident that the depth of field provided by f/16 at my 18mm would render El Capitan, the trees, and the reflection acceptably sharp.

Another noteworthy exposure setting in this image is my 50 ISO decision. Though the leaves were completely still, there were slight ripples disturbing the river where most of my reflection lay. Stopping down to f/16, dialing my sensor’s sensitivity to ISO 50, combined with a polarizer carefully tuned to cut the reflective glare on the leaves without diminishing the rest of the reflection too much, allowed a 2-second exposure that smoothed the ripples enough to enhance the reflection.

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A fall color gallery

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3 Comments on “Fall color explained

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