A simple how and when of fall color

Autumn Bouquet, Zion National Park
Canon EOS-1Ds Mark III
200 mm
4 seconds
F/16
ISO 200

Few things get a photographer’s heart racing more than the vivid yellows, oranges, and reds of autumn. And the excitement isn’t limited to photographers—to appreciate that reality, just try navigating New England backroads on a Sunday afternoon in October.

Innkeeper logic

But despite all the attention, the annual autumn extravaganza is fraught mystery and misconception. Showing up at at the spot that guy in your camera club told you was peaking at this time last year, you might find the very same trees displaying lime green mixed with just hints of yellow and orange, and hear the old guy behind the counter at the inn shake his head and tell you, “It hasn’t gotten cold enough yet—the color’s late this year.” Then, the next year, when you check into the same inn on the same weekend, you find just a handful of leaves clinging to exposed branches—this time as the old guy hands you the key he utters, “That freeze a few weeks ago got the color started early this year—you should have been here last week.”

While these explanations may sound reasonable, they’re not quite accurate. Because the why and when of fall color is complicated, observers resort to memory, anecdote, and lore to fill knowledge voids with partial truth and downright myth. Fortunately, science has given us a pretty good understanding of the fall color process.

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 and the tree stays green. Even though this chlorophyl is quickly broken down by sunlight, the process of photosynthesis that sustains the tree, during the long days of summer it is continuously replaced.

As the days shrink toward autumn, things begin to change. Cells at the abscission layer at the base of the leaves’ stem (the knot where the leaf connects to the branch) begin the process that will eventually lead to the leaf dropping from the tree: thickening of cells in the abscission layer blocks the transfer of carbohydrates from the leaves to the branches and the movement of minerals to the leaves that had kept the tree thriving all summer. Without these minerals, the leaves’ production of chlorophyl dwindles and finally stops, leaving just the yellow and orange pigments. Voila—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, and 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 the red. Ample moisture, warm days, and cool (but not freezing) nights after the chlorophyl replacement has stopped are most conducive to the creation and retention of the sugars that form the 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. And of course all these weather factors come in an infinite number of variations, which makes each year’s color timing and intensity a little different from the last.

Despite our understanding of the fall color process, Mother Nature still holds some secrets pretty close to her vest—just when we think we’ve got it all figured out, she’ll surprise us. For example, last year’s Eastern Sierra fall color featured lots of black leaves that I attributed to California’s extreme drought conditions. With the drought persisting, and in fact intensifying, this year, I feared this fall would be even worse. So I was quite pleased to find everything going along right on schedule, with lots of yellow, more red than usual, and hardly a black leaf to be seen. Go figure.

About this image

My first visit to Zion National Park, three years ago, found the fall color peaking. I’d love to say this was through expert knowledge and careful planning, but it just happened that I’d been helping Don Smith with a workshop in Moab and we’d tacked on an extra day to play in Zion. We arrived early enough in the afternoon to explore and shoot for several hours before sunset, and were so thrilled by what we’d found that we decided to return for an hour the or so the next morning before heading home.

Though my time was limited, a couple of things made this morning’s shoot even more productive than previous afternoon’s. First was the familiarity I’d gained the day before. And second was the morning’s soft light and utter stillness. Anxious to get going, we started before sunrise and were the first people to enter the canyon that morning—without wind or human interference, the air was so still that it seemed even the river was whispering. In these conditions it’s easy to forget time, ignore the chill, and immerse myself in world devoid of human obligation and discomfort.

What struck me most about Zion’s color was the crimson maples, a color we just don’t get in California. While yellow was ubiquitous, red leaves were quite plentiful too, and I tuned my vision to identify any red I could highlight against the predominant yellow. Identifying this bunch of red leaves was just the beginning of my composition. Isolating a subject requires more than positioning it in the frame’s two-diminsional up-down/left-right planes; it also requires controlling the virtual third dimension, depth, by careful management of the background and depth-of-field. In this case I refined my find by moving left/right and up/down until I was satisfied with the way the background complemented the red leaves.

Equally important was finding the appropriate depth of field—too little DOF would mean not enough of the nearby red leaves, my subject, would be sharp; too much DOF much would risk resolving so much background that it would compete with my leaves. I decided to use my 70-200 lens, moving back far enough to include all of the red leaves at 200mm. That long focal length compressed the distance separating the foreground leaves and background trees (make the yellow trees seem closer to the red leaves). Because depth of field decreases with focal length, even at f16 background trees were soft enough.

A few other subtle but significant considerations went into this image. First, note the long shutter speed: the air was so still that I had no qualms about using ISO 200, f16, and a polarizer, even though it dropped my shutter speed to four seconds. Also, don’t underestimate the importance of a polarizer in shady or overcast scenes: color-robbing glare from leaves’ waxy sheen is reduced significantly by a properly oriented polarizer. And finally, in front of these leaves were a few fluffy white seed pods—I knew they were close enough that at 200mm they would be blurred to little puffs of white, and simply decided to shoot through them.

Read how to photograph fall color in my Fall Color Photo Tips article.