Few things get my heart racing more than the vivid yellows, oranges, and reds of autumn. Unfortunately for peepers and photographers alike, you can’t just circle a date on the calendar and show up expecting the fall color to be peaking.
The truth is, timing of the fall color peak is fraught with mystery and misconception. Show up at the lake where someone in your camera club said the color was peaking at this time last year, and you might find the trees displaying lime green, mixed with faint hints of yellow and orange. When you check in to the lakeside inn and ask the old guy behind the counter inn what happened to the color, he shakes his head and says matter-of-factly, “The color’s late this year—it hasn’t gotten cold enough yet.” Arriving at the same inn on the same weekend the following year, you find just a handful of tattered leaves clinging to mostly bare branches—this time the old guy hands you your keynd proclaims, “That freeze a couple of 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 entirely accurate. The truth is, the why and when of fall color is complicated, and armchair experts resort to memory, anecdote, and lore to fill knowledge voids with partial truth and downright myth. But while we still can’t predict fall color the way we do the weather, science does provide pretty good insights of the fall color process upon which to base our plans.
A tree’s color
The leaves of deciduous trees contain a mix of green, yellow, and orange pigments—year-round. During the spring and summer growing season, the volume and intensity of the green chlorophyl pigment overpowers the orange and yellow pigments, and the tree stays green. Even though chlorophyl is quickly broken down by sunlight, the process of photosynthesis that turns sunlight into nutrients during the long days of summer continuously replaces the spent chlorophyl and the tree stays green.
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 to thicken. This thickening of the abscission cells inhibits the transfer of carbohydrates from the leaves to the branches, and the movement of minerals to the leaves. Without these nutrients, the leaves’ production of chlorophyl dwindles and finally stops, while the yellow and orange pigments persist. Voilà—fall color!
The role of sunlight and weather
Contrary to popular belief, the timing of the onset of this fall color chain reaction depends much more on daylight and the tree’s genetics than it does on temperature and weather. Triggered by a genetically programmed day/night-duration threshold (and contrary to innkeeper-logic), a tree will commence its transition from summer green to autumn 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 ultimate demise of the color season. Because sunlight breaks down the green chlorophyl, cloudy days after the suspension of chlorophyl creation will slow the chlorophyl’s demise and the coloring process that follows. 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, that tree’s red and purple pigments are manufactured from sugar stored in the leaves—the more sugar, the more vivid a tree’s 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 amidst a canopy of red and gold, and wake the next morning to find the trees bare and the ground blanketed with color.
Since the fall color factors come in a virtually infinite number of possible variations and combinations, the color timing and intensity can vary a lot from year to year. Despite expert advice that seems promise precise timing for the fall color, when planning a fall color trip, your best bet is to try to get there as close as possible to the middle of the color window, then cross your fingers.
Read more about photographing fall color
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