But why are fall colors so spectacular? We often think we understand how the sun affects plant life and creates the four seasons, but how exactly does that make a bright green leaf turn crimson in only a month's time? Surprisingly enough, the answer can be linked to an obscure film reference in which Adam Sandler obnoxiously utters the faux word, "borophyll."
See also: Meet the tree that's making your neighborhood smell like Semenville, USA
If you haven't figured it out by now, the real reason leaves change color in the fall can largely be contributed to chlorophyll. Many other factors play a role in the exact time of the year that the leaves change color and the varying pigments they turn, but the growing absence of chlorophyll is why leaves actually change from green to red, yellow, orange or, in unfortunate cases, just pure brown, before they plunge to the ground.
"During the winter months trees live off the food they stored during the summer," explains Rebecca Kao, manager of conservation programs at the Denver Botanic Gardens. As fall arrives, says Kao, "the green chlorophyll they use in the summer to produce food is no longer needed and disappears from the leaves. As the bright green fades away, the color of the other pigments present in the leaves becomes more evident."
Essentially, the less chlorophyll present in leaves, the more colorful they become. During the summer, when the days are long and the trees are photosynthesizing at a high rate, chlorophyll (the green color) is abundant. Other colors are present in the leaves during this time as well; however, the green chlorophyll overpowers them. As fall progresses and chlorophyll disappears, the other organic pigments that were hiding there all summer are unmasked. These are called carotenoids and are responsible for the yellows and golds we see in the fall. Still other pigments such as anthocyanins are created during the trees' leaf-shedding process and produce dark reds and even oranges when combined with carotenoids at the proper temperatures.
As for why some trees are able to maintain their leaves throughout winter while others must shed them, Kao says it's all about adaptation. And, sticking with the Adam Sandler theme, high-quality H20.
"Plants have several adaptations to deal with drought stress," Kao says. "For trees growing in seasonally water-stressed environments, plants are thought to either tolerate drought (evergreen phenology) or avoid drought (deciduous phenology). During times when water is not available to the plants, leaves of evergreen species are thought to conserve water better than deciduous species by having lower photosynthetic and transpiration rates due to things like high surface-area-to-volume ratio, a heavy wax coating and substances resistant to freezing. Thus, evergreen species are adapted to keep their leaves and tolerate low-water periods, whereas deciduous trees drop their leaves to avoid losing water during drought periods."
For Coloradans wondering about the best time to head into the mountains for a fall leaf excursion, the calculation is a little less scientific. While daylight is often the main determining factor for when chlorophyll beings to dissipate, many other elements combine to determine the peak viewing time for fall colors. Warm, sunny days in combination with cool, crisp nights make for the most vibrant colors, as veins inside the leaves tend to close more gradually then, allowing for more sugar production and increased anthocynans that are responsible for the darker reds and oranges. On the other hand, lots of wind or rain can obstruct leaves from fully maturing and cause them to depart their branches before the reds, yellows and oranges reach their colorful zeniths.
The 2014 Farmers' Almanac claims the best dates to view fall leaf foliage are from October 5 through 14. "Data are being collected to monitor leaf change this fall across the country, but we don't yet know what will happen," Kao observes. "It is thought that climate change could be impacting the transition to fall, pushing it later in many regions. We still know way less about the science behind fall than we do about spring."
But at least after all these years, we finally know what Billy Madison was missing out on in his high school chemistry class -- and how it's a key component in making the great state of Colorado so colorful.
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