Why trees change color

The result is a vibrant and magnificent display of colors. It can explain why some trees turn the color they do, why some regions have better displays of foliage and how that changing of colors benefits the tree itself.

A drought in May could lead to a quick, underwhelming tinge of foliage in November; a relentless heat wave in August can scorch tree leaves badly enough that they drop early and suddenly come autumn; and an early freeze from a cold front has the potential of sending trees into a panicked, sudden dormancy. Leaves are colored by the same compound that makes up our complexion — pigment. That is why green is the dominant color of any tree leaf for the majority of its life cycle.

The other pigments — xanthophylls yellows , carotenes oranges , and anthocyanins reds, purples, blues and blacks — have also been there all along. The question of why some trees change certain colors has a more tenuous answer.

Carotenes are pigments found in fruits and vegetables, including carrots, oranges, some bell peppers and evsquash. Xanthophylls, the yellow pigment seen in most transitioning trees, is the same pigment that colors egg yolks and, occasionally, parts of the human eye. It is produced exclusively in plants, though, so it appears in humans and animals only through consumption.

The last of the primary pigments, and the most impressive of the fall colors, comes from anthocyanin. This is the same pigment that can be found in blueberries, blackberries, and red or violet roses. The coloration of the pigment depends on the PH level of the plant. The higher the PH level, the darker the coloration. This is the color seen in red maples, black cherry trees, Shumard oaks and more.

All of these pigments are attached to chemicals that serve a purpose for the plant. This is the same cherry planted around the Tidal Basin. Getting the story meant getting to Chevy Chase at peak bloom.

But this wasn't that hard because there's a National Park Service website you can go to where an expert on cherry trees examines the flowers every day and tells you with great accuracy what percentage of flowers will be in full bloom on a given day. There's no such site for fall color. Oh sure, some tourism sites will give you a week when they think fall color will be nice, but they really don't know.

Any time you go looking for fall color, it's basically a crap shoot. Why do trees change color anyway? Scientists say the color change for trees that turn yellow and orange is basically no change at all.

The pigments for those colors are always in the leaves, only masked by green chlorophyll used for photosynthesis. As trees prepare to drop their leaves, chlorophyll breaks down, and voila -- yellow and orange fall foliage. Red fall foliage is a different matter. The chemical compound responsible for red in the leaves -- anthocyanin -- isn't produced until late summer. How come? And why is it produced at all? Here's the deal. Traits in plants not managed by people are passed along because they provide those plants with a competitive advantage.

Traits like fast growth, extensive seed production, tolerance of dry or wet soil, and resistance to disease all make it more likely that a particular plant will survive to pass along these traits to offspring, while those lacking them will not.

So what advantage do trees like Japanese maple, dogwood, Bradford pear, and black gum gain by turning red in fall? They don't do it to impress potential mates.

Last time I checked, trees were all blind and pollination was pretty much random like going on eHarmony for the first time. I've heard two theories. One says trees turn red to chase away egg-laying aphids, because aphids don't like red. This is the key difference between a conifer and deciduous trees. Conifer trees are the ones that bear cones and have those needle-like leaves. Think of forests in colder places — full of spruce trees, pine trees, the Christmas tree type of trees.

For color, you need deciduous trees. They have leaves that do change color. These are the trees that, in general, also shed their leaves every year at the end of their growing season. Just like we focus on environmental cues to usher in fall and pumpkin spice season, so do trees. Anything that clues you into knowing that sweater weather is coming; things like the days getting shorter and the temperature getting colder. We pick up on seasonal changes and so do trees.

This magic revolves around photosynthesis, which is the process of how plants harness energy from sunlight and water and carbon dioxide to make food for themselves.