Green is to a plant what beige is to the country club set: a neutral mask hiding the riotous circulation of other substances beneath the surface. But a cold snap strikes and whoops—the paisley underwear starts to show through.
What happens is the chlorophylls are gone. Chlorophylls are the chemicals that makes leaves green. They catalyze sugar and starch production. Gone might not actually be the right word. Used up is more like it. Trees sense the approach of autumn, and grow a layer of cork between the main stem and the leaf, making the transfer of chemicals more difficult. It's like corking a bottle to preserve the contents. And when the corks go on, then the lights are turned up—whatever is left in those cellular rooms is caught in the bright glare of crystalline autumn light.
So who are the late summer partiers? The yellows and oranges are the caretenoids. If you want a memory device to impress your companions with your command of botanical terms, think orange, think carrots . . . caretenoids. Caretenoids are also the coloring agents for egg yolks, daffodils, and canaries.
The alarming reds and purples are caused by anthocyanins (which also color plums and sometimes the edges of new spring leaves). You know how it's hard to get out of a nice warm sleeping bag on a cold morning? Warmth helps circulation. Similarly, anthocyanins are red pigments formed from sugar trapped in the leaves by the cold night air. The only memory device I can think of for anthocyanin is "cyan," which is actually a blue-green color. That may not be a big help. Try cyanide, a ghoulish poison which may seem like a viable alternative when you're deep in the midst of a botany exam.
If you're on the track for fall color, it helps to know the best conditions. It's a short list. Combine dry, autumn days. Nighttime temperatures in the 40s. And deciduous trees—that is, trees that lose their leaves over the winter. That's it.
If it's been a rainy, gray week, the foliage display will probably be so-so, at best. But if it's been a clear, brilliant week, and suddenly you've needed a sweater every night, rev up the engine. The trees are likely to be putting on a pageant.
I say this with only a hint of regional pride, but the best place in the world to see leaves change is the northeastern U.S. and southeastern Canada. The forests here have a wide variety of deciduous trees and the climate cooperates, frequently stunningly. Generally, the leaves turning travels north to south, and higher to lower. In the northeast, Maine leads off in mid-September, ending with the coastal areas of southern New England around the fourth week of October. Sugar maples turn a brilliant orange red. Sassafras, dogwood, sweetgum, black tupelo, and northern red oak and scarlet oak turn scarlet, flushed with anthocyanin. Birch, hickory, poplar, and mountain ash, service berry, butternuts, and witch hazel turn bright yellow. And with different dominant trees and understory trees and streamside trees and upper and lower slope trees all growing in visual proximity, it's natural psychedelia. Totally.
The Midwest is a close rival to the Northeast. Wisconsin, Minnesota, and Michigan all can have brilliant displays. The forests of the Rocky Mountains and the west tend to be evergreen—ponderosa pine, redwood, spruce, and the like—so mainly it's the bright yellow aspens that change color in these climes, which, truth be told, can be amazing.
The forests of the south don't have the right mix of trees, nor the sudden cold snaps. The autumnal hardwood forests here tend towards warm russet brown with maybe touches of bright yellow—pleasant, but a far cry from the fiery displays of New England. Call me a damn Yankee all you want.
National forests, being forests, have lots of trees changing color. And being public land, offer superior opportunities to get out of the car and experience the leaves close up. GORP has the best information around on national forests, with many suggested hikes, drives, and paddles. Some of the best for New England leaf peeping are the White Mountain Forest in New Hampshire and the Green Mountain Forest in Vermont.
The Monongahela Forest in West Virginia is no fall slouch, and even areas of the George Washington Forest in Virginia and the Nantahalla Forest in North Carolina have lots of fall interest. All of the Midwest national forests feature fall color—take a look at the Hiawatha and Ottawa in Michigan, the Chippewa and Superior in Minnesota, the Shawnee in Illinois, and the Hoosier in Indiana. For Rocky Mountain color, try any of the forests in Colorado and Wyoming, or Montana and Idaho.
So go explore. And do me a favor. Make a big pile of fallen leaves and pick out the stones and sticks. Then dive in!
Details mentioned in this article were accurate at the time of publication