Deciduous Trees Change Color, But Coniferous Trees Don't

The bright crimson and gold tones of fall foliage are found primarily on the branches of deciduous trees, an arboreal subset that includes oaks, maples, birches, and more. The word "deciduous" itself stems from the Latin decidere, meaning "to fall off," and the term is used to describe trees that — unlike conifers and other evergreens — lose their leaves during the autumn as they transition into seasonal dormancy. Deciduous trees have broadleaves: flat, wide leaves that are more susceptible to weather-induced changes compared to the thin needles of their coniferous counterparts.

As sunlight decreases and temperatures drop, chlorophyll production in these broadleaf trees ramps up, which in turn gives way to other pigments that produce the red, orange, and yellow tones of autumn. There are some geographic exceptions to this rule, however. Deciduous trees in the southern United States are more likely to maintain their green color than those in the North, primarily due to the region’s milder winters.

No matter the location, most coniferous trees — a group that includes pines, spruces, and firs — will maintain their green needles year-round. The needles feature a waxy coating that protects them from the elements and contain a fluid that helps them resist freezing. Those factors create conditions that allow coniferous trees to survive harsh winters with their verdant colors intact, although conifers will lose some of their oldest needles each fall. A rare subset, called deciduous conifers, crosses both worlds, with needles that change to brilliant hues and then drop off each fall.

A Leaf's Color Is Determined by Its Tree Type

There are three different pigments responsible for the coloration of autumn leaves: chlorophyll, carotenoids, and anthocyanin. Chlorophyll, the most basic pigment that every plant possesses, is a key component of the photosynthetic process that gives leaves their green color during the warmer, brighter months. The other two pigments become more prevalent as conditions change. Carotenoids are unmasked as chlorophyll levels deplete; these produce more yellow, orange, and brown tones. Though scientists once thought that anthocyanin also lay dormant during the warmer months, they now believe that production begins anew each year during the fall. The anthocyanin pigment not only contributes to the deep red color found in leaves (and also fruits such as cranberries and apples), but it also acts as a natural sunscreen against bright sunlight during colder weather.

During the transformative autumnal months, it’s easier to discern the types of trees based on the color of their leaves. Varying proportions of pigmentation can be found in the chemical composition of each tree type, leading to colorful contrasts. For example, red leaves are found on various maples (particularly red and sugar maples), oaks, sweetgums, and dogwoods, while yellow and orange shades are more commonly associated with hickories, ashes, birches, and black maples. Interestingly, the leaves of an elm tree pose an exception, as they shrivel up and turn brown.

The Etymology of the Word "Fall" Refers to Falling Leaves

Prior to the terms "fall" and "autumn" making their way into the common lexicon, the months of September, October, and November were generally referred to as the harvest season, a time of year for gathering ripened crops. Some of the first recorded uses of the word "fall" date back to 1500s England, when the term was a shortened version of "fall of the year" or "fall of the leaf." The 1600s saw the arrival of the word  "autumn," which came from the French word automne and was popular among writers such as Chaucer and Shakespeare. By the 18th century, "autumn" became the predominant name for the season in England, though over the following century, the word "fall" would grow in popularity across the Atlantic. But while some proper British English linguists consider fall to be an Americanism, the term actually originated in England, and both “autumn” and “fall” are used interchangeably today.

Tempura-Fried Maple Leaves Are a Japanese Delicacy

While most Americans rake up autumn leaves and throw them into a garbage bin, in Japan, they are the main ingredient of a delicacy. Momiji tempura is a popular snack that originated in the city of Minoh, about 10 miles north of Osaka, where the first commercial fried leaf vendor opened in 1910. Legend has it that around 1,300 years ago, a traveler was so taken by the beauty of the autumn maple leaves in the region that he decided to cook them in oil and eat them. Fear not if you're a germaphobe, though — the leaves used in momiji tempura are freshly picked off trees, never scooped up from the ground. Preparation involves soaking the maple leaves in salt water (sometimes for up to a year), frying them in a tempura batter, and coating them with sugar and sesame seeds for a sweet, crunchy treat.

American Trees Produce Redder Leaves Than Northern European Ones

While America is home to a wide array of both reddish and yellow autumnal hues, trees in Northern Europe are more universally yellow in color. One fascinating theory for why that is goes back to 35 million years ago. During the ice age of the Pleistocene era, America's north-to-south mountain ranges allowed for animals on either side to migrate south to warmer climates, whereas the east-to-west Alps of Europe trapped many animal species that became extinct as freezing conditions took hold in the north. The result was American trees producing more anthocyanins — and thus a darker red color — to help ward off insects, whereas European trees didn't need to do the same, since extinct insect species no longer posed a threat. This phenomenon also occurred in East Asia, where forests bear a similar resemblance to those in America, as opposed to the uniquely yellow forests of Northern Europe.

Modern-Day Leaf Peepers Have a Centuries-Old Japanese Precedent

There’s a term for serious fans of fall leaves: leaf peepers. These hobbyists travel near and far to view some of the most spectacular autumn forests around the world. In certain areas across the United States, such as New England, leaf peeping has proven to be a multi-billion-dollar industry, with those states welcoming millions of tourists annually to view the breathtaking foliage. People can even join up with fellow leaf peepers on online forums to report fall foliage sightings, view webcams, and utilize other tools for those who may not be able to travel to see these forests in person.

A similar tradition in Japan is called momijigari, or "autumn-leaf hunting." The custom is believed to have started among the elite during the Heian Period toward the end of the eighth century, and later gained widespread popularity during the Edo Period in the 18th century. With around 1,200 species of trees (out of an estimated 73,300 on Earth), Japan is certainly a prime location for leaf peeping.