By Stephen Smoot
Last week, images spread across the internet showing fall’s first color changes emerging in the highest ridges of the Appalachian Mountains. The view came from space and showed hints of brown and other earth tones marking the most elevated areas.
“Leaf peeper season” has started in West Virginia.
Color changes follow the whims of the weather, not dates on the calendar. Every year, as autumn approaches, experts advise West Virginia Tourism on which counties will see color when, then a map comes out in August to help visitors prepare their itineraries
Mountainous areas between Greenbrier and Preston counties saw their colors emerge in late September into October, although some trees in Canaan Valley start their changes before the end of August.
The Potomac Highlands see the colors next, between early to mid October, followed by mid-October for the Morgantown through Parkersburg region down through the higher elevations of Nicholas and Summers counties and surrounding areas. Charleston and Huntington and points south, and low lying areas in the northern and eastern panhandles may have to wait until November to see fall’s glory.
Two years ago, New River Gorge Park and Preserve Park Ranger Dave Bieri explained to West Virginia Public Broadcasting the science behind why leaves change colors.
In fact, as he shared, leaves do not change color in fall so much as they stop producing some pigments. Bieri stated that “Chlorophyll is the pigment in the leaves that gives it that green color. And that’s used for photosynthesis which is basically the way that trees produce food.”
Under the dominant green hue of the chlorophyll, trees have other colors hidden beneath through the spring and summer months. He went on to add that “throughout the year, the chlorophyll is giving the leaves their green color, and we don’t see some of the other pigments.”
Those other pigments have a purpose as well. An article placed on the Appalachian State University biology department’s website describes what they do. Orange and yellow pigments come from carotenoids, the same biological agents that give carrots their hue. As the article explains “one function of carotenoids is to absorb light in wavelengths that chlorophyll is inefficient at absorbing.”
Visible light appears white to the human eye, but as one sees when it is sent through a prism or rain to form a rainbow, it actually contains a number of different colors. Leaves absorb light as energy through its different pigmentations. Chlorophyll absorbs most hues of light, with the notable exception of blue-green to green wavelengths.
This dynamic causes the leaf to appear green in spring and summer “because light reflected to your eye is enriched in the green wavelengths relative to the blue or red.”
As any human being knows, skin uncovered all day in high summer can lead to painful sunburns. Human skin cannot deflect, absorb, or channel that much solar energy, so it creates damage to the cells. Carotenoids in various ways keep the light energy that chlorophyll cannot absorb from either damaging the cells of the plant or overheating the chlorophyll powered cellular engines that turn energy from the sun into sugars for food.
When fall conditions reach a certain point, as Bieri notes, “that chlorophyll shuts down, some of those other pigments start to show up.” He explained the colors as well, adding “the yellows are pigments that are already in the leaves that start to show themselves, the reds have to do more with the sugars that are stored in the leaves. The trees that turn more of a red color have more sugar present in the leaves.”
Reds and purples come from pigments called anthocyanins. One of their functions lies in acting as a shield against excessive solar radiation. When growth starts in the fall in certain trees, such as sugar maples, sugars build up and enhance the reds.
Fall conditions also encourage the forming of an abscission layer that cuts the flow of nutrients from the tree to the leaf
Color changes also depend on the type of plant bearing the leaves. Bieri stated that “so different species of trees do turn different colors. When it gets cold the veins and those leaves seal off and the sugars are trapped in the leaves. And that’s what you’re seeing with the bright red and orange colors.”
The colors come regardless, but their brilliance depends on a number of factors. Scientific American last week published an article that explained that “rainfall during the summer increases soil moisture, making leaves more vibrant when autumn arrives, whereas summer drought can mean dull foliage.”
While the Mountain State experienced significant rainfall for the first half of the year, rain nearly halted across the state in late summer. This produced federally determined drought conditions. Moist soils generally contribute to lush colors in fall, but that vanished in many parts of the state before September.
Drought, early frost, and other stressors can cause leaves to simply turn brown, shrivel, and fall without revealing color at all.
The onset of cool night temperatures as summer ends and fall begins also encourages the process of bringing bright autumn hues in trees such as maples.
