The Science of Fall Colors
Fall foliage is considered to be the most beautiful time of year by many nature lovers, and some will travel far and wide to see the incredible colors nature provides. While fall colors can vary significantly from year to year, there are three primary factors that influence the vibrance of the fall season:
Leaf pigments
Length of night
Weather
All colors require natural pigmentation to appear to our eyes in the yellows, oranges, and reds we often see as the leave change with the season. The specific colors that a leaf turns depends on the type of pigment that is stored in the leaf at a given time. In autumn, the three most prevalent pigments are:
Carotenoids: Produces yellow, orange, and brown colors in such things as corn, carrots, and daffodils, as well as rutabagas, buttercups, and bananas.
Anthocyanin: Gives color to such familiar things as cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums. They are water soluble and appear in the watery liquid of leaf cells.
Chlorophyll: Gives leaves a basic green color. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for food.
Chlorophyll and carotenoids are present in leaf cells throughout the entire growing season, while anthocyanin is produced only in the autumn in response to bright light and excess plant sugars within leaf cells. As night length increases in the autumn (earlier sunset and later sunrise), chlorophyll production slows down and then stops, and eventually all chlorophyll is destroyed. The carotenoids and anthocyanin that are present in the leaf are then dominant.
Certain colors are also characteristic of particular species of trees:
Oaks: red, brown, or russet
Hickories: golden bronze
Aspen and yellow-poplar: golden yellow
Dogwood: purplish red
Beech: light tan
Sourwood and black tupelo: crimson
Maples: differ significantly by species
Temperature and soil moisture conditions when chlorophyll supplies begin dwindling has a big influence on the vibrance of color that will be exhibited. A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring the most spectacular color displays. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.
Leaves begin falling from trees as temperatures turn colder as a survival mechanism. If trees did not shed their leaves, their soft vegetation would freeze during wintertime, damaging and eventually killing the tree.
2024 Fall Foliage Prediction
Due to the many factors that influence fall color, it is fairly finicky to predict for a specific area. One of the most commonly used tools is a statistical model from SmokeyMountains.com, which takes into account historical and current meteorological data such as temperature, moisture, sunlight, and precipitation, producing a custom forecast with new data each year.
Peak fall foliage is indicated by red shading on the map above. This will first occur along the U.S.-Canada border around September 30th, only two weeks from now. The Northeast will see peak fall color roughly one week later, followed by the Rockies and Pacific Northwest by mid-October. Much of the Great Lakes and Ohio Valley region will have to be a bit more patient, with the most vibrant colors expected the last week of October. Leaves will continue to change southward through the end of November.
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