Brilliant Tree Leaf Color

In autumn, people are revved up by the fall color phenomenon and “leaf peepers” make trips to view fall foliage and changing forest colors. Strongbad1982's Autumn Leaf map (right) is released to the public domain. Albert Camus noted Autumn is a second spring where every leaf is a flower. "  

Autumn color occurs at the end of summer as the days get shorter because green chlorophyll levels in the leaves begin to decrease, revealing the yellow and orange pigments that have been hidden since spring. Carotenoid pigments are present in the leaves year-round, but are masked by chlorophyll, so leaves look green in summer. In fall as the supply of chlorophyll dwindles, the other pigments are able to show through. Carotenoids are the dominant pigment in the autumn coloration of 25% of the hardwood tree species producing brilliant yellows and oranges (for example, ash, aspen, birch, hickory, maple and sassafras).

Sometimes carotenoids are present in such abundance that the plant has an orange or yellow color all year long. Take carrots for instance. Or take the leaves of  The Rising Sun™ Redbud from Garden Debut®. New growth (left) remains apricot-tangerine all year (at right), while mature leaves are bright yellow until late spring, turning green in summer, then changing to golden yellow for fall.

The bright reds and purple combinations that enliven tree species in autumn in temperate regions result from another pigment, called anthocyanin.  Anthocyanins develop in late summer as the glucose in leaf sap breaks down in the presence of bright sunlight and decreasing levels of phosphate. The most brilliant colors occur during a period of cool-but-not-freezing nights and days filled with bright, plentiful sunlight, which increases production of anthocyanins and results in the most eye-catching color displays.  In New England, forests appear vivid with reds, purples and brilliant maroons because up to 75% of tree species produce these colorful anthocyanins (such as Cherry, Dogwood, Maple, Oak, Parrotia, Persimmon, Sourwood/Tupelo and Sweetgum).  

In spring, anthocyanins temporarily color the edges of some young leaves as they unfurl from buds. One example is Garden Debut®'s Fire Dragon™ Shatung Maple PP 17367. Acer truncatum is also known as ‘Purple Blow’ Maple, due to this light reddish-purple spring color on new growth. After a green summer, fall color is strong, pure, bright red reported from Oregon to New York and Virginia to Arkansas, Oklahoma, Texas and all the way to Houston. 

Another example of a pigment overcoming chlorophyll in summer is the dark wine red leaf color of Burgundy Hearts® Redbud PP19654.  An abundance of anthocyanins suppress the chlorophyll, yielding the dark red heart-shaped leaves.  

The combination of all of these pigments produce the beautiful fall foliage colors ranging from the palest buttercream yellow to deep orange, fiery reds, purples and bronzes, while brown colors like leathery Oaks) are made from the cell walls and metabolic wastes left in the leaves.

What's your favorite? Will you post favorite fall leaf photos?