When we moved to Gig Harbor from New York in March a few years ago, I wondered why Japanese maples were so popular with large nurseries offering dozens of varieties here. That September when the only trees in our yard to turn red were Japanese maples, I knew the answer. The two trees whose color palette dominates the New England landscape each autumn, the red and sugar maples, are widely cultivated here, as well.
There are several reasons why we are color deprived here each fall. Most obvious is the lack of deciduous trees in an overwhelmingly evergreen flora. Neither of our most common broadleaf trees, big-leaf maple nor red alder, have the ability to produce bright colors. That leaves a few less common colorful small native trees; most notably the Vine Maple (Acer circinatum).
With a sprawling growth habit in the deep forest, vine maples’ vine-like, ankle-twisting branches were the scourge of bushwhacking foresters — but oh, the fall color! In cultivation, this maple has a more upright shape. There are a few other colorful trees and shrubs for those interested in landscaping with native species: serviceberry, Western larch, Pacific ninebark and high bush cranberry.
The main reason we haven’t riotous color displays is the lack of color-producing trees. Broad geographic autumn color displays are rare worldwide. Landscape-dominating trees of several species must have the genetic ability to produce reds and oranges. Japan and the Eastern states are the most spectacular areas attracting tourists from all over the world. Tour buses full of leaf peepers, with frequent stops at country stores and outlet malls, add millions of dollars to the New England economy just before the holiday season.
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Color intensity varies with the weather and tree location. Color is sun dependent; late summer bright sunny days and cool nights produce the most intense colors. Shade-grown trees will have less color, turning only yellow instead of red or orange.
The chemistry of color change
Throughout the growing season, the green pigment chlorophyll, essential in the conversion of oxygen and water to sugars and starches, is used up and continually replaced. The yellow pigment carotene is also present but masked by the chlorophyll. Shortening days of late summer trigger the formation of a corky layer on the twig at the point of leaf stem attachment; effectively cutting the leaf off from its water supply. As the chlorophyll fades, the carotene pigment that was there all summer but masked by the chlorophyll appears as bright yellow. In some trees and shrubs, the red pigment anthocyanin forms as the chlorophyll fades producing shades of oranges, reds and purples. Anthocyanin is also the pigment that turns ripe apple skins in bright sunlight red and grapes purple.
Colors that contrast with that of leaves has survival value for fruit-producing plants. Red, blue or even white fruit hiding among leaves help birds find this sweet food often swallowed whole. Dropped seeds neatly wrapped in a little poop package of fertilizer have a good chance of beginning a new stand of blueberries or blackberries.
Fun with leaves and fruit
Knowing the dependence on bright light for red and orange color formation, the reason for the heart shape on the apple in the photo here becomes obvious: an apple leaf shaded the apple. Deliberately making shadows can be a fun activity, especially for children. Glue a letter or a star in the summer to the side of a green apple or leaf on a tree facing the sun. Return after the colors have formed, remove the letter or symbol for a monogrammed fruit or leaf.
Our fall foliage displays are rather subtle here in Washington. Tour the back roads of New England in early October to enjoy the horizon-spanning displays of reds, oranges, yellows and burgundy. And be sure to stop at a country store for mulled cider and a cinnamon sugared donut!
Naturalist Ramblings columnist Frank Knight can be reached at firstname.lastname@example.org.