2010- An excellent year for fall color

This year is shaping up to be an excellent fall color season

The brilliant red, yellow and orange colors of fall are just starting to appear in southeastern WI.  Experts say that in southeastern WI we are still have about 2 weeks to go before the peak color of the season.  Leaf fall is most directly affected by the increasing length of night.  The brightness of the color can be affected by other environmental influences such as temperature, amount of rain fall and energy reserves in the trees.  As days grow shorter and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape.  During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops. Eventually all the chlorophyll is destroyed. Then the other pigments within the leaves, - carotenoids and anthocyanins  are finally unmasked and show their colors.

Certain colors are characteristic of particular species. Oaks turn red, brown, or russet; hickories, golden bronze; aspen becomes golden yellow; beech turns to a light tan.  Ash  vary by species, green ash tend to become a yellow, while some white ash varieties turn a purplish red.  Maples differ species by species. Red maple turns brilliant scarlet while sugar maple leafs become orange-red, while Norway maple tends to turn a rather drab yellow. Leaves of some species, such as elms, simply shrivel up and fall, exhibiting little color other than a plain looking brown.

So what conditions make the best fall colors? A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions -- lots of sugar and lots of light -- spur production of the brilliant red, purple and crimson pigments.   The yellow pigment, carotenoids are always present in leaves, therefore the yellow and gold fall colors remain fairly constant from year to year.  The amount of moisture in the soil also affects autumn colors. Like the weather, soil moisture varies greatly from year to year. The countless combinations of these two highly variable factors assure that no two autumns can be exactly alike. 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.

Our 2010 season has had all of the requirements for a spectacular fall color season.   A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.  If our stretch of fine fall weather continues we should have quite season to enjoy.

August Hoppe

Certified Arborist WI-0477A

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