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Fall Colors

Why do some trees have bright red and yellow colors in the fall while others have very little color change?

The primary force driving the color change is the decreasing amount of sunlight in autumn. Shorter days and cooler nights signal a change in the leaves biology and the fall mosaic of color begins to appear. As this change starts to take place, a few "biological artists" commence their work behind the scenes.

Chlorophyll is the compound that gives tree leaves their green color and is essential for photosynthesis. As the fall season grows near, trees produce very little chlorophyll, causing the green color to fade away. Another important element affecting leaf color are carotenoids, these are pigments responsible for producing yellow, brown, and orange colors in leaf cells. In the spring and summer these hues are masked by the green chlorophyll.

Lastly, as the cool weather arrives anthocyanins start to be produced in the leaf cells. Anthocyanins are pigments responsible for blue, red and purple colors. In foods such as blueberries and raspberries, anthocyanins are what give color to these tasty fruits. In trees, these pigments are produced primarily in the autumn and add the most vibrant colors to fall leaves.

As the growing season ends in late summer, chlorophyll in the trees is mostly removed. The removal of chlorophyll allows the carotenoids and recently produced anthocyanins to show their true colors. The best set of circumstances for producing fall colors is to have clear cool sunny days and cool nights without the freezing temperatures. Wet days will dull the fall show and drought years will cause the leaves to brown and fall off quickly

In the Driftless, the most opportune time to view the medley of fall colors is typically around the 10th of October. Some of the best leaf viewing in Fayette can be found at Goeken Park, Echo Valley State Park, and by driving the Rivers and Bluffs Scenic Byway. More information about this scenic road ca be found here

Iowa DNR Leaf Color Guide:

Walnut: Leaves turn bright gold and are often the first to drop in the fall.

Ash: Green ash leaves turn golden yellow, but white ash leaves have a purplish cast. Ash leaves fall after walnut trees, but earlier than those of oaks and maples.

Elms: Elm leaves turn various shades of yellow. Some turn brown before falling, while others fall while still yellow.

Hickory: Leaves turn yellow, then turn brown before falling.

Silver Maple: The leaves of soft maples turn yellow but do not turn brown before falling.

Sugar Maple: Brilliant flame-red hues are the signature of hard maple leaves. The red pigmentation of some leaves breaks down before falling.

Bur oak: Buff to yellow colors predominate in bur oaks. The leaves typically remain on the tree and turn brown before falling.

Red Oak: Red oaks have brilliant red leaves in fall and typically hold their color into early November.

White Oak: White oaks have a more subdued purple fall leaf color. The leaves then turn brown and often stay on the trees until new leaves begin to grow in the spring.

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