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Why Do Leaves Change Color in the Fall?

September 28, 2017

 

 

The French writer Albert Camus called fall “a second spring where every leaf is a flower.”  In Colorado, we are lucky enough to have one of the most dazzling “second spring” color displays in the world.  Colorado aspens transformed into a shimmering sea of gold on a warm September afternoon is truly a sight to behold and the next few weeks should be prime fall foliage viewing.  But have you ever wondered why it is that leaves change colors in the fall? 


Chlorophyll

 Throughout the spring and summer, a tree’s leaves are filled with chlorophyll.  If you recall from your 12th grade science class, chlorophyll is the amazing chemical that converts sunlight into energy during photosynthesis.  It is also responsible for the green pigment that is visible throughout the year. 

Though leaves also contain other chemicals, such as carotenes and xanthophyll pigments which create colors like orange and yellow,  all of the active green chlorophyll covers up all the other colors and makes the leaves green.


Chemical Changes
During the fall, the shortened days and cool nights are a signal for the tree to begin preparing for winter.  The tree slows its food making processes and the chlorophyll begins to drain from the leaves.  As the green colored chemical exits the plant leaves, other pigments that have always been there are finally revealed.  The leaves emerge in vibrant oranges and yellows.  Sometimes other chemical reactions occur creating anthocyanin pigments, which result in the brilliant reds of maples or dogwoods. 

At the same time, a special layer of cells forms at the base of the leaf.  This gradually cuts the tissue connecting the leaf to the tree until it is gently carried away on the autumn breeze.


Just like flowers in the spring, the beauty of the autumn leaves is fleeting.  Temperature and weather play a big part in just how vibrant the spectacle will be.  For the best fall color viewing, cross your fingers  for clear, dry and cool - but not freezing - weather this fall.  An early hard frost can mute fall leaf colors.  Search the Colorado Department of Parks and Wildlife's Park Search for up to date fall color information.