Why are Leaves Green?

• Green maple leafImage by Flickr.com, courtesy of tanakawho
  
  The green pigment in leaves comes from chlorophyll, a chemical produced during photosynthesis. Photosynthesis is the process by which the leaf absorbs sunlight and carbon dioxide and converts it to chlorophyll.
  
  

What Triggers Color Change?

• Short days mean less sunlightImage by Flickr.com, courtesy of Adam Baker
  
  While cooler temperatures and changes in weather are part of the fall season, the most consistent and probable triggers of color change are the shorter days. Less sunlight means the trees can no longer produce enough chlorophyll to maintain their green color.
  
  

Orange and Yellow

• Maple trees beginning their transformationImage by Flickr.com, courtesy of John Talbot
  
  Most trees, including maples, begin their color change with orange and yellow pigments. The orange comes from a substance called carotene, and yellow comes from a substance called xanthophyll. These chemicals are always present in leaves, but they are covered by the vibrant green of the chlorophyll. When the leaves no longer produce chlorophyll, the carotene and xanthophyll become visible. These substances most likely aid in photosynthesis.
  
  

Red Leaves

• Red maple leavesImage by Flickr.com, courtesy of Paul Keleher
  
  Maples are one of the few trees that turn a vibrant red in the fall. This is due to a particular substance called anthocyanine. After photosynthesis stops, there is still some glucose trapped in the leaf. The breakdown of that glucose produces anthocyanine, which turns the leaf bright red. Anthocyanine protects the leaf from frost.
  
  

Brown Leaves

• Brown maple leafImage by Flickr.com, courtesy of Patty O'Hearn Kickham
  
  Some leaves eventually turn brown before falling from the tree. The brown color is caused by tannin, which is a bitter waste product that builds up in the leaf. This is the last stage of maple leaf transformation.