Why do Leaves Change Color?

Our landscape is bursting with color right now. It’s full of yellows, oranges, reds, purples, and browns of deciduous trees – just check out Instagram or Facebook and your eyes will feast on the beauty of the changing leaves caught by so many of us on our cameras. The river valley, especially, gets a lot of coverage at this time of year.

So why DO deciduous leaves turn color?

Let’s take a quick look at photosynthesis and the role of chlorophyll first as a background to this question. Leaves provide essential nutrients for trees via photosynthesis. Photosynthesis is the process by which sunlight energy is converted into food (sugar) energy. Chlorophyll is a green substance that is essential for photosynthesis to occur. When chlorophyll is active, it gives the dominant green color to leaves all summer and spring.

The factors that influence the color leaves turn are the following:

  • Day & Night Length
    • In response to a shortened amount of sunlight – the longer nights and shorter days of autumn signals chlorophyll to begin to breakdown and disappear from the leaves. At the same time, trees produce a protective seal at the point where the leaf meets the stem or branch. This seal reduces the amount of water and other substances available for photosynthesis causing shift in its focus from production to storage.
    • Cooler and longer nights increase the intensity of leaf colors.
  • Color Pigments
    • Yellow & orange pigments are actually a natural part of the leaves but chlorophll masks those colors
    • There are basically 3 color pigments for leaves:
      • Chlorophyll = is green in color, it gives the dominant green hue during the active growth phase.
      • Carotenoids = give the deeper yellows, oranges, browns – you don’t see these colors until autumn
      • Anthocyanins = give shades of red & purples and all the colors in between – these pigments are not present until the autumn, they are produced by chemical changes that happen as sugars get trapped & stimulate this production of these chemicals. The red color of maple leaves is caused from trapped glucose in the leaves