Why do Leaves Change Color in the Fall?

October 20, 2009

You may be curious as to why a tree’s leaves change color during fall and what makes some fall seasons better than others for vibrant color. Visit http://www.davey.com/fall to download the full Davey fall tree care checklist.

Fall foliage is particularly spectacular in Northeastern North America because it is one of the few places in the world with the unique combination of deciduous trees and the right climate to produce brilliant fall colors.

Greg Mazur, Davey Tree Service expert and ISA certified arborist, explains why trees’ leaves change color in the fall and why fall colors can be intense one year and less so the next.
Four pigments provide the spectacular array of fall color:

1. Cholorphylls – This pigment gives leaves their green color during spring and summer, when the rate of photosynthesis should be vigorous

2. Carotenoids – This yellow or orange pigment gives the carrot its familiar color. It gives Norway Maples, Ohio Buckeyes, Sycamores, Birches and many other species their golden hues during the fall.

3. Anthocyanins – Think the pink, red and purple you see on sassafras, scarlet oaks, and some maples during the fall.  Often mixed with yellow carotenoids to form brilliant orange coloration, seen on maple species. 

4. Tannins – The brown hues popular on many oaks as well as the copper coloration of beech leaves, when mixed with yellow carotenoids. 

Really striking, intense color occurs when warm, sunny days are followed by cool nights – temperatures below 45, but above freezing. Why do some fall seasons have better color than others?

• Rainy and cloudy days limit photosynthesis and decrease the intensity of fall color. 
• Freezing temperatures can kill or severely injure leaves before the pigment in the leaf hits maximum development. 
• Heavy winds and rains can sweep leaves off trees, ending fall color early.

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