The science behind why leaves change color
September 23, 2018
Fall has fallen upon the Vail Valley and the aspen groves are providing quite a show. Beyond the beauty, there is a science behind this chemical color change. We met up with Peter Suneson, community programs manager for Walking Mountains Science Center to learn more.
Despite different theories and prognosis from the public, the changing colors are due to the amount of daylight hours the trees experience. Trees and other plants are able to sense day length or photoperiod by means of a substance called phytochrome. "Scientists believe that changes in the photoperiod are linked to the phytochrome’s production of growth regulators in the plants. Long days produce lots of auxins and gibberellins, chemicals that stimulate growth, and produce low levels of abscisic acid, which is a growth inhibitor," said Suneson.
"Trees that are close to street lamps or artificial light tend to change color later than trees far removed. This is because they are experiencing an artificial day length when the street lights are on," said Suneson.
With a shorter phototrophic period, the aspens prepare for dormancy by forming a cork-like dam where the leaf attaches to the branch. This dam prevents the flow of nutrients needed for photosynthesis, leading to a decline in the production of chlorophyll, or the green color present. As the chlorophyll breaks down, the colors previously masked by the green begin to appear.
Aspen trees are dominant in our area, so we see quite a bit of yellow-colored leaves. This is due to carotenoids, which absorb blue and green light. Sometimes aspen groves will have more of a red tint on their leaves, this is due to the anthocyanins.
Leaves tend to change faster north-to-south and in higher elevations first. "Elevation is visual representation of things like temperature, oxygen availability, nutrients, and genetics coming together to influence color change," said Suneson.
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Whether you need to know the exact reason why leaves change color or just want to sit back and enjoy the beauty, don't delay, the colors don't last long. Weather conditions such as wind and precipitation can play a factor in how long spectacular foliage will stick around.