We live in an area of the world where we can experience the phenomenon of fall color change. Every year we ask ourselves, Will we have good fall color? Every year the show of colors is different, but why? With the glory of fall now in full effect, it’s time to look at the science of autumn beauty.
As many of you remember, clorophyll is what makes leaves green. Through the process of photosythensis sunlight is used to transform carbon dioxide and water into carbrohydrates which fuels the growth of the tree. During the spring and summer sunlight levels and tempuatures are high, making the photosynthetic process very active and keeping leaves green. As daylight hours and temperatures decrease the process slows down and the colors that remain in the tree leaves appear. Different tree species contain different chemicals such as: Anthocyanins (Reds & Purples), Carotenoids (Orange & Golds) and Tannins (Browns).
With that simple rule in place we now look to what causes yearly and locational differences.
Temperature: The greatest opportunity for great fall colors are cool nights, but not below freezing. Early frosts will reduce the brilliancy of colors as it slows or stops the production of anthocyanins. New England states are known for their great fall colors because freezing rarely occurs early in the fall due to its proximity to the ocean.
Moisture: Stressed plants show their colors earlier than healthy plants. Drought years will produce more reds than usual as there is an increase of anthocyanins. Drought years will also produce colors earlier than usual. A wet spring will promote good color as stored sugars in the leaves are released.
Sunlight: Optimum conditions are for bright sunny days. During the ‘changing’ period sugars in the leaves are produced more rapidly when exposed to direct sunlight. This is why leaves on the outside of the canopy change faster and with more brilliancy. Fall weather that is overcast and rainy does not provide very showy displays.
To summarize, for optimum fall colors we would want all of the following conditions to be in place thoughout the year: A warm wet spring with favorable summer weather followed by sunny fall days with cool temperatures at night but not freezing. Easier said than done but certainly a dynamic part of nature that everyone can appreciate.
http://www.fs.fed.us/news/fallcolors/ US Forest Service Fall Color Hotline
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