Have you ever wondered what triggers leaves to change color in the fall? The most important regulator of fall color change is the lengthening of night. Longer, cooler nights and less intense sunlight during the day trigger leaves to prepare to fall from the tree. Chlorophyll production slows and eventually stops, and the veins that carry fluids into the leaf close off, trapping sugars in the leaf and promoting production of anthocyanin, a pigment that produces red colors. The green chlorophyll in the leaves is eventually destroyed, leaving behind the yellows, oranges and reds that signal fall.

Weather and climate conditions also impact when leaves begin to change color, how intense color is, and how long color lasts. A warm wet spring followed by typical summer weather and a fall with warm, sunny days and cool (but not freezing!) nights generally produce the best color. A late spring or severe summer drought can delay the onset of color, while a warm period during the fall season may dampen fall colors. Wind and rain storms can bring leaves down early, shortening the fall foliage season. Other environmental factors, like damage from insects or wildfire, can also impact tree foliage.

Enjoy what fall has to offer. Take a walk in your neighborhood, visit a local park, or hit the road on one of Americas National Scenic Byways, many of which were planned with fall color in mind. Use this illustration to identify some common trees and their fall foliage where you live and dont forget to upload your fall foliage photos to the Eyes on Central PA Mission!

Want to go a step further? Fall into Phenology with Project Budburst by observing plants in your community during September and October and sharing your observations to help scientists study trends in how plants change in the fall. Dont know much about plants or need help with identification? No problem. Project Budburst has tips for beginners and experts alike. Learn more.

(Sources: U.S. Forest Service Science of Fall Colors. http://www.fs.fed.us/fallcolors/2012/science.shtml; William Deedler, National Weather Service. Faster Fall Foliage? http://www.crh.noaa.gov/dtx/foliage.php Project BudBurst, http://www.budburst.org)

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What Causes Our Bright Colors of Fall?