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Senescense: Why leaves change color

Here at Sierra Outdoor School we have few large trees that provide the bulk of our autumn color: black oak, big leaf maple, and Pacific dogwood. All of these trees are deciduous - meaning that each year they shed all of their leaves, remain leafless for a period of time, and then grow all new leaves. The process where the leaves prepare to fall from the tree, or the cells gradually deteriorate as they age, can be referred to as senescense. During this process of senescense, the pigment levels in the leaves change producing the much awaited fall colors.

Pacific dogwood leaves changing along the ditch trail at S.O.S.
The change in day length and temperature signals deciduous trees to begin the process of senescense by first sending any nutrients available in the leaf to other parts of the tree. The next step is to breakdown chlorophyll, the pigment that gives leaves their green color and allows for photosynthesis to occur. As the dominant green pigment slowly disappears, other colors are revealed: yellow, orange, red, and purple. After the chlorophyll is gone, the other pigments will breakdown. At the same time, the cells of the leaf stem are changing so that the leaf will eventually fall off the tree and leave a sealed, leaf scar behind.

Unusually colorful black oak leaves at S.O.S.
In addition to light and temperature, water availability also helps to determine the intensity and duration of the fall colors. If you live in an area with maple, dogwood, and sumac trees they are known for their bright red and orange leaves. These colors are at their peak when temperatures are low, yet above freezing, and also after an early frost. While less intense colors are created from rainy and overcast weather. These photos were all taken along the ditch trail here at S.O.S. Wherever you are, we hope you take the time to enjoy these beautiful changes around you!
Big leaf maple leaves in various shades of yellow

If you'd like to learn more about autumn colors, check out these reference pages:




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