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Fall Colors in Winter: A Reason Why

Fall Colors in Winter: A Reason Why
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Swale Leaves by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.Swale Leaves

Swale Leaves: Leaves of multiple colors lie in a drainage swale at Bainbridge Island's Battle Point Park. Photograph taken January 1, 2012.

I enjoyed a New Year’s walk in Battle Point Park on Bainbridge Island, Washington yesterday. Although numerous trees looked wintery, some still hung on to their bright, fall color foliage. Near those trees, at least the ones giving up to winter, vibrant, multi-color leaves filled drainage swales.

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Fall Colors in Winter by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.Fall Colors in Winter

Fall Colors in Winter: Autumn sugar production creates the reddish purple, but the yellow from the growing season hangs on. Photo taken January 1, 2012.

Here’s a bit about fall colors, all gleaned from the United States National Arboretum website (2011). It begins with the growth process, discussing buds growth, nutrient absorption, and fall colors. The possible reason for the extended vibrancy this season is given at the end.

Deciduous Trees’ Growth Process

A tree’s growth process determines how it reacts to its environment with respect to fall leaves.

Buds

  • New buds emerge from stems when days lengthen and the temperature rises enough to support growth
  • Growth usually ends in June within the Northern Hemisphere (where Bainbridge Island is)
    • At this time, the leaves are fully expanded
    • The leaves convert the sunlight to chlorophyll to nourish the tree
    • The chlorophyll gives them the green color
    • During the longer days and higher temperatures, the leaves absorb carbohydrates and transport them to the rest of the tree
  • Next year’s buds will not open until the following year when the days lengthen and temperatures rise again

Chlorophyll Production Ceases

  • The tree’s roots, branches and buds store carbohydrates to support the following year’s growth
  • When the days shorten and temperatures drop beyond growth and carbohydrate absorption abilities, the corky cell layer (abscission layer) blocks flow of carbohydrates from the leaf to the branch
  • During this time, minerals from the tree are blocked from the leaf
  • The leaf slows, and eventually stops its production of chlorophyll
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Fallen Color by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.Fallen Color

Fallen Color: Most of the leaves fell off this tree, though both red and yellow ones still hang on. Photo taken January 1, 2012.

Fall Colors Revealed

  • The chlorophyll masked the leaves true colors
  • yellow = xanthophylls (harvests light energy)
  • orange = carotenoids (harvests light energy)
  • red and purple = anthocyanins (manufactured from sugars in fall – typically not in growing season)
  • browns – from tannins (left after the yellow, orange, red and purple colors break down)

Leaves Fall

  • The corky cell layer (abscission layer) dries and weakens during the fall process
  • As the connection weakens, it breaks and the leaves fall off the tree

So Why the Length in Fall Color during 2011 – 2012?

This isn’t specifically discussed in the United States National Arboretum website. However, we had a fairly cool and EXTREMELY late summer (I’m still a little bitter), and a fairly mild winter with quite a bit of sun, at least in the Pacific Northwest.

Reference

The United States National Arboretum

2011   The Science of Color in Autumn Leaves. In Arboretum Plant Photo Gallery. In the United States National Arboretum website. Electronic document, http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html, accessed January 2, 2012.

 

Creative Commons License
Fall Colors in Winter: A Reason Why by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.


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