What exactly causes the trees back east to change colors in autumn? The answer might surprise you in how the cause actually has less to do with what’s in the leaves, than what disappears from them when the days get shorter. Fall Foliage – What’s Up With Those Colors, and Why Are the Trees in Tahoe so BORING? | Unofficial Networks

Fall Foliage - What’s Up With Those Colors, and Why Are the Trees in Tahoe so BORING?

Fall Foliage - What’s Up With Those Colors, and Why Are the Trees in Tahoe so BORING?

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Fall Foliage - What’s Up With Those Colors, and Why Are the Trees in Tahoe so BORING?

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An Aspen Grove in…Aspen, CO

This week, I’m thinking forward to winter, and my favorite time of year that stands between it and the end of summer – autumn. I spent my high school years in western Pennsylvania, where autumn brings an explosion of colors to the leaves on the deciduous trees that comprise the forests of the region.

Fall leaves, from elegantstagers.com

While I love the thick pine forests of Tahoe, every fall I always feel a little underwhelmed by the lack of a fall foliage season like that enjoyed by the East Coast. Don’t get me wrong, there are some magnificent aspen groves around Tahoe, but they don’t quite measure up to the endless rolling hills of fiery maples and oaks of Vermont.

What exactly causes the trees back east to change colors in autumn? The answer might surprise you in how the cause actually has less to do with what’s in the leaves, than what disappears from them when the days get shorter.

Leafy green plants turn sunlight and carbon dioxide into sugar (glucose more specifically) via a process called photosynthesis. This process is made possible by an incredible chemical compound called chlorophyll. Clorophyll is naturally green, and it has such an intense color that it overwhelms the more subtle natural colors that lie in the leaves of many deciduous trees.

Vermont in Autumn, from Wikipedia

The term “deciduous” means “falling off at maturity,” and refers to trees that lose their leaves at the end of their primary growing season. In the Northern Hemisphere, this occurs in a September – November timeframe. When these months come around, the days get shorter and along with them their decline, the amount of sunlight diminishes. As a result, photosynthesis declines, and the chlorophyll in the leaves of deciduous trees starts to die as cork cells close off the veins in the leaves.

This decrease in the green color lets the fiery, vibrant colors that naturally reside in the leaves come through, and the leaves appear to change colors right before they fall off and die. Yellows come from xanthophylls, orange is derived from beta-carotine and other carotenoids, and reds and purples from anthocyanins. Several different theories as to why deciduous trees shed their leaves after an explosion of color – ranging from attraction of birds, to conservation of metabolic energy to get the trees through winter, to stunting the growth of nearby saplings via the chemicals that color the leaves when they fall on the ground.

Fall leaf colors, from the USDA

Why don’t the pine trees of Tahoe lose their needles? For one thing, coniferous trees are “evergreens,” in that they do not lose their leaves (actually needles) in autumn. Most conifers replace their needles in a timeframe of decades, not every year like the eastern oaks and maples. Also, unlike their more colorful cousins back east, coniferous trees only have green chlorophyll in their needled, and lack the other colors that lie dormant in the broad leaves of deciduous trees. So when the needles die, they stay  a plain, boring old green.

As I mentioned above, there are some really beautiful groves of quaking aspen trees in Tahoe, and these deciduous trees do turn a brilliant yellow color in late fall before they shed their leaves for the winter. Notable groves of Aspens grow on the side of CA Route 267 between Truckee and Northstar, and also high up in the Mt. Rose wilderness behind Incline Village.

One interesting factoid about Aspen trees – groves of them actually have interconnected root systems, and the “trees” are really shoots branching up and out from the same organism, or what’s called a “clonal colony.” A few weeks ago, I wrote about the oldest living organism on earth being one of the magnificent ~4,800 year-old bristlecone pine trees living up on the crest of the White Mountains down near Bishop, CA. While these pine trees are accepted as being the oldest living single organisms, there is an enormous grove of quaking Aspens in Utah called “Pando” that has been aged at over 80,000 years, and covers as much as 107 acres. Heated arguments continue as to whether these massive colonies of cloned Aspen trees with connected roots are legitimate competitors for the title of “oldest living thing.”

Wet Aspen leaves on a rock, Colorado

Lots of great tools exist to help you find the fall foliage hotspots, get out and go check them out if you are on the East Coast.

Fall Foliage Timeframe Map, from stormfax.com

Weather Channel Guide:
http://www.weather.com/activities/driving/fallfoliage/

Vermont:
http://www.foliage-vermont.com/

Maine:
http://www.maine.gov/doc/foliage/

Boston.com:
http://www.boston.com/travel/explorene/specials/foliage/specials/foliagemap/

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