Why Leaves Change Color and Other Fall Facts

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Autumn is a second spring when every leaf is a flower.

-Albert Camus

I like to think of fall from an Alice In Wonderland perspective. That is, autumn is a time when we shrink in proportion to our gardens while the leaves ‘bloom’ above us. And every year nature charts new territory, unveiling color schemes so daring they leave little doubt as to her ability to create designs far superior to our own.

IT’S NOT JUST ABOUT THE COLD

Many people think that cold temperatures cause leaves to change color. But the process is in fact a bit more complex. Although weather can affect the intensity and duration of color, the color itself is a part of each tree’s biology. And just like flowers in a garden, each tree has its own ‘bloom’ period that occurs at different times during the fall season.

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Nature’s garden

WHY DO LEAVES CHANGE COLOR?

Leaves change color as a part of their natural life cycle. During the growing season, leaves act as food factories for trees, capturing sunlight to turn carbon dioxide and water into oxygen and sugar. A chemical called chlorophyll, which absorbs light energy, is responsible for making this happen. It is also the reason why most leaves are green.

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Chlorophyll gives leaves their green color

But in the fall, shorter days and cooler temperatures trigger the leaves to stop their food-making process. As the chlorophyll breaks down, the green color disappears from the leaf surface. Yellow and orange (two colors which until now have been masked by the stronger pigment green) start to become visible. These accessory pigments have a different molecular structure than chlorophyll, and take longer to break down.

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Orange-yellow sassafras leaves on Maryland’s Eastern Shore

Some trees like maples, sourwoods and sweet gums, however, start making brand new pigments, producing brilliant shades of red, scarlet and purple with the onset of fall. Often you’ll see these colors mixed in with the orange and yellow accessory pigments.

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Maple tree in fall

As the season progresses and temperatures drop further, the cells near the juncture of the leaf and stem weaken and the leaves start falling from the tree. The accessory pigments begin to break down, the leaves dry up, and only a brown color remains. Some plants, like oaks, retain this brown foliage for most of the winter.

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Sycamore leaves turn shades of brown

WEATHER HAS A BIG EFFECT

No, weather won’t cause leaves to change color, but it will affect color intensity and duration. This is the reason why each year the landscape looks slightly different. Temperature, amount of sunlight and available water supply all play a role in leaf color.

Lots of sunlight combined with low temperatures, for instance, produces brighter reds but shortens their duration. An early frost, however, spells the end of the show. And drought stress during the summer can result in early dropping of leaves before they have a chance to develop any color at all.

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Sugar maple leaf in process of changing color

Surprisingly, a combination of rain and overcast days tend to increase color intensity.

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The best and brightest show, however, usually follows a growing season with lots of rain followed by a dry spell.

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Looking for a great location to see leaves change color? Click here for America’s 10 Best Places to See Spectacular Fall Foliage. It provides an overview of each area and great places to stay. Happy fall!

 

 

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