Fall season: Why do leaves change color in the fall?

CW39

How did Sept. 22 become the official first day of fall? Why is it called fall? And why are pumpkins such a big thing this time of year? (AP Photo/Toby Talbot)

HOUSTON, Texas (KIAH) Though fall is now here, we may not see those leaves changing outside in Houston just yet, other areas across the country have began welcoming the hues of yellow, orange and red.

While there are places to locate fall foliage on the prediction map this early in the season, November 15th is usually when our location in Southeast Texas sees near peak, and peak foliage conditions. Red Maples, different oak species, especially the Shumard oak, bald cypress and sweet gum sometimes called red gum are trees are native to Texas and well-known for their fall foliage.

So what causes the leaves to change during the fall season?

The short answer:

As autumn arrives the days start getting shorter and there’s also less sunlight. As this change begins to happen it also acts as an indicator for leaves to begin preparing for cooler weather and stop making chlorophyll. Once this happens, the green color starts to fade and we begin to see the reds, oranges, and yellows. Click here to see

Meteorologist Russ Pappas joins CW39 Houston’s meteorologist Star Harvey with more details on the science behind the changes. Here’s a look:

During the growing season, leaves are working constantly to produce sugars via photosynthesis, which is the conversion of light to energy. These sugars are shipped throughout the plant for growth and storage. It is during this active production time that the vibrant green colors are dominant.

Chlorophyll (the green pigment) is found in nearly all plants and is a key component in photosynthesis. It breaks down readily in sunlight and is replaced constantly throughout the growing season. Further information about leaf color change follows.

Carotenoids and xanthophylls (the orange or yellow pigments) also aid in photosynthesis and are produced throughout the season but are masked by the “green machine” of chlorophyll production. However, when photosynthesis slows and chlorophyll breaks down, the “hidden” orange and yellow pigments become more apparent and fade at a much slower rate. Quaking aspen, ginkgo, Norway maple, ash, birch and honey locust are a few examples of trees containing these pigments.

Anthocyanin (the pink, red or purple pigment) can vary from year to year. Anthocyanin is produced primarily in the fall and is found in species such as certain maples (like our native Bigtooth maple), burning bush, flowering pear, sumac and dogwood. The determining factors influencing the production of these pigments are the amount of sunny days and cool (but not freezing) nights.

Tannin (the boring brown pigment) is the last pigment to break down in a leaf before it falls. Oaks or other non-showy species, notorious for having leaves containing tannin, are the final reminder that winter doldrums are soon to follow.

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