Why Do Leaves Change Color?

Source: Lisa Allen of Madison, Alabama.

Source: Lisa Allen of Madison, Alabama.

Who doesn’t enjoy the vibrant yellow, orange, red an deep purple hues of the leaves during the Fall season….but ever wonder why leaves change color?

To explain why leaves change color, we’ll have to take a visit back to grade school science. Photosynthesis is the process in which plants make food, by using sunlight and carbon dioxide and turning them into oxygen and glucose. A chemical called chlorophyll is necessary for photosynthesis to occur and is present in the leaves and is actually responsible for giving plants their green color.  Below is an image to try and help explain the process of photosynthesis.

As Summer ends and Autumn begins, the days get shorter and shorter and the food making process starts to shut down and chlorophyll is no longer produced. That’s when we start to see the yellow and orange hues which have been in the leaves all along and are the pigments of carotenoids which are also present in leaves, but their color is masked by the green pigment of chlorophyll.

What causes the deep reds and purples, like in the red maple leaf below are anthocyanins, which are produced when there is glucose that is trapped in some of the leaves after the growing season ends.  The combination of cooler nights and sunlight, along with the glucose, produce the anthocyanins.

Source: Lisa Allen of Madison, Alabama.

According to Jeff Bennett of Bennett Nurseries the most abundant trees across the Tennessee Valley are several varieties of maple, oak, birch and dogwood.  Jeff also states that tulip poplar, river birch and some of the sugar maples are trees that you will see start turning yellow early in the season, whereas other sugar maples and dogwoods are a couple of the last trees that start changing color.

Temperature and moisture are the two main influences on the brightness of Fall colors. Thanks to above average monthly rainfall totals from July and continuing into October, the early Summer drought across the Tennessee Valley disappeared. By looking at the Weekly Palmer Drought Index below, most of North Alabama is moderately moist. There have been similar conditions in southern middle Tennessee. With ample rainfall and warm days and cool nights, but no freezing overnight temperatures, has allowed for a vibrant display of Fall colors this year.

The colors are starting to peak right now and will continue into early November.  Though keep in mind the longer you wait to take time to view nature’s beauty, the more leaves will have fallen.  With a cold front moving through late Friday, early Saturday and the rain and gusty wind expected with it’s passage, it will help to blow more leaves off the branches. The two images below are from The Foliage Network that collects data from foliage spotters twice a week to give the most accurate foliage information.  Unfortunately they do not have maps for Alabama, but basically the data for southern, middle Tennessee can be applied to most of North Alabama. The first image is showing colors nearing peak, which will continue over the next couple of weeks.  The second image shows the observed “leaf drop” or the observation of leaves starting to fall off of the trees, which has become ‘moderate’.

Lastly, below is a picture I do from Chapman Mountain looking toward Monte Sano, with radiant red already painting the landscape.

So take an hour out of your day this week and appreciate what Mother Nature has to offer!

- Jennifer Watson

Twitter: @JWatson_Wx

Facebook: Jennifer Watson WHNT