Fall is a beautiful time of year in some places because we see leaves changing color from green to red, orange, brown, and more. In this lesson we’ll explore why this happens.
A Colorful Season
If you live in the northern part of the U.S. you’ve seen the beautiful phenomenon of the leaves changing color in the fall.
They turn from bright green to yellows, reds, purples, oranges, and browns. But why does this happen? And why in the fall?
Chlorophyll is Colorful
Plants are living organisms and they need sunlight, air, and water to survive. They process sunlight into food through photosynthesis, and the major player in this chemical conversion is chlorophyll. Chlorophyll is what makes plants green because it absorbs other wavelengths of light in the visible spectrum like red and blue.
During the spring and summer plants look green because they are producing a lot of chlorophyll in order to photosynthesize and make lots of food.
But there are other pigments in plant leaves as well that take a backseat during these high production times. These other pigments are called carotenoids and anthocyanins. Carotenoids produce colors such as yellow, orange, and brown.
You can remember this because carotenoids are found in carrots, which are orange and which sounds like carotenoid. We also find them in bananas, daffodils, and corn. Anthocyanins are reddish colors and we find this pigment in other things like cherries, red apples, and strawberries.
Fall Triggers New Colors
So if these other colors are there, why don’t we see them during the rest of the year? Turns out they are masked by all that chlorophyll because there’s just so much of it being produced. But come fall, both the temperature and the amount of daylight change which tells the plants that winter is coming. In response, plants slow their chlorophyll production and eventually stop it altogether.
The chlorophyll that’s left starts breaking down, allowing carotenoids and anthocyanins their time to shine. These colors come out in full force and create beautiful displays that we associate with fall in these regions.
Weather is an important factor in the intensity and amount of color we see each fall, but soil is also a player in this game. The moisture in both the air and the soil influences when the leaves change and how intense the colors become.
Leaf color and timing is also species-specific. Some trees like oaks, turn brown and red, while aspens turn yellow. Oaks are also knowns for holding onto their summer colors until after other trees have already lost their leaves, while more southern sourwoods might change color as early as late summer.
Unfortunately, as you know, leaves don’t stay these beautiful colors until spring. Instead, they eventually fall off the trees leaving them bare for the cold winter months. This is a trick of the plant that helps it conserve energy throughout a time when food isn’t being produced like it is in the spring and summer.
Instead of sending food and water to all those leaves, the tree cuts off their supply, closing off the veins that carry fluids out to them. A layer of cells forms where the leaf meets the tree, eventually separating the leaf completely from the tree. The leaf then falls to the ground.It sounds harsh, but it’s actually very beneficial for trees to dispose of their leaves during this time period. Leaves just aren’t equipped to deal with the cold temperatures of winter, but twigs and stems are up for the task. So instead of wasting energy on leaves that will only freeze and die, they shed them and focus on the parts that will survive the season.
In some areas fall is a spectacular time of year. This is because the leaves on the trees change from green to brilliant reds, yellows, oranges, purples, and browns. These pigments are actually in the leaves during the rest of the year, but because the production of green chlorophyll is so high, they are masked.During spring and summer when the leaves are green the tree is taking in sunlight and photosynthesizing to make food. However, when the temperature cools and the amount of daylight decreases, the plants slow and eventually stop their chlorophyll production altogether.
That’s when the carotenoids (orange, yellow, and brown pigments) and anthocyanins (red pigments) get to shine.Eventually, the leaves will fall off the tree as the veins that supply nutritious fluids to them close up and seal off the connection. The tree does this because the leaves are not equipped to handle the cold winter months.