Science behind the changing leaves

autumn leaves

(By Nick Paliswat, Belmont SWCD)

Fall is fast approaching and some weeks have already felt like fall this time around. Yet, inevitably the temperatures seem to keep staying in the 80s through the end of August and into September.

Officially, Sept. 23 is the first day of fall. But outside of this dreadful rain we’ve been experiencing, with fall comes an immense change in seasons.

The air begins to cut through you instead of providing a replenishing cool from the hot sun. My personal favorite is watching the leaves turn and seeing the beautiful trees Ohio has to offer.

If I had to bet, I would guess that most people have never sat down and asked themselves how or why the leaves change. I have heard people say that the trees just know to do it every year.

Leaf science

It’s not quite that simple. There are three major factors that play into leaves turning and giving them their brilliant color. We first have to look at the pigments in the leaf itself.

Chlorophyll, which is what gives leaves their basic green color during the summer, has a role in the process of photosynthesis to help the plant make sugars to use as food. Carotenoids are pigments that give yellow, orange, and brown colors and are found in the chloroplasts of plants.

The third pigment is anthocyanin, which appear in liquid parts of leaf cells. Here you get your reds and purples. All of these, combined, determine the color of the leaves. All trees have different amounts of these pigments, which generally gives each species its yearly red or yellow leaf color in the fall like oaks and poplars.

The kind of species also seems to determine when the leaves change color.

Shorter days

Length of day is the next key factor that plays a major part in when the leaves actually start to change. As the daylight gets shorter in the fall, the leaves have less time for photosynthesis causing less sugars and food to be produced.

At this time, the amount of chlorophyll in the leaves is falling off and this is where the color starts to come through. Weather is the third player in color change. The amount of sunny days, rainfall and temperature can all affect how well leaf color comes out.

More sunlight and moderate rainfall mixed with warmer temperatures will cause the best colors to show. The trick is to have cooler nights to stop the sugars from leaving the veins and backing up. This is what causes the anthocyanins to be produced.
Dying off.

As fall wears on and the temperatures cool off into freezing points, this causes a layer of cells to build over the veins, completely closing off the end of the leaf. At this point, the leaves are ready to fall.

They will be broken down and recycled back into the earth as if they never had existed. As a side note, I would also have to bet that about half of the population doesn’t know the two most basic names for how trees are separated in the world.

The two categories are deciduous trees, which means their leaves drop every fall and coniferous trees, which generally have needles instead of leaves and they do not drop every fall. Wouldn’t you know, there are exceptions to this like everything in science.

There are deciduous conifers like the larch tree. When looking out your window this fall or driving down the highway, hopefully a stronger appreciation for one of nature’s most captivating processes can start to build as the beauty of color fills your soul.

(Nick Paliswat is an administrator with the Belmont County SWCD. He can be reached at 740-425-1100, Ext. 3)

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