The science behind the scenery – a lesson in leaf peeping

Why do leaves change colors and fall? We'll learn about it all.

RAPID CITY, S.D. — Every year, we wait patiently for the leaves to begin making their transition from green to yellow, marking the appropriate moment to splurge on our first pumpkin spice latte of the year. After summer, the air gets colder, which makes the leaves change colors and dry up, right?

Aspen trees begin to turn yellow.

Leaves on Aspen trees begin to turn yellow this fall.

Well, not exactly. There’s a lot more to the transition than meets the eye.

The green color in leaves comes from chlorophyll, which is the chemical that allows plants and trees to transform sunlight into energy.

Green isn’t the only color present in leaves though- yellow, orange, red, and even purple are in there too. During the spring and summer, the chlorophyll is so active and strong that green overpowers all of the other colors.

When fall starts, there are less hours of sunlight, and the trees sense the drop in the amount of sunshine their leaves receive. They begin to produce less chlorophyll and the green pigments break down, so the other colors shimmy into the spotlight. Drought conditions can also lead trees to stop producing chlorophyll, so leaves usually turn earliest after a dry summer.

There’s also more to the shedding of leaves than you might initially think. As chlorophyll production decreases, a special layer of plant cells forms right where the stem of the leaf meets the tree. This layer slowly cuts the leaf off from the tree, so the leaf starts receiving less nutrients and water and eventually falls off.

So, it’s not the colder air that dries up the leaf, it’s actually the tree itself, letting go of the parts it won’t need to make it through the winter.

How come some trees keep their leaves then? There are two types of trees- deciduous and coniferous.

Deciduous trees are the ones we’ve been talking about- they lose their leaves, conserving energy and storing nutrients for winter. Coniferous, trees, on the other hand, keep their needles season after season.

The two kinds of trees simply choose to spend their energy differently. Deciduous trees spend their energy dropping and then re-growing their leaves, but don’t have to put as much effort into staying alive during the winter. Coniferous trees don’t have to drop and then re-grow their needles, but they do have to function and produce energy through the winter, when resources are harder to come by.

Next time you bundle up in a scarf and jump into a big pile of leaves, think of all of the little plant cells and pigments that went into that pile, and remember that spring’s new buds are just around the corner.

Categories: Local News, South Dakota News