Connecticut
NATURE
Science and Common Core State Standard 3.2.B.3, 4,2.B.10, 4.3.B.12, 5.3.B.22, C.INQ.6, 6.2.C.4, 8.3.C.28, 3.MD.1, 4.NBT.3, 4.NBT.4, CC.RI,10
WHY ARE THE LEAVES FALLING?
Article written by Michelle Eckman, Connecticut Audubon Society
It’s raining leaves in colors of red, orange, and gold! Back when I was a child, my father used to rake the fallen leaves into piles and me and my
brother used to jump and play in those mini mountains of color. What I didn’t know then is that there is a wonderful and scientific story behind this
beautiful phenomenon.
When you look around as you drive in a car or on a bus, you may notice that not all trees lose their leaves each fall. Some keep them all year. We
call these plants evergreens. The plants that lose their leaves each year are called deciduous plants – like maple and oak trees. The reasons why
their leaves change colors and fall off the plant are all because of earth’s shape and behavior in the solar system. Really, it’s true! Something as
simple as what a plant does is completely driven by the shape of our planet and what it is doing as we exist in the universe. Wow!
Think about it – what does our planet do throughout the course of a day, a month, a year? All year long, we are in continuous movement around
the sun – this movement is called a revolution. This process takes one year, or 365 days. What else is earth doing? Earth is also rotating on its axis,
spinning around and around which takes one day or 24 hours. Is there anything else special about earth’s behavior? There is something else pretty
important that we cannot forget – earth is tilted on its axis. This tilt plays a pretty important role in the story of why leaves fall off the trees, too. In
the winter, the North Pole is “pointed” away from the sun, and during the summer the North Pole is pointed towards it. What does the sun provide
for us? Heat and light. Keep this in mind.
As earth is on its tilt, revolving around the sun as we spin on our axis (whoa – I’m getting dizzy just thinking about it!), what do we experience? Our
revolution and tilt give us our seasons, but does every part of our earth experience the same seasons, the same climate, the same weather? Of course
not! Places close to the equator are warm throughout the year, and the seasons do not change much. As you move further from the equator, climates
are cooler and have more differences between the seasons. As you get closer to the North and South Poles, you are even colder because those areas
are further from the sun and do not receive the same amount of heat energy as areas that are physically closer, like the equator. Where you are on
the planet is also an important part of this story.
Let’s think back to what plants need to survive: sunlight, water and carbon dioxide. Recall this past summer and compare it to yesterday. What time
did you go to bed? What time did it get dark? There is a pretty big difference, right? That’s because of where we are on the planet, because we in
the Northern Hemisphere are “pointed” away from the sun right now and receiving less of its heat and light energy – its colder and we have much
shorter days and longer nights. Plants need plenty of sunlight to photosynthesize and if they do not receive enough
of it, they simply will not survive. Evergreens have really small, thick leaves that can survive throughout a long, cold
winter. Deciduous trees have larger leaves that can easily freeze and cannot absorb enough sunlight during short days.
It would not make sense for these trees to die every winter (how else would they grow so big and tall?), so deciduous
trees have a different adaptation for survival. Rather than die each year, they essentially stop photosynthesizing. In this
process, the trees absorb the nutrients from the leaves back into the stems – this causes the leaves to change color!
Then, when a nice breeze blows, the dying leaves fall off the trees in a shower of color.
As earth continues its revolution and we head towards spring, the days start to get longer. The deciduous plants then
send out a signal to start growing new leaves once again. It is a wondrous and beautiful cycle we are lucky in
Connecticut to experience each year. Hopefully now that you know the story of the cycle, it is still magical for you.
Did You Know
Did you know that deciduous trees like maples
and oaks “hibernate” for the winter?
Prove it
to
yourself
Prove it to Yourself:
We know that the days change in length throughout the year, but it is fun to get the proof. Keep a daily
journal of sunrise and sunset from now until the end of your school year. In your journal, write down the date,
the exact time of sunrise and the exact time of sunset. You can find this specific information easily on the
internet or on the front page of most newspapers. Every once in a while, total the number of hours and
minutes of daylight for each day. What do you notice happening over time? Do you notice there is a time
when the days get shorter and then start to get longer? Compare this information to your observations of
what is happening to the plants outside.