Have you ever wondered how, or why the leaves on the trees start to change from green to all sorts of colors in the fall? And why do we call it “Fall Foliage”?
“Foliage” is just a fancy term meaning plant, or leaves from a tree. We refer to the term “Fall Foliage” when referencing the changing of the leaves on the trees. Why does this happen?
It all comes down to the changing of the seasons, and the amount of sunlight we receive throughout the year. Weather also plays a pivotal role in how much the leaves change and how vibrant they become from year to year.
During the summer, our length of daylight increases and the temperatures are the warmest, which signals to the leaves that it’s time to start making food again after a long winter.
Once fall comes around, the days get shorter and the temperatures get cooler, which signals to the leaves to stop their food making process. This results in the gradual breakdown of a pigment called chlorophyll that’s found in plants that gives them that lush, green color. Chlorophyll gives plants their green color because it does not absorb the green wavelengths of light. Since this color is not absorbed, it’s reflected off the leaves, and that’s the color we see!
Mini Chemistry Lesson Below
The color change we see ultimately occurs due to the chemical processes that happen when less chlorophyll is produced by the leaves, causing their colors to change in appearance as the sunlight reflects off of them. When chlorophyll breaks down, the leaves begin to absorb more green wavelengths of light, and reflect other colors such as brown, red, yellow, orange, and even purple.
To jog your memory, chlorophyll is essentially a molecule in plants that absorbs sunlight and uses that energy to make food in a process you’re most likely familiar with: photosynthesis!
Chlorophyll is located within a plant’s chloroplast, which is where photosynthesis takes place, and photosynthesis is the process plants go through to turn sunlight and carbon dioxide into oxygen and glucose (sugar). See the photo below:
All in all, the resulting colors of the leaves come from the different amounts of chlorophyll that the leaves are producing, which becomes significantly less the closer we get to winter.
Fun Fact: Without the presence of chlorophyll in plants, the leaves would always have yellow, red, and orange colors to them!
Besides the weather and seasons, other factors that affect fall foliage include location and latitude, elevation, and differences in tree species. Other facts about the colors of leaves include:
- Temperature and moisture have the most influence over the brilliance of the colors
- Certain trees will change color faster than others
- Early season frosts can bring the beautiful colors to an end
- The combination of warm, sunny days and cool (not freezing) nights will give leaves their best looking display
During warm, sunny days the leaves are as active as they can be producing lots of sugars, and once the cooler nights fall it causes these sugars to become trapped as the veins trap them shut. This produces an abundance of anthocyanin, a chemical that produces colors like red and purple.
- Carotenoids are a common chemical found in leaves that give them yellow colors frequently throughout the year
- Having a late spring or summer drought can delay the offset of the colors by a few weeks while a warm, rainy summer will produce the most favorable conditions.
Written by Christine Gregory