Amsterdam News in the Classroom: The magic of fall
JASMIN K. WILLIAMS Amsterdam News Staff | 10/12/2012, 12:22 p.m.
Fall is here. With cool, crisp mornings, pleasant daytime temperatures, bright blue skies and brilliant, colorful foliage on display, no wonder fall is a favorite time of year.
Autumn, as the season is also known, marks the transition from summer to winter. It begins in September in the Northern Hemisphere and in March in the Southern Hemisphere. The season is also known as "harvest," taken from the Old Norse word "haust," which means to pluck or gather, because it's this time of year when crops are gathered for winter.
A key feature of the fall season is the changing colors of the leaves. Just how do they go from deep, rich green to the fall-defining colors of bright gold, orange and red? It's an amazing process that only Mother Nature could pull off. The days grow shorter, meaning less sunlight and less rainwater, thus the tree no longer produces chlorophyll. With that, the leaves soon turn brown and die, and the cycle of transformation is one of the most beautiful displays in nature.
All of the colors (pigments) that we see during the fall season are contained in the leaf all along. The combination of sunlight and water that the tree received during the spring and summer will determine just how brilliant the colors will be. Here's how it works:
Leaves themselves are pretty amazing. They're like mini food factories, using sunlight, water and carbon dioxide--which is what we and animals exhale--to produce food and oxygen, through the process of photosynthesis. During photosynthesis, leaves convert the carbon dioxide into oxygen, which is necessary for life. This is why the Amazon Rainforest is often called "the lungs of the planet," as 20 percent of the world's oxygen is produced there.
The leaves of spring and summer are green because of chlorophyll. At the end of the summer season, the trees stop producing it, allowing the other hidden pigments in the leaf to come out. The amount of glucose (sugar) is another factor in determining the color of the leaf.
During the fall season, carotenoids and xanthophylls take over and turn the leaves from green to varying shades of yellow and orange. The red hues come from anthocyanins. These are not contained in all leaves and only appear under certain circumstances. Anthocyanins are produced during dry and sunny conditions to protect the leaves from too much sunlight. Anthocyanins also cause more sugar or glucose to be produced in the tree sap in a final push to create as much energy as possible to help the tree during winter. When the spring and summer have been excessively rainy, you won't see too much red color in fall. Without lots of sunlight, the tree doesn't need to produce anthocyanins to protect the leaves.
The height of the color changes lasts about three weeks as the leaves go from green to yellow, orange, red and brown as the last of the nutrients are taken by the tree. Red comes from the food left in the leaf while brown comes from tannin, the waste left in the leaf. The leaves die and fall from the tree, leaving a scar.