Colors. Falling. Autumn is here. As summer turns to cold and the sweaters are brought out, leaves start to change from green to orange and brown. Have you ever wondered why?
“Leaves get their green color from a chemical called chlorophyll,” according to Dylan Stuntz, a writer for The Official Blog of American Forests, “trees use the sunlight in a process called photosynthesis, which is how the tree eats.”
According to Mrs. Patricia Massetti, a biology teacher, “as the amount of daylight shortens and the temperatures drop, the process of photosynthesis slows down and eventually stops.” She also adds that “this causes the main pigments, chlorophyll, to break down and disappear. This allows for other pigments such as red, yellow, and orange to become visible.
Two chemicals are responsible for the fall coloration of leaves, according to Stuntz, carotenoids create orange and yellow pigments while anthocyanins create shades of red and purple. Carotenoids are present in the leaf all summer long, but they’re masked by the green of the chlorophyll.
“Unlike carotenoids, anthocyanins form as a result of the glucose formed by the remaining, faded chlorophyll.”
The effect on animals is significant during this time, “many animals feed on the leaves that have dropped from the trees,” Massetti says. Mr. Brady Green also mentions that in the fall, leaves can become “more or less visible to certain animals.”
Many animals also grow warm winter coats in the autumn months, writes Raechelle A, a writer for Our Beautiful Planet. “Other animals enter a state of hibernation, where they lower their body temperatures and enter a sleep-like state for months.”
So why do evergreens stay green all year?
Massetti says that “unlike deciduous trees that lose their leaves in the fall, coniferous trees do not.”
“Evergreens have very strong leaves that are rolled up as long, thin needles,” Blog.Davey.com writes, “the special needle shape, along with waxy coating, allows the evergreens to conserve water during summer and winter.”
Needles shed happens annually, usually in the spring, however this is mostly unnoticed, according to Davey, because they are growing new leaves while they shed their old ones. White pine sheds their leaves every 2-3 years while mugo pine only sheds every 5 years.
Most evergreens follow these rules, except for a few exceptions such as the bald cypress which loses all its needles every year.
If all trees were evergreens and never died off in the winter seasons, Massetti feels as though “from an aesthetic standpoint, it would be drab and boring,” and from a science standpoint, “as leaves fall and decay, the nutrients go back into the soil for new plant growth.” Green adds that “it would be a lot like living in Florida.”
Therefore, without any dead fallen leaves, plant growth would struggle meaning there would be less food for animals and less food for us.