Why are some leaves red and others yellow?

autumn-2The colors of fall are breathtaking — especially when different varieties of trees and other foliage are grouped together on a hillside lit by bright sunlight. However, it occurs to me to wonder why some leaves turn yellow or orange, and others turn red or brown. Thank you to our friends at Nationals Geographic for this explanation:

Autumn leaves of trees in North America often turn red. But in Europe the leaves mostly go yellow. Scientists think that the regional difference can be explained by the geographic orientation of each continent’s mountains. A new theory provided by Simcha Lev-Yadun of the Department of Science Education-Biology at the University of Haifa-Oranim in Israel and Jarmo Holopainen of the University of Kuopio in Finland proposes taking a step 35 million years back to solve the color mystery, says a news statement by the University of Haifa.

“According to the theory provided by Prof. Lev-Yadun and Prof. Holopainen, until 35 million years ago, large areas of the globe were covered with evergreen jungles or forests composed of tropical trees,” the university said.

“Trees also began an evolutionary process of producing red deciduous leaves in order to ward off insects.”

“During this phase, a series of ice ages and dry spells transpired and many tree species evolved to become deciduous. Many of these trees also began an evolutionary process of producing red deciduous leaves in order to ward off insects.”

Scientists have determined that leaves turn yellow when the green pigment, chlorophyll, recedes prior to the onset of winter, as trees prepare to shed their leaves for the cold weather. Leaves that turn red are the result of trees producing anthocyanin, a red pigment, which some scientists think is an evolutionary response that deters insects from laying their eggs in the trees.

To read the entire National Geographic article, click here to visit the website.

Whatever the reason, this is arguably the most beautiful time of year in cold-climate areas where the transition takes place — especially with small children who express such delight and wonder at the beautiful leaves.

Written by Vicki


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