Science behind seasonal changes

For many of us, the changing of colors and falling of leaves in autumn is only an accepted fact of life. However, not every region in the world gets to experience different seasons or the brilliant transformation from green leaves to reds, oranges, golds and browns.

In fact, the Earth can be divided into separate biomes by characteristics such as average rainfall and temperature. These aspects strongly influence the species diversity present in each biome. The Smoky Mountains as well as most of the Eastern United States falls within the “temperate deciduous” forest biome.

This is because we are inside a low-pressure zone of the global air circulation, allowing for a great amount of precipitation. In fact, temperate deciduous forests are second only to the tropics regarding annual rainfall amounts. Temperate deciduous forests are among the oldest and most beautiful forests in the world, famous for their dramatic color changes that occur every fall. The term deciduous refers to the plants ability to lose its leaves as a biological survival strategy.

While this incredible transformation completely alters our entire landscape for at least a few months, the process begins within every individual tree cell. Three factors influence autumn leaf color:  pigments, length of night and weather.

The first pigment to consider is chlorophyll, which gives leaves their usual green color. This is necessary for photosynthesis, as it enables plants to use sunlight to produce sugars for their food. The second pigment involved in this process is carotenoid, which produces the yellow and orange colors seen in things such as corn, carrots and daffodils. A third pigment that factors in is anthocyanins, which give red color to things such as strawberries, cherries and plums.

During the growing season, chlorophyll is continuously produced and broken down, giving leaves their green color. However, as night length increases and the temperature drops, the chlorophyll production slows, and the carotenoids and anthocyanins that have been in the background of the picture are revealed through vivid leaf colors.

Interestingly enough, certain colors can be linked to different species. For example, oaks turn red and brown, dogwoods turn a purplish red and ginkgos turn a breathtaking sunshine yellow.

As mentioned before, trees do this as a biological response designed to increase their productivity. Trees require sunlight for productivity, and shortening days and declining intensity of sunlight in the fall goes against this. Therefore, fragile tissues unable to survive winter (leaves) must be sealed off and shed to ensure the plants continued survival. The tree then enters a dormant stage that lasts throughout the winter until it starts the process all over again in the spring by growing a new set of leaves full of chlorophyll.

The fact that all of this occurs on a cellular level as a result of the changing of seasons and that it only occurs in certain places in the world, is a beautiful fact. Everything in nature is connected from the wind patterns to a maple tree turning into a beautiful scarlet. So next time you are appreciating the brilliance of the Smoky Mountains in autumn, stop for a second and consider the thousands of years of succession that have occurred to present the rich and diverse forest around us.


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