Why Do Leaves Change Color in the Fall?

Picture of an Autumn LeafEvery year Mother Nature regales us with a fantastic display of color in the fall. But have you ever wondered why the leaves change color? Well read on and we will explain why leaves change color every Autumn.

Two Types of Trees

First realize that there are two types of trees. There are the deciduous or broadleaf trees that change color and loose their leaves every fall. These are contrasted with the evergreen trees that maintain their green color year-round. Deciduous trees loose their leaves because their leaves are delicate and can not survive winter’s freezing temperatures. The needle-like foliage of evergreens is covered in a waxy substance and contain fluid in their cells that resists freezing allowing them to survive all but the most severe winter conditions.

Shorter Days – Winter is Coming

Picture of Up Close Fall FoliageAs we progress into late summer days become shorter and the sun less intense. It is this, more than any other factor, that signals to deciduous trees that winter is coming. This tells the trees to slow down and eventually cease the production of chlorophyll, the main chemical of photosynthesis.

Where do the Fall Colors Come From?

Tree leaves are green in color because of the predominance of chlorophyll in them. There are other chemical pigments in leaves that cannot be seen during the growing season because of the presence of a large amount of chlorophyll. When trees start to slow and eventually cease the production of chlorophyll in autumn, the amount of chlorophyll in the leaves declines allowing the other pigments to become visible. These other pigments include:

  • Carotenoids – Carotenoids produce yellow, orange, and brown colors in plants.
  • Anthocyanins – Anthocyanins provide the types of colors that you would see in things such as cranberries, red apples, concord grapes, blueberries, strawberries, and plums.

The chemical makeup of the leaves of certain trees determines what color the leaves will turn in the fall.

The Impact of Weather

Weather before and during the fall impacts this process in several ways. A good predictor of spectacular fall color is a warm wet spring, followed by a seasonable summer without sustained temperature extremes and drought, followed by warm fall days and cool but not freezing temperatures at night. Drought in the spring and summer, or hot temperatures in the fall tend to mute autumn colors.

Wind also plays a part in the intensity of the fall display. High winds in the fall will cause leaves to drop, also muting fall colors.

When Will the Leaves Turn Color?

Picture of a Grist Mill in the FallIn New England, the first leaves will start to turn in late August and early September. Peak color is reached the earliest in Northern New England and in the mountains and comes last to southern coastal New England. Peak color varies from year to year depending on the weather that precedes fall. A cool/cold late spring will tend to push peak color later into the fall than a normal spring. An early warm spring will have the opposite effect.

Keep Columbus Day in Mind

A good rule of thumb is to keep Columbus Day weekend in mind. The peak in Northern New England is typically a little before Columbus Day weekend, although there would usually still be spectacular colors that weekend as well. Massachusetts and northern Connecticut and Rhode Island are typically right around peak foliage over Columbus Day weekend. Southern coastal New England’s peak autumn colors will typically come a little after Columbus Day.

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