Michael A. Stecker

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New England's Autumn Leaves
During the first half of October the New England states of Connecticut, Massachusetts, New Hampshire, Vermont and Maine put on a color foliage show that attract thousands of visitors.

But why do the leaves change color? The answer is a change in the pigment mixture within the leaves. During the spring and summer growing seasons most tree leaves are green because they are full of chlorophyll bound up in chloroplasts. Plants use chlorophyll to produce sugars from water and carbon dioxide through a sunlight mediated process called photosynthesis. The amount of chlorophyll is so high during the summer that its green color masks all other pigments present in the leaf. However, chlorophyll is not a very stable compound and bright sunlight causes it to decompose. The synthesis of chlorophyll in plants requires sunlight and warm temperatures. Therefore, during summer chlorophyll is continuously broken down and regenerated so the leaves maintain their green color. But, during autumn the days shorten (less sunlight) and the temperature cools triggering changes in the tree. One of these changes is the growth of a corky membrane between the branch and the leaf stem. This membrane interferes with the flow of nutrients into the leaf. Because the nutrient flow is interrupted, the production of chlorophyll in the leaf declines, and the green color of the leaf fades. Other pigments then become dominant and the leaves change color before they drop. The three most prominent pigments are:

Chlorophyll -- gives leaves their green color.
Carotenoids -- provide the yellow, orange, and brown colors
Anthocyanins -- give the red and purple colors.

Unlike chlorophyll and carotenoids (carotene), anthocyanins are not attached to cell structures, but are dissolved in the cytoplasm. The color produced by these pigments is sensitive to the pH of the cell. If the tissue is quite acidic, the pigments impart a bright red color; if less acidic, its color is more purple.
The range and intensity of autumn colors is greatly influenced by the weather. Low temperatures destroy chlorophyll, and if they stay above freezing, promote the formation of anthocyanins. Bright sunshine also destroys chlorophyll and enhances anthocyanin production. Dry weather, by increasing sugar concentration in sap, also increases the amount of anthocyanin. So the brightest autumn colors are produced when dry, sunny days are followed by cool dry nights.

Autumn leaf color is specific to the species of tree:

Oaks turn red, brown, or russet
Hickories turn golden bronze
Dogwood turns purplish red
Beech turns light tan
Red maple turns brilliant scarlet
Sugar maple turns orange-red
Black maple turns glowing yellow
Sourwood and black tupelo turn crimson
Aspen, birch, and yellow-poplar turn golden yellow

Slide Shows
(These are Windows Executable .exe files requiring the MS Windows operating system to run.  Will not run with Apple/Mac operating system)
New England Fall Foliage
New England Fall Color

Photos of New England Fall Foliage
Please mouse click on any of the thumbnail photos below to see an enlargement