Edward Tweedly

Fall Foliage Colors
After four years in the U.S. I left in 1985 before seeing the autumn foliage of that year. I consoled myself by writing in my travel diary a description of how and why the foliage colors can be so good (my thanks to the Forest Service for the information; any mistakes are my fault).

There are two main types of colors, from two main types of trees, with two corresponding botanical mechanisms at work. Firstly there are the large broadleaf trees of the type that I know from Europe: these turn yellow or brown. Actually their leaves are always yellow or brown in pigment, but this is obscured by the presence of chlorophyll which makes them green until Autumn. The chlorophyll is removed (and the underlying pigment revealed) when the weather gets cold. Secondly, there are the trees of the Sugar Maple type: these turn red and purple. This too is masked by any chlorophyll that is still there, but (unlike the yellow of the other trees) the red colors are not always lying in wait underneath the green. The pigment is produced by the breakdown of sugars in the presence of phosphates: the breakdown of sugars is an Autumn happening, triggered not by cold but by shortening days; the intensity of color is increased by greater concentrations of phosphates, which are produced by strong sunlight. So the red and purple pigments appear when the days get short; are more intense if the days are bright, but are masked by green until it gets cold. Or some combination much like that. That gives plenty of room for variation in the reds alone (when will they come? How good will they be?), but it is the mixture of colors that makes a really impressive display. In southern New York State, my third year was a yellow year, but a great one. My fourth year was a red one, but good only for a brief period. Explanation? In the third year it became cold early, drove out the chlorophyll, and then warmed up again (good strong yellow leaves) but the days were not bright (weak reds). In the fourth year it became cold more slowly and stayed so (yellow-brown only appeared as the leaves were almost dead) but it was sunny (strong reds). The beauty is not in my understanding it, it is in the leaves. However, it is even better for the understanding, and knowing the process is certainly better for seeing what it does. There is a final thought, interesting to contemplate: the Autumn leaves turn color all over North America, but at different times because northern areas become cold earlier. A wave of exploding color rushes from Alberta to Alabama at fifty miles a day. Curious Ė it canít be seen, but the thought has visual beauty.

The U.S. National Forests are a national treasure beyond compare.

The basis of their structure and infrastructure, including the campgrounds I made such good use of, was constructed in the 1930s by the Civilian Conservation Corps.

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