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The trees of the deciduous or leaf-shedding forests of the East are preparing for their long period of winter rest. In the process of changing from the lush green of summer to the stark bareness of winter they stage the most extravagant color display to be seen anywhere in the world.
Residents tend to take this autumnal phenomenon for granted. During October and November they make pilgrimages to their favorite vantage points for viewing the brilliant foliage. They collect leaves with which to decorate their homes and shop windows. The autumn leaf becomes the symbol of the season, but despite its familiarity, there is misunderstanding about it.
PREPARATION FOR WINTER
There is a widespread belief that fall coloring is brought on by frosts and cold weather, but this is not strictly the case. Many trees start preparing for winter long before freezing weather arrives. Some of them, like the black gum, begin to turn in early August.
The leaves are factories in which the food of the tree is manufactured. In the leaves are chlorophyll bodies which convert inorganic substances into organic foods. These chlorophyll bodies are green and give the living leaf that color. When it comes time for a truly deciduous tree such as the maple to go into its resting period, it has its own method of shutting up shop.
At the base of the petiole, or leafstalk, the cells thicken and cut off the circulation of water in the leaf. Without water the chlorophyll bodies crumble and die. As they do, the other pigments in the leaf which had been hidden by the chlorophyll come into view. The wide range of colors—reds, yellows and browns—included in these pigments produces the mass display.
The oaks are imperfectly deciduous in that their leaves remain most of the winter and frost helps in killing the chlorophyll and revealing the other pigments. Half-turned oak leaves showing both green and red are the delight of connoisseurs of autumn color.
The eastern United States puts on the greatest show because it has the greatest variety of deciduous trees. The Appalachian region of the Southeast, for example, has twice as many species of trees as all of Europe. These deciduous woodlands extend north through New England into eastern Canada until they are gradually replaced by the spruce and fir forests of the North. They spread westward in diminishing intensity, and on the south they reach down through the Great Smoky Mountains. There the proper conditions for fall color are provided by altitude. In the Great Smokies the fall coloring begins on the mountain-tops and moves down to the valleys.
Scientists have long had difficulty in establishing the exact composition of this varying deciduous forest. Now a new method is being used experimentally. In the fall when the coloring is at its height aerial color photographs are made of a stretch of woodland. By studying the various colors the scientists can determine just which species make up the area photographed.
The procession of color begins in August with yellow beginning to show here and there in the woods. In September the dogwoods begin to get a bronzy tinge which gradually deepens. Vines and shrubs then contribute to the show. Sumac growing along the roadside will also provide a spot of fire. The maples, which bear some of the most beautiful fall colors, become light red and gold. The oaks join the procession, and the countryside blazes.