Light, Water, Soil, and Space for Growth
What are the National Forests from which much of our timber comes?
Trees are their dominant characteristic, but trees are hardly alone or even self-sufficient, for a forest is a vibrantly complex, interwoven community of many forms of life. Within its depths the tree, shrubby plant, large animal, and minute creature struggle together and against each other to survive and to perpetuate their species.
From the beginning to the end of its days, the tree exerts a ceaseless effort in the contest for life. Like man, it must have air, light, heat, water, and food. Having once taken root, it can never move to another spot—yet within its own sphere it acts and reacts in drawing nourishment from soil and air. Roots penetrate downward for water and mineral foods. The trunk carries these to the crown and outward to the leaves. Meanwhile, within tiny leaf cells the amazing green pigmentation called chlorophyll captures light waves and the energy of the sun. These combine with carbon dioxide breathed from the air to form a simple sugar, later converted into other carbohydrates and then into wood. The tree shows its growth and age through the addition each year of a coat of new wood cells formed by the cambium layer between the outside layer of the sapwood and the bark. The sapwood is the living tissue through which water passes from roots to crown.
In field and lawn, the shade tree has space to reach upward and outward for its sunlight. As it grows, the limbs spread and the crown becomes broad and rounded. But the forest tree lives close to its neighbors, and in turning to the sun must reach upward. Its lower branches, cut off from sunlight, wither and fall. It develops height, with a long, clean trunk, attractive to the eye and highly suited for the milling of its wood into thousands of useful products.
Beneath the canopy of upper limbs and leaves, openings on the forest floor fill with little trees. They shoot up from the ground or sprout from the stumps of old trees which have died or been cut. They test their strength to survive against lesser plants, insects, and animals, for whom they are the sustenance of life. And they must compete with each other.
But survival of the fitter does not produce National Forests of the fullest value in our modern day, for not all tree species are useful to man. These and other undesirable forest vegetation fight for their share of soil and water and, if strong enough, crowd out or slow the growth of more desirable trees. Very old trees, like very old people, become afflicted with infirmities. They suffer disease and decadence; unlike people, they seldom die alone, for they threaten an entire forest by inviting infestation by insects and creating conditions favorable to fire.
Through forest management and its implements, including timber cutting, National Forests are cared for in their own best interests and in the interests of man. The most useful trees are perpetuated in their proper environment through silviculture (silva, the forest, and culture, to cultivate), the science of producing and caring for a forest.