THE FOREST ORGANISM.
The forest is much more than an assemblage of different trees, it is an organism; that is, the trees that compose it have a vital relation to each other. It may almost be said to have a life of its own, since it has a soil and a climate, largely of its own making.
Without these conditions, and without the help and hindrance which forest trees give to each other, these trees would not have their present characteristics, either in shape, habits of growth or nature of wood grain. Indeed, some of them could not live at all.
Since by far the greater number of timber trees grow in the forest, in order to understand the facts about trees and woods, it is necessary to know something about the conditions of forest life.
A tree is made up of three distinct parts: (1) the roots which anchor it in the ground, and draw its nourishment from the moist soil; (2) the trunk, or bole, or stem, which carries the weight of the branches and leaves, and conveys the nourishment to and from the leaves; (3) the crown, composed of the leaves, the branches on which they hang, and the buds at the ends of the branches. As trees stand together in the forest, their united crowns make a sort of canopy or cover, Fig. 55, which, more than anything, determines the factors affecting forest life, viz., the soil, the temperature, the moisture, and most important of all, the light.
Fig. 55. The Forest Cover. Spruce Forest, Bavaria, Germany. U. S. Forest Service.
On the other hand, every species of tree has its own requirements in respect to these very factors of temperature,—moisture, soil and light. These are called its silvical characteristics.