PRESERVATION.
The second object of forestry is the preservation of the forest, or continued reproduction.
In addition to obtaining crops of trees, the forester plans to keep the forest in such condition that it will constantly reproduce itself and never become exhausted.
This does not mean that no forests are to be cut down, or that a given area, once a forest, is to be always a forest. Just as the individual farmer needs some land for fields, some for pasture, and some for woodlots, so the nation needs some for cities, some for farms, some for pleasure grounds, and some for forests. But it does mean that fruitful forests shall not be turned into wildernesses as thousands of square miles now are, by the methods of destructive lumbering.
In general, better land is necessary for agriculture than for forestry, and it is therefore only the part of wisdom to use the better land for fields and reserve the poorer land for forests. There are in the United States enormous regions that are fit for nothing but forests, but many of these, as in Wisconsin, Minnesota, and Michigan, have simply been denuded of their trees and no provision has been made for their reproduction. This then is the second aim of forestry,—to treat the forest so that it will continue to reproduce itself.
In order to obtain this result, certain forest conditions have to be preserved. What these conditions are, we have already noticed (see Chap. V, The Forest Organism). They are partly topographical and climatic and partly historical. They include such factors as, soil, moisture, temperature, and light, the forest cover, the forest floor, the density and mixture of growth, all conditions of forest growth. It is only as the forester preserves these conditions, or to put it otherwise, it is only as he obeys the laws of the forest organism that he can preserve the forest. For a long period of our national history, we Americans were compelled to conform our life and institutions to the presence of the primeval forest, but by long observation of what happens naturally in the forest, there have been developed in Europe and in America certain ways of handling it so as to make it our servant and not our master.
These ways are called silvicultural systems. They are all based on the nature of the forest itself, and they succeed only because they are modifications of what takes place naturally in the woods.
As we have seen above (p. 220) trees reproduce themselves either by sprouts or by seeds. This fact gives rise to two general methods of reproduction, called the coppice systems and the seed systems.
Fig. 123. Chestnut Coppice. U. S. Forest Service.