The destruction of forests has been most wasteful. When a forest-covered region is settled, a large area is burnt off in order to clear the land for cultivation. In many instances the fires are never fully extinguished until the forest disappears. The timber of the United States has been depleted not only by frequent fires but in various other ways. The lumbermen take the best trees and these are cut into building-lumber. The railways follow the lumbermen, cutting out everything suitable for ties. The paper-makers vie with the tie-cutters, and what is left is the plunder of the charcoal-burner. =Forestry.=--In most of Europe the care of the remaining forests is usually a government charge. Only a certain number of mature trees may be removed each year, and many are planted for each one removed--in the aggregate, several million each year. In the United States, where the value of the growing timber destroyed by fire each year nearly equals the national debt, not very much has been done to either check the ravage or to reforest the denuded areas. Many of the States, however, encourage tree-planting. In several, Arbor Day is a holiday provided by law. The general Government has established timber preserves in several localities in the West. The State of New York has converted the whole Adirondack region into a great preserve. Forest wardens and guards are employed both to keep fires in check and to prevent the ravages of timber thieves; excepting the State preserves however, the means of prevention are inadequate for either purpose. [Illustration: THE LUMBER INDUSTRY--A LOG JAM] To be valuable for lumber of the best quality, a forest tree must be "clear"; that is, it must be free from knots at least fifteen feet from the ground. In the case of pines and cedars, the clear part of the trunk must have a greater length. To produce such conditions, the trees must grow thickly together, in order that the lower branches may not mature. The growth of trees thus set is very slow. Isolated pine-trees will reach the size large enough for cutting in about fifty years, but the lumber will be practically worthless because of the knots. On the other hand, pine forests with the trees so thickly set as to make a clear, merchantable lumber require at least a century for maturity.[49] Oak forests require a much greater period. As a rule, the forest growths of the United States are found in the areas characterized by sandy and gravelly soils. Thus, the glaciated region of the United States and Canada for the greater part is forest-covered. The sand barrens along the Atlantic coast usually are forest areas. The older bottom-lands of most rivers are often forest-covered, especially when their soil is coarse and sandy.