So long as the supply seemed exhaustless, forests might be and were treated as mines are, _i.e._, exploited for the sake of immediate profit; but now that lumbermen begin to realize that the end of the supply is in sight, more conservative methods are being adopted. We cannot afford to kill the goose that lays the golden eggs. In order then to obtain as rich harvests as possible, the modern forester makes use of various methods, some negative, some positive. Waste is avoided in all possible ways, stumps are cut low and tops high on the trunk, first class trees are not used for skids, bridges, roads, etc., care is taken in "falling" trees and in dragging out logs, that they will not injure other trees. Just as economical disposal of the log has already been carried to a high degree of perfection in the saw-mill, (see _Handwork in Wood_, Chapter II,) so one object of forestry is to carry this economy back into the woods. One of the underlying ideas in conservative lumbering is that the "yield," _i.e._, the amount of wood taken out of a healthy forest in a given time, shall be equal to the amount grown during the same period. If less is taken out than grows, some trees will overmature and decay; if more is taken out than grows, the forest will ultimately be exhausted. This principle may be carried out in a number of ways; but in any case it is necessary to know how fast the forest is reproducing itself, and this is one of the functions of the forester. The United States Forest Service makes a definite offer of cooperation with farmers and lumbermen and owners of forests to provide them with skilled foresters for direction in this matter. In the United States, the most practicable way of determining the yield is by area, _i.e._, a certain fraction of a forest is to be cut over once in a given length of time, a year or longer. The time between two successive cuttings on the same area must be long enough to allow the young trees left standing to ripen. In a word, conservative lumbering involves (1) the treatment of the forest as a source of crops, (2) systematic gathering, and (3) young growth so left as to replace the outgo. The important place that forests fill in the national economy may be realized partly by the citation of a few facts as to the forest products. The lumber industry is the fourth in value of products among the great manufacturing industries of the United States, being exceeded only by the iron and steel, the textile, and the meat industries. It turns out a finished product worth $567,000,000.00. And yet lumber constitutes only about one-half of the value of the total output of forest products. Its annual value is three-fourths of a billion dollars, ($666,641,367 in 1907,) while the annual value of wood fuel, is $350,000,000. More than two-thirds of the people burn wood for fuel. The next largest single item in the list is shingles and laths, $32,000,000. (See _Forestry Bulletin_ No. 74, p. 7.)