287. "Felling Timber1 should always, if possible, be practiced at the period of maturity; if earlier, the wood will not have acquired its greatest strength and density, and will 1 Quotation marks refer to Thurston's "Materials of Engineering." contain too great a proportion of sapwood; if later, the wood will have become weakened by incipient decay." The age at which maturity is reached varies with different trees. The oak is said to come to maturity when about one hundred years old, and it should not be felled at less than sixty. "Pine timber should be cut at from seventy to one hundred years of age, and ash and elm at fifty to one hundred." In practice, however, trees are often cut before their age of maturity, it being not uncommon, in dealing with a forest growth, either to clear the ground of all trees, whether large or small, or to cull from time to time all trees which are of sufficient size to be marketable. As opposed to this custom, a modern theory of forestry favors a division of the forest tract into many parts, certain of which may be cut each year, the plan being such that when the last subdivision has been cut, sufficient time will have elapsed to permit the first to become completely reforested, and, therefore, ready to give up its second growth. An alternative plan, applying especially to forests of mixed growth, provides for the systematic removal of mature trees only, the work being done under careful supervision. By either of these methods the forest, like other products of the soil, may be made to yield a certain revenue each year. The complete development of any such plan necessarily involves a long series of years, and as yet, in this country, no great progress has been made; but it seems probable that the large government forest reservations will hereafter be managed by some method of this kind.

"The season of the year best adapted to felling timber is either midwinter or midsummer. The months of July and August are often selected, as at those seasons the sound trees can be easily distinguished, from the fact that they remain green while the unsound trees are then turning yellow. Healthy trees then have tops in full foliage, and the bark is uniform in color, while unsound trees are irregularly covered with leaves of varying color, having a rougher and often a loosened bark, and decaying limbs." After felling, "the trunk should be immediately stripped of its bark, and when heart-wood only is wanted, the sapwood removed as soon as possible." This gives the wood a chance to dry quickly and at the same time prevents deterioration by the action of worms and decay. "The bark is often removed from trees in spring and the felling deferred till autumn or winter." This, ordinarily, can be done only with small trees, but it is a good course to pursue when possible.

In the actual felling of the trees, the method has been from time immemorial to use the ax, and very small trees are still cut in this way; for larger trees the saw is used in connection with the ax. The cut is usually made high enough above the ground to avoid the very hard grain, the heavy sap, and in some cases the accumulation of pitch at the base of the tree. For large trees this height is from six to eight feet above the ground. Notches are first cut on opposite sides of the tree, into which are inserted boards on which the workmen stand. After the direction of the fall is decided, an "undercut" is made with the ax at right angles to it and on the side next to the fall, extending into the tree a distance equal to one-third of its diameter. The saw is then applied to the opposite side, and when the kerf has been advanced nearly through to the undercut, wedges are driven into the saw-cut so as to bring the tree down in the proper place. In this way the possibility of doing injury to other trees may be avoided. Machines have been invented to take the place of the method described, but they are not in general use.

After the tree has been felled it is sawed into logs of suitable length. Barkers then chop or strip away the bark, either from the whole surface of the logs or from the side on which they are to be dragged, and clear away the underbrush to form a way along which they may be moved.

288. Transportation of the logs to the sawmill is effected in different ways, which depend upon the locality and surrounding conditions. In all regions except the West, where redwood and other very large trees must be handled, the common practice is to drag the logs by means of horses or oxen to the nearest stream or railroad. For this purpose tramways are made by placing logs of similar size parallel to each other across the way, at intervals of from four to eight feet. The logs are moved to the tramway from the places where they have fallen, by rolling if the distance is very short, or if the ground is inclined in the proper direction; otherwise, they are pulled into position by a horse. A number of logs are then fastened together by chains and a team of horses or oxen drags them along the tramway, which leads either to a logging railroad or to a stream or pond. In the latter case the logs are placed within the high-water zone at a time when the water is low, and when the spring freshets cause them to float they are guided to the sawmill, which is usually built near a pond or stream. This is the cheapest and most common method of transportation. In the northern part of the United States and in Canada, the common practice has been to carry on the logging in the winter time, and in the spring to float the logs on the water courses to the mill, which does not run during the winter season. Here, instead of a tramway, an "ice run" is made by cutting a shallow trench in the ground and pouring water upon it. When it is frozen, the logs are dragged over it by a team. This forms an efficient, and compared with the tramway a very inexpensive, means of transportation. The methods here described are those common in the eastern part of the United States, and in fact in all places where the operations are not extensive. In the West, where bulky material must be handled, and the work is pursued upon a large scale, the tendency is to rely upon machinery for moving the logs. Chains are secured to them by means of grappling hooks, and they are drawn from the place of fall to the tramway, or "skid-road," by the action of a "yarding" engine, which is similar in form to engines used in hoisting; on the tramway another engine pulls them to the nearest railroad or water way. Where the course is down a mountain side, the logs may be slid down a suitably constructed chute.

289. Sawmills contain all the machinery necessary for converting logs into lumber. As has been stated, they are usually situated upon the shore of some stream or pond, in order that they may be easily reached from the lumber camp. The process of making lumber from logs is effected by means of a saw, fixed in position, to which the log is fed. The log is mounted upon a carriage, which is arranged to reciprocate, advancing toward the saw for the cutting stroke and returning after the cut is made. Various means are employed for propelling the carriage, which in a large mill is made to move with great rapidity. The two classes of machinery used in general sawmilling are the circular sawmill and the band sawmill. The former is the older and, for general purposes, is still more used. The objections to the circular saw arise from the width of its kerf, which causes a great waste of material, the loss in sawdust for some cuts being one-fifth the whole amount of wood used.

The band saw has much to recommend it, especially in the reduced width of the kerf, which, ordinarily, is but little more than half that of a circular saw of the same power and capacity; hence, the amount of material wasted in the form of sawdust is less. The band saw is more expensive and not so portable as the circular saw, and is therefore more suitable for large and permanent establishments.