Improvement.
Pruning.—The object of pruning forest trees is to produce clear lumber. If that object can be accomplished without going to the expense of prun ing, it may be dispensed with. If trees are grown at the correct distance apart, the side branches will be shaded to death while they are small, and in most cases will drop off in a few years. There are exceptions to this rule, however. Some trees retain their (lead side limbs for many years ; and it may be wise to assist the tree, in such cases, in ridding itself of them. The question then resolves itself into whether the clear lumber is worth more than the cost of pruning.
In one case, at least, it is worth while to prune. The white pine (Pinta Strohus) is one of the trees that holds its side limbs. The price of clear pine lumber justifies a small outlay on pruning.
It is a waste of time to prune trees that have reached a diameter over six or eight inches. As just stated, the object of pruning is to secure clear lumber ; and to prune large trunks is to lock the door after the horse is stolen, for large knots are already formed.
It is also a waste of time to prune more than two hundred or three hundred trees to the acre. The very best trees, ten or fifteen feet apart, should be selected. If more than these are pruned, some of them will be shaded out before the stand is mature, or will be taken out in improvement thin ning, if thinning is practiced. In either case, a part of the labor put into pruning will be lost.
In pruning, any number of dead limbs may be removed without injury to the trees ; but live limbs should be taken sparingly. It is a good plan to take the dead limbs up to where the live ones begin, and, if necessary, to take two or three whorls of the dying and dead ones, and then to wait a few years before going farther.
The work may be done with an axe or with strong pruning-shears. The cuts should be close to the trunk, so that the knots will grow over as soon as possible. If the axe is used, great care should be exercised not to bruise and hack the bark of the trunk.
Thinning (Figs. 471, 472).— Thinning is the
most important improvement work which may be done in the woodlot. By thinning is meant the sys tematic removal of a part of the trees in a grow ing crop of timber to benefit those that remain. It should not be confused with the removal of mature trees, which is a very different operation.
The practicability of thinning has been ques tioned. Among other things, the cost of the work, the injury by falling trees, lodgment of trees against those remaining, and increased liability to windfall have been urged. As to the cost of the work, it is conceded that in some circum stances it is prohibitive. For this reason, a young stand should be allowed to wait until the material to be removed has reached such a size that its sale will pay for its removal ; and it should not be thinned again until the material to be removed has accumulated in sufficient quantity to pay for its removal. If the wood more than pays for its removal, so much the better: but if it pays only for its removal, the improvement is a net gain. The farmer who knows the price of labor, the cost of drawing to market, and the price to be secured, can easily determine when a thinning may be safely undertaken.
In reply to the other objections, it may be said that, when thinning is done properly, the falling trees do little injury, they do not lodge so that they can not down with a twist of a cant-hook, and the remaining trees do not blow down.
The principal object of thinning is to preserve the balance between height-growth and diame ter-growth of the trees that are to form the final stand. Increase in volume is determined by height- and diameter-growth. If the trees stand too close together, height-growth will be in excess, followed by a reduction in vitality. If the trees stand too far apart, diameter-growth will be in excess, accompanied by large side limbs. In either case the quantity and quality of the timber will be affected. Therefore, by preserving the balance between the two, an acre of land is made to produce more and better lumber in a given period of time.