8. Thinning should be commenced at the central or most sheltered point of a plantation, or section of same, so that the outer intact boundary may continue to form a barrier to cold winds, which might prove injurious to trees that had hitherto stood in close order. 9. In economic forestry, timber trees should be cut down when they have arrived at maturity or have ceased to grow. With coniferous trees this generally occurs at from seventy to ninety years; but with hardwoods, excepting the ash and chestnut, which are of most value, say, up to fifty years’ growth, the period may be greatly extended. 10. Thinning is usually performed in autumn and early winter, but it may be well to remember that at the latter period the lowest percentage of moisture (about 47 per cent.) is present, and the timber consequently of the greatest value for constructive purposes. CHAPTER XV TREE-PRUNING IN ECONOMIC FORESTRY Where trees are grown for profit, they will, if properly managed, prune themselves, and where for ornament the natural outline is far better than any of the contortions and symmetrical shapes that have been recommended by various writers on the subject. A broken or dead branch may be removed, a rival leading shoot cut away, or an ungainly or dangerous limb amputated, but here all pruning should cease, the practice being wholly wrong and unreasonable, and without one recommendation to be adduced in its favour. In an economic way the finest plantations of either coniferous or hard-wooded trees in this country are those where the individual specimens are growing so thickly together that the branches are killed outright for fully one-half of their height. Here the stems will be straight and clean, and the timber when converted free from the knots and warping that are so characteristic either of standard specimens or such as have been grown too thinly on the ground. Every one knows that an Oak growing alone or along the margins of a wood is in nine cases out of ten branched almost to the ground, and the bole in consequence rough and ill-fitted for any particular constructive purpose, and the same may be said of every other tree, be it hard-wooded or coniferous. Larch and Scotch Fir trees growing along the margins of plantations are rough and knotty, and sell at a considerably lower figure compared with those further in, where the branches have been killed back gradually as the trees increased in size.