Rings per inch
Douglas fir             24
Shortleaf pine          12
Loblolly pine            6
Western larch           18
Western hemlock         14
Tamarack                20
Norway pine             18
Redwood                 30

No satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood.  Several factors may be involved.  In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true.  The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it.  In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen.  But in choosing a particular specimen it is not the width of ring, but the proportion and character of the late wood which should govern.

In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties.  This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood.  This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.

In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant.  As the breadth of ring diminishes, this middle portion is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma.  In good oak these large vessels of the early wood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more.  The late wood of good oak, except for radial grayish patches of small pores, is dark colored and firm, and consists of thick-walled fibres which form one-half or more of the wood.  In inferior oak, such fibre areas are much reduced both in quantity and quality.  Such variation is very largely the result of rate of growth.

Wide-ringed wood is often called “second-growth,” because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in the forest, and in the manufacture of articles where strength is an important consideration such “second-growth” hardwood material is preferred.  This is particularly the case in the choice of hickory for handles and spokes.  Here not only strength, but toughness and resilience are important.  The results of a series of tests on hickory by the U.S.  Forest Service show that “the work or shock-resisting ability is greatest