| Species. |
Broadcast over entire area. | Strips. |
Seedspots, 6' apart. |
| Douglas fir | $3.20–4.75 | $1.00–2.60 | $2.75–6.00 |
| Yellow pine | 5.20–6.25 | 1.85–2.35 | 2.75–6.00 |
| Western white pine | 4.70–6.25 | 2.00–2.40 | 2.75–6.00 |
RATE OF GROWTH AND PROBABLE RETURNS
Of all factors in calculating the financial possibilities of second forest crops, the growth to be expected is the easiest to determine with fair accuracy. Future stumpage value, tax burden and fire risk are all subject to uncertain influences, but the approximate yield of a given species under given natural conditions will be the same in the future that it is now. To predict it requires only study of existing stands without being misled by the influence of conditions which will not be repeated.
On the other hand, an immense amount of misinformation is circulated because of superficial observation. Enthusiasts discovering individual trees which have made prodigious growth, or even fairly extensive stands on fertile soil with heavy rainfall, will compute sawlog yields at 40 or 50 years which are much too optimistic for general application. Others, remembering some stand they have seen in unfavorable localities, or noting shade-suppressed trees which will not be paralleled after the virgin forest is removed, are unduly discouraged. It is most essential that yield tables be made by trained observers who know how to reach the true average, and that the figures either actually come from the region to which they are to be applied or are accompanied by a systematic analysis of climatic and other conditions which permits intelligent comparison.
In calculating another yield on cut-over land, the system for an even-aged new growth, such as will follow clean cutting of Douglas fir, for example, is quite different from that necessary if the cutting amounts only to selection of the merchantable trees and leaves a fair stand of smaller ones. In the latter case, yield tables based on average acreage production are of little use because so much depends upon the character of the stand which remains on the tract in question. Here the basis must be the rate of growth of the average individual tree. An estimate by the number in each present diameter class may be made of the trees which will escape logging, showing, let us say for example, about five trees of each diameter from 6 to 12 inches, or thirty-five in all which are over 6 inches. If the growth study indicates that in 20 years there will have been added 6 inches in diameter we can estimate a crop of five trees each of classes extending from 12 to 18 inches. Actually the process will not be so simple, for the different aged trees will not grow with equal rapidity, and several other factors must be reckoned with, but the general principle is to apply rate of growth knowledge to the material on hand, and study of this material is essential.
For predicting even-aged crops resulting from entire restocking, the acquisition of necessary basic information is as difficult, or more so, but its application is far simpler. That the ground will be fully stocked by natural or artificial means must be assumed, but we can also assume that the result will be influenced only by normal locality conditions and not by accidental condition of the present forest. Therefore we use a yield table and not a growth table. This can be made by actual measurement of existing second growth stands of different ages, which proves not only the growth rate but also the number of trees which the natural shade-thinning process results in at different periods of the forest life. The chief danger of inaccuracy in such information lies in basing it on insufficient measurements or in applying it where soil or moisture conditions are greatly different. The latter error can be guarded against, however, by use of growth figures taken in conjunction with it. For example, if a yield table showing 25,000 feet to the acre at 50 years from seed is accompanied by one showing that the average stand it represents is 125 high at 50 years and its average 50-year-tree is 14 inches in diameter, little investigation is necessary to determine whether in any given locality the growth falls far above or below that.
An attempt to reproduce here any considerable number of growth and yield tables would be of doubtful use without more space than is allowed to explain how they are made and used. There are many technicalities, both mathematical and silvicultural, and unfortunately most of the available figures for the Northwest, obtained by the Forest Service, have not been generalized enough for wide popular value. This is particularly true of yield tables which necessarily require assuming standards of merchantability. While the best western white pine table assumes that by the time a new crop is cut 7-inch white pine will be salable, the best fir table was worked upon a 12-inch diameter basis. Obviously this would show an unfairly greater yield of a pine forest containing trees between 7 and 12 inches and be very misleading in calculating financial results at the same age and stumpage rates; yet without the original data there is no way of reducing both tables to the same basis. As an example, however, to indicate how the financial possibilities of second growth can be arrived at if a systematic study is made, let us take the Douglas fir figures referred to.
DOUGLAS FIR
These are exceedingly reliable. Measurements were taken by the Forest Service of practically pure fir on about 400 areas in thirty-five different age stands from 10 to 140 years old, ranging along the western Cascade foothills from the Canadian line to central Oregon. Since reforestation investment is likely to be confined mainly to the more promising opportunities, only such growth was measured as gave an average representation of the better class of the two should all the general territory covered be graded in two quality classes of all around ability to produce forests. On the other hand, care was taken not to represent the maximum of the better class, data being taken only from permanent forest land and not from rich potential agricultural land which might show unfairly rapid forest growth. The average areas were actually measured and the number, age, form, diameter growth, height growth, board foot contents, etc., of all the trees on them were accurately determined. Trees 12 inches in diameter 4-1/2 feet from the ground were considered merchantable, and it was assumed they could be used to 8 inches in the top. From this data were prepared tables and diagrams showing the average development of trees and stands under fairly favorable conditions in the region west of the Cascades.
This gave the following yield per acre: