Popular Science Monthly/Volume 81/December 1912/Practical Forestry Explained
| PRACTICAL FORESTRY EXPLAINED |
By Gen. C. C. ANDREWS
FORMERLY FORESTRY COMMISSIONER OF MINNESOTA
FORESTRY is the science of deriving a sure and fairly good revenue from the production of valuable timber trees on such hilly, rocky or sandy land as is unfit for field crops. The pine takes from the soil only a twelfth part of the mineral matter that is required for field crops. Air and light are its principal food.
The average net income from the German state forests is about three per cent, per annum. The average value of the land containing the forest is about $150 per acre. Much of the land is mountainous.
A normal forest is one from which enough trees can be cut annually for revenue, without impairing the capital. The forest crop has this advantage over field crops that it is not absolutely necessary to cut it at any particular time, but that the cutting can be at a time that will best suit the market. If we had a natural or virgin forest of considerable extent, we should find in it trees of various sizes and ages. (In the Minnesota National Forest, December, 1906, a white pine was cut that was 425 years old, six feet in diameter breast high, and which yielded 6,200 board feet.) If our natural forests were handy to a permanent railroad or the logs could be floated from it by water to a saw
mill, we could every year cut the more mature trees, leave the younger ones to grow, and in reasonable time bring it into a normal forest. Usually, however, natural forests are remote from established lines of transportation, and the lumberman who handles them must construct temporary logging railroads which are taken up when the timber has all been cut. He has invested his money, expecting to get it back soon with a profit and can not wait for trees to grow. He usually cuts clean as he goes. He can not afford to practise forestry and no reasonable person expects him to do so. It would take too long for nature unaided to renew forest. Natural reforestation has as good a chance in Germany as anywhere because fire there does little damage. But Germany plants over a hundred thousand acres of forest annually.
If we were to start an artificial pine forest it would be by planting seedlings—nursery grown trees—two years old, four feet apart, requiring at that rate 2,722 seedlings per acre. If land we purpose using happens to be part of an abandoned farm or is land from which natural forest was cut twenty or thirty years ago, probably five per cent, of the area is already well stocked by nature with valuable kinds of timber trees. Probably another five per cent, of the area consists of rocks or wet places that can not be planted, so that only ninety per cent, of our area will require to be planted.
Why should trees be planted as close as four feet? To get the ground shaded as soon as possible, to promote moisture and fertility; also to promote height growth. In a crowded forest the shade causes the trees to shed their lower limbs. It is only in this way that long smooth logs, free from knots, are produced. Every one has seen that a tree in the open grows too many branches to make good timber. In a forest that is crowded when young, a natural thinning occurs as it develops. The weaker trees die out. An average acre of mixed woods in the Black Forest of Germany, which at the age of twenty years contained 3,960 trees, contained at the age of forty years 1,013 trees and at the age of eighty years, 346 trees.
A person intending to start a forest should plant the trees in the spring as soon as the frost is out of the ground. The most economical plan probably will be to buy them of a reliable nurseryman. The forestry departments of some states now furnish seedlings at cost. In 1910 the Superintendent of Forests of the state of New York supplied to private parties at cost 2,733,200 trees, being mostly white pine seedlings two years old. The pine produces a crop of cones every two or three years, and if conditions are very favorable, one might gather the cones, which should be done about the first part of September. By drying them in the sun, the seeds can be shaken out. The seeds should be kept in a cool safe place, and can be sown in the spring in a garden bed in the same way that garden seeds are sown, and the first summer must be protected from the sun by lath screens about two feet above the beds, or by an arbor of boughs ten feet high. In muggy weather, the delicate pine plant is liable to a blight called "damping off" and as a preventative should obtain good air currents. When ready for planting they should be carefully taken up with a spade, not pulled up. The roots must not be exposed to the sun at all. The plants must be carried
to the place of planting in pails of mud. The holes in which they are to be set should be made with a grub hoe or light spade, the soil pulverized, and in planting the roots should be given their natural position, the soil firmed around them, and they should be set two or three inches deeper than the surrounding surface. A young forest should have the sides that are exposed to the prevailing winds more densely planted than elsewhere; wind being one of the forest's worst enemies.
In planting a small tract of even five acres, there may occasionally be a small piece of ground such as the bottom of a ravine, with soil fertile enough to sustain hardwood trees such as the sugar maple, ash, chestnut or oak, and if so, such kind of trees had better be planted, both to improve the appearance of the forest and to attract birds. Two men
Natural Reproduction of White Pine, twenty-five feet high and six to eight inches in diameter, on the Daniel Webster farm at Marshfield, Mass. Grown from seed of pines that were planted by Mr. Webster eighty-six years ago. (Photographed August, 1902.)
can work well together. The first digs the hole; the other, following with the young trees, plants the tree. If the job is large, quite a number of men may be employed; in such case, the two men who started the first row should keep two trees in advance of the men on their right. Two men can plant 1,400 trees in eight hours.
Pine grows very slowly the first ten years, but afterwards rapidly up to about its eightieth year; after that it will grow for two centuries or more, but too slowly to earn good interest on the capital it represents. 
In a pine forest, therefore, intended for revenue, eighty years is generally considered the fiscal age of the trees. To derive good revenue the trees should be cut at about that age, at which time they will have reached on an average a diameter of thirteen inches breast high. After removal of the timber where natural regeneration does not prevail, the blank spaces must be planted.
If the forest is extensive one would need in due time to have a skilled forester make a map of it and a working plan, showing the character of surface and soil, location of roads and trails; kinds, localities and age of trees, and all other facts indicating the work necessary to be done to maintain a sustained yield. The forest should be fenced as animals do injury to trees. After a forest crop has been cut enough of the brush to prevent future danger should be burned at a safe time by piling it upon a fire. Fire in a forest should never be allowed to run nor left to smoulder.
A good rule for estimating the number of board feet in a tree is this one, called Doyle's: from the average diameter in inches deduct 4 (as representing slabs); square one quarter of the remainder and multiply by length in feet. For example, suppose a tree is 65 feet high and its average diameter 16 inches; deduct 4 leaves 12 inches, one quarter of which is 3, which squared makes 9; this multiplied by the height of the tree, 65, gives 585 board feet as the contents of the tree.
We have thus seen that by forestry, refuse land can be converted into interest yielding capital as good as government bonds.
In a normal forest the average annual growth on third and fourth rate land amounts to about 280 feet board measure per acre. At that rate we shall expect that our planted forest of red (Norway) and white pine would in eighty years contain on an average 22,000 board feet per acre of merchantable timber, a fairly conservative estimate. I have seen on my native farm in New Hampshire white pine grow to a diameter of two feet breast high in fifty years, but it was on fresh loamy soil, such as is most favorable for the white pine.
We can assume that the expense of planting per acre will be as follows: cost of land, $5, trees, $6, planting, $10, total, $21, being the capital invested in one acre of forest. This sum at 3 per cent, compound interest will amount in eighty years to $223.44. The price of pine stumpage in this country has trebled in the past twenty years, and we can very safely assume that in eighty years its value will at least be $20 per thousand board feet. The acre crop of 22,000 board feet will then be worth $440, so that the average acre of forest will have yielded a net revenue of 3 per cent, on the capital invested, and left a surplus of $216.56 which will have paid the expense of management and taxes. There will also be a little revenue from thinnings and from game.