Page:Popular Science Monthly Volume 81.djvu/537

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ORESTRY 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