PEACTICAL FORESTRY. 7 



product if at one time there are too many ripe trees and at another 

 too few. For example, if 100 acres become fit to cut this year, and 

 200 next year, and after that none at all until 500 acres become ripe 

 fifteen years later, it is easy to see that the yield would come at very 

 irregular and perhaps very inconvenient times. But a forest of 10,000 

 acres, composed of 100 even-aged groups of trees of every age from 

 1 to 100 years, each group 100 acres in extent, would plainly be able 

 to furnish every year 100 acres of 100-year-old trees ready for the 

 ax. In such a forest the right proportion of young trees would always 

 be coming on. 



The fourth requirement is growing space enough for every tree, 

 so that the forest as a whole may not only produce wood as fast as 

 possible, but the most valuable sort of wood as well. If the trees 

 stand too far apart, their trunks will be short and thickly covered 

 with branches, the liunber cut from them will be full of knots, and its 

 value will be small. If, on the other hand, the trees stand too closely 

 together, although their tnmks will be tall and clear of branches, 

 they will be small in diameter, and for that reason low in value. 

 With the right amount of growing space, trees grow both tall and of 

 good diameter, and their trunks supply lumber of higher price because 

 it is wide and clear. 



THE YIELD OF A FOREST. 



One of the central ideas of forestry is that the amount of wood 

 taken from any healthy forest and the amount grown by it should 

 be as nearly equal as possible. If more grows than is cut, then the 

 forest will be filled with overmature, decaying trees; but if more 

 wood is cut than is grown, then the supply of ripe trees will be ex- 

 hausted, and the value of the forest will decline. To make the cut 

 equal to the growth does not mean that the volume of wood grown 

 each year on every acre should be cut from that acre, but that the 

 total growth of all the acres, for one or for a number of years, should 

 be cut from the forest in the corresponding period. Thus, if the 

 growth or increase is 100 cords a year, that amount might be harvested 

 yearly by cutting every tree on a small area, by cutting fewer trees 

 per acre on a larger area, by distributing the cut every year over the 

 whole surface of the forest, or by cutting 1,000 cords in any one of 

 these ways once in ten years. 



There are many different methods of finding what is the annual 

 increase of wood in a forest. One of the simplest is to count the 

 number of trees upon an acre and select an average tree, then to cut 

 it down, measure its cubic contents, and find its age by counting the 

 annual rings. That done, the yearly increase of the average tree 

 may be found by dividing its cubic contents by the years of its age, 



358 



