PRACTICAL FORESTRY. 15 



and weeds. Forests' which closely resemble two-storied seed forests 

 are common in the United States, but usually as the result of fire or 

 careless cutting. Such are, for example, the forests of pine over oak 

 in the southeastern United States, and of birch, beech, and maple 

 under white pine in Michigan, Wisconsin, and Minnesota. It often 

 happens, as in the case of the spruce and aspen, that both stories can 

 not live on in good health together, and that the upper one must die 

 or.be cut away if the lower is to prosper. 



Selection forest. — ^When a staad of aspen dies away from a young 

 crop of spruce, the ground is no longer completely shaded, and there 

 is light and room for other kinds of trees to come in. Thus, birch 

 and maple seeds may be blown in by the wind and beechnuts carried 

 and planted by squirrels, and eventually the pure stand of spruce is 

 changed into a mixed forest of various ages. As the trees grow older, 

 some of the spruce may be destroyed by beetles or thrown by the 

 wind, and some of the broadleaf trees may die from fungous disease. 

 Into the openings made by the death of older members of the forest 

 fall the seeds from which younger members spring. So little by little 

 the forest loses its even-aged character and there comes into existence 

 what is called a natural or selection forest, in which trees of all ages 

 are everywhere closely mixed together. Most virgin forests are 

 selection forests. 



The silvicultural system called pure selection is applied to forests 

 of this kind. It is used chiefly for protection forests in places where it ♦ 

 is desirable to keep the cover always unbroken; elsewhere it is out 

 of place. Under this system the annual increase of the forest must 

 be found before the yield can be determined. (See p. 7.) Then the 

 fully mature trees are cut in every part of the forest every year. 

 The cost of logging is high, for where single trees are taken here and 

 there, roads or other means of transport must be very numerous and 

 costly in proportion to the amount of the cut. 



localized selection. — Logging under the system just mentioned is 

 so expensive as to prevent its application in the United States, except 

 for woods like cherry and black walnut, which have a special and 

 unusual value. But if, instead of taking the yield from every part 

 of a selection forest, a comparatively small area is cut over each year, 

 the cost of logging may be very greatly reduced. Such a method is 

 admirably adapted to certain forest regions in the United States, as, 

 for example, to the Adirondack Mountains of New York, where the 

 forest is composed equally of coniferous and broadleaf trees. The 

 conifers are the more valuable, and among them the principal lumber 

 tree is the spruce. 



The Forest Service has found by many careful measurements that 

 if all spruce trees 12 inches and over in diameter are cut from certain 



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