138 North American Forests and Forestry 



profitable to cut them down will be the same for 

 the whole body of timber. If an owner wishes to 

 have a regular annual revenue from his forest of 

 this kind, he must evidently have a series of tim- 

 ber bodies of different ages side by side. For in- 

 stance, if the cutting age is a hundred years, he 

 must have a hundred bodies of timber, each a year 

 apart in age, from the one-year-old seedlings to 

 the hundred-year-old ripe wood. Such a system is 

 known as a normal forest, which, however, proba- 

 bly nowhere actually exists in its complete form. 



Again, the same body of timber may contain in- 

 dividuals of all ages, from the seedling to the ripe 

 wood. In this case, the trees arriving at the cut- 

 ting age are each year culled out. This system of 

 culture is known as a selection forest. Like the 

 preceding form, it is rarely found in its complete 

 development. Some of the age-classes are usually 

 missing, for reasons springing from the phenomena 

 of struggle for life outlined in Chapter II. 



Forests may be composed entirely of one species 

 of timber trees, or a number of species may grow 

 together on the same tract. We speak accordingly 

 of pure or mixed forests. Either form is favored 

 by foresters, according to various considerations. 



An interesting form of forest culture is occasion- 

 ally adopted under special conditions, and is known 

 as coppice wood. Some trees among American 

 species — for instance, most oaks, many maples, and 

 the basswood — have the capacity of sending up 

 shoots from their stumps, or stools. These shoots 



