PURE AND MIXED FORESTS 65 



natural intrusion by mankind has tended to cause the forest to grow 

 up more densely with hardwoods such as the beech, birch, and maple, 

 rather than to be regenerated with spruce and white pine. Natural 

 and unnatural forces are constantly at work to develop or to disturb 

 the formulation of forest types. A study and understanding of forest 

 types and their development are most necessary in the application of 

 silvicultural technique. The forester must understand the natural 

 forces governing the development of forest types and must handle 

 the forest so that the most efficient results may be obtained in the 

 shortest length of time. 



In the organization of any forest, one of the first duties is carefully 

 to survey and map the tract and separate the forest into types. These 

 types form the basis of the cutting cycles and rotations followed in 

 the management of any tract. For example, most of our National 

 and many of our State Forests as well as private tracts have been 

 carefully surveyed to determine the location and condition of each 

 type found within them. Information secured in these studies and 

 surveys is used in making timber sales, logging plans, fire protection 

 and road construction plans, and management plans for sustained 

 yield. 



5. PURE AND MIXED FORESTS 



The relative advantages and disadvantages of growing trees in 

 pure or mixed forests have been subjects for wide discussion among 

 foresters. The problem applies both to naturally reproduced and to 

 planted forests. Virgin forests are generally of mixed species. Pure 

 forests are most frequently found in alpine regions. In artificially 

 reproducing forests by planting, the general practice in the United 

 States has been to use one species, thus forming pure forests. 



According to Tourney and Korstian,* advantages of pure stands 

 are that the management is very simple, thinning requires little tech- 

 nical skill, natural pruning is much more uniform than in mixed 

 forests, and the crop can be harvested more economically because only 

 those species are grown which enjoy highest market prices. The 

 planting of pure stands is much simpler, easier, and less expensive, 

 and the resultant stand is generally more dense and the yield is ac- 

 cordingly higher. 



The advantages of mixed stands or, conversely, the disadvantages 

 of pure stands are that the pure stands do not generally improve the 

 fertility of the soil, the danger from injury such as from fire, wind, 



*See "Seeding and Planting in the Practice of Forestry," second edition, 

 John Wiley & Sons, 1931. 



