CHAPTER V 



THE PRINCIPLES WHICH GOVERN THE COMPOSI- 

 TION OF THE STAND 



1. PURE WOODS COMPARED WITH MIXED 



THE virgin forest is nearly always mixed in composition. Only 

 tolerant species mature in pure stands. Pure stands are most 

 frequent in alpine regions and in other localities where the climate 

 is cold. Even the most tolerant species seldom grow in pure 

 stands in tropical regions. Existing pure stands are largely the re- 

 sult of tolerant species driving out those that make greater demands 

 on light, or else they are artificial stands produced primarily for 

 financial reasons. 1 



In artificial regeneration a decision must be made between the 

 development of a pure or a mixed crop for each particular site. 

 In making this decision, Mayr 2 emphasizes the importance of the 

 following : 



a. A knowledge of the climatic and soil factors of the site in 

 order to judge whether all the species will grow equally well. 



6. A knowledge of the habit and growth characteristics of 

 the species in order to know whether they can be brought to 

 economic maturity best in pure stands or in mixed stands. 



Species differ greatly in their requirements for growth and de- 

 velopment. They differ greatly in height, diameter, and volume 

 growth. Some grow slowly, while others grow with great rapidity. 

 They exhibit great variation in tolerance and longevity. Because 

 of these and other differences some species can be brought to 

 maturity in pure stands, while others form successful stands only 

 when mixed with other species. 



The tendency, both in the United States and abroad, is to re- 



1 Nisbet, John: On mixed forests and their advantages over pure forests, 

 p. 4. London, 1893. 



2 Mayr, Heinrich: Waldbau auf naturgesetzlicher Grundlage. S. 431. 

 Berlin, 1909. 



61 



