64 SEEDING AND PLANTING 



5. The Advantages of Pure Stands 



Although, silviculturally considered, pure crops are usually un- 

 desirable, there are often economic advantages which overbalance 

 silvicultural defects. The most important of these advantages 

 are as follows: 



a. The management is very much simplified, and the thinning 

 operations require much less skill. 



b. When properly spaced, natural pruning is more uniform than 

 in mixed crops. 



c. The crop can be harvested more economically and only the 

 species grown which command the best market. 



d. The restocking is simpler, usually less expensive, and the re- 

 sulting stand is usually more complete. 



Because of the advantages herein enumerated, particularly the 

 much less experience required to bring pure crops to maturity, 

 seeding and planting in pure stands is usually encouraged in the 

 United States. Imperfect knowledge of the silvical character- 

 istics of our native trees mitigates against seeding or planting in 

 mixtures, because the advantages that result from suitable mix- 

 tures are so often unattainable. The wrong species for the mix- 

 tures are often selected and early thinnings cannot be made. 

 Under present conditions, therefore, it is usually safer to seed 

 and plant all but the dependent species in pure stands. Even 

 with dependent species, only in exceptional instances should more 

 than two species be used in the mixture. Furthermore, it is usu- 

 ally much safer to seed or plant dependent species like larch, oak, 

 walnut, cherry, tulip, and ash in pure stands with the expectation 

 of underplanting with a tolerant species when the soil begins to 

 deteriorate than it is to run the danger of using wrong species in 

 the mixture. 



6. MIXED CROPS IN ARTIFICIAL REPRODUCTION 



Under suitable management all species can be grown in mixed 

 crops. Acceptable mixtures, however, should form and preserve 

 a complete canopy and properly conserve the soil. Thin-foliaged 

 trees should usually be mixed with dense-foliaged ones. 



In the formation of mixed woods by seeding or planting, we 

 may plan to have the mixture by single trees, by lines, or by 

 groups. When the mixture is by single trees the trees of one spe- 



