PRINCIPLES WHICH GOVERN COMPOSITION OF STAND 63 



3. Dependent Species in Pure Stands 



Although most tolerant species may be grown as pure crops, 

 dependent species should be grown in pure stands only under the 

 following conditions: 1 



a. Under short rotation for special purposes, i.e., when the in- 

 tention is to harvest the crop before the leaf canopy has opened 

 up excessively. This is illustrated in growing catalpa and black 

 locust for fence posts under a rotation of from 12 to 25 years. 



b. Where the rotation is for a long period with the expectation 

 of underplanting when the canopy becomes too open properly to 

 conserve the quality of the site. This is illustrated in larch, 

 white oak, black cherry, walnut, and a great variety of other 

 species which 20 to 35 years after planting open up too much to 

 sustain an adequate layer of forest litter and humus. 



c. On sites where the soil is sufficiently deep and fertile to main- 

 tain good growth, even with imperfect cover and want of humus. 

 This is illustrated in successful pure stands of walnut on the deep, 

 fertile bottomlands of eastern Nebraska and Kansas where the 

 water level is but 8 or 10 feet below the surface. 



d. In some instances, we may be justified in growing dependent 

 species in pure stand where the particular site is suitable only for 

 a dependent species or where it is the only species that finds a 

 ready market or can be used for a special purpose. 



4. The Disadvantages of Pure Stands 



Although much depends upon the particular conditions of the 

 site, the species and the economic considerations, the most impor- 

 tant disadvantages that result from seeding or planting for pure 

 crops are as follows: 



a. As a rule, pure crops do not maintain or improve the fer- 

 tility of the soil, this being particularly true of thin-foliaged species. 



6. Pure crops, as a rule, increase the danger from fire, wind, 

 insects, fungi and other external agents. 



c. Pure crops do not occupy the site so completely as is the 

 case with mixed crops and, consequently, the total wood product 

 is usually less. 



1 Heyer, Carl: Der Waldbau oder die Forstproduktenzucht. 5. Aufl. I. Bd., 

 S. 87. Leipzig, 1906. 



