66 FOREST INFLUENCES 



insects, and fungi is greatly increased by using a single species, and 

 pure crops may not occupy the ground or the site so completely, espe- 

 cially with intolerant species. 



6. FACTORS DETERMINING THE SELECTION OF SPECIES 



Among the more important factors which must be considered in 

 selecting species to be grown in any part of the country, the following 

 may be mentioned. 



1. Rapidity of growth. It is important that trees mature or reach 

 a merchantable size as early as possible because financial invest- 

 ments may accumulate more rapidly than the wood accumulates in 

 volume and value. 



2. Freedom from fire, insects, fungi, and other damage. Occasion- 

 ally one or more of these factors may prevent the use of certain spe- 

 cies in some regions. White pine is susceptible to the blister rust and 

 weevil attacks, and therefore, under some conditions, it is not ad- 

 visable to plant it. 



3. Adaptability. The tree must be adaptable to the site, including 

 the type of soil, character and amount of precipitation, slope, and 

 aspect. 



4. Marketability of forest products. This is of paramount im- 

 portance. Unless trees can be profitably marketed, the financial 

 phases of forestry may be seriously jeopardized. 



5. As the objectives of forest management may be the cultiva- 

 tion and improvement of wild life, grazing, recreation facilities, or 

 aesthetic effects, trees should be selected, planted, or left in cultural 

 operations, that will lend themselves best to the objectives sought. 

 For example, food-bearing plants should be encouraged when the pri- 

 mary objective is deer raising. When shelterbelts, windbreaks, erosion 

 control, or other specialized objectives are sought, the trees must lend 

 themselves best to achieve these results. For example, conifers furnish 

 better wind protection for shelter projects throughout the year than 

 do hardwoods. 



6. The species that will best preserve and maintain the soil con- 

 ditions. Under certain circumstances, the maintenance of proper soil 

 fertility may be of paramount importance. 



7. Location. Native species are generally preferred to exotics. 

 If, however, exotics offer decided advantages, they should be used on 

 the best locations and usually on small areas. 



