AMEEICAN SYLVICULTURE 



Valuable species might be raised beyond the limits of their 

 habitat in mixed forests. 



D. Objections to mixed forest. 



Tlie administrative and the sylvicultural management of mixed 

 woods is more difficult and hence more expensive than that of 

 pure woods. 



In America logging expenses are much increased where only 

 one species can be utilized in mixed forests. Logging for Spruce 

 on " Black Spruce Slopes " in the Adirondacks is relatively cheaper 

 per thousand feet board measure than logging for Spruce where 

 Spruce forms but one-third of the growing stock. This objection 

 does not hold good, of course, where all species are marketable at 

 the same time. Still, the logging, milling and marketing of 

 numerous kinds is more difficult than that of a few. 



E. Rnles governing the composition of a mixture and 

 rules for treating mixed forests (holding good for artificial and 

 semi-artificial forests) : 



I. Species selected for a mixture must improve one another. 



II. Each species should occupy that section of ground on which 

 it thrives best. 



III. The mixture should at least maintain the productiveness 

 of the soil. 



IV. A light-demanding species mixed with a shade bearer must 

 either be given an advance in age or else must naturally possess 

 an advantage in rapidity of height growth; otherwise it soon dis- 

 appears. This relative height growth is not a fixed quantity; it 

 usually differs according to the soil and to the climate. 



V. The denser the forest cover is, the earlier and the more 

 intense must be the help given to the species likely to be suppressed 

 (Sassafras and Locust in mixture with Chestnut). 



After Henry Mayr, species which are botanically different, form 

 the most natural mixture (Oak and Pine at Biltmore: Birch and 

 Spruce in Balsams; Vv'hite Pine, Linden and Elm in Michigan). The 

 number of exceptions to this rule is great (Norway and Jack Pine in 

 Michigan; Red Firs and "Uliite Firs in the Pacific Coast States). 



Paragraph VIII. Dr. Henry Mayr's fundamental 

 principles of Sylviculture. 



A. Forest is possible only where the mean temperature of 

 the four months of most active growth averages 50 degrees Faht. 

 or over. 



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