222 JOURNAL OF FORESTRY 



area is logged over it is left to itself, exposed again to cumulative risk 

 from the cull factors encroaching upon the area from the outside. In 

 other words, we have to a certain degree forest sanitation, but no 

 forest hygiene. A large field for research and practical v^^ork lies before 

 us, almost fallow. The sooner reliable and definite information con- 

 cerning the factors of cumulative risk is available, the sooner will 

 intelligent forest hygiene become a possibility instead of a chimera. 



Immense areas of virgin forest are cut over annually in the 

 United States, a comparatively small fraction on Government land, 

 by far the greater part on private holdings. The practice of burning 

 over the latter after logging and of leaving malformed trees as well 

 as those of so-called inferior species tends to retard for a number 

 of years natural reproduction, to alter to a certain degree the repre- 

 sentation in favor of the inferior species and to prevent an equal and 

 advantageous distribution of individuals. Since diseased trees gen- 

 erally are not cut, the young stand grows to maturity helplessly and 

 hopelessly exposed to the host of unchecked, uncontrolled components 

 of cumulative risk. In other words, the act of man here results in 

 conditions very similar to those caused by the uncontrolled fires of 

 the past, with this exception, that fires do not choose between valuable 

 and inferior species. The future forest will be a duplicate of the 

 virgin forest preceding it, with a possible preponderance of the inferior 

 species. On the National Forests conditions are more favorable in so 

 far as under the selection system prevailing at present only young, 

 thrifty trees are left on timber-sales areas and reproduction is carefully 

 protected against injury from logging operations and fire. Under the 

 sanitation clause diseased trees and, wherever possible, malformed 

 trees and snags are cut. In general the attempt is made to maintain 

 the representation of inferior species or even to alter it in favor of 

 more valuable timber through heavy marking, but more often the 

 prejudice against inferior species on the part of the purchaser renders 

 this eminently important operation illusorical or impossible. However, 

 an area cut over under Government regulations starts on its career 

 of producing a new timber crop with many advantages over adjacent 

 privately owned areas logged under the prevailing system of turning 

 timber into cash without regard for the future. Advance growth is 

 protected, reproduction favored and controllable diseases are elimi- 

 nated. But the total area of Government land annually cut over is 

 small in comparison with that in private ownership. Furthermore. 



