32 H. B. HUMPHREY AND J. E. WEAVER 



continent; notwithstanding the fact that great practical benefit 

 would very likely result from an extended and careful scientific 

 study of the factors which determine such growth. 



Ordinarily the denudation of any considerable area of conif- 

 erous forest land means an end of that chapter of forest his- 

 tory. Witness, for example, the thousands of acres of "pine 

 barrens" in Minnesota, Michigan, and Ontario where but a few 

 decades ago stood splendid mixed forests of white and Norway 

 pine, and spruce and fir, holding their own against time and the 

 elements. It is because man in his exploitation of these forests 

 imposed upon their territory an absence of certain growth factors 

 vital to natural reforestation that it has since been impossible 

 for these coniferous species to reestablish themselves. Time 

 has shown that protection from destructive ground fires will in 

 many instances promote natural reforestation. Zavitz, 1 who 

 has made an extensive and careful study of forest conditions in 

 Ontario, states that the reforestation of the denuded land areas 

 is a problem involving fire control rather than one calling for the 

 hand planting of pines. In Sincoe County, for example, a cer- 

 tain district comprising approximately 50,000 acres, and at one 

 time covered with valuable red pine, still supports enough old 

 seed-bearing red and white pines to insure reforestation were it 

 not for the fact that destructive ground fires are allowed to run. 



That the production of a coniferous forest depends greatly 

 upon a real balance of physiological factors can not be denied. 

 No matter how favorable may be the moisture supply, an ex- 

 cessive rate of evaporation will inhibit or make impossible the 

 growth of a crop of seedlings for as long as a single season. Then, 

 again, extreme exposure to sunlight may prove destructive. Or, 

 two or more factors in excess or deficiency may prevent altogether 

 the growth of young plants. 



The following example is illustrative. On Kamiak Moun- 

 tain, an isolated butte near Viola, Idaho, evaporation stations 

 were maintained during the summer of 1913. One Livingston's 

 porous cup atmometer was operated on a south slope a few 



1 Zavitz, E. J., Report on the Reforestation of Waste Lands in Southern On- 

 tario, 10, 1908. 



