THE ROLE OF LIGHT IN NATURAL AND ARTIFICIAL 

 REFORESTATION* 



By Carlos G. Bates 

 Forest Examiner, Forest Service 



In the common conception the word "light" refers only to visible 

 rays of the solar or other spectrum. In the physical conception the 

 word is synonomous with radiant energy, and includes the calorific 

 as well as the visible and actinic rays of the spectrum. In physiological 

 and ecological works there is reason to believe that the term is used 

 rather loosely. Thus Schimper^ in his "Plant Geography" neither 

 defines the term light, nor makes any mention of the effect of radiant 

 energy on transpiration, and throughout the discussion of light appears 

 to be treating solely of visible and actinic light. On the other hand 

 Warming- states that the term is used to express radiant energy, and 

 states that "light is one of the most important factors influencing 

 transpiration." Clements^ treats of the infli4ences of light as those of 

 radiant energy in general, but treats of the measurement only of the 

 chemically active rays. 



The foresters' conception of the term "light" is generally the 

 common conception of visible rays. For the time being I shall consider 

 the role of light in the forest only in the sense of rays measurable by 

 photometric means. This may include some of the ultra-violet as well 

 as visible rays. 



The four important forest trees of the central Rocky Mountains 

 may be listed in the following order as regards their apparent require- 

 ments for light, the most light-demanding appearing first : Yellow 

 pine, lodgepole pine, Douglas fir, and Engelmann spruce. At the end 

 of this Hst might be added alpine fir, the least demanding of all, and 

 at any point in the list might be placed limber pine, which is exacting 

 neither as regards light nor soil nor soil moisture. The above is purely 

 an empiric "scale of tolerance" such as all foresters make from general 

 observation. Such scales are ordinarily based on the densities of the 



♦Presented at the New York meeting of the Ecological Society, Dec. 29, 1916 . 



1 Schimper, A. F. W. "Plant Geography upon a Physiological Basis." Oxford 

 1903. 



2 Warming, Eug. "Oecology of Plants." Oxford, 1909. 



3 Clements, F. E. "Plant Physiology and Ecology." New York, 1907. 



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