SOME PROBLEMS IN LIGHT AS A FACTOR OF FOREST 



GROWTH^ 



By Raphael Zon 



No other climatic factor has such direct bearing upon forest growth 

 as hght. It enters into the question of natural reproduction of the 

 forest, in the artificial raising of stock for planting in the forest; it 

 plays an important part in regulating the degree of cutting and thin- 

 ning; it determines the structure of the forest stand — whether one- 

 storied or many-storied forest. It is light which largely determines 

 the height growth of the trees in the forest, the rate with which stands 

 begin naturally to thin out with age, the progress of natural pruning, 

 the character of the living ground cover, the vigor of young tree growth, 

 the natural differentiation of trees in a stand into dominant, codomi- 

 nant, intermediate, oppressed, and suppressed ; it affects the seed pro- 

 duction of trees occupying a different position in the stand with relation 

 to each other and affects many other phenomena upon which the man- 

 agement of the forest depends. In no other plant community does light 

 play such an important part as in a forest. A thorough understanding, 

 therefore, of the effect of light upon the life of trees in the forest, and 

 a knowledge of the methods by which the extent of this effect can 

 be determined, are essential for a proper understanding of the life 

 of the forest and successful handling of the forest. 



From the standpoint of the forester there are three points in the 

 study of light that deserve particular consideration : 



1. Should there be undertaken comparative measurements of total 

 solar radiation at different latitutes or should the investigator confine 

 himself only to the measurements of light actually utihzed by the differ 

 ent life processes of the plant, such as the formation of chlorophyl, 

 photo-synthesis, and so on? 



2. Should there be qualitative measurements of light which pene- 

 trate the canopy of the forest or should the light in the forest be con- 

 sidered as of the same quality as the light in the open, but only of 

 lesser intensity? 



3. To what extent do heat, moisture, and fertility of the soil modify 

 the effect of light upon the life processes of the same species and by 

 what methods can the effect of each of these compensating factors be 

 determined? 



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



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