24 SEEDING AND PLANTING 



and development because of the greater assimilation of carbon. 

 With the majority of forest trees, the optimum light intensity at 

 which the leaves function best and at which the production of 

 flowers and fruit is most abundant lies much nearer the maximum 

 amount of light available for the use of the tree than to the mini- 

 mum light under which it can still exist. 1 The chief reason why /<" 

 the time between blossoming and fruiting in any given species be- 

 comes shorter as we proceed north or south from the equator is 

 because of the increase of daylight during the growing season. 

 Although light is essential for tree life, there is no site where 

 light is too attenuated or too intense for the growth and develop- 

 ment of trees in the open. Light becomes an important factor- 

 chiefly from the standpoint of the shading influence of one tree upon 

 another when they are grown in stands or because of its influence 

 upon other factors of the site such as heat and moisture. 



10. CONDITIONS UNDER WHICH LIGHT INFLUENCES THE CHOICE 

 OF SPECIES. Light influences the choice of species for seeding 

 and planting operations when: 



a. The species are grown in mixtures. 



b. The reproduction takes place under an overwood. 



In planting or seeding with a single species, the result of shading 

 is to suppress the weaker trees. The stand at all times remains 

 complete but with fewer trees per acre as it becomes older. In 

 mixed stands, unless good judgment is shown in the selection of 

 the species which form the mixture, the result of shading is to 

 suppress one or more of the species in the mixture to the advantage 

 of the others. When the reproduction takes place under an over- 

 wood, careful attention must be given to the density of the 

 overwood and the light requirements of the species used in the 

 regeneration. 



11. THE INDIRECT INFLUENCE OF LIGHT UPON THE CHOICE OF 

 SPECIES. When seeding and planting operations are conducted 

 on open sites, light indirectly affects the regeneration because of 

 the effect of direct sunlight upon the moisture conditions of the 

 surface layers of the soil. Soil exposed to direct sunlight dries 

 out quickly and subjects both seeds and plants to extremes of 

 moisture during the critical period following seeding and planting. 

 Species like oak and hickory having large seeds which in seeding 



1 Zon, R. and Graves, H. S.: Light in relation to tree growth. (U. S. 

 Forest Service, Bui. 92, p. 11. 1911.) 



