16 FORESTRY 



veloped from small sizes, under the same conditions, and 

 have adjusted their root system to the moisture supply, 

 and their boles and crowns to the exposure to wind and 

 abundant light. The ground about such trees may be baked 

 hard by the wind and sun, or covered with a dense sod, but 

 the tree will resist these drying influences since it has al- 

 ways had them to contend with, and its roots have spread 

 out and struck deep, insuring abundant moisture. At the 

 same time, the trunk at the base has swelled into a strong 

 buttress, and the crown lies low on a tapering bole, so that 

 the form and strength of the stem are ideal for resisting 

 the sudden onslaught of a fierce wind. Competition with 

 other trees is eliminated, and the tree easily masters the 

 opposing forces of the elements. 



The Struggle for Moisture and Light and its Effect on 

 the Form of Trees. But in the forest, single trees grow 

 so closely together that there is a struggle between them 

 for the necessities of life, light and moisture. Plant food 

 is taken up by means of water, always in solution, and the 

 amount of moisture present is of more importance in its 

 effects on tree growth than the richness of the soil in chem- 

 ical food supplies. This struggle for light and moisture 

 gives the forest its distinctive form. Wherever there is 

 sufficient soil moisture to support a full stand of trees, the 

 competition is fiercest for light. But in many places the 

 moisture is very scant, and then the struggle becomes whol- 

 ly one of root competition for water. The form of a forest 

 growing on dry soil is necessarily open. Trees are spaced 

 at considerable intervals, and their crowns have room to 

 develop. But investigations show that the stand is really 

 as dense as the soil will support. Young seedlings which 

 may spring up, die out in a few years, because they are 

 unable to get moisture. The roots of the old trees, larger 

 and more vigorous than the seedling, and penetrating deep- 

 er, suck up all the water, and the seedlings perish of 

 drought. Such stands are true forests, although they may 



