224 



WOOD AND FOREST. 



lentless struggle against its neighbors for light, water and food, the three 

 things trees need most. On the other side each tree is constantly working 

 with all its neighbors, even those which stand at some distance, to bring 

 about the best condition of the soil and air for the growth and fighting power 

 ^f every other tree. 



The trees in a forest help each other by enriching the soil in 

 which they stand with their fallen leaves and twigs, which are not 

 quickly blown or washed away as are those under a tree in the open. 

 This collection of "duff" or "the forest floor" retains the moisture 

 about their roots, and this moist mass tends to keep the temperature 

 of the forest warmer in winter and cooler in summer. The forest 

 cover, Fig. 55, p. 212, consisting largely of foliage, has the same effect, 



. 70. Shallow Roots of Hemlock. Bronx Park, 

 New York, N. Y. 



and in addition protects the bark, the roots, and the seedlings of the 

 trees from the direct and continuous hot rays of the sun. Without 

 the shade of the leaves, many trees, as white pine, would quickly die, 

 as may readily be seen by transplanting them to the open. The mass 

 of standing trees tempers the force of the wind, which might over- 

 throw some of them, and hinders the drying up of the duff. 



But trees hinder as well as help each other. There is a constant 

 struggle between them for nourishment and light. To get food and 

 water, some trees, as spruces and hemlocks, Fig. 70, spread their roots 

 out flat; others, as oak and pine, send down a deep tap root. Those 

 succeed in any environment that find the nourishment they need. 

 Still more evident is the struggle for light and air. However well a 



