THE WILDWOODS 23 



Ha\ing seen what the soil does m determining the com- 

 position of the woods, we might also inquire whether the 

 forest can do anything to alter the soil. 



As we have learned in our former studies, the tree gets 

 from the soil only water and certain useful salts, while 

 the rest of the material of the tree comes from the air. 

 The salts which it gets from the soil are its soil-food, and 

 when these salts are lacking in a soil we call it poor and 

 say that it needs fertilizing; i.e., it needs to have these 

 salts replaced to make it fertile or enable it to sustain 

 plants. The salts wliicli the tree uses, reappear as ashes 

 when we burn the leaves, twigs, or wood. 



Now when a beech tree takes up twenty pounds of such 

 salts in a season, and perhaps fifteen pounds find their 

 way into the leaves which are shed in the fall, these 

 fifteen pounds may be taken up again by the tree, or its 

 neighbor, as soon as the water has leached out and carried 

 the salts down among the roots. In this way the trees 

 take and give all the time. But besides these mineral 

 salts the soil also needs decayed plant matter ; it needs 

 mold or humus to make it really fertile. This is sup- 

 plied by leaves and twigs which are shed by the forest 

 trees, and these tend, therefore, to enrich the soil. It is 

 due chiefly to this mold that " new-cleared " land is so 

 fertile. In many districts people clear land, use it for 

 some time, and then restock it with forest growth, which 

 in due time reestablishes the former fertility. 



