320 The Farm Woodlot 



and give up their mineral content. This mineral matter is 

 either taken from the air by the leaves themselves or drawn 

 up from the ground by the roots. The roots of the trees 

 pierce to the subsoil and bring up mineral foods that the 

 roots of smaller plants would never reach. In the same 

 way large amounts of humus are added to the soil and keep 

 it porous and retentive of moisture and gases. The roots 

 by their decay also open up the subsoil and let in air and 

 moisture. In this way the surface soil is being continually 

 improved. It has been estimated that after a sandy soil 

 in New England is so exhausted that it will produce no 

 other crop, it may be renewed to its original fertility and 

 productiveness by the growth of trees on it for thirty years. 

 This should always be kept in mind in locating the woodlot 

 and in calculating the benefits to be derived from it. 



