the capacity for production of food is increasing or diminishing'. 

 On the farms the one problem is how to maintain the fertiHty of 

 the soil ; in the forest the soil of itself renews its fertility. 



Under all conditions there is a certain wear of the earth's surface. 

 It is greatest on steep, treeless slopes, unless they are so rocky as to 

 resist erosion. There are thousands of acres of such steep hillsides 

 on which nothing but rocks appear, the soil having been washed 

 away. But trees or no trees, the wear goes on, though infinitely 

 slower with than without trees. 



When the forests are cut and removed, the soil follows. It is fil- 

 tered out, washed away, and with it disappears all prospect of im- 

 mediate reforestation, except at great expense. 



The oldest seats of civilization are abandoned and in desert condi- 

 tion now, where the utter removal of the forest marked the beginning 

 of desolation and the disappearance of man's power over nature, 

 when the soil was removed faster than it was being made ! 



The greatest function of the forest, possibly, aside from yielding 

 materials useful to man, is soil improvement. Forests not only hold 

 the soil in place against the erosive action of wind and water, but 

 what is even more important, the roots penetrate to the deeper layers 

 of the soil, absorb the mineral substances found there and deposit 

 them again on the surface in the form of detritus, which soon be- 

 comes humus. The acid secretions of the roots, and their mechan- 

 ical action even aid in breaking up rocks and so forming new soil 

 as well as making more mineral salts available for plant growth. 

 They help to break up soils that are too stiff and hard, and they 

 aerate and greatly improve the physical condition of the soil in 

 bringing about the valuable "crumb-structure." 



Thus the surface soil is being constantly fed, and the mineral 

 ingredients conserved. This deposit, gradually rising to the surface, 

 raises the level and aids in the process of drainage. 



Worn out soils, and poor sandy soils may be brought back to 

 virgin fertility by a crop of trees being grown on them for about 

 30 years. 



Trees are one of the very few crops that can be said to actually 

 improve the soil rather than lessen its fertility. Mineral food is 

 returned to the soil by the tree crop, and the physical conditions are 

 greatly improved. 



Some forest trees act as land formers as well. The mangrove of 

 our southern swamps and bayous grows in mud flats even along the 

 shores of salt-water. Together with the cocoa palm, buttonwood, 

 and sea-grape, it consolidates the muddy shores, catches driftage, 

 and gradually extends the boundary of solid land into the ocean. 

 It also forms a valuable protection to the shores in heavy storms. It 

 is being planted along the line of the Florida East Coast Railway, 

 to protect and build up the land along the route to Key West. 



30 



