318 



ELEMENTS OF GENERAL SCIENCE 



forests. There are other types in which the grasses are most 

 important ; these are known as grasslands or meadows. 



321. Value of wild plants. Forests are usually regarded 

 as the most valuable natural plant associations. They supply 

 us with wood, which we use for many purposes. If it were 



FIG. J53. Careful lumbering 



The young trees have been protected while the older trees were cut, and the 



brush is piled for burning. After a few years another crop may be harvested. 



Photograph by the United States Forest Service 



not for our forests we should be deprived of the use of wood, 

 and it is difficult to see how we should secure adequate sub- 

 stitutes for some uses to which wood is put. It is of the 

 greatest importance to our nation that the wood of our for- 

 ests should be used in such a way as to prevent waste and 

 destruction (figs. 153 and 154). The forest is also of much 

 importance in preventing the erosion of the soil, as we have 

 seen (sect. 308). If the forests are removed in mountainous 



