370 NATURE-STUDY 



several centuries. The cypress lives five hundred years. 

 The giant sequoias of the West probably saw the light 

 before the Christian era. 



Forest Influences and Uses 



Forests exert some important physiographic influences. 

 It is still a moot point how far the presence of forests affects 

 the rainfall of a region. It is probably more correct to say 

 that there are trees because it rains, than that it rains in 

 places where there are forests. The cooling effect of the 

 transpiration of a forest may hasten the precipitation of 

 passing clouds. But on the whole the rainfall has not 

 been noticeably affected in this country by the clearing 

 away of the forests, or the planting of trees on the prairies. 

 The cases of Persia, Spain, and other countries usually 

 mentioned to show that the absence of extensive forests 

 causes aridity of climate are now considered rather doubt- 

 ful illustrations, as it is not well proved that those lands ever 

 had extensively wooded areas, in historic times. 



Forests temper the force of the winds, and are very useful 

 as windbreaks for the hot winds of summer and the cold 

 winds, in winter. 



Forests protect the soil from erosion. In level regions 

 this is not so evident as in hilly or mountainous countries. 

 The hills should be capped with forest growth, not only to 

 keep the soil on the hills and to prevent their being gullied 

 with water courses, but also to protect the fertile valley lands 

 from the gravel and sand that would otherwise be carried 

 down upon them. 



Forests conserve the rainfall. The spongy, porous mass of 

 leaf mould on the floor of the forest very materially acts as 



