62 FORESTS AND MANKIND 



For the United States as a whole, grass land occupies thirty 

 per cent of our land area, desert twenty-two per cent, and for- 

 est land forty-eight per cent. The forests themselves form two 

 broad belts of tree life, one a belt of western forests extending 

 inland from the Pacific and the other a belt of eastern forests 

 bordering the Atlantic. In the central United States a broad 

 prairie of grass land lies between these two belts, known as 

 the Great Plains. This area in ages past fostered tree growth, 

 and today is treeless probably as the result of many factors 

 chiefly climatic changes that decreased the rainfall. Fires of 

 long ago may also have played a role here in preventing in- 

 vasions of tree growth that would bring these plains back to 

 forest. But whatever caused these great expanses of grass land, 

 they have effectually acted as a broad barrier to keep the species 

 of east and west from mingling and so have been one cause 

 of the differences in the composition of our eastern and west- 

 ern forests. 



Originally four fifths of our forests were in the eastern 

 United States. But because settlement began on the Atlantic 

 Coast and because the East today supports eighty per cent of 

 our total population, the eastern forests have suffered greater 

 and much more rapid depletion than the western. Not until 

 the partial exhaustion of our eastern forests through lumbering 

 and fire were men forced to go south and west for their wood. 



These two forest belts are quite dissimilar in extent, as well 

 as composition. Along the eastern seaboard, the first settlers 

 in this country found a heavy, unbroken forest extending over 

 more than a million square miles. The western forests are 

 much less extensive, covering about two hundred thousand 

 square miles almost equally divided into two parts, one in the 



