FOREST TREES AND FOREST REGIONS OF THE U. S. 33 



FOREST REGIONS OF THE UNITED STATES 



Different kinds or species of trees are found in natural association 

 or mixtures and prevail in different portions of the United States. 

 This is largely the result of varying conditions of temperature and 

 rainfall or snowfall, and secondarily, of soil conditions. There are 6 

 natural forest regions in continental United States, 2 each in Alaska 

 and Hawaii, and 3 in Puerto Rico. 



Most of the trees of a given forest region are different from those 

 in the others, yet a considerable number are found in at least 2 and a 

 few in 3 regions, especially in the eastern part of the United States 

 where the large regions intergrade gradually. This difference in the 

 predominance of various species is rather marked in the 2 forest regions 

 of the western portion of the United States, divided partly at least by 

 the extensive and nearly treeless interior basin extending from south- 

 east Washington south to Mexico. 



The 4 forest regions of the eastern half of the United States are 

 the northern, central hardwood, southern, and tropical; the 2 of the 

 western portion, the Rocky Mountain and Pacific coast. These are 

 shown in figure 7. The forests of Alaska divide themselves into the 

 coast and interior forest regions; those of Puerto Rico into mangrove 

 swamp, wet, and dry forests; and those of Hawaii into the wet and 

 dry forests, as shown respectively in figures 8, 9, and 10. 



EXTENT OF FORESTS 



The original forests of the United States, exclusive of Alaska and 

 the island possessions, are estimated to have covered a total area of 

 about 820,000,000 acres, or nearly one-half (42 percent) of the total 

 land area. Reduced mainly by clearing land, there now remains a 

 little over one-half (60 percent) of this or a total forest area estimated 

 at 495,000,000 acres. The bulk of this is classed as commercial 

 forest land, which means land that is in timber or capable of producing 

 it from young growth. 13 



About three-fourths of the forest-producing land area of the United 

 States lies east of the Great Plains. This land contains only about 

 one-tenth of the remaining virgin timber, but a very large quantity 

 of second-growth or young timber. The other one-fourth of the 

 forest land, with nine-tenths of the total virgin timber but little 

 second growth, is located in the Rocky Mountain and Pacific coast 

 regions. 



The change in the past from forest to cleared land has obviously 

 taken place in the most fertile and accessible regions. In the Central 

 and South Atlantic States less than one-half of the original land still 

 remains in timber growth. In the Rocky Mountain States the re- 

 duction in area has been only slight. New England, a hundred years 

 ago, had much cleared land in farms, of which a considerable amount 

 has since gone back to forest, so that the present forest area is about 

 70 percent of the original. This same process has tended to increase 

 slightly the area of forest land elsewhere in the United States. 



is This and the next topic are based upon data in the following publication: United States Department 

 of Agriculture, Forest Service, a national plan for American forestry. Letter from the Sec- 

 retary of Agriculture in response to S. Res. 175 .. . the report of the Forest Service of the Agriculture 

 Department on the forest problem of the United States. 2 v., illus. 1933. (73d Cong., 1st sess., S. Doc. 

 12.) 



