CHAPTER THIRTY-THREE 



THE VEGETATION OF NORTH AMERICA 



North America extends from the North Polar Sea nearly to 

 the equator, and consequently its vegetation includes climatic 

 plant formations belonging to the frigid, temperate, and tropical 

 realms. In this chapter the more important of these plant 

 formations, and the factors which determine or limit their dis- 

 tribution, will be discussed. There are at least nine of these 

 natural divisions of the vegetation of North America: (i) Tun- 

 dra, (2) Northern evergreen forest, (3) Deciduous forest, (4) South- 

 eastern evergreen forest, (5) Prairie, (6) Plains grassland, (7) West- 

 ern evergreen forest, (8) Desert, and (9) Tropical hroadleafed 

 evergreen forest. 



Climate — especially moisture, temperature, and light — 

 determines the particular part of North America where each of 

 these several types of plants may live. The habitats within the 

 climatic formations determine the number and location of the 

 plant associations. In the paragraphs that follow, the vegeta- 

 tion is described as it was before it was modified or destroyed 

 by man. In the next chapter attention is called to the close 

 correlation that exists between the climatic plant formations and 

 the distribution of the industries directly dependent upon plant 

 life. 



The tundra formation. There is no more distinctive type of 

 vegetation on the earth than the low-growing vegetation of the 

 frigid realm, to which the name tundra has come to be generally 

 applied. Originally used to designate the vast stretches of low, 

 swampy, and rocky plains of northern Russia, this term is now 

 applied also to the vegetation that covers the " barren grounds " 

 from northwestern Alaska to Hudson Bay and eastern Labrador. 



The tundra is a region of shallow, poorly drained soils, where 

 the winters are long and the average temperature so low that the 

 ground thaws only a few inches, or at most a few feet, during the 



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