The Vegetation of North America 



325 



U.S. Forest Service 



Fig. 201. Buttressed trunks of mahogany trees in southern Mexico. 



is reduced sHghtly by low mountains and greatly by high moun- 

 tains, and the vegetation changes accordingly. 



In Florida the tropical forest is poorly developed, but its 

 relationship to the tropical forest is shown by the presence of 

 palmettos, palms, and other tropical trees. Along the coast 

 are mangrove swamps, very similar to those found on all muddy 

 coasts in the tropics. The Everglades constitute a vast area of 

 shallow water largely occupied by saw grass, with narrow open- 

 water channels forming a labyrinth of passages. Interspersed 

 are many small islands covered with tropical trees, which support 

 numerous epiphytic bromelias and orchids on their branches. 



In the West Indies and in Central America the original tropical 

 evergreen forest has been destroyed by centuries of migratory 

 agriculture. This term is appHed to a general practice in tropical 

 countries, of clearing a piece of forest land and growing crops on 

 it for a few years, while the returns are large and the weeds are 

 easily controlled. When crop growing becomes more difficult, 



