[Chap. LIU THE VEGETATION OF NORTH AMERICA 789 



Tropical forests (Figs. 418-420). The tropical forests of southern Mex- 

 ico and Central America are made up of a large number of broad-leaved 

 evergreens, including palms, tree ferns, figs, rubber trees, various kinds 

 of mahogany, silk-cotton trees, Spanish cedar, logv^ood, and hundreds 

 of other species. The rainy tropical forest when undisturbed attains 

 heights of 200 feet, and there may be several tree layers beneath the 



Fig. 418. Natural live oak forest near Miami, Florida. Photo from U. S. 



Forest Service. 



highest canopy, but the forest is open below. Stands of this kind still 

 occur on certain of the Caribbean islands, and in Guiana and Venezuela. 

 Mostly the present-day rainy tropical forests are jungles: tangled growths 

 of trees, vines, shrubs, and tall herbs difficult to penetrate, and containing 

 so many species that they can scarcely be described. The rainfall is as 

 much as 200 inches a year and the dry season is very short. Temperatures 

 are always high. 



Jungles result from repeated cutting, burning, and clearing of the 

 land. The lateritic soils of the rain forest are not rich in mineral salts 

 and are soon leached and eroded under native methods of cultivation. 

 Furthermore, weeds from seeds and from underground roots and 



