FREE INSTITUTE OF SCIENCE 



75 



VEGETATION OF SOUTH FLORIDA 



that this chapter is written, but merely to give a detailed account of the 

 general geographic distribution of the mangrove swamps, as well as a few 

 points which the conditions of growth in Florida emphasize as important addi- 

 tional facts. 



On the east coast of the state the northern limit of the red-mangrove, 

 Rhizophora mangle L., which is the most characteristic mangrove of Florida, is 

 approximately 27 15' N. The last trees of this species growing separated by 

 considerable intervals from each other were seen along both banks of the St. 

 Lucie River at Stuart. On the west coast, the mangrove vegetation does not 

 extend beyond Tampa Bay at latitude 28 N., so that the northern limits on 

 both the east and west coasts of southern Florida approximate the boundary 

 which the writer has set as that of this monograph. The mangrove vegeta- 

 tion extends along the coast in the quieter water of the lagoons, the rivers, 

 and the salt estuaries rarely exposed to the full force of the ocean surge.* In 

 the enclosed bays, it gradually encroaches upon the shallow water until in the 

 Whitewater Bay region of southwest Florida, we probably have an open shallow 

 bay almost completely invaded by mangrove trees, which have formed islands 

 separated by tortuous and labyrinthine channels of tidal saltwater. The action 

 of these trees in advancing the shore line has been described by a number of 

 botanists. On the immediate east coast, the mangrove fringe is best seen along 

 the shores of Bay Biscayne. It extends up the Miami River to where the river 

 forks into a north and a south branch. (Plate I, Fig. 2.) Here observations 

 made with the hydrometer indicate that fresh water prevails. Many of the 

 lower flat keys, or mud banks, of the chain of islands extending to Key West are 

 covered with mangrove trees, notably the red-mangrove, Rhizophora mangle 

 L., with strong prop roots, and the black-mangrove, Avicennia nitida Jacq., 

 with asparagus-like roots the thickness of the little finger. Such low flat trees 

 with intricately crossed roots are important agents infixing the muddy bottom, 

 and it has been suggested to plant these trees along the new embankments of 

 the "oversea" railroad to Key West to prevent the wash of the waves and the 

 undermining of the banks. 



Mangrove vegetation was noted along the following Florida keys: 



Card Sound is mangrove fringed and so is Barnes Sound, as seen in crossing 



from the mainland to Key Largo via the drawbridge over Jewfish Creek. 



Blackwater Sound is surrounded by the mangrove formation. The northern 



* On good authority, it occurs on the ocean side of Virginia Key and Key Biscayne. 



