TRANSACTIONS OF WAGNER 



VEGETATION OF SOUTH FLORIDA 



Apparently, we have from these figures, the red-mangrove trees growing 

 with their roots exposed to fresh water conditions and yet until we reach the 

 fork of the Miami River, the trees retain their usual form and usual height. 

 How is this to be reconciled with the hydrometric readings of the surface 

 water? The explanation seems to be that the salt water, which flows into the 

 Miami River from Biscayne Bay, is denser than the fresh water which flows 

 from the Everglades. Hence the fresh water flows out on top of the salt water, 

 which is beneath. The lower parts of the roots may be influenced by salt 

 water, while the upper part of such roots is bathed with fresh. It will be noted 

 that the temperature of the river water is colder than either that of the Ever- 

 glades, or that of Biscayne Bay. No correction was made in these hydro- 

 metric readings for differences in temperature, so that the figures are only 

 approximations. At Billy's Creek at n A. M. on a bright sunny day, June 4, 

 1912, the air temperature of the mangrove thicket was 90 F. (=32 C.), and 

 the relative humidity 72%, while in the neighboring salt marsh the air 

 temperature was 96 F. (=35 C.) and the humidity 72%, just before a violent 

 thunderstorm after which the temperature dropped to 78 F. (=25.6 C.) in 

 20 minutes. 



Another fact of considerable interest previously mentioned in a descrip- 

 tion of the general distribution of mangrove vegetation is the gradual 

 replacement of mangrove trees by the encroachment of the saw-grass 

 vegetation of the coastal prairie-everglade and by the saw-grass vegeta- 

 tion of river-bank marshes along the Miami River. The shore line of the 

 extreme southern end of Florida is fringed by mangrove swamps, and back 

 from the Bay of Florida the thicket begins to thin out and as we proceed inland 

 the red-mangrove trees become scattered. Between these scattered trees the 

 saw-grass vegetation of the coastal prairie-everglade has invaded, and with 

 the increase of fresh water conditions, which in itself is not inhibitory, the 

 mangrove trees become shorter, smaller, with few branches and leaves that 

 begin to assume a light, yellowish-green color. Finally in the competition 

 with the saw-grass vegetation, the mangrove is worsted and gradually thins 

 out and disappears. This fact is also demonstrated along the Miami River. 

 On the river banks the mangrove trees are of the usual size, but back from the 

 river in wet depressions controlled by fresh water and saw-grass, the man- 

 grove trees become low, sparingly branched bushes, widely arched and ex- 

 tended prop roots, yellow-green leaves. This change in vegetation has an 



