The vegetation of emergent wetlands in Tampa Bay consists of 
various mixtures of five major plant species, two of which are tidal 
marsh species, black needlerush (Juncus roemerianus ) and smooth cordgrass 
( Spartina alterniflora ), and the remaining three being mangroves. Minor 
species in these tidal marshes include leather fern ( Acrostichum 
danaeofolium ), the brackish water cattail ( Typha domingensis h and 
bulrush ( Scirpus spp.). 
Estimates of the percentage of the total emergent wetlands which 
are tidal marsh vary from 10% to 18% (Estevez and Mosura 1985; E. 
Pendleton, [U.S. Fish Wildlife Service, Slidell, Louisiana] pers. 
comm.). Mangroves are the dominant vegetation, but periodic freezes 
allow substantial areas of tidal marsh to persist as cold-sensitive 
mangroves are pruned or killed (Estevez and Mosura 1985). These authors 
also noted that "regrettably little is known of the organization or 
functioning of tidal marshes in Tampa Bay". 
In contrast to tidal marshes, mangrove forests on the bay have 
received some study (Estevez and Mosura 1985), although it has been 
primarily descriptive in nature. The forests are composed of three 
species (Figure 2); red mangrove ( Rhizophora mangle ), black mangrove 
( Avicennia germinans ). and white mangrove ( Laguncularia racemosa). 
Unlike mangrove forests farther south (Odum and Heald 1972), mangrove 
forests on Tampa Bay are composed of a mixture of all three species, and 
while exhibiting natural zonation similar to that described by Davis 
(1940), have some unique features (Estevez and Mosura 1985; Lewis et al. 
1985). 
The latitude of Tampa Bay is near the northern limit of the 
distribution of mangroves, and low temperature stress is common in the 
mangrove forests. Repetitive freezes can intensify temperature effects 
on the structure of the forest. Initially, the canopy is partially 
destroyed; if another freeze quickly follows, the damaged trees are 
killed. In recent years, two freezes have occurred relatively close 
together (1977 and 1983). During January 1977, a minimum temperature of 
-5°C was reached and snow fell for the first time in more than 100 years. 
The Christmas freeze of 1983 involved two days during which the 
temperature in Tampa fell to -6.7°C, followed by -7.2°C the next day. 
Such low temperatures had not occurred in Tampa since the historical 
freeze of 1894-1895 dealt a serious blow to the then flourishing citrus 
industry in Florida. The freezes in 1977 and 1983 caused significant 
losses of mangroves, and the total area of tidal marsh on the bay may 
increase as more cold-tolerant marsh plants invade areas left barren by 
the death of the mangroves (Figure 3). Selective survival of mangroves 
has been observed during a less severe frost or freeze, with the black 
mangrove having the greatest resistance to freeze damage and the white 
mangrove the least. The black mangrove is typically the largest diameter 
tree in the forest (Table 2), particularly in the fringe and overwash 
forests which are the dominant types in the bay. 
94 
