All species of mangroves may be present. 

 Trees rarely exceed 5 m (16 ft) in height. 



(6) Scrub or dwarf forests - this 

 community type is limited to the flat 

 coastal fringe of south Florida and the 

 Florida Keys. All three species are 

 present. Individual plants rarely exceed 

 1.5 m (4.9 ft) in height, except where 

 they grow over depressions filled with 

 mangrove peat. Many of these tiny trees 

 are 40 or more years of age. Nutrients 

 appear to be limiting although substrate 

 (usually limestone marl) must play a role. 



Throughout this publication we have 

 attempted to refer to Lugo and Snedaker's 

 classification scheme wherever possible. 

 Without a system of this type, comparisons 

 between sites become virtually 

 meaningless. 



1.6 SUBSTRATES 



Understanding mangrove-substrate 

 relationships is complicated by the 

 ability of mangroves to grow on many types 

 of substrates and because they often alter 

 the substrate through peat formation and 

 by altering patterns of sedimentation. As 

 a result, mangroves are found on a wide 

 variety of substrates including fine, 

 inorganic muds, muds with a high organic 

 content, peat, sand, and even rock and 

 dead coral if there are sufficient 

 crevices for root attachment. Mangrove 

 ecosystems, however, appear to flourish 

 only on muds and fine-grained sands. 



In Florida, the primary mangrove 

 soils are either calcareous marl muds or 

 calcareous sands in the southern part of 

 the State and siliceous sands farther 

 north (Kuenzler 1974). Sediment distribu- 

 tion and, hence, mangrove development, is 

 controlled to a considerable extent by 

 wave and current energy. Low energy 

 shorelines accumulate fine-grained sedi- 

 ments such as mud and silt and usually 

 have the best mangrove growth. Higher 

 energy shorelines (more wave action or 

 higher current velocities) are charac- 

 terized by sandy sediments and less pro- 

 ductive mangroves. If the wave energy 



becomes too great, mangroves will not be 

 present. Of the three species of Florida 

 mangroves, white mangroves appear to 

 tolerate sandy substrates the best (per- 

 sonal observation), possibly because this 

 species may tolerate a greater depth to 

 the water table than the other two 

 species. 



Mangroves in Florida often modify the 

 underlying substrate through peat deposi- 

 tion. It is not unusual to find layers of 

 mangrove peat several meters thick under- 

 lying well-established mangrove ecosystems 

 such as those along the southwest coast of 

 Florida. Cohen and Spackman (1974) pre- 

 sented a detailed account of peat forma- 

 tion within the various mangrove zones of 

 south Florida and also in areas dominated 

 by black needle rush (Juncus roemerianus ), 

 smooth cordgrass ( Sparti na al terni fl ora ) 

 and a variety of other macrophytes; Cohen 

 and Spackman (1974) also provide descrip- 

 tions and photography to aid in the iden- 

 tification of unknown peat samples. 



The following descriptions come from 

 Cohen and Spackman (1974) and from the 

 personal observations of W.E. Odum and 

 E.J. Heald. Red mangroves produce the 

 most easily recognized peat. More recent 

 deposits are spongy, fibrous and composed 

 to a great extent of fine rootlets (0.2 to 

 3.0 mm in diameter). Also present are 

 larger pieces of roots (3 to 25 mm), bits 

 of wood and leaves, and inorganic 

 materials such as pyrite, carbonate 

 minerals, and quartz. Older deposits are 

 less easily differentiated although they 

 remain somewhat fibrous. Peat which has 

 recently been excavated is reddish-brown 

 although this changes to brown-black after 

 a short exposure to air. Older deposits 

 are mottled reddish-brown; deposits with a 

 high content of carbonates are greyish- 

 brown upon excavation. 



Cohen and Spackman (1974) were unable 

 to find deposits of pure black mangrove or 

 white mangrove peat suggesting that these 

 two species may not form extensive depos- 

 its of peat while growing in pure stands. 

 There are, however, many examples of peats 

 which are mixtures of red mangrove 

 material and black mangrove roots. They 



