CHAPTER 3. ECOSYSTEM STRUCTURE AND FUNCTION 



3.1 STRUCTURAL PROPERTIES OF MANGROVE 

 FORESTS 



Published information about the 

 structural aspects of Florida mangrove 

 forests is limited; most existing data 

 have been published since the mid-1970's. 

 This lack of information is unfortunate 

 since quantitative structural data greatly 

 aid understanding of processes such as 

 succession and primary production. Even 

 more important, the response of mangrove 

 forests to stress, both climatic and man- 

 induced, can be followed quantitatively 

 with this type of data. 



Ball (1980) contributed substantially 

 to understanding the role of competi- 

 tion in mangrove succession by measuring 

 structural factors such as basal area, 

 tree height, and tree density. Lugo and 

 Zucca (1977) monitored the response of 

 mangrove forests to freezing temperatures 

 by observing changes in structural proper- 

 ties of the trees. 



Baseline studies of forest structure 

 have been published by Lugo and Snedaker 

 (1975), and Pool, Snedaker and Lugo 

 (1977). For example, Lugo and Snedaker 

 (1975) compared a fringing mangrove forest 

 and a basin forest at Rookery Bay, near 

 Naples, Florida. They found the fringing 

 forest, which was dominated by red man- 

 groves, to have a tree diversity of H = 

 1.48, a basal area of 15.9 m z /ha, an 

 aboveground biomass of 17,932 g/m , and a 

 non-existent litter layer. The nearby 

 basin forest was dominated by black man- 

 groves, had a tree diversity of H = 0.96 

 and a basal area of 23.4 m /ha. The lit- 

 ter layer in the basin forest averaged 550 

 dry g/m . Tree diversity in a hurricane 

 disturbed section of the Rookery Bay 

 forest was 1.62. Similar data were pre- 

 sented for mangrove forests in the Ten 

 Thousand Islands area (Table 2). 



Data of this type are useful for many 

 purposes including impact statements, en- 

 vironmental surveys, and basic scientific 

 questions. Cintron et al. (1978) gave an 

 indication of the direction in which fu- 

 ture research might proceed. Working in a 

 mangrove stand in Puerto Rico, they found 



tree height to be inversely proportional 

 (r = 0.72) to soil salinity in the range 

 30 to 72 ppt. Above 65 ppt salinity, dead 

 tree basal area was higher than live tree 

 basal area and above 90 ppt there was no 

 live tree basal area. 



It should be possible to investigate 

 the relationship between a variety of 

 mangrove structural properties and factors 

 such as flushing frequency, soil depth, 

 nutrient availability, pollution stress, 

 and other measures of human impact. Ulti- 

 mately, this should lead to an ability to 

 predict the form and structure of mangrove 

 forests resulting from various physical 

 conditions or artificial impacts. One 

 example of this potential tool is Ball's 

 (1980) documentation of structural changes 

 in mangrove forests resulting from altera- 

 tions in the hydrological conditions of 

 south Florida. 



3.2 Z0NATI0N, SUCCESSION AND "LAND- 

 BUILDING" 



Much of the world's mangrove litera- 

 ture consists of descriptive accounts of 

 zonation in mangrove forests and the spe- 

 cies composition within these zones. Al- 

 thouqh general agreement has been lacking, 

 various hypotheses have been put forth 

 concerning the possible connection between 

 zonation, ecological succession, competi- 

 tion, and the role of physical factors 

 such as soil salinity and tidal amplitude. 

 In this section we review briefly the 

 dominant ideas about mangrove zonation and 

 succession and present our interpretation 

 of the current status of knowledge. 



Davis (1940), working in south Flori- 

 da, was one of the first investigators to 

 describe distinct, almost monospecific, 

 zones within mangrove ecosystems. In what 

 has become the classical view, he argued 

 that mangrove zonation patterns were 

 equivalent to serai stages in succession. 

 The most seaward zone, dominated by red 

 mangroves, was regarded as the "pioneer 

 stage". More landward zones were 

 dominated by white mangrove, black 

 mangrove, buttonwood and, finally, the 

 climatic climax, a tropical forest. Since 



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