turnover of one, which is supported by the 

 data of Heald (1969) and Pool et al. 

 (1977). 



Mangrove productivity is affected by 

 many factors; some of these have been 

 recognized and some remain totally ob- 

 scure. Carter et al. (1973) propose 

 lumping these factors into two broad cate- 

 gories: tidal and water chemistry. We 

 believe that a number of additional cate- 

 gories should be considered. 



A minimal, though incomplete, list of 

 factors controlling mangrove productivity 

 must include the following: 



* species composition of the stand 



* age of the stand 



* presence or absence of competing 

 species 



* degree of herbivory 



* presence or absence of disease and 

 parasites 



* depth of substrate 



* substrate type 



* nutrient content of substrate 



* nutrient content of overlying water 



* salinity of soil and overlying water 



* transport efficiency of oxygen to root 

 system 



* amount of tidal flushing 



* relative wave energy 



' presence or absence of nesting birds 



* periodicity of severe stress (hurri- 

 canes, fire, etc.) 



* time since last severe stress 



* characteristics of ground water 



inputs of toxic compounds or nutrients 

 from human activities 



human influences such as diking, 

 ditching, and altering patterns of 

 runoff. 



In spite of the difficulties with 

 various methods and the interaction of 

 controlling factors, it is possible to 

 make general statements about certain 

 aspects of mangrove productivity. For 

 example, Waisel's (1972) statement that 

 mangroves have low transpiration rates 

 seems to be generally true in Florida. 

 Lugo et al. (1975) reported transpiration 

 rates of 2,500 g HoO/m /day for mangrove 

 leaves in a fringing red mangrove forest 

 and 1,482 g h^O/m /day for black mangrove 

 leaves. This is approximately one-third 

 to one-half the value found in temperate 

 broad leaf forests on hot dry days, but 

 comparable to tropical rainforests (H.T. 

 Odum and Jordan 1970). The low transpira- 

 tion rates of mangroves are probably re- 

 lated to the energetic costs of main- 

 taining sap pressures of -35 to -60 atmo- 

 spheres (Scholander et al. 1965). 



Litter fall (leaves, twigs, bark, 

 fruit, and flowers) of Florida mangrove 

 forests appears to average 2 to 3 dry 

 g/m day in most wel 1 -devel oped mangrove 

 stands (see discussion in section 3.4). 

 This can be an order of magnitude lower in 

 scrub forests. 



Wood production of mangroves appears 

 to be high compared to other temperate and 

 tropical trees, although no measurements 

 from Florida are available. Noakes (1955) 

 estimated that the wood production of an 

 intensively managed Malayan forest was 

 39.7 metric tons/ha/year. Teas (1979) 

 suggested a wood production estimate of 21 

 metric tons/ha/year for a mature unmanaged 

 red mangrove forest in south Florida. His 

 figure was calculated from a litter/total 

 biomass relationship and is certainly 

 subject to error. 



Representative estimates of gross 

 primary production (GPP) net primary 



18 



