detritus varies enormously from one site 

 to the next depending upon the amount of 

 fluvial transport. The biomass charac- 

 teristics of a scrub forest probably bear 

 little resemblance to those of a fringing 

 forest. At the present time, there is not 

 enough of this type of data available to 

 draw many conclusions. One intriguing 

 point is that red mangrove leaf biomass 

 averages between 700 and 800 g/m at 

 various sites with very different forest 

 morphologies (Odum and Heald 1975a). This 

 may be related to the tendency of mangrove 

 canopies, once they have become estab- 

 lished, to inhibit leaf production at 

 lower levels through self-shading. 



Golley et al. (1962) showed that the 

 red mangrove canopy is an extremely effi- 

 cient light interceptor. Ninety— five 

 percent of the available light had been 

 intercepted 4 m (13 ft) below the top of 

 the canopy (Figure 5). As a result, 90% 

 of the leaf biomass existed in the upper 4 

 m of the canopy. Chlorophyll followed the 

 same pattern of distribution. 



The leaf area index (LAI) of mangrove 

 forests tends to be relatively low. Gol- 

 ley et al. (1962) found a LAI of 4.4 for a 

 Puerto Rican red mangrove forest. Lugo et 

 al. (1975) reported a LAI of 5.1 for a 

 Florida black mangrove forest and 3.5 for 

 a Florida fringe red mangrove forest. A 

 different black mangrove forest, in Flori- 

 da, was found to have values ranging from 

 1 to 4 and an average of 2 to 2.5 (Lugo 

 and Zucca 1977). These values compare 

 with LAI's of 10 to 20 recorded for most 

 tropical forests (Golley et al. 1974). 

 The low leaf area values of mangrove 

 forests can be attributed to at least 

 three factors: (1) effective light inter- 

 ception by the mangrove canopy, (2) the 

 inability of the lower mangrove leaves to 

 flourish at low light intensities, and (3) 

 the absence of a low-light-adapted plant 

 layer on the forest floor. 



2.5 PRIMARY PRODUCTION 



Prior to 1970 virtually no informa- 

 tion existed concerning the productivity 



of mangroves in Florida. Since that time 

 knowledge has accumulated rapidly, but it 

 is still unrealistic to expect more than 

 preliminary statements about Florida man- 

 grove productivity. This deficiency can 

 be traced to (1) the difficulties asso- 

 ciated with measurements of mangrove pro- 

 ductivity and (2) the variety of factors 

 that affect productivity and the resulting 

 variations that exist from site to site. 



Productivity estimates come from 

 three methods: (1) harvest, (2) gas ex- 

 change, and (3) litter fall. Harvest 

 methods require extensive manpower and 

 knowledge of the age of the forest. They 

 are best employed in combination with 

 silviculture practices. Since silvicul- 

 ture of south Florida mangroves is practi- 

 cally non-existent, this method has rarely 

 been used in Florida. Noakes (1955), 

 Macnae (1968), and Walsh (1974) should be 

 consulted for productivity estimates based 

 on this technique in other parts of the 

 world. 



Gas exchange methods, based on 

 measurements of CO? changes, have the 

 advantage of precision and response to 

 short-term changes in light, temperature, 

 and flooding. They include both above- 

 ground and belowground production. On the 

 negative side, the necessary equipment is 

 expensive and tricky to operate properly. 

 Moreover, extrapolations from short-term 

 measurements to long-term estimates offer 

 considerable opportunity for error. 

 Nevertheless, the best estimates of pro- 

 ductivity come from this method. 



The litter fall technique (annual 

 litter fall x 3 = annual net primary pro- 

 duction) was proposed by Teas (1979) and 

 is based on earlier papers by Bray and 

 Gorham (1964) and Golley (1972) for other 

 types of forests. This is a quick and 

 dirty method although the lack of pre- 

 cision remains to be demonstrated for 

 mangroves. An even quicker and dirtier 

 method proposed by Teas (1979) is to (1 ) 

 estimate leaf standing crop (using various 

 techniques including harvesting or light 

 transmission relationships) and (2) multi- 

 ply by three. This assumes an annual leaf 



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