there is still a good deal of real 

 variation in the productivity of a single 

 species in different environments. This 

 is best shown by differences in peak 

 bioinass, which although not equivalent to 

 production are a pretty good index of 

 relative production. These differences 

 are temporal as well as spatial. At 

 Airplane Lake in the Barataria basin, peak 

 biomass has varied by over 300 g/m^ from 

 year to year (Table 16). 



Turner (1979) found a positive rela- 

 tionship between biomass and potential 

 evaporation (which is in turn related to 

 the average air tenperature) during the 

 growing season. By implication, dif- 



ferences in biomass among years at one 

 location should be related to annual 

 differences in the accumulated potential 

 evaporation. While this kind of 



relationship has been confirmed for many 

 agricultural crops, it has not been studied 

 in marshes, perhaps because long-term data 

 sets are not available. 



Spatial variations in biomass have 

 been the subject of many investigations, 

 both to determine the correlation of 

 biomass with environmental variables and 

 to identify the physiological mechanisms 

 of adaptation to the marsh environment. 

 Figures 43, 44, and 45 show three typical 

 examples of spatial variations in marsh 

 biomass. It is instructive to examine 

 them because they throw light on the 

 physiological responses of plants. 



The first of these is the "tidal 

 subsidy", discussed by Oduin and Fanning 

 (1973) as a reason for the high produc- 

 tivity of coastal marshes. Tides 



Table 16. Year-to-year variation in peak 

 1 ive biomass of Spartina al terniflora at a 



TIDE RANGE (m) 



Figure 43. Production of intertidal S_. 

 al terni flora vs. mean tide range for 

 various Atlantic coastal marshes. 

 Different symbols represent different 

 data sources (adapted from Steever et 

 al. 1975). Note the position of 

 Mississippi delta marshes on the graph. 



media 



facto 



size, 



secon 



illus 



north 



propo 



that 



study 



much 



tidal 



te such plant growth-influencing 

 rs as nutrient supply, sediment grain 

 Hrainano 5oii Oxygenation, and 



drainage 1 



dary chemical changes. m lims 



tration, peak plant biomass along the 



Atlantic coast is directly 



rtional to the tide range. Notice 



biomass from one Louisiana delta 



does not fit the trend. Biomass is 



higher than expected considering the 



range. 



In this 



The second example illustrates the 

 well-known "streamside" effect - the 

 stimulation of growth along the edge of 

 natural streams, or conversely its 

 inhibition inland. This effect is similar 

 to the tidal subsidy in that tidal action 

 is weaker inland than streamside so the 

 plants receive less "subsidy." 



49 



