p. australis 



1600 



E 



X 



-8 

 a 



4000 |- 



3500 



3000 



2500 - 



2000 



1500 



1000 



DEAD 



-k. 



1974 



'-I-—. 



/ 



A972 



I' - 



3i00r 



E 



2600 



2100 



1600 



J 



J J A 



Tim«, monthj 



1100 



600 



DEAD 



1975,' 





/V'''.'\ 



1973 





M J J A 



Tim«, months 



Figure 42. Seasonal changes in live and dead biomass of Phragmite s au stral is and Spartina 

 patens during 1973 - 1975 (Copyright. Reprinted from "Aboveground production of seven 

 coastal marsh plant species in coastal Louisiana " in Ecology , 1978, by C.S. Hopkinson, 

 J.G. Gosselink, and R.T. Parrondo with permission of Ecological Society of America). 



gradually tapers into the fall with a 

 resurgence after the hottest months, and 

 the plants die to the ground each winter. 

 S^. al terni fl ora maintains active growth 

 throughout the year, with a maximum rate 

 during the early summer. The pattern of 

 streamside and inland plants is similar, 

 but the inland rates are lower. 



All the production data reported so 

 far have been for aboveground growth. 

 Root production is difficult to measure 

 because it is difficult to determine, in a 

 substrate that is nearly all root 

 material, which roots are living. Table 

 14 lists reports of root biomass from a 

 number of studies in the delta. The 

 reported biomass varies widely, partly as 

 a result of differences in techniques. 

 Fresh and brackish marsh species in 



established, highly organic marshes have 

 enormous belowground biomass, whereas the 

 same species (for example, Sagittaria 

 spp.. Table 14) in the mineral sediments 

 of the Atchafalaya Delta produce few 

 roots. 



Outside of the del ta, root production 

 measurements have been almost as variable. 

 Good et al, (1982) reported S_. al terni - 

 flora root production estimates ranging 

 from 220 to 3500 g/mVyr for tall form 

 (streamside) locations and 420 to G200 

 g/m^/yr for short form (inland) locations. 

 High root:shoot ratios have been con- 

 sidered indicative of unfavorable soil 

 conditions requiring greater root surface 

 area to support a unit of aboveground 

 material (Shaver and Billings 1975). This 

 relationship seems to hold in marshes 



47 



