o 

 o 



X 



o 



<>- 



3.0 



2.8 

 2.6 

 2.4 

 2.2 

 2.0 



1.8 

 1.6 



1.4- 

 1.2- 

 1.0- 

 0.8- 

 0.6- 

 0.4- 

 0.2 



\ 



Seedlings transported from field 



\ 



\ 



Log Y : 2.36819 - 0.24540x 



— Seedlings grown in laboratory 

 from seed 



Log Y -- 2.86073 - 0.62326 ^. 



\ 



\ 



\ 



* 



0.5 



4.0 



1.0 2.0 



X - Salinity (%NaCI) 



Figure 4-10. The inhibitive effect of salt on growth of saltmeadow cordgrass (Seneca 1972). 



near the mouth of the Mississippi Riverwere described 

 by Chabreck and Palmisano (1973). They found that 

 although this area was regularly flooded by fresh river 

 water, the increase in salinity caused by the hurricane 

 tide was ephemeral. The major effect of the hurricane 

 seemed to have been widespread destruction of vegeta- 

 tion by wind and water, which uprooted and ripped 

 apart stands of plants. Recovery of most species was 

 rapid so that prehurricane levels of abundance were 

 approached within a year. In the small lakes and 

 ponds, however, the submerged and floating vegetation 

 was slow to recover. Valentine (1977) described a 

 long-term effect of Hurricane Audrey (1957) in saw- 

 grass marshes of the Chenier Plain, apparently caused 

 by increased soil salinity. Sediment salts became con- 

 centrated first directly from hurricane tides, then 

 secondarily from the dry summers following. Initially, 

 161,874 ha (400,000 a) of sawgrass marshes were 

 killed. The following year 86% of this area was open 

 water. During the 1960, '62, '63, and '65 drought 

 years, annual grasses and sedges became abundant. By 

 1972 bulltongue occupied 74% of the area and white 

 water-lily occupied 1 1%. Other floating and submerged 



aquatics were also common. Sawgrass never reestab- 

 lished itself in any extensive areas, perhaps because 

 seed viability was very low. Secondary effects of 

 these vegetation changes on duck food habits were 

 dramatic. Prior to 1959 sawgrass seeds were an im- 

 portant component of duck diets. In the years imme- 

 diately following the hurricane, duck stomachs con- 

 tained primarily rice seeds, indicating heavy depen- 

 dence on agricultural areas outside of the Chenier 

 Plain. During succeeding drought years, when the 

 marshes produced large quantities of annual grass 

 seeds, large numbers of both ducks and geese were 

 attracted to these habitats. 



Seasonal Dynamics of Organic Production and 

 Loss from Wetlands. Although each plant species has 

 its own seasonal growth pattern, smooth cordgrass has 

 been extensively studied and data from this species is 

 used to show a typical wetland seasonal pattern of 

 organic production, mortality, and export (fig. 4-1 1). 

 Smooth cordgrass maintains a year-round growth rate 

 of about 8 g/m^/day (Hopkinson et al. 1977). Mor- 

 tality during spring and summer is low so that the 



163 



