37-46 ppt, and upper, 59-84 ppt over the 

 one-year experiment. 



Overall, pickleweed grew better than in 

 the nearby intertidal salt marsh, with 

 biomass averaging over 2.5 kg/m 2 in the 

 upper rows by late summer. In contrast, 

 cordgrass biomass was lower than in the tidal 

 salt marsh, with maximum values well under 

 1 kg/m 2 . Griswold's (1988) findings 

 support the observation that pickleweed can 

 thrive in semitidal wetlands within the region 

 (and in the southern arm of Tijuana Estuary), 

 while cordgrass is restricted to fully tidal 

 situations (and the northern arm of Tijuana 

 Estuary). Although the mesocosms did not 

 mimic the tidal hydrology of Tijuana Estuary, 

 the relative growth of each species provides a 

 test of their hypothesized differential 

 inundation tolerance. 



o 



T3 



a. 



a. 



Cordgrass aboveground biomass decreased 

 with elevation, in relation to the gradient of 

 inundation and soil moisture (Figure 5.10). 

 The pickleweed response was the opposite; 

 biomass increased as surface soil moisture 

 declined (Figure 5.10). 



5.4.3 Manipulation of a Competitor in a Field 

 Experiment 



In order to test the hypothesis that 

 pickleweed outcompetes cordgrass, Griswold 

 (1988) set up a field experiment at Tijuana 

 Estuary. Pickleweed was removed from 

 replicate plots of mixed pickleweed-cordgrass 

 vegetation. Griswold then compared the 

 growth of cordgrass with that in control plots. 

 The experiment was established in January 

 1987, and responses were documented 

 monthly through October. By June, plots with 

 pickleweed removed had significantly more 

 stems of cordgrass present, supporting the 

 hypothesis of competitive exclusion. By 

 October, cordgrass had increased 6 times as 

 fast in plots without pickleweed present. 

 Average densities were 120/m 2 (s.e. 29.2) 

 without pickleweed and 36/m 2 (s.e. 17.2) 

 with pickleweed present (Griswold 1988). 



Figure 5.10. Growth of salt marsh vegetation 

 at three elevations, which differed in 

 inundation, soil moisture, and soil salinity. 

 Top graph: Response of pickleweed 

 (Salicornia virginica) aboveground biomass. 

 Bottom: Response of cordgrass (Spartina 

 foliosa) biomass. Data are from the outdoor 

 mesocosm study by Griswold (1988). 



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