100 -i 



90 - 



o 

 o 



c 



t_ 



o 

 o 



O 



t: 60 



80 - 



70 - 



o 

 cr 



50 - 



40 - 



Spartina foliosa 



30 



-i — i — i — i — i — i — i — | — i — | — 



1978 1980 1982 1984 1986 1988 



Figure 5.3. Frequency of occurrence of 

 cordgrass (Spartina foliosa) and pickleweed 

 (Salicornia virginica) in original low-marsh 

 sampling stations (n = 102) from 1979 

 through 1988. Data are from September of 

 each year. The estuary was nontidal for 8 

 months during 1984. 



plants that still had some green leaf material 

 were clearly dead, and the annual census 

 showed minimum occurrences. The 

 widespread pattern of mortality was 

 unprecedented in our data base, and there is 

 every reason to conclude that it was caused by 

 drought and hypersalinity. Recovery of the 

 cordgrass did not immediately follow the 

 restoration of tidal flows, which was 

 completed in December of 1984. After four 

 years, the species had not quite regained its 

 average frequency before closure. 



Pickleweed (Salicornia virginica) was the 

 second most abundant species in the lower 

 marsh, but its occurrence changed little from 

 1979-1984 (Figure 5.3). After closure, 

 however, there was a gradual increase in the 

 distribution of the species. The habitat 

 changed in ways that were not documented; 

 this expansion is not explained by soil 

 salinity. Perhaps the one-time reduction in 



waterlogging during 1984 removed barriers 

 to establishment, and once mature plants were 

 present, they were able to persist. 



Species interactions may explain some of 

 the patterns of occurrence for cordgrass and 

 pickleweed, although data other than 

 occurrence are needed to test their potential 

 interactions. Biomass data are useful 

 measures of plant abundance, but sampling for 

 biomass is very destructive, especially at 

 permanent monitoring stations. Instead, we 

 use surrogates of biomass. Cordgrass is 

 sampled as the total stem length (sum of all 

 plants heights in a quadrat). The correlation 

 between cordgrass TSL and dry weight is 

 significant for September data at Tijuana 

 Estuary (r = 0.85, n = 104, p <0.001). 

 Thus, it provides a good, nondestructive 

 estimate of end-of-season live aboveground 

 biomass. Because pickleweed is highly 

 branched and often trailing, we assess its 

 abundance by estimating cover in standard 

 classes, rather than attempting to count 

 stems. This is a crude measure, so only large 

 changes in cover can be identified. 



Cordgrass had increased TSL in both the 

 1980 and 1983 flood years and minimal TSL 

 in 1985, as averaged for stations where it 

 occurred (Figure 5.4). The specific effects of 

 flooding and nontidal drought are explored in 

 greater detail in section 5.4. Where 

 pickleweed occurred, it was low in cover in 

 both 1980 and 1983. After the 1984 period 

 of nontidal drought, pickleweed reached its 

 maximum cover, with 62 quadrats having 

 >75% cover in 1985. This species changed 

 little in its spatial distribution (Figure 5.3); 

 instead it changed in growth, a finding that is 

 consistent with earlier suggestions that 

 pickleweed is a highly tolerant species capable 

 of survival in a wide variety of salinity and 

 moisture conditions (Zedler 1982b). 

 Expansion in 1985 occurred in many areas 

 that were previously occupied by cordgrass. 



Competitive interaction probably enhanced 

 the effect of nontidal drought in 1984, as 

 pickleweed is known to reduce cordgrass 

 growth within its range of overlap at Tijuana 

 Estuary (Covin 1984, Griswold 1988). 



103 



