Table 5.3. Change in pickleweed canopy cover in cordgrass transects from 1979 to 

 1984 (no data in 1982). The Kolmogorov-Smirnov two-sample test was used to 

 compare cumulative distributions for consecutive years. The 1981-83 comparison was 

 not significant; all others were different at the 10% level (p<0.1). 



a Mean cover was calculated from cover class midpoints using quadrats where 

 pickleweed occurred (0's omitted). 



Both annual pickleweed and sea-blite are 

 good invaders. In 1985, both species 

 appeared in abundance on newly dredged 

 habitat at Sweetwater Marsh (San Diego Bay), 

 where the California Transportation 

 Department has a major marsh restoration 

 project. However, recovery of both species 

 has been slow at Tijuana Estuary. First, the 

 seed bank was depleted, because many seeds 

 germinated in 1984 and died before reaching 

 maturity. Second, the predrought abundance 

 of annual pickleweed was related to an open 

 canopy of saltwort (Batis maritima; Zedler 

 1977). After the drought, the canopy of 

 saltwort closed (total cover averaged only 

 40% for all elevations of occurrence in 

 1984). Like the perennial pickleweed, 

 saltwort appears to have increased its biomass 

 during estuary closure. These two hypotheses 

 of reduced seed bank and competitive effects of 

 the overstory were later tested in a field 

 experiment. The results (Covin and Zedler, 

 unpubl. data) support the hypothesis that 

 annual pickleweed died out because its seed 

 bank was eliminated and that a dense canopy of 



perennial pickleweed would have limited its 

 reestablishment. 



It is likely that expansion and shrinkage of 

 species distributions is the norm for the 

 region's highly dynamic wetlands. The 

 estuary's history of variable rainfall and 

 streamflow, fluctuating sea levels, and 

 alternating conditions of good and sluggish 

 tidal flow, all suggest that the abundance and 

 distributional limits of marsh species should 

 also vary. However, the combination of 

 severe environmental stresses, such as 

 drought combined with estuary closure, is 

 probably rare. Thus, local extinction is not 

 viewed as a common event for this estuary. 

 Species richness in the region's wetlands is 

 high for systems with good tidal flushing and 

 low for systems that frequently close to tides 

 (Zedler 1982b); the near loss of annual 

 pickleweed and sea-blite was no doubt due to a 

 combination of events. 



Similar patterns of species distributions 

 have been documented at a Mexican site along 



1 06 



