cordgrass canopy architecture to characterize 

 habitats that could and could not support the 

 endangered clapper rails. Widespread 

 sampling had documented major changes to the 

 distribution of cordgrass following extreme 

 events, but with those responses in the 

 record, it became more important to 

 understand finer-scale responses to less 

 dramatic variations in the environment. The 

 need to track canopy architecture changes 

 suggested intensive sampling of selected pure- 

 cordgrass sites. 



Third, the use of cover classes was 

 adequate only for assessing gross change in 

 species abundance (such as followed flooding 

 or tidal closure). Other year-to-year 

 variations could not be detected, and it was 

 unclear if the reason was their absence or the 

 crude sampling regime. Third, soil salinities 

 proved to be very consistent among stations of 

 similar elevation, thus suggesting a 

 subsampling program and greater efficiency. 

 Lack of data on salinities at depth was also 

 noted. 



Fourth, it became desirable to compare 

 salt marsh structure at locations that 

 represented a greater range of tidal flushing 

 conditions, since a tidal restoration program 

 was being developed for the estuary. More 

 information on the upper marsh was needed. 

 Throughout the reevaluation, it was 

 recognized that the ten-year record for the 

 original stations and the five-year record for 

 the additional 115 stations should not be 

 abandoned. 



A revised monitoring program was 

 designed to respond to all the above concerns. 

 It is adaptive in that as new problems or 

 methods arise, the program expands to 

 accommodate these concerns, and as sampling 

 is shown to be unnecessary or inadequate, it is 

 dropped or modified. It is hierarchical in that 

 the larger areas are sampled less frequently, 

 and selected sites are studied more intensively 

 and more often. 



Intensive sampling was indicated for three 

 segments of the elevation gradient at Tijuana 

 Estuary: lower, middle, and upper marsh 

 elevations. A lower marsh community with 

 cordgrass is obvious at the estuary, since the 



dominant plant is a clonal species with 

 relatively discrete boundaries. However, only 

 the lowest elevations have pure cordgrass; 

 elsewhere both pickleweed and saltwort co- 

 occur, and before 1984, the annual 

 pickleweed was a common associate. To 

 evaluate the dynamics of cordgrass, the 

 interference of other species was considered 

 undesirable. Hence, the lower-marsh 

 transects were placed in pure cordgrass at the 

 lowest elevations, along tidal creeks. 



An upper-elevation glasswort and shore 

 grass-dominated community is also obvious at 

 Tijuana Estuary. The bushy, densely branched 

 glasswort often forms a relatively discrete 

 lower boundary that suggests a clear zonation. 

 Two species of the upper marsh have narrow 

 elevation ranges and rarely extend below the 

 distribution of glasswort; these are the salt 

 marsh bird's beak and Atriplex watsonii. 

 Since neither is abundant, they fail to 

 reinforce the concept of distinct species 

 association. In fact, each marsh species has a 

 unique distribution, such that the marsh 

 vegetation is not readily characterized as 

 forming discrete zones (Zedler 1977). Still, 

 the change in marsh canopy architecture that 

 accompanies the shift to glasswort dominance 

 at higher elevation may well be important to 

 birds and other animals that use the marsh. 

 Spider webs, for example, are very abundant 

 in the upper canopy of glasswort, which is 

 rarely inundated by tides. For this reason, 

 upper-elevation transects were placed in 

 marsh dominated by glasswort. 



The elevations between the upper limit of 

 cordgrass and the lower limit of glasswort are 

 dominated by pickleweed, which does not have 

 discrete upper or lower boundaries. The 

 largest area of the salt marsh has this 

 intermediate elevation, which forms the 

 marsh plain. The middle marsh is 

 characterized by the absence of cordgrass and 

 glasswort, rather than by the presence of 

 pickleweed, which overlaps with both the 

 lower and upper marsh dominants. Co- 

 occurring with pickleweed are most of the 

 region's salt marsh species (Figure 3.2). 



Four stations were chosen to represent 

 each of the marsh elevation transects (Figure 

 5.11). The four stations differ in distance 



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