The Ecology of Tijuana Estuary, California: An Estuarine Profile

1979 pickleweed was significantly lower in cover than in
c\1 1980 (Flood Year) 1979 (Table 26). By 1983, it had increased again
w 1981
and in 1984, through a major drought, it reached its
3 1982 maximum cover, with 33 quadrats having 75%-
t-
1983
100% cover of pickleweed. This species changed
little in its spatial distribution until 1985 (Figure
1984 (Drought Year)
LC
63); instead it changed in growth, a finding that is
1985 consistent with earlier suggestions that pickleweed
W
3
is a highly tolerant species capable of survival in a
t- wide variety of salinity and moisture conditions
(Zedler 1982b). Expansion in 1985 occurred in
many areas that were previously occupied by
cordgrass.
5.3.2 Succulent-Dominated Marsh Responses to
Drought
The 1984 expanston of the monitoring program
to include 115 quadrats beyond the cordgrass
habitat provrded an opportunfty to compare 1974
and 1984 data sets in detail and to document
species that were el~minated by the 1984 drought
The upper marsh was sampled for the first time in
1974 using 357 quadrats (cf Zedler 1977 for
detailed communtty descriptton) Additional
informatton was obtatned in 58 stat~ons used for
product~vity measurement in 1976 (Winfreld 1980)
and 9 quadrats along one transect used for a study
of annual pickleweed (Sailcornla brgelov~i) in 1975
(Zedler 1975) While less extensive, these intertm
censuses help to determine when compositional
changes occurred Throughout our work at Tijuana
Estuary, we have assessed species composttion
with the same cover classes and 0 25 m2 crrcular
quadrats, so that data are readily comparable
Figure 62. A graphical summary of cordgrass
distribution changes along eight transects that extend
from channels (on the left) inland (see Figure 60).
Sampling stations (0.25 m2 circular quadrats) were at
5-m intervals; each is represented by a rectangular
box; darkened boxes indicate presence; open boxes
indicate absence. Through time, holes in the
distribution have developed and persisted. The
frequency of cordgrass changed as follows: 1979 =
89O/o, 1980 = 94%, 1981 = 86'10, 1982 = 83%, 1983 =
89%, 1984 = 72'10, 1 985 = 38%.
and its pattern of change was nearly the opposite
of the cordgrass. Because of the highly bianched,
trailrng form of pickleweed, we assess its
abundance by estimating cover in standard
classes, rather than attempting to count stems
This is a crude measure, so that only large
changes in cover can be identified In 1980,
Some of the cornposittonal differences between
1974 and 1984 may be due to sampltng in different
locations The 1974 data set included three
transects, located at TJE-36, 40, and 43 In
add~tion, the 1984 data set inciuded a larger
proportion of samples from cordgrass-dominated
areas. [The higher frequency of cordgrass in 1984
is a consequence of having more quadrats within
its distr~bution, rather than a real increase in the
marsh.] For these reasons, the 10-year
comparison should ascribe significance only to
large changes in occurrence or cover. If drought is
affecting the salt marsh, it should have its greatest
impact on shallow-rooted specles, espec~ally
annuals Species known to have broad ecological
tolerance as adults (e.g., the perennial pickleweed
and alkal~ heath, Frankenla grandlfoira) should
show little decline in response to drought
Most notable in the 10-year comparison are the
absences of annual pickleweed (Sai/corn~a
btgelovi!] aqd sea-blite (Suaeda esteroa, formerly
called S cal~forn~ca) tn the 1984 data Annual
pickleweed was a dominant component of the
marsh tn 1974 (64O% frequency), as well as during
the 1976 product~vity study (Chapter 43 and the
1975 population study of annual pickleweed, when