. Bulletin. Science; Natural history; Natural history. CATASTROPHIC FLOODING AND CORDGRASS DISTRIBUTION #— OCCURRENCE OF Spartina foliosa IN SOUTHERN CALIFORNIA COASTAL WETLANDS 75 CONCEPTION. PACIFIC OCEAN 50 MILES LOS PENASQUITOS LAGOON' MISSION BAY MARSH* CALIFORNIA MEXICO SAN DIEGO BAY MARSHES TIJUANA ESTUARY Fig. 1. Cordgrass occurs in only 7 of southern California's 26 coastal wetlands (darkened circles) Sometime after 1939, it disappeared from Los Penasquitos Lagoon (half-darkened circle). However, the factors measured at Tijuana Estuary explained little of the vanaoinL^ in the cordgras
. Bulletin. Science; Natural history; Natural history. CATASTROPHIC FLOODING AND CORDGRASS DISTRIBUTION #— OCCURRENCE OF Spartina foliosa IN SOUTHERN CALIFORNIA COASTAL WETLANDS 75 CONCEPTION. PACIFIC OCEAN 50 MILES LOS PENASQUITOS LAGOON' MISSION BAY MARSH* CALIFORNIA MEXICO SAN DIEGO BAY MARSHES TIJUANA ESTUARY Fig. 1. Cordgrass occurs in only 7 of southern California's 26 coastal wetlands (darkened circles) Sometime after 1939, it disappeared from Los Penasquitos Lagoon (half-darkened circle). However, the factors measured at Tijuana Estuary explained little of the vanaoinL^ in the cordgrass data (J. Zedler unpublished data), and results were put aside. After the catastrophic floods of 1980, cordgrass distribution expanded within the Tijuana Estuary, and a monitoring program (1979-present) documented signifi- cant increases in cordgrass growth. The post-flood responses of the species sug- gested new cause-effect hypotheses. This paper summarizes a variety of obser- vations and field experiments that help to explain patchiness of cordgrass within clones, within the intertidal zone, and within the region. Methods Monitoring the Cordgrass Marsh In March 1979, 8 transects were established in the cordgrass-dominated low marsh at Tijuana Estuary (32°34'N, 117°7'W). Each transect began at a random point on the adjacent channel edge and proceeded landward to a point just beyond the 1979 upper limit of cordgrass. Sampling stations were permanently staked at 5-meter intervals, with 9-20 stations per transect and a total of 101 stations. Each September, cordgrass stems were counted and heights were measured in m^ circular quadrats at all stations. Cover of other species (not readily counted) was estimated by cover class (Kershaw 1973). Several environmental factors were assessed at the onset of monitoring, and at intervals thereafter. Interstitial salinities were measured by expressing a drop of soil water onto an A-O Salinity Refractometer. Because root biomass is
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