Variable rainfall limits the germination of upper intertidal marsh plants in southern California

Temporal variation in rainfall created a germination window for seedling establishment in the upper intertidal marshes of southern California. In this highly variable climate, total annual rainfall was highly variable, as was the timing and size of rainfall during the wet season. Daily rainfalls > 3.0 cm were rare in the long-term record but created germination opportunities that had two components: low salinity and high moisture. During the 1996-1997 wet season, only one-day rainfalls > 3.0 cm resulted in large increases in soil moisture and decreases in soil salinity. Germination in the upper intertidal marsh of three wetlands followed two large (> 3.0 cm) rainfall events in the relatively dry 1996-1997 season and multiple medium and small rainfall events in the wetter 1997-1998 season. In addition to rainfall, plant cover and soil texture influenced spatial and temporal variation in soil salinity and moisture. Daily and weekly sampling adequately described soil moisture and salinity so that germination could be predicted; monthly sampling would have missed the low-salinity and high-moisture events that trigger germination.