Ecology of a mediterranean-climate estuarine wetland at Carpinteria, California: plant distributions and soil salinity in the upper marsh

We examined seasonal changes in soil salinity in four different vegetative zones in a mediterranean-climate estuarine wetland in southern California. Each zone had a characteristic seasonal pattern of soil salinity: (i) the low marsh zone was high in salinity throughout the year; (ii) the salt flat zone was hypersaline throughout the year; (iii) the transition zone was hypersaline in the summer and fall, and low in salinity in the winter and spring; and (iv) the nonflooded grassland was low in salinity throughout the year. The transition zone was densely populated with winter annuals that were distributed along gradients of elevation and soil salinity. This occurrence of annuals is a characteristic feature of mediterranean-climate marshes. We found that the relative growth rates and the germination of each of these annuals in experimental solutions of different salinities corresponded with the winter and spring soil salinities of the subzones they occupied in the field.