The Ecotone Between Spartina Foliosa Trin. and Salicornia Virginica L. in Salt Marshes of Northern San Francisco Bay: I. Biomass and Production

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Abstract
On the shores of San Pablo Bay [California, USA] distinct zones are occupied by nearly monospecific communities of S. foliosa (in the mid-littoral zone) and S. virginica (in the upper littoral zone). Measurements of above-ground and below-ground standing crop and seasonal production were made in 1972 along 2 transects crossing the ecotone between the 2 spp. at Mean High Water Level: 1 on Mare Island and 1 on the Petaluma River. The above-ground standing crop and production of Spartina declined in all respects as the ecotone was approached on both transects. The above-ground standing crop and production of Salicornia also decreased toward the ecotone, but at Mare Island Salicornia was more productive per unit biomass or per stem in the Spartina zone than in the Salicornia zone. Living rhizomes and roots of Salicornia were found primarily in the upper 15 cm of soil. Living rhizomes and roots of Spartina were distributed throughout the soil profile but tended to be absent from the upper 15 cm in the Salicornia zone. Total standing crop and production, including both species, decreased to a minimum at the middle of the ecotone. It appears that the zonation is dependent on physical factors and physiological responses rather than on interspecific competitive effects.