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Dynamics and Ecosystem threats of Bidirectional Cordgrass Hybridization in San Francisco Bay

  • Author(s): Strong, Donald R.
  • Ayres, D R
  • et al.
Abstract

Hybrids between alien cordgrass, Spartina alterniflora, introduced in the 1970s, and native California cordgrass, S. foliosa are a menace to the ecology of San Francisco Bay, spreading to aggressively invade open mud, displacing native species, hindering flood control, navigation, and other uses of this habitat. We proposed to determine the key elements of the ecology of the hybrid cordgrass invasion: ecological amplitude of parental species and hybrids, dynamics of seedling movement and recruitment, and broad spread of hybrids around the Bay and up the Sacramento Delta. Our previous field and molecular work suggested that vigorous hybrids grow taller and more densely than either parental species; they should have greatest competitive abilities and tidal range. To experimentally compare ecological amplitudes among cordgrass plants, we measured vegetative vigor and sexual reproduction of cordgrass genotypes planted in common gardens on the intertidal plane. To identify essential components of seedling recruitment, we planned to characterized seed movement on the tides, persistence in the soil seed bank, and germination and establishment of cordgrass genotypes in experimental field plots. To document the rate and extent of the spread of hybrids around the Bay, we annually surveyed and genetically characterized cordgrass seedlings and plants in marshes where hybrids were established as well as previously un-invaded marshes.

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