Plant zonation in low-latitude salt marshes: disentangling the roles of flooding, salinity and competition

Authors

  • STEVEN C. PENNINGS,

    Corresponding author
    1. University of Georgia Marine Institute, Sapelo Island, GA 31327, USA, and
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  • MARY-BESTOR GRANT,

    1. University of Georgia Marine Institute, Sapelo Island, GA 31327, USA, and
    2. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
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    • Present address: 2628 Carriage Place, Birmingham, AL 35223, USA.

  • MARK D. BERTNESS

    1. University of Georgia Marine Institute, Sapelo Island, GA 31327, USA, and
    2. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
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*Present address and correspondence: Steven C. Pennings, Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA (tel. +1 713 7432989; fax +1 713 7432636; e-mail spennings@uh.edu).

Summary

  • 1We investigated the factors producing zonation patterns of the dominant plants in south-eastern USA salt marshes where Juncus roemerianus dominates the high marsh, and Spartina alterniflora the middle and low marsh.
  • 2Juncus did not occur naturally in the Spartina zone and performed poorly when transplanted there, irrespective of whether neighbours were present or removed, indicating that its lower limit was set by physical stress.
  • 3In contrast, although Spartina occurred naturally at low densities in the Juncus zone, it performed well if transplanted there only if neighbours were removed, indicating that its upper limit was set by competition.
  • 4Parallel laboratory and field manipulations of flooding, salinity and competition indicated that the lower limit of Juncus was mediated by both flooding and salinity, but not by competition.
  • 5The general mechanisms producing zonation patterns of vegetation in coastal salt marshes may be universal, as suggested by previous studies, but the importance of particular factors is likely to vary geographically. In particular, salinity stress probably plays a much more important role in mediating plant zonation patterns at lower latitudes.
  • 6Our results suggest that the nature of ecological interactions is likely to vary geographically because of variation in the physical environment, and this variation must be taken into account in order to successfully generalize the results of field studies across geographical scales.

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