Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States |
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Authors: | Laura Gough James B Grace |
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Institution: | (1) Department of Plant Biology, Louisiana State University, Baton Rouge, LA 70803, USA, US;(2) National Wetlands Research Center, U.S. Geological Survey, 700 Cajundome Blvd., Lafayette, LA 70506, USA, US |
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Abstract: | Flooding and salinity stress are predicted to increase in coastal Louisiana as relative sea level rise (RSLR) continues in
the Gulf of Mexico region. Although wetland plant species are adapted to these stressors, questions persist as to how marshes
may respond to changed abiotic variables caused by RSLR, and how herbivory by native and non-native mammals may affect this
response. The effects of altered flooding and salinity on coastal marsh communities were examined in two field experiments
that simultaneously manipulated herbivore pressure. Marsh sods subjected to increased or decreased flooding (by lowering or
raising sods, respectively), and increased or decreased salinity (by reciprocally transplanting sods between a brackish and
fresh marsh), were monitored inside and outside mammalian herbivore exclosures for three growing seasons. Increased flooding
stress reduced species numbers and biomass; alleviating flooding stress did not significantly alter species numbers while
community biomass increased. Increased salinity reduced species numbers and biomass, more so if herbivores were present. Decreasing
salinity had an unexpected effect: herbivores selectively consumed plants transplanted from the higher-salinity site. In plots
protected from herbivory, decreased salinity had little effect on species numbers or biomass, but community composition changed.
Overall, herbivore pressure further reduced species richness and biomass under conditions of increased flooding and increased
salinity, supporting other findings that coastal marsh species can tolerate increasingly stressful conditions unless another
factor, e.g., herbivory, is also present. Also, species dropped out of more stressful treatments much faster than they were
added when stresses were alleviated, likely due to restrictions on dispersal. The rate at which plant communities will shift
as a result of changed abiotic variables will determine if marshes remain viable when subjected to RSLR.
Received: 8 April 1998 / Accepted: 15 June 1998 |
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Keywords: | Biomass Louisiana Nutria Species density Species diversity |
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