mangrove-hammock - Ecosystems (2007) 10: 648660 DOI:

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Competition between Hardwood Hammocks and Mangroves Leonel da Silveira Lobo Sternberg, 1, * Su Yean Teh, 2 Sharon M. L. Ewe, 3 Fernando Miralles-Wilhelm, 4 and Donald L. DeAngelis 1,5 1 Department of Biology, University of Miami, Coral Gables, Florida 33124, USA; 2 Universiti Sains Malaysia, Penang, Malaysia; 3 Southeast Environmental Research Center, Florida International University, Miami, Florida 33199, USA; 4 Department of Civil and Environmental Engineering, Florida International University, Miami, Florida 33174, USA; 5 Florida Integrated Science Center, U.S. Geological Survey, Florida, USA A BSTRACT The boundaries between mangroves and freshwater hammocks in coastal ecotones of South Florida are sharp. Further, previous studies indicate that there is a discontinuity in plant predawn water potentials, with woody plants either showing predawn water potentials re±ecting exposure to saline water or exposure to freshwater. This abrupt concurrent change in community type and plant water status suggests that there might be feedback dynamics between vegetation and salinity. A model examin- ing the salinity of the aerated zone of soil overlying a saline body of water, known as the vadose layer, as a function of precipitation, evaporation and plant water uptake is presented here. The model predicts that mixtures of saline and freshwater vegetative species represent unstable states. Depending on the initial vegetation composition, subsequent vegeta- tive change will lead either to patches of mangrove coverage having a high salinity vadose zone or to freshwater hammock coverage having a low salinity vadose zone. Complete or nearly complete coverage by either freshwater or saltwater vegetation repre- sents two stable steady-state points. This model can explain many of the previous observations of veg- etation patterns in coastal South Florida as well as observations on the dynamics of vegetation shifts caused by sea level rise and climate change. Key words: vadose layer; sea level rise; man- groves; hammocks; steady-state; fragmentation. I NTRODUCTION Recent analysis of ecosystem dynamics has shown the possibility of a sudden, catastrophic change from one ecosystem type to another (Scheffer and others 2001 ). Certain species or functional group assem- blages can be considered as stable states, whereas other assemblages, even those characterized as steady-states, are easily perturbed from their stable state. Slight perturbations from an apparent stable state will lead to changes towards one of the eco- systems characterized as a stable steady-state. Our understanding of these types of ecosystem changes is in part due to a body of evidence indicating that terrestrial vegetation does not always react passively to climate. Ecosystems can have a complex interac- tion with climate, where climate–vegetation feed- back loops can in±uence vegetation structure and function (Charney 1975 ; Brovkin and others 1998 ; Rodriguez-Iturbe and others 1999 ; Sternberg 2001 ; Oyama and Nobre 2003 ). In addition to a regional scale of feedback between vegetation and climate,
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This note was uploaded on 07/09/2011 for the course CWR 5104C taught by Professor Miralles during the Spring '11 term at FIU.

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mangrove-hammock - Ecosystems (2007) 10: 648660 DOI:

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