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Predicting Future Mangrove Forest Migration in the Everglades Under Rising Sea Level

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Predicting Future Mangrove Forest Migration in the Everglades Under Rising Sea Level Predicting Future Mangrove Forest Migration in the Everglades Under Rising Sea Level Mangroves in the Everglades punctuate the vulnerability of mangrove ha) on an annual basis for the entire simu- forests to rising sea level and other climate lated landscape. Each land unit is defined Mangroves are highly productive changes. Global climate change has been by habitat type (forest, marsh, aquatic), ecosystems that provide valued habitat for projected to increase seawater tempera- land elevation, water level, and salinity fish and shorebirds. Mangrove forests are tures and accelerate the rise in sea level conditions. SELVA also calculates prob- universally composed of relatively few which may further compound ecosystem ability functions of disturbance for each tree species and a single overstory strata. stress in mangrove-dominated systems. forest unit relative to potential sea-level Three species of true mangroves are com- These forests are subject to coastal and rise, lightning, and hurricane strikes. In- mon to intertidal zones of the Caribbean inland processes of hydrology largely tertidal forest units are then simulated with and Gulf of Mexico Coast, namely, black controlled by regional climate, disturbance the MANGRO model based on unique sets mangrove (Avicennia germinans), white regimes, and human decisions about water of environmental factors and forest history. mangrove (Laguncularia racemosa), and management. MANGRO is a spatially explicit red mangrove (Rhizophora mangle). Man- Mangroves are halophytes, mean- stand simulation model constructed for grove forests occupy intertidal settings of ing they can tolerate the added stress of mangrove forests of the Neotropics (fig. the coastal margin of the Everglades along waterlogging and salinity conditions that 2). As an individual-based model com- the southwest tip of the Florida peninsula prevail in low-lying coastal environments posed of a set of functions predicting (fig. 1). influenced by tides. While early research- ers attributed zonation patterns to salinity gradients, more recent field and labora- tory studies indicate that mangroves have adapted wide tolerances to salinity and may be influenced to a greater degree by local hydrology and episodic disturbance events. Increases in relative sea level will eventually raise saturation and salinity Gulf of Mexico FLORIDA conditions at ecotonal boundaries where mangroves are likely to advance or en- croach upslope into freshwater marsh and swamp habitats. SELVA-MANGRO Landscape Model Figure 2. Sample graphics interface of the MANGRO Study area model and a recruitment phase of mixed mangrove Mangrove forest of South Florida Mangrove Forests species composition (red = red mangroves, white = white mangroves, black = black mangroves). The wide range of environmental Figure 1. Study area of mangrove communities in the settings and mangrove expanse in the Florida Everglades. Everglades coastal margin warranted the application of a landscape ecosystem the growth, establishment, and death of model to predict potential habitat changes individual trees, MANGRO predicts the from sea-level rise. An integrated land- tree and gap replacement process of natu- Current Status and Stresses of scape model, SELVA-MANGRO, was ral forest succession influenced by stand Mangrove Ecosystems developed to simulate the dynamics and structure and environmental conditions. distribution of mangrove communities of The SELVA-MANGRO landscape The flat slope and near sea-level el- south Florida. model hierarchially integrates the scale evation of the protected Everglades system SELVA is a Spatially Explicit and functions of the SELVA and MAN- account for one of the largest contiguous Landscape Vegetation Analysis model that GRO models into a single framework by tracts of mangrove forests found anywhere tracks predicted changes in the biotic and coupling model parameters at the land- in the world; these factors also, however, abiotic conditions of each land unit (1 sq scape and forest scales, respectively. U.S. Department of the Interior USGS Fact Sheet FS-030-03 U.S. Geological Survey March 2003 Development of an Everglades based on mean annual tide records (1940 3500 to present) projected into the 21st century 3000 Digital Elevation Model m) with the addition of curvilinear rates of 2500 q k A high resolution model of surface eustatic sea level expected from climate (s 2000 change. The data record was extended topography was developed for SELVA- gain 1500 MANGRO to predict the rate and fate of into the next 100 years for sea-level rise at scenarios of 15 cm to 1.1 m by year 2100 1000 coastal inundation from projected sea- Habit 500 level rise scenarios. The ability to predict based on low, mid, and high projections 0 landward migration of mangroves caused obtained from global climate change 15 33 45 66 95 110 by sea-level rise depends on the relation- models. Sea-level rise scenarios (cm) ship between landward slope and eleva- SELVA-MANGRO results show Figure 3. Contemporary and predicted distributions tion in relation to tide range and extent. that species and forest cover will change and species composition from inland mangrove Historic topographic and drainage maps over space and time with increasing tidal migration under selected sea-level scenarios, low (15 cm), moderate (45 cm), and high (95 cm), expected by (Davis, 1943) with 1 ft (0.3048 m) contour inundation across the simulated landscape intervals across the south Florida Ever- for all sea-level rise scenarios. The degree glades were rectified and digitized into a of mangrove migration compared with geographic information system and spatial contemporary distribution and selected template of SELVA-MANGRO. sea level scenarios (low, moderate, high) hydrology of the Everglades, sea-level rise expected by the year 2100 are contrasted of even conservative estimates must not be in figure 3. The model shows that fresh- Forecasting Sea-Level Rise and ignored given the potential for saltwater water marsh and swamp habitats will be intrusion and mangrove migration. Mangrove Migration across South displaced as the tidal prism increases over Florida time and moves upslope. The greater the rate of sea-level rise, the faster or more References Cited SELVA-MANGRO applications extensive will mangroves encroach onto forecasted mangrove migration under the Everglades slope. Figure 4 shows the Davis, J. H., 1943, Vegetation map of projected climate change scenarios of predicted land area that mangroves may Southern Florida, Bulletin 25: Tallahas- sea-level rise and saltwater intrusion for gain over the next century at the ex- see, Florida Geological Survey, scale: 1: the Everglades coastal margin. Sea-level pense of other freshwater habitats. While 400,000. rise was modeled as a function of historic scientists are evaluating various freshwa- sea level conditions at Key West, Florida, ter alternatives for restoring the natural For Further Reading Doyle, T.W., and Girod, G., 1996, The frequency and intensity of Atlantic hur- ricanes and their influence on the struc- ture of south Florida mangrove com- munities, in H. Diaz and R. Pulwarty, eds., Hurricanes, Climatic Change and Socioeconomic Impacts: A Current Perspective, pp. 111-128: New York, Westview Press, pp. 325. Doyle, T.W., 1998, Modeling global change effects on coastal forests, in G. R.Guntenspergen and B. A.Vairin, eds., Vulnerability of coastal wetlands in the southeastern United States: Climate change research results, 1992-97: U.S. Geological Survey, Biological Resourc- es Division Biological Science Report USGS/BRD/BSR-1998-0002, pp.105. For More Information, Contact Thomas W. Doyle U.S. Geological Survey National Wetlands Research Center 700 Cajundome Blvd. Lafayette, LA 70506 Figure 3. Digital elevation model (DEM) of south Florida based on spatial interpolation of elevation contour and proxy zonation heights taken from historic vegetation and topographic maps. NOTE: Modified from vegetation 337-266-8500; Fax: 337-266-8513 map of southern Florida by J.H. Davis, Jr., 1943. http://www.nwrc.usgs.gov.
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