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Dynamics of Mangrove-Marsh Ecotones in Subtropical Coastal Wetlands: Fire, Sea-Level Rise, and Water Levels

Thomas J. Smith III1*, Ann M. Foster2, Ginger Tiling-Range3, and John W. Jones4

This article was originally published in Fire Ecology 2013 9(1): 66-77. doi: 10.4996/fireecology.0901066. Abstract and figure posted here with permission from the Association for Fire Ecology. The full article is available for download from the Association for Fire Ecology website.


map showing study region on the southwest coast of Florida within Everglades National Park

Study region on the southwest coast of Florida within Everglades National Park is depicted. The background image is a mosaic of 2004 Digital Orthophoto Quarter Quads (DOQQs). Locations of the three study areas are indicated: 2nd Onion Bay, SH5, and P35-SH1. The bold yellow line is the boundary for Everglades National Park. Also shown are all fire polygons from the fire history database for the period 1948 to 2010 that occurred within this area. [larger image]

Ecotones are areas of sharp environmental gradients between two or more homogeneous vegetation types. They are a dynamic aspect of all landscapes and are also responsive to climate change. Shifts in the position of an ecotone across a landscape can be an indication of a changing environment. In the coastal Everglades of Florida, USA, a dominant ecotone type is that of mangrove forest and marsh. However, there is a variety of plants that can form the marsh component, including sawgrass (Cladium mariscus [L.] Pohl), needlegrass rush (Juncus roemerianus Scheele), and spikerush (Eleocharis spp.). Environmental factors including water depth, soil type, and occurrence of fires vary across these ecotones, influencing their dynamics. Altered freshwater inflows from upstream and increasing sea level over the past 100 years may have also had an impact. We analyzed a time series of historical aerial photographs for a number of sites in the coastal Everglades and measured change in position of mangrove–marsh ecotones. For three sites, detailed maps were produced and the area of marsh, mangrove, and other habitats was determined for five periods spanning the years 1928 to 2004. Contrary to our initial hypothesis on fire, we found that fire did not prevent mangrove expansion into marsh areas but may in fact assist mangroves to invade some marsh habitats, especially sawgrass. Disparate patterns in mangrove–marsh change were measured at two downstream sites, both of which had multiple fires over from 1948 to 2004. No change in mangrove or marsh area was measured at one site. Mangrove area increased and marsh area decreased at the second of these fire-impacted sites. We measured a significant increase in mangrove area and a decline in marsh area at an upstream site that had little occurrence of fire. At this site, water levels have increased significantly as sea level has risen, and this has probably been a factor in the mangrove expansion.

Keywords: disturbance, Everglades, fire, hurricane, marl, peat, sea level, soil

1 Southeast Ecological Science Center, US Geological Survey, 600 Fourth Street South, St. Petersburg, Florida 33701, USA
2 Southeast Ecological Science Center, US Geological Survey, 7920 NW 71st Street, Gainesville, Florida 32653, USA
3 Cherokee Nations Business Solutions, c/o 600 Fourth Street South, St. Petersburg, Florida 33701, USA
4 Eastern Geographic Science Center, US Geological Survey, 12201 Sunrise Valley Drive, Mail Stop 521, Reston, Virginia 20191, USA
* Corresponding author: Tel.: 001-727-803-8747; e-mail: tom_j_smith@usgs.gov

Related information:

SOFIA Project: Fire, Hydrology and Soils along the Mangrove Ecotone within the Greater Everglades Ecosystem