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Project Summary Sheet

U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (GE PES) Initiative

Fiscal Year 2006 Study Summary Report

Study Title: Development and Stability of Everglades Tree Islands, Ridge and Slough, and Marl Prairies
Study Start Date: 10/1/00   Study End Date: 9/30/06
Web Sites:
Location (Subregions, Counties, Park or Refuge): Loxahatchee NWR, WCA 2, 3, Everglades National Park, Big Cypress National Preserve
Funding Source: USGS Greater Everglades Priority Ecosystems Science (GE PES) Initiative
Principal Investigator: Debra A. Willard
Study Personnel: C. Bernhardt, M. Corum, C. Holmes, B. Landacre, H. Lerch, M. Marot, W. Orem, T. Sheehan
Supporting Organizations: South Florida Water Management District, Florida Fish & Wildlife Conservation Commission, Loxahatchee NWR, Everglades National Park, Big Cypress National Preserve
Associated / Linked Studies: Interrelation of Everglades Hydrology and Florida Bay Dynamics (Ecology Component), Tides and Inflows in the Mangrove Ecotone (TIME) Model Development, Ecosystem History of the Southwest Coast-Shark River Slough Outflow Area

Overview & Objectives: Everglades restoration planning requires an understanding the impact of natural and human-induced environmental change on wetland stability. This project initially focused on tree-island development and trends and expanded to include the sawgrass ridge and slough system and marl prairies. For each system, restoration targets are being proposed, even though little data exists on their predrainage extent and ecosystem dynamics. Initial goals of the project included: determine geologic and hydrologic controls on tree-island formation, development and sustainability; establish vegetational trends in tree-island development; determine the role of tree islands in the geochemical budget of nutrients; and investigate the use of sediment phosphorus as a tracer of historic bird populations in the Everglades. Investigations of the Ridge and Slough system are directed to: determine the longevity of the features; document changes in spatial extent of sawgrass ridges and sloughs; determine past rates of peat accretion in ridges vs. sloughs; determine whether sawgrass ridges are analogs for sites of tree-island formation; and assess the response of ridges and sloughs to natural and anthropogenic hydrologic changes. Investigations of marl prairies are designed to determine whether the distribution and vegetational composition of marl prairies has changed over the last century.

Status: Cores were collected on 39 tree islands in Loxahatchee NWR, WCA 2A, 3A, 3B, and Everglades National Park (Shark River Slough, Taylor Slough, Eastern Everglades Expansion Area). Pollen and geochronologic data have been generated from 33 cores representing 20 tree islands. Six transects of cores were collected across "pristine" and altered sawgrass ridges and sloughs sites in WCA 3A. From these, pollen analysis is complete on surface samples and four transects, representing a total of 11 cores. An open-file report summarizing these results was published in 2003, and a manuscript has been submitted to a journal for review. In Big Cypress National Preserve, seismic lines were run in FY06 to determine sediment distribution and thickness. A 1.5 m freeze core was collected that represents about the last 500 years of deposition. These data complement the long core (5 meters) collected in FY04, which contains sediments up to 1500 years old. Data from these cores will allow evaluation of natural and anthropogenic patterns of change in an ancient sink-hole lake in a relatively pristine area of the Preserve. Analysis of sediment cores collected in marl prairies in the western Everglades as a pilot study indicated that pollen, plant macrofossil, and ostracode records all provide good records of vegetational and hydrologic change in marl-accumulating systems, showing the potential of such research to document the timing of vegetational changes, correlate them with specific hydrologic events, and evaluate the pre-drainage spatial distribution of marl-prairie habitats. In Loxahatchee NWR, we collected cores on nine tree islands and nine marshes in the northern, central, and southern reaches of the Refuge to establish the original ecosystem structure and composition and evaluate changes in response to 20th century management changes.

Recent Products:

Willard, D.A., Holmes, C.W., Korvela, M.S., Mason, D., Murray, J.B., Orem, W.H., and Towles, D.T., 2002. Paleoecological insights on fixed tree island development in the Florida Everglades: I. Environmental Controls. In Sklar, F.H., and van der Valk, A. (Eds.), Tree Islands of the Everglades: 117-152.

Orem, W.H., Willard, D.A., Werch, H.E., Bates, A.L., Boylan, A., and Corum, M., 2002, Nutrient geochemistry of sediments from two tree islands in Water Conservation Area 3B, the Everglades, Florida. In Sklar, F.H., and van der Valk, A. (Eds.), Tree Islands of the Everglades: 153-186.

Willard, D.A. and Orem, W.H. 2003, Tree-Islands of the Florida Everglades - A Disappearing Resource, U.S. Geological Survey Open-file Report 03-26: 2 pp.

Bernhardt, C.E., Willard, D.A., and Holmes, C.W., 2003, Development and Stability of the Everglades Ridge and Slough Landscape. U.S. Geological Survey Open-file Report 03-54: 128.

Willard, D.A., 2004, Tree Islands of the Florida Everglades Long-term Stability and Response to Hydrologic Change, U.S. Geological Survey Open-file Report 2004-3095: 4 pp.

Bernhardt, C.E., Willard, D.A. 2004. Influence of 20th century water management on plant communities in Everglades marl prairies. First National Conference on Ecosystem Restoration.

Willard, D.A., 2004. Impacts of land-cover and hydrologic change on vegetation of the south Florida coast. First National Conference on Ecosystem Restoration.

Bernhardt, C.E. and Willard, D.A., 2004. Development and Stability of the Everglades Ridge and Slough Landscape: Records from three transects in Water Conservation Area 3A. U.S. Geological Survey Open-file Report 2004-1448.

Willard, D.A., Bernhardt, C.E., Weimer, L.E., Cooper, S.R., Gamez, D., and Jensen, J., 2004. Atlas of pollen and spores of the Florida Everglades. Palynology 28: 175-227.

Willard, D.A. and Bernhardt, C.E., 2005. Everglades wetland response to climatic and anthopogenic hydrologic change: implications for management of the Everglades ecosystem. George Wright Society Annual Meeting, March, 2005.

Bernhardt, C. E. and D.A. Willard. 2006. Tree island paleoecology and their response to hydrologic change, Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida. Northeastern Section Geological Society of America Meeting Paper 24-14.

Bernhardt, C.E., Willard, D.A., Schwadron, M., and Horton, B., 2006. Relationships among climate variability, Native American tree island occupation, and wetland development in the Florida Everglades. Geological Society of America Annual Meeting, October, 2006.

Bernhardt, C.E., Willard, D.A., Holmes, C.W., and Marot, M., in review. Climate variability and anthropogenic impacts on wetland development: the sawgrass ridge and slough landscape, Everglades, Florida. Submitted to Wetlands.

Orem, W.H., 2006. Tree island wading bird biomarker study. Final report for PC P501993, South Florida Water Management District and U.S. Geological Survey, 50 pp.

Willard, D.A., Bernhardt, C.E., Holmes, C.W., and Marot, M., 2006. Impacts of 20th century hydrologic change on Everglades tree islands. Greater Everglades Ecosystem Restoration Conference, June, 2006.

Willard, D.A., Bernhardt, C.E., Brandt, L.A., and Marot, M., 2006. Response of Loxahatchee tree islands and marshes to 20th century hydrologic change. Greater Everglades Ecosystem Restoration Conference, June, 2006.

Willard, D.A., Bernhardt, C.E., Holmes, C.W., Landacre, B., and Marot, M., 2006 (in press). Response of Everglades tree islands to environmental change. Ecological Monographs (Nov., 2006).

Planned Products:

Bernhardt, C.E. and Willard, D.A., in prep. Influence of 20th century water management on plant communities in Everglades marl prairies. Fall 2006.

Orem W., Newman S., Lerch H., Corum M., Bates A., and Willard D. (2006) Biomarkers of wading bird populationd on tree islands of the Everglades. Organic Geochemistry. Winter 2006.

Willard, D.A., Bernhardt, C.E., Holmes, C.W., and Marot, M., in press. Everglades wetland response to hydrologic fluctuations: climatic vs. human impacts. In Jones, J.W. (Ed.), Topical Report on Everglades land surface history and process modeling. USGS Bulletin. Winter 2006.

Specific Relevance to Information Needs Identified in DOI Science Plan in Support of Ecosystem Restoration, Preservation, and Protection in South Florida: [See Plan on SOFIA's Web site:]:

This study supports several of the projects listed in the DOI science plan (specifically: Arthur R. Marshall Loxahatchee NWR Internal Canal Structures; Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement; and Combined Structural and Operational Plan) by (a) documenting the timing of tree-island formation across the region; (b) establishes patterns of vegetation development and geochemical changes on the islands; (c) comparing development of different types of tree islands; (d) developing a model of tree-island formation that may be used in restoration of degraded islands and, possibly, creation of new islands; and (e) determining the duration of flooding or drought that tree islands can tolerate before changes in aerial extent occur.

The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures project (LNWR; p. 39) as it (1) provides data about historic hydrologic and ecological conditions on the refuge (p. 40) and (2) helps understand the ecological effects of hydrology and water quality on refuge resources (p. 40) The study supports the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement project (DECOMP; p. 66) as it (1) helps understand the linkages among the geologic, hydrologic, chemical, and biological processes that shaped the predrainage Everglades (p. 68); (2) helps understand the critical factors for sustaining tree islands, ridge and slough habitats, and marl prairies (p. 68); and (3) helps understand the effects of different hydrologic regimes and ecological processes on restoring and maintaining ecosystem function (p. 69).

This study supports the Combined Structural and Operational Plan project (CSOP and Mod Waters; p. 70) as it (1) generates information that will improve ecological models and make them more suitable for application of the Natural Systems Model (p. 71).

Key Findings:

  1. Formation of Everglades tree islands typically predates significant human alteration of wetland hydrology. Tree islands examined in this study began developing 500-3500 cal yrBP, during multidecadal intervals of sustained drought.
  2. Fixed tree island development follows a common pattern throughout the Everglades. Fixed tree islands formed on topographic highs, and trees and shrubs became increasingly prominent as peat accumulation resulted in increasing surface elevation. Mature tree island vegetation became established during later sustained periods of drought. The great impact of climate variability on Everglades plant communities indicates that allogenic processes played a dominant role in development of the Everglades wetland.
  3. Hydrologic modification of the Everglades wetland during the 20th century altered composition of tree island plant communities and affected tree island size. Vegetational response depends on the location within the system and the magnitude of hydrologic change.
  4. The basic Ridge and Slough structure of WCA 3A has existed for at least 1,000 years; the position of the ridge-slough transition zone has fluctuated in response to recent changes in hydrology.
  5. Pollen, seed, and ostracode assemblages from cores collected in marl prairies indicate changes in sediment type and plant community composition in the early 20th century. The shift from peat-accumulating sawgrass marshes to marl prairies ~1930 indicates that altered hydrology affected the spatial distribution of marl prairie communities.

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