Ridge & Slough Projects

2005-Present — Slough Project (vegetation component):
The south Florida slough habitat is a long hydroperiod, deeper-water habitat that dries out only on a decadal scale. Under pre-drainage conditions, much of the central Everglades was ridge and slough habitat, characterized by "corrugated" topography with higher sawgrass ridges and deeper water sloughs. Maintenance of this regularly varying topography was likely via two different mechanisms. The elevation of sawgrass ridges may have been based on an equilibrium between peat accretion and oxidation (i.e. decomposition and fire), and was probably regulated by long-term mean water level. Slough depths, however, were likely maintained by water flow scouring that prevented sedimentation and infilling in a disequilibrial process. Drainage and compartmentalization in the last 100 years effectively reduced mean water levels and water flow rates in much of the central Everglades. Effective ENP slough restoration will require detailed knowledge of the ridge and slough ecosystems and how they interact. The broad objective of this study is to compare these adjacent environments, including comparisons of soil biogeochemistry, hydrology, vegetation composition and structure, and nutrient content.

2005-Present — Tree islands in Everglades landscapes: current status, historical changes, and hydrologic impacts on population dynamics and moisture relations.

Tree islands are a prominent feature in the Ridge and Slough landscape of the Everglades, where they have undergone extensive damage from drought, fire and extreme flooding. They are also prevalent in the short-hydroperiod prairies, where they have been adversely impacted by fire and encroaching exotic plants. Changes in water management associated with hydrologic restoration will result in changes in the internal water economy of tree islands, as well as their risk of fire, which in turn will lead to changes in plant function and species composition. It is therefore important to understand how restoration translates into impacts in these unique ecosystems. This project is an expansion of our 2004 tree island project and includes collaboration with the Sternberg and Oberbauer labs. The project is designed to provide a better understanding of tree island structure and function in the Everglades and the wetlands bordering it. Focus is on the raised portions at the upstream end of the islands, where tropical hardwood species adapted to well-drained conditions usually are the most prominent component of the vegetation. The study design is hierarchical, with four levels; in general, a large number of sites is to be surveyed once for a limited set of parameters, and increasingly small sets of islands are to be sampled more intensively, more frequently, and for more aspects of ecosystem function. As the project continues to include more islands and repeated measurements, we expect to develop a better grasp of tree island dynamics across the Everglades ecosystem, especially with respect to moisture relations and water levels in the adjacent marsh.

2000-2004 — Tree Islands in the Shark Slough Landscape: Interactions of Vegetation, Hydrology, and Soils.

Shark Slough tree islands have been influenced by the same uneven environmental history that has affected other Everglades wetland communities. Vegetation patterning within these tree islands resembles patterns in the marshes that surround them; species composition is largely arranged along a single strong gradient represented in this study by hydrologic measures. Hydrology is in fact one aspect of a multi-factorial environmental complex that includes nutrient availability, canopy openness, and possibly temperature and other climatic variables. Paleoecologically, these tree islands are the product of a non-linear, successional process subject to long-term climatic variation and significant local and regional disturbances. Within the landscape, tree islands play many important functional roles (e.g., by providing wildlife habitat). Because tree islands are very much a part of the ridge and slough landscape of Shark Slough, they can probably best be protected by managing for the health of the landscape as a whole. Therefore, the principle objective of this study was to provide knowledge useful for restoration and management planning through characterization of the interactions between vegetation, hydrology and soils within ENP tree islands, regarded as components of the larger Shark Slough landscape.

1998-2003 — Vegetation: Environment Relationships and Water Management in Shark Slough, Everglades National Park.

The hydrologic regime of Shark Slough is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Especially where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. Three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) are found throughout Shark Slough. Existing literature suggests hydroperiod and water depths increased in the order Tall Sawgrass < Sparse Sawgrass < Spikerush Marsh. Although variation in hydroperiod and soil depths may reflect a natural gradient within the Slough, some may be the result of management and compartmentalization within the marsh. In this project we used data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. A sixth, NE-SW oriented transect incorporates a coastal gradient near the marsh-mangrove interface. We concluded that hydroperiod or water depth is the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades. The "phase shifts" we observed in vegetation-hydrology relationships among management units appear to be disequilibrial, and suggest that current water management will eventually result in large scale changes in landscape pattern within Shark Slough.