Vegetative Habitats of Water Conservation Area-3A: Impact of Interim Operational Plan

Vegetative Habitats of Water Conservation Area-3A: Hydrologic Impacts of IOP

Wiley M. Kitchens

USGS/Florida Cooperative Fish and Wildlife Research Unit, Gainesville, FL

Paul Wetzel and Erik Powers

University of Florida, Gainesville, FL

A vegetation monitoring study has been initiated in Water Conservation Area-3A (WCA-3A) to document impacts of a new hydrologic regulation schedule implemented 1 July 2002 under the Interim Operation Plan for the Protection of the Cape Sable Seaside Sparrow, Everglades Park – Alternative 7R (IOP-Alt.7R). This study was implemented to address the concern that IOP-Alt.7R could adversely affect the endangered snail kite (Rostrhamus sociabilis) and their habitat in WCA-3A, the largest and most consistently utilized of designated critical habitats. Much of the area is already currently seriously degraded. Various studies have documented the conversion of wet prairies (preferred foraging habitat) to aquatic sloughs in that area along with losses of interspersed herbaceous and woody species essential for nesting habitat. The concern is carrying capacity (habitat quality) will be further impaired from elevated water depths and increased hydroperiods indicated by hydrological predictions.

The principal objective is to separate plant community responses due to typical seasonal and year-to-year variances from effects due to new and /or predicted hydrologic regimes. The vegetative community structure of these sites is an expression of both recent past and current hydrological conditions. It is critically important to determine how the species associations within these communities respond differentially to changes in hydrology through time and over space. Given the immense area of WCA 3A, this study focuses on areas represented by 2 Indicator Regions (IR’s 14 and 17). The areas include major gauging stations (GS 63, 64, and 65) and traditional foraging and nesting regions used by kites.

A multi-tiered approach was required to determine community change through time and space while differentiating seasonal responses from projected hydrologic changes.

1) Spatial Patterns and Change Detection at the Broad Vegetation Class Level- (example, sawgrass strands, tree islands, cattail patches, and wet prairie/slough). Aerial or satellite imagery will be used to remotely sense spatial distributions, extent, and patterning of broad major vegetation classes. Change detection will conducted on at least 3 sets of imagery, 4-5 years pre-project, at project onset, and 3-4 years post-project.

2) Development of “modeled-topographic” database and hydrologic characterization of Indicator Regions. Stage information generated by SFWMM model for the units comprising each Indicator Region is gridded 2 mi. on a side. Stage duration curves generated from this data are determined from estimated ground surface elevations generalized from a weighted mean over the 4 sq. mi. area of each grid. This level of detail is far too generalized for assessment impacts to habitat suitability of wetland vegetation for subtle changes in hydroperiods and inundation depth regimes. To resolve this issue, we have located 10 sample complexes (1 kilometer on a side) within each of the indicator regions (14 and 17) (Fig. 1) using a stratified random approach (peat depths, general elevation, and snail kite nest density). Water levels will be continuously monitored in each complex. Each complex is subdivided into a grid 100-m on a side. Replicate ground surface elevations will be measured (survey-grade GPS) in each major plant community types (as per vegetation maps as per above) near the intersection points in the grid. Elevations will be surfaced for each of the plant types separately in each grid by confining kreiging routines for the elevations for that plant type only within polygons labeled for that type. This is repeated for each plant type and each cell. Polygons are re-composited and merged in a GIS providing a topographic database driven by plant community types. Stage data for the sample complex will be relativised to elevation data specific to each plant community type creating stage duration curves for each vegetation type in the individual cells. Long term and predicted hydroperiod and depth duration data for each vegetation type in each cell will be generated by statistical regression with the nearest permanent gauging station.

3) Establishment of permanent transects plots across elevation gradient in each Indicator Region. Permanent monitoring plots (combinations of quadrats and transects) have been established in the sample complexes across the local elevation gradient in each complex. Regularly placed multiple or replicate quadrats arrayed as continuous belts along a transect perpendicular to the elevation gradient within each sample complex. Each site is sampled seasonally (3 times/yr) for species numbers, stem counts and biomass (both living and standing dead). Water depths are monitored continuously within each sample complex for determinations of hydroperiods and depth duration curves. Each complex consists of three belt transect complexes, 5 plots of the principal habitat types (sawgrass, wet prairie, sloughs), and 5 permanent tree island/shrub heads plots sites typical of kite nest habitat. Multivariate techniques (NMS and multivariate regression tree, and structural equation models) will be used to resolve relationships between plant community structure and hydrology. Structural equation modeling (SEM) will define statistical correlations among species and associated hydrologic and other environmental parameters and provide probabilistic measures for environmental mechanisms involved in plant community succession.

Figure 1. Image of WCA-3A indicating IR and sample complex locations.

Kitchens, Wiley, Florida Cooperative Fish and Wildlife Research Unit, Bldg. 810, University of Florida, Gainesville, FL 326211- Phone: 352-836-0536, Fax: 352-846-0841, , Ecology

This is for oral presentation in the ecology sessions.