Ken Rutchey

The ecological–societal underpinnings of Everglades restoration

The biotic integrity of the Florida Everglades, a wetland of immense international importance, is threatened as a result of decades of human manipulation for drainage and development. Past management of the system only exacerbated the problems associated with nutrient enrichment and disruption of regional hydrology. The Comprehensive Everglades Restoration Plan (CERP) now being implemented by Federal and State governments is an attempt to strike a balance between the needs of the environment with the complex management of water and the seemingly unbridled economic growth of southern Florida. CERP is expected to reverse negative environmental trends by “getting the water right”, but successful Everglades restoration will require both geochemical and hydrologic intervention on a massive scale. This will produce ecological trade-offs and will require new and innovative scientific measures to (1) reduce total phosphorus concentrations within the remaining marsh to 10 µg/L or lower; (2) quantify and link ecolo...

ANALYSIS AND SIMULATIONS OF FRAGMENTATION PATTERNS IN THE EVERGLADES

Sawgrass (Cladium jamaicense) communities of Water Conservation Area 2A (WCA-2A), a 43281 ha Northern Everglades impoundment, are being invaded by cattail (Typha spp.). Results from analyses suggest that the yearly invasion rate of cattails has increased from 1% in 1973 to 4% by 1987. The total area of the landscape impacted by cattail increased from <5% (2054 ha) in 1973 to more than one-third of the landscape (16017 ha) by 1991. The landscape also became more fragmented. The number of sawgrass patches increased from 173 in 1973 to 5709 by 1991. During the same period the lacunarity index of sawgrass changed from 2.8 to 3.9. The effects of agricultural phosphorus (P) runoff and water depth (D) on invasion of cattail were expressed as, Probpe = 1/(1 + αe−βP) + ζD/P. The threshold for accelerated cattail invasion was estimated at ≈650 mg/kg soil total phosphorus. Cattail dispersal was mostly spatially dependent. For a given year, the probabilities of sawgrass changing to cattail based on the number of 1–8 adjacent cattail cells (20 × 20 m) were calculated to be Probad = [0.049 0.052 0.061 0.065 0.069 0.072 0.076 0.094]. The probabilities Probpe and Probad were used as Markov chain probabilities in a spatial model to simulate vegetation dynamics. The simulated landscape matched the actual landscape with an overall accuracy of 72.8% and predicted that cattail would invade 50% of WCA-2A in another 6–10 yr if the driving forces remain unchanged.

Distribution of Wading Birds Relative to Vegetation and Water Depths in the Northern Everglades of Florida, USA

Abstract The response of Great Blue Herons (Ardea herodias), Great Egrets (Casmerodius albus), Wood Storks (Mycteria americana), and White Ibises (Eudocimus albus) to water level (index of depth) and vegetation in the northern Everglades of Florida was studied in two years, each with dissimilar water levels. A regression model was constructed for each species in an average year (1988) and a dry year (1989) to examine the relationship of bird abundance to water depth and area of eight vegetation classes. The analyses showed that bird abundance is related to both water level and the vegetation community, but water level generally had the greatest effect. Models showed that in the average year (1988), there was a water level threshold, above which bird abundance was predicted to decline. The level threshold varied among species and may have reflected species-specific foraging constraints. However, in the dry year (1989), the relationship between bird abundance and water level was positive and linear, indicating that few places had water deeper than the thresholds observed in the average year. Overall, the area of slough vegetation appeared to have the second greatest effect on bird abundance. Generally, all models had low coefficients of determination (R2 range 0.06-0.42) suggesting that factors other than water level and vegetation were important, or birds were responding to variables in the model, but at different spatial scales than that which the data were collected. Models for Great Blue Herons and Great Egrets had higher coefficients of determination than models for Wood Storks and White Ibises. The more solitary feeding behavior of the herons and egrets resulted in a more even distribution across the marsh than for storks and ibises, which were usually found in flocks. Our study suggests that if restoration of the Everglades results in more natural hydrologic cycles, an increase in the amount of slough habitat, and a decrease in the proportion of cattails, foraging conditions for wading birds may improve.

MULTIPLE REGIME SHIFTS IN A SUBTROPICAL PEATLAND: COMMUNITY-SPECIFIC THRESHOLDS TO EUTROPHICATION

Ecosystems have a natural resilience to perturbations, where resilience is the magnitude of a disturbance that an ecosystem can resist before changes in structure, function, and services result in a regime shift. The Everglades region of Florida, USA, has been detrimentally impacted by phosphorus (P) enrichment and a regime shift from Cladium (sawgrass) to Typha (cattail) marsh has been described. We examine another facet of the low nutrient Everglades stability regime, open-water sloughs, to determine if eutrophication leads to similar regime shifts. We analyzed surface water P and soil P as controlling variables that, once a critical threshold is surpassed, alter ecosystem state variables. Nonlinear relationships between P and vegetation were observed along a northern Everglades eutrophication gradient. In addition to the Cladium-Typha regime shift, a second independent regime shift, slough-Typha, was identified. Synoptic surveys of 49 sloughs within the boundary between the slough and Typha regime revealed that surface water total phosphorus (TP) and the benthic algal floe layer (BAFL) were the controlling variables, with critical thresholds of 11 ug/L and 412 mg/kg, respectively. The slough regime below these thresholds was characterized by calcareous periphyton (BAFL TP = 298 mg P/kg; BAFL calcium = 149 g Ca/kg). Above the TP thresholds, vegetation composition shifted to open-marsh species with significantly higher BAFL TP (700 mg P/kg) and total organic carbon (TOC) (350 g C/kg). A second BAFL TP threshold occurred at 712 mg P/kg, above which Nymphaea dominated and BAFL TP (1034 mg P/kg) and TOC (417 g C/kg) significantly increased. Nymphaea sloughs transitioned to the Typha regime. The boundary reflects the loss of ecosystem resilience due to eutrophication. Both low-nutrient stability regimes (slough and Cladium) lie precariously close to the P critical threshold but differ in how eutrophication is absorbed and resisted. The slough regime transitions rapidly through a series of ecosystem state changes linked to positive feedback loops that affect P dynamics, whereas the Cladium regime does not. An adaptive management strategy has been implemented to address the surface water TP threshold; however, to ensure successful restoration of the Everglades, the BAFL and soil TP thresholds also need to be considered.

DEVELOPMENT OF VEGETATION MAPS FOR ASSESSING EVERGLADES RESTORATION PROGRESS

One critical component of any wetland restoration program is reliably documenting temporal changes in the spatial extent, pattern, and proportion of plant communities within the landscape. This study describes the development of a 2003 baseline vegetation map for a 42,635 ha wetland impoundment located in the northern portion of the remnant Everglades, Florida. Vegetation communities were photointerpreted and mapped with a 1/4 ha minimum mapping grid unit from 1:24,000 scale color infrared aerial photography utilizing 1st order analytical stereo-plotters. Results show an impoundment that has significantly changed in comparison to an earlier 1940s mapping effort. These included the loss of most of the tree island habitat and the establishment of large expanses of invasive cattail adjacent to and downstream of inflow structures with 28% of the grid cells containing cattail. Our techniques will be very useful in evaluating Everglade’s restoration and are applicable to wetlands around the world.

Fire simulations in the Everglades Landscape using parallel programming

Abstract Fire can significantly influence vegetation patterns in the Everglades. Unfortunately, fire is a difficult process to experimentally manipulate, especially at a landscape level. An Everglades Landscape fire model (ELFM) was developed using parallel-processing algorithms and transputer-processors to understand fire behavior in Water Conservation Area 2A (WCA 2A) in the Everglades. Fuel characteristics, water depth, wind velocity and direction, rainfall, lightning, and humidity determined the physical state and rate at which fire spreading and spotting occurred in the ELFM. The ELFM simulated fire spread across a heterogeneous landscape using a grid-based system. Parallel processing enabled the model to simulate fire on a large spatial scale with fine resolution (i.e., 1755 × 1634 pixels with 20 × 20 m resolution). The model was designed as a multiprocessor program with the ability to compile and run on UNIX workstations, the CM-5 supercomputer, and Mac Transputers with no change in the code. The ELFM was used to conduct a series of fire experiments that indicated how current fire regimes differ from historical ones due to cattail ( Typha spp.) invasion and longer and deeper water depths. In an Everglades dominated by cattail, the predicted average annual area burned and fire frequency were significantly reduced by 23% and 21%, respectively. The ELFM experiments also suggested that altered hydroperiod have changed fire patterns by reducing fire frequency 63% while increasing fire size during drought years. Airboat trails did not significantly influence total area burned in the ELFM. However, they did seem to function as breaks in upwind fires and tended to reduce the size of potentially large fires.

Selection of scale for Everglades landscape models

This article addresses the problem of determining the optimal “Model Grain” or spatial resolution (scale) for landscape modeling in the Everglades. Selecting an appropriate scale for landscape modeling is a critical task that is necessary before using spatial data for model development. How the landscape is viewed in a simulation model is dependent on the scale (cell size) in which it is created. Given that different processes usually have different rates of fluctuations (frequencies), the question of selection of an appropriate modeling scale is a difficult one and most relevant to developing spatial ecosystem models.The question of choosing the appropriate scale for modeling is addressed using the landscape indices (e.g., cover fraction, diversity index, fractal dimension, and transition probabilities) recently developed for quantifying overall characteristics of spatial patterns. A vegetation map of an Everglades impoundment area developed from SPOT satellite data was used in the analyses. The data from this original 20 × 20 m data set was spatially aggregated to a 40 × 40 m resolution and incremented by 40 meters on up to 1000 × 1000 m (i.e., 40, 80, 120, 160 … 1000) scale. The primary focus was on the loss of information and the variation of spatial indices as a function of broadening “Model Grain” or scale.Cover fraction and diversity indices with broadening scale indicate important features, such as tree islands and brush mixture communities in the landscape, nearly disappear at or beyond the 700 m scale. The fractal analyses indicate that the area perimeter relationship changes quite rapidly after about 100 m scale. These results and others reported in the paper should be useful for setting appropriate objectives and expectations for Everglades landscape models built to varying spatial scales.

Spatial Simulations of Tree Islands for Everglades Restoration

The Florida Everglades, a vast wetland dotted with diverse tree islands, is a uniquely difficult wetland to manage because of competing urban, agricultural and environmental water demands. Tree islands in certain sections of the Everglades have experienced altered hydroperiod due to water management practices that has, at times, caused tree island vegetation to die. This study uses the Everglades Landscape Vegetation Model (ELVM) to investigate whether an observed trend in tree island loss is reversible, and if tree islands can be used as performance measures or ecological indicators for the success of Everglades restoration actions. The ELVM was developed and designed to be a tool to understand the spatial and temporal interactions among vegetation, water, fire and nutrients. Simulation results from this model suggest that hydroperiod is a major factor contributing to tree island development and stability in the Everglades. Simulations of the ELVM indicated that tree island water depths greater than 30 cm and hydroperiods longer than 150 days were decreasing tree island survival rates. According to the model, about 60% of tree islands lost in the Water Conservation Area 2A (WCA-2A) in the last few decades can be recovered by restoring the natural hydrological regimes. As a result, tree island health could be used as a performance measure to evaluate the effects of various hydrological restoration alternatives in the Everglades.

Assessing drought-related ecological risk in the Florida Everglades

In the winter-spring of 2001, South Florida experienced one of the worst droughts in its recorded history. Out of a myriad of ecological concerns identified during this time, the potential for catastrophic peat fire and negative impacts to wading bird reproduction emerged as critical issues. Water managers attempted to strike a balance between the environment and protection of water supplies for agriculture and urban interests. It became evident, however, that a broad-scale, integrated way to portray and prioritise ecological stress was lacking in the Florida Everglades, despite this being considered a necessary tool for addressing issues of environmental protection. In order to provide a framework for evaluating various water management operations using real-time information, we developed GIS-based indices of peat-fire risk and wading bird habitat suitability. These indices, based on real physical, chemical, and biological data, describe two ecological conditions that help define the physical and biological integrity of the Everglades. In addition to providing continuous, updated assessments throughout the drought period, we incorporated predictive models of water levels to evaluate how various water management alternatives might exacerbate or alleviate ecological stress during this time.

Impacts of fire and phosphorus on sawgrass and cattails in an altered landscape of the Florida Everglades

IntroductionAlthough fire as a critical ecological process shapes the Florida Everglades landscape, researchers lack landscape-based approach for fire management. The interactive effect of fire, nutrients, water depth, and invasive cattails (Typha spp.) on vegetation communities is of special concern for ecosystem restoration. In particular, questions concerning the effect of fire on nutrient release and, by extension, the potential thereof to stimulate sawgrass (Cladium jamaicense Crantz) re-growth and cattail expansion under varying hydrological conditions are of immediate relevance to ecologists and land managers who work to restore the Everglades.MethodsIn late April of 1999, a 42,875 ha surface fire, including a 100 ha peat fire, burned the northern section of Water Conservation Area 3A (WCA-3A) in the Everglades. In this study, total phosphorus (TP) in soil, surface water, pore-water, and vegetation was sampled at non-burned, surface-burned and peat-burned areas within one and five months after the burn. Four years after the initial fire, field data were collected in a large scale survey to analyze how the 1999 fire affected cattail distribution in the altered landscape of high soil TP and cattail habitats. Existing GIS maps were utilized to select field sampling locations and to provide additional information for the analysis.ResultsThe analyses showed that five months after the fire, sawgrass biomass re-growth was about 5 times higher in burned areas (611 ± 47 g/m2) than in non-burned areas (102 ± 18 g/m2). Sawgrass re-growth in water depths less than 30 cm was 4.9 ± 0.4 g/m2/day while sawgrass re-growth in water depths deeper than 60 cm decreased to 0.5 ± 0.3 g/m2/day. Cattail biomass re-growth in peat-burned areas was as high as 1,079 ± 38 g/m2. The data also showed that post-fire cattail expansion could be related to cattail stands existing before the fire. Furthermore, post-fire cattail appeared more significant expansion in the areas with soil TP above 900 mg/kg than in that with soil TP below 900 mg/kg.ConclusionsThe data showed that fire within altered landscapes (e.g. high soil TP and/or cattail) of the Everglades could stimulate the re-growth and expansion of cattails, and post-fire re-growth of sawgrass could be severely impeded by deep water after a surface-burn. This research indicates that fire continues to be an effective ecological process for maintaining the Everglades; therefore, ecologists and land managers may have to reevaluate the future management of natural fire with regard to its dynamic relationship with high soil TP and cattail expansion in the altered Everglades landscape.