A spatially distributed,deterministic approach to modeling Typha domingensis(cattail)in an Everglades wetland

Introduction:The emergent wetland species Typha domingensis(cattail)is a native Florida Everglades monocotyledonous macrophyte.It has become invasive due to anthropogenic disturbances and is out-competing other vegetation in the region,especially in areas historically dominated by Cladium jamaicense(sawgrass).There is a need for a quantitative,deterministic model in order to accurately simulate the regional-scale cattail dynamics in the Everglades.Methods:The Regional Simulation Model(RSM),combined with the Transport and Reaction Simulation Engine(TARSE),was adapted to simulate ecology.This provides a framework for user-defineable equations and relationships and enables multiple theories with different levels of complexity to be tested simultaneously.Five models,or levels,of increasing complexity were used to simulate cattail dynamics across Water Conservation Area 2A(WCA2A),which is located just south of Lake Okeechobee,in Florida,USA.These levels of complexity were formulated to correspond with five hypotheses regarding the growth and spread of cattail.The first level of complexity assumed a logistic growth pattern to test whether cattail growth is density dependent.The second level of complexity built on the first and included a Habitat Suitability Index(HSI)factor influenced by water depth to test whether this might be an important factor for cattail expansion.The third level of complexity built on the second and included an HSI factor influenced by soil phosphorus concentration to test whether this is a contributing factor for cattail expansion.The fourth level of complexity built on the third and included an HSI factor influenced by(a level 1–simulated)sawgrass density to determine whether sawgrass density impacted the rate of cattail expansion.The fifth level of complexity built on the fourth and included a feedback mechanism whereby the cattail densities influenced the sawgrass densities to determine the impact of inter-species interactions on the cattail dynamics.Results:All the simulation results from the different levels of complexity were compared to observed data for the years 1995 and 2003.Their performance was analyzed using a number of different statistics that each represent a different perspective on the ecological dynamics of the system.These statistics include box-plots,abundance-area curves,Moran’s I,and classified difference.The statistics were summarized using the Nash-Sutcliffe coefficient.The results from all of these comparisons indicate that the more complex level 4 and level 5 models were able to simulate the observed data with a reasonable degree of accuracy.Conclusions:A user-defineable,quantitative,deterministic modeling framework was introduced and tested against various hypotheses.It was determined that the more complex models(levels 4 and 5)were able to adequately simulate the observed patterns of cattail densities within the WCA2A region.These models require testing for uncertainty and sensitivity of their various parameters in order to better understand them but could eventually be used to provide insight for management decisions concerning the WCA2A region and the Everglades in general.

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

Introduction:Although 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.Methods:In 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.Results:The analyses showed that five months after the fire,sawgrass biomass re-growth was about 5 times higher in burned areas(611±47 g/m^(2))than in non-burned areas(102±18 g/m^(2)).Sawgrass re-growth in water depths less than 30 cm was 4.9±0.4 g/m^(2)/day while sawgrass re-growth in water depths deeper than 60 cm decreased to 0.5±0.3 g/m^(2)/day.Cattail biomass re-growth in peat-burned areas was as high as 1,079±38 g/m^(2).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.Conclusions:The 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.