The replacement of sawgrass by cattail in areas of the historically oligotrophic Everglades has resulted from decades of phosphorus loading from surrounding agricultural areas. Recently, phosphorus loads to the Everglades have decreased through the implementation of Best Management Practices and the creation of Stormwater Treatment Areas. Along with the declining nutrient input, a process of natural recovery of the impacted areas is expected. However, natural recovery is expected to take too long and options for accelerating the recovery of the impacted areas are being explored. Prescribed fire has been identified as one possible option to accelerate the recovery of the impacted areas since fire can alter the biogeochemistry of phosphorus in enriched systems which may lead to a shift of the dominating species. We developed a process-based Wetland Ecosystem Model (WEM) to simulate the effects of fire on phosphorus cycling and plant growth and applied it to a cattail dominated nutrient-enriched area of Water Conservation Area 2A (WCA-2A) in the Everglades Protection Area. The WEM is a spatially-explicit biogeochemical model that integrates the interactions of carbon, nitrogen and phosphorus, vegetation community composition and dynamics, and water flow and balance. The model was evaluated against data from a three year field experiment in the area. Then we applied the WEM to the entire WCA-2A at a spatial resolution of 300m×300m to simulate fire effects on phosphorus cycling and plant growth when one grid was burned in a cattail dominated area with high P enrichment.
Results/Conclusions
The simulated results showed the capacity of WEM in capturing post-fire vegetation recovery processes and nutrient dynamics in water and soil. Within the burned grid cattail biomass reallocation was influenced but did not cause a shift in dominating species of the vegetation community. Water total phosphorus within the burned grid increased immediately after the fire but was back to normal in several weeks. The pulse of phosphorus released from the fire was transported downstream from the burned grid in a discreet plume which lasted about two months. Soil phosphorus, on the other hand, showed no major response to fire. To better simulate biogeochemical cycling and vegetation dynamics in wetland ecosystems, we need to take into account more complex processes of plant communities including competition, vegetation recruitment and seed dispersal. More research is needed to quantify the role of prescribed fires for active management to aid in the recovery of nutrient-impacted areas in the Everglades.
