The Autecology of Sawgrass in the Florida Everglades

Abstract

Investigations were conducted in 1971 and 1972 to characterize typical stands of sawgrass (Cladium jamaicense Crantz) in the southern Everglades. Estimates were obtained of standing crop, plant density, stem length, leaf numbers, growth rate, and nutrient relationships in plant tissue, soil, and water. Measurements were also made of daily rainfall and water depths. These various parameters were estimated monthly over a 12—18 mo period in mature stands, as well as in stands regrowing after wild fires. The mature stands showed little seasonal variation in standing crop, plant density, and concentration of most inorganic nutrients. Plant nutrient requirements were estimated to be low, because tissue levels of nutrients were low as compared to those of other species of Everglades macrophytes. Copper (Cu) and phosphorus (P) were particularly low. Levels of available nutrients in soil varied, with no seasonal pattern. Most nutrients were in adequate supply, except that available nitrogen (N), P, potassium (K) and Cu were generally very low. Reserve soil supplies of N and P were plentiful, but not of K. Accumulation of K in sawgrass leaves was more closely related to reserve supplies in soil than to available soil supplies. Waters in the marsh contained on an average 3%, 10%, and 8%, respectively, of the N, P, and K contained in a comparable area of sawgrass standing crop. Concentration of most nutrients in culms regrowing after fires was high during early growth stages, but decreased to levels found in older culms after 3—5 mo. Conenctrations of calcium (Ca), iron (Fe), and zinc (Zn) were exceptions, however. During the 1st year's growth after fires, 1 ha of sawgrass had accumulated 48 kg N, 1.8 kg P, and 38 kg K. After 18 mo growth, burned stands of sawgrass had produced only 38% of the standing crop contained in unburned mature stands. The apparent low nutrient requirements of sawgrass may partially explain the dominance of this plant in the marsh community.

Spatial Dependency of Vegetation?Environment Linkages in an Anthropogenically Influenced Wetland Ecosystem

“…Within the Transition and Reference zones, highest N (and K) concentrations were associated with periphyton mats and slough-community species, particularly the water lily Nymphaea odorata. Decomposing Nymphaea tissue has been shown to have greater N concentrations than more recalcitrant species like Cladium (Steward and Ornes 1975b;J. Vymazal unpublished data).…”

“…Fire disturbance was expected to play a role in vegetation pattern because Cladium is considered fire tolerant (Steward and Ornes 1975b), and intense fires are believed to be partially responsible for maintaining the sawgrass-slough mosaic (Craighead 1971;Gunderson and Snyder 1994). A composite map of recent, large fires constructed using aerial photographs indicated that more than 50% of WCA-2A had burned at some point during 1981-98 (Florida Game and Freshwater Fish Commission unpublished data).…”

Resilience, Flexibility and Adaptive Management - - Antidotes for Spurious Certitude?

“…The resulting landscape mosaic had small areas of enhanced nutrients or eutrophy in tree islands that were maintained by wading bird nesting, or in local refugia maintained by the cycles of flooding and drydowns that first collected diffuse energy and then concentrated it locally. The remainder of the landscape (sawgrass marshes and wet prairies) adapted to low nutrient thresholds (Steward and Ornes 1975).…”

Macroinvertebrate and Fish Responses to Experimental P Additions in Everglades Sloughs

“…One of the most publicized perturbations to the system has been excessive inputs of phosphorus (P). The Everglades is a P-limited ecosystem, and its biota are adapted for survival under highly oligotrophic conditions (e.g., Browder 1982, Steward and Ornes 1975a, Steward and Ornes 1975b, Swift and Nicholas 1987, Davis 1991. Indeed, numerous experiments have demonstrated the sensitivity of Everglades biota to P enrichment.…”