FLUCTUATIONS IN SAWGRASS AND CATTAIL DENSITIES IN EVERGLADES-WATER-CONSERVATION-AREA-2A UNDER VARYING NUTRIENT, HYDROLOGIC AND FIRE REGIMES

A 6 year ( 1986-1991) study in Water Conservation Area 2A (WCA2A), a r emnant portion of the Florida Everglades, was conducted in which multi ple plots within six study sites across a surface water nutrient gradi ent were monitored for water quality, depth, and sawgrass (Cladium jam aicense Crantz) and cattail (Typha domingensis Pers.) densities. A neg ative logarithmic relationship was demonstrated between total P concen trations and distance from the nutrient source (levee L-39). Dense cat tail stands illustrated by remote sensing in 1987 coincided spatially with high sediment total P concentrations measured in 1990. Cattail de nsity appeared to increase more rapidly than did sawgrass densities du ring wet years. Cattail decline was greater at nutrient enriched sites than at the low nutrient site during dry years. Drought stimulated sa wgrass expansion at nutrient enriched sites, but not at the low nutrie nt site. Cattail increased at both nutrient enriched and low nutrient sites following fire, yet fire and nutrient enrichment together appear ed to stimulate greater increases in cattail density. Multi- and univa riate ANOVA revealed significant nutrient effects on plant density dur ing the last 3 years of the study (P< 0.05). Stepwise regression analy sis suggested that total P loading into WCA2A best explained plant den sity fluctuations at three of the four sites closest to the levee, whi le hydrology best explained plant density fluctuations at the site mos t distant from the levee. Although the single low nutrient site provid ed an inadequate basis for understanding sawgrass and cattail dynamics under low nutrient conditions, the results of this study support two hypotheses of causal factors leading to the spread of cattail in WCA2A : (1) nutrient enrichment stimulates cattail growth; (2) a prolonged h ydroperiod is conducive to cattail proliferation.