Fluctuations in sawgrass and cattail densities in Everglades Water Conservation Area 2A under varying nutrient, hydrologic and fire regimes

Abstract

A 6 year (1986–1991) study in Water Conservation Area 2A (WCA2A), a remnant portion of the Florida Everglades, was conducted in which multiple plots within six study sites across a surface water nutrient gradient were monitored for water quality, depth, and sawgrass ( Cladium jamaicense Crantz) and cattail ( Typha domingensis Pers.) densities. A negative logarithmic relationship was demonstrated between total P concentrations and distance from the nutrient source (levee L-39). Dense cattail stands illustrated by remote sensing in 1987 coincided spatially with high sediment total P concentrations measured in 1990. Cattail density appeared to increase more rapidly than did sawgrass densities during wet years. Cattail decline was greater at nutrient enriched sites than at the low nutrient site during dry years. Drought stimulated sawgrass expansion at nutrient enriched sites, but not at the low nutrient site. Cattail increased at both nutrient enriched and low nutrient sites following fire, yet fire and nutrient enrichment together appeared to stimulate greater increases in cattail density. Multi- and univariate ANOVA revealed significant nutrient effects on plant density during the last 3 years of the study ( P<0.05). Stepwise regression analysis suggested that total P loading into WCA2A best explained plant density fluctuations at three of the four sites closest to the levee, while hydrology best explained plant density fluctuations at the site most distant from the levee. Although the single low nutrient site provided 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 hydroperiod is conducive to cattail proliferation.