Macrophyte Community Responses in the Everglades with an Emphasis on Cattail (Typha domingensis) and Sawgrass (Cladium jamaicense) Interactions along a Gradient of Long-Term Nutrient Additions, Altered Hydroperiod, and Fire

Collectively, these studies suggest that multiple factors are responsible for the alteration and maintenance of plant community structure in the Everglades (Fig. 9.1). Historically, the primary factor controlling the long-term development of all Everglades communities is climate. The native seed bank was responsible for the regeneration of endemic plant communities once they were disturbed or altered (van der Valk and Rosburg 1997). Massive landscape development has resulted in regulated hydroperiods (i.e., the number of days that the Everglades ecosystem has standing water at or near the surface) and altered hydropatterns (the distribution of water within the wetland), which in turn have changed fire frequency patterns and fire intensity. Increased P and N loadings from agriculture and urban runoff and introduced exotic species in the early 1900s have all significantly affected plant and animal communities of the Everglades and the Water Conservation Areas (WCAs) of today (Craft and Richardson 1993a; Davis and Ogden 1994a; DeBusk et al. 1994; Qualls and Richardson 1995; Vaithiyanathan and Richardson 1997). Importantly, it has been demonstrated by numerous studies that P is the limiting plant nutrient in the Everglades (Steward and Ornes 1983; Koch and Reddy 1992; Richardson and Vaithiyanathan 1995; Craft and Richardson 1997; Richardson et al. 1999; Noe et al. 2001).

The main difficulty for ecologists is in separating the influence of primary climate-driven factors like rainfall, hydroperiod, and fire from the secondary human factors of drainage and flooding, nutrient additions, site disturbance, and exotic species invasions. Moreover, the influence of anthropogenic inputs of nutrients and water varies greatly in each portion of the Everglades depending on proximity to canal input structures, mode of delivery (i.e., point or nonpoint source), and whether water delivery is seasonally pulsed or continuously released. In other regions like WCA-3A vast stands of exotic species, such as Melaleuca quinquenervia and Schinus terebinthifolius (Brazilian pepper) provide a seed source for the everincreasing invasions by these species, although intensive and expensive control measures are underway by state and federal agencies.