Use of morphological variability in Cladium jamaicense and Typha domingensis to understand vegetation changes in an Everglades marsh

摘要

The northern Florida Everglades have experienced an expansion of cattail (Typha domingensis) and a decrease of sawgrass (Cladium jamaicense) communities. In this study, spatial and temporal within-species variability in plant performance were used to explore the mechanisms causing the distributional changes of cattail and sawgrass. Biomass, shoot density, plant weight, shoot height, and biomass allocation to different plant components (leaves, shoot bases, roots and rhizomes), were sampled in cattail and sawgrass stands along a nutrient gradient within water conservation area 2A during two sequential years with different water level conditions. The shoot height-leaf weight relationships were analysed with allometric methods. Sawgrass exhibited responses to nutrient limitation that resembled functional responses to deep water, indicating that impact of deep water was stronger when plant growth was limited by nutrient deficiency. In cattail, responses along the nutrient gradient were less pronounced. Plant responses along the nutrient gradient differed between years. This was most evident in sawgrass, showing that this species was more affected by water depth than cattail. Responses in sawgrass suggested that this species had to sacrifice important plant functions in deep water at low-nutrient sites. The results in this study emphasise that, to preserve and restore sawgrass communities, lower water levels are required. For cattail, a combination of low phosphorus availability and disturbances (such as extended droughts and outbreaks of herbivores) is needed to stop the ongoing expansion. Management of these ecosystems must consider the relative roles of water level, nutrient enrichment, and disturbances, for vegetation development