Wetlands of the Magellanic Steppe (Tierra del Fuego, Argentina)

Abstract

Our main objective was to classify vegetation and soils of wetlands in northern Tierra del Fuego (Argentina) along a latitudinal precipitation gradient within the Magellanic Steppe Zone. We presented the first detailed ecological characterization of these wetlands by relating floristic composition to local site conditions, bedrock and climate. The survey consisted of 125 phytosociological censuses and 52 soil profile descriptions. Soils were classified according to FAO, and vegetation samples were explored by applying numeric methods such as cluster analysis and indirect ordination that included a post-hoc correlation with environmental variables. Floristic composition of freshwater communities was strongly related to a latitudinal gradient, and to soil pH, base cations and C/N ratio. Most eutrophic marshes were found on organic soils situated in springs on Tertiary sediments at mid-latitudes. Most acidic marshes occurred within Pleistocene catchment areas at higher latitudes (higher precipitation). Wet grasslands on mineral soils of low C/N ratio within formerly glaciated areas at lower latitudes (lower precipitation) represented the dry end of the moisture gradient covered by this study. Saltwater communities predominated on playas of Tertiary sediments and in estuarine systems. They were characterized by alkaline soils and high Na concentrations. Magellanic wetlands form a floristic continuum from the semiarid north to the subarid south with composition not necessarily related to landscape position and soil units, but strongly related to soil variables of secondary taxonomic level. We conclude that at least at the resolution level of our study, floristic composition along the observed gradient is strongly influenced by regional climate.