Seasonal variation of plant communities and their environments along a topographic gradient in the Ibera wetland, ancient Parana floodplain, Argentina

Recently, wetlands have declined worldwide due mainly to habitat loss by human activities. In order to achieve a better understanding of the impacts that are being generated on the Thera wetland in northeastern Argentina, the objective of this study is to analyze seasonal variation of the environments present in the sandy ridges areas of this wetland. The different environments were identified and characterized according to their topography, vegetation physiognomy and dominance of species. In addition, the seasonal variation in the vegetation communities occurring in the different environments was analyzed and characterized in terms of floristic composition, abundance-cover and attributes. A thematic map of environments was generated and validated through the analysis of abundance-cover of the vegetation. Surveys were conducted seasonally, resulting in a total of 600 plots randomly selected. The percentage of dry matter, bare ground, vegetation-free water surface, vegetation height and depth of the water column were determined where appropriate. Six environments were identified: the upland areas, the temporary ponds, the upper and lower transition zones (between aquatic and terrestrial environments), the low-lying area and the "embalsados" (with aquatic-palustrine species). The environment classification suggests that the topographic gradient and associated edaphic factors would determine the presence of the different communities. The great intra-annual variation in water regime originating from seasonal precipitation in the study area produces a variety of plant communities. The patterns of plant zonation in this wetland are changed from season to season as water levels fluctuate in space and time making the system very susceptible to changes in the hydrometric level.