Productivity Dynamics of a Native Temperate Grassland in Argentina

Studies of aerial net primary productivity (ANPP) were made on a grassland that had been excluded from livestock grazing for four years. ANPP was calculated by summation of individual species and corrections based on fluctuations of standing dead litter. The grassland produced a minimum of 4 kg of dry material ha-' d1' in the fall and a maximum of 30 kg of dry material -ha 1d - during the spring. Salado River Basin occupies an area of 5,800,000 ha in Buenos Aires Province, Argentina, 80% of which is covered by native grassland utilized for cattle production. The proximity of the area to the city of Buenos Aires makes it important as a source of beef to this large area of population. The general aspect of the basin is that of an extensive plain with little or no slope. This results in a great number of permanent ponds and areas subjected to frequent flooding. However, vegetation of the area also suffers from severe summer droughts because of shallow soils. Climate is temperate and humid. Annual precipitation is 900 mm of rainfall that is evenly distributed throughout the year. No snow deposition occurs. This mild weather permits the grasses to maintain productivity during the entire year. The objectives of this study were to describe the (1) dynamics of the aerial biomass and (2) the dynamics of the aboveground net primary productivity (ANPP) of a native grassland of the Salado River Basin and of its major species throughout an entire year. The study was conducted in one of the most conspicuous communities of the basin. This community was described by Leon (1975) using Braun-Blanquet (1950) techniques and named Piptochaetium montevidense, Ambrosia tenuifolia, Eclipta bellidioides, and Metha pulegium.