Banco de semillas en ambientes de las sierras de Azul (Buenos Aires, Argentina) con distinta intensidad de disturbios

in order to evaluate the impact of agriculture on the potential flora of grasslands of the sierras of azul (buenos aires province, argentina), the soil seed bank in the top 20 cm from two adjacent areas on the first foothill spurs were compared. one is submitted to continuous agriculture. the other area has grasslands under grazing and non programmed burning. the latter showed a mean density of 70.000 seeds m-2 against a mean density of 36.720 seeds m-2 in the first area. the proportional representation of native species seeds decreased strongly in the agricultural environment. the most abundant species in the grasslands was stipa caudata (31.360 seeds m-2). in the agricultural environment, its density decreased to 9940 seeds m-2. it was surpassed by the density of chenopodium album (10.560 seeds m-2). the similarity in composition of the seed bank was 55% in qualitative terms and 27% in quantitative terms. these results prove that, in the study area, the replacement of grasslands by agriculture reduces strongly the seed reserve in soil and modifies its qualitative and quantitative composition by decreasing the proportion of native species seeds.