Banco de semillas del suelo en un pastizal de una reserva natural del Sistema de Tandilia (Buenos Aires, Argentina) invadido por Racosperma melanoxylon

Abstract

The restoration of natural grasslands invaded by exotic plant species depends on the composition of the soil seed bank. We analyzed the composition of germinable soil seed bank in two environments of the Paititi Natural Reserve (Buenos Aires, Argentina): Paspalum quadrifarium Lam. grasslands (natural grassland) and grasslands invaded by species of exotic trees that were no more than five years old, Racosperma melanoxylon (R. Br.) Pedley, synonymous Acacia melanoxylon (invaded grassland). Soil samples from each environment were taken at three sites, and by recording seedling emergence under controlled conditions we determined: 1) the total soil seed bank density of the functional groups (dicots, grasses and graminoids), richness, equitability and diversity indices, and specific abundance, 2) floristic dissimilarity,and 3) zootechnical value. The seed bank of native and exotic species was not significantly different between environments. Average seed bank density and species richness were not significantly different between environments (~10000 seeds/m2 and 30 species, respectively). Seed density of the functional groups and the diversity and equitability indices were not significantly different between environments. Still, floristic dissimilarity among environments was as low as 0.36, explained by the absence of a greater number of species in the invaded grassland. The seed bank of invaded grasslands was poor in forage species, consistent with a zootechnical value 26% lower than in the natural grassland. In the invaded grassland all P. quadrifarium plants were dead and their germinable seed bank was a third than in the natural grassland. The results suggest that an early intervention removing R. melanoxylon trees in the grassland invaded may preserve a soil seed bank comparable to those uninvaded grassland.