Postfire seed bank dynamics in semiarid grasslands S. Gonzalez Æ L. Ghermandi Received: 23 November 2007 / Accepted: 25 March 2008 / Published online: 8 April 2008 Ó Springer Science+Business Media B.V. 2008 Abstract We evaluated the combined effects of fire after drought on the seed bank composition and its role in the postfire recovery of NW Patagonia grasslands. During three years, we monitored the seed bank and the aboveground vegetation. Species were arranged in functional groups and Detrended Correspondence Analysis was used to separate sites according to species and functional groups. Similarity between aboveground vegetation and seed bank was calculated with SØrensen Index. In the first year, the seed density was similar in the control and burned sites and was lower than following years in all the sites. The species that survived the high temperatures were all annuals with the exception of the perennial species Fabiana imbricata and Rumex acetosella. In the second postfire year, the diversity and seed density increased due to the contribution of fugitive species (rare in the community) and exotic annual species. Seed bank of perennial species was the most affected by fire and just recovered in the third year. Drought did not affect the similarity between the seed bank and vegetation. Fire had low impact on the total seed bank, probably due to the heat buffering nature of the soil, whereas drought reduced significantly seed bank size and richness. Seed bank contributes to grassland richness maintenance. Keywords Drought  El Nin ˜o/Southern Oscillation  Fire  Functional groups  Patagonia  Seed bank regeneration Introduction Grassland fires are large scale disturbances, which drive non-linear processes that induce vegetation changes (Westoby et al. 1989; Bond 2005). Fires destroy biomass and release resources, principally space and light (Whelan 1995). Postfire recovery depends on the characteristics of plants (e.g., resp- routers and seeders) and on the meteorological conditions before fire (Bond and van Wilgen 1996). Drought conditions dry the biomass of grasses increasing fire damage, and limit seed production, seed germination, and seedling establishment (Til- man and Downing 1994). Thus both fire and drought will have important implications on grasslands diversity and richness. Most of postfire seed bank studies have been focused in Mediterranean shrublands and savannas (Ferrandis et al.1999; Valbuena and Trabaud 2001; Andrade et al. 2002; Esposito et al. 2006) being few in temperate grasslands (Gonzalez 2002; Alzuguray et al. 2003; Snyman 2005). Fire effect is opposite in different communities showing low impact (Gonzalez S. Gonzalez (&)  L. Ghermandi Laboratorio Ecotono, INIBIOMA, CRUB-UNCo., Quintral 1250, 8400 Bariloche, Argentina e-mail: sgonzalez@crub.uncoma.edu.ar 123 Plant Ecol (2008) 199:175–185 DOI 10.1007/s11258-008-9422-1