Variation in vegetation and seed bank in a Chilean semi-arid community affected by ENSO 1997

We followed plant cover and soil seed density of shrubs and herbs in two markedly contrasting years with regard to annual rainfall in two opposite-facing slopes (mesic vs xeric) and an intervening, relatively wet, ravine of a typical creek in semi-arid Chile. During the ENSO year 1997 cover of ephemerals increased in all three sites; 43% vs 8% on the xeric slope 75% vs 26% on the mesic slope and 57% vs 32% in the ravine. The number of species was almost three times higher. On the xeric slope (27 vs 10 species), increased by 47% on the mesic slope (28 vs 19) and by 14% in the ravine (24 vs 21). Cover of shrubs plus perennial grasses increased from 52% in 1996 to 59% in 1997 on the xeric slope, but no significant cover changes were found on the mesic slope or the ravine. On the xeric slope peak density of seeds was 4500/m(2) in 1996, while during the ENSO year it was 24000/m(2). On the mesic slops equivalent values were 3000 and 17000 seeds/m(2) while in the ravine figures were 8500 and 27000 seeds/m(2). The strong responses of ephemerals and seed bank to the ENSO-driven wet year of 1997 demonstrate the importance of this phenomenon in replenishing, recovering and probably maintaining ephemeral vegetation in this region.