SEED PRODUCTION AND DISPERSAL IN THE SEMIARID TUSSOCK GRASS STIPA-TENACISSIMA L DURING MASTING

Exceptionally heavy flowering and fruiting (masting) was observed in the semi-arid perennial tussock grass Stipa tenacissima L. in south-eastern Spain during the 1993 growing season. High winter rainfall, high spring temperatures, and exceptionally high June rainfall in combination with below average temperatures provided favourable environmental conditions for floral initiation in the preceding growing season. Quantitative data on spike production per plant, mean number of flowers and fruits per spike, dry mass and potential viability of seeds, and seed density on the ground are presented, as well as preliminary estimates for pre- and post-dispersal predation. The data show high allocation to sexual reproduction, although S. tenacissima is a clonal plant which normally reproduces vegetatively by tillering. Heavy predation of the soil seed bank by seed-harvesting ants was observed. (C) 1995 Academic Press Limited.