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

Exceptionally heavy flowering and fruiting (masting) was observed in t he semi-arid perennial tussock grass Stipa tenacissima L. in south-eas tern Spain during the 1993 growing season. High winter rainfall, high spring temperatures, and exceptionally high June rainfall in combinati on with below average temperatures provided favourable environmental c onditions for floral initiation in the preceding growing season. Quant itative 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 whic h normally reproduces vegetatively by tillering. Heavy predation of th e soil seed bank by seed-harvesting ants was observed. (C) 1995 Academ ic Press Limited.