FLORISTIC FLUCTUATIONS IN ANNUAL PASTURES - THE ROLE OF COMPETITION AT THE REGENERATION STAGE

Many studies have shown the existence of large between-year fluctuatio ns in the floristic composition of annual Mediterranean pastures, and these fluctuations have been linked to autumn rainfall patterns. It ha s been postulated that differing interannual weather patterns may play a decisive role in competitive processes, especially during the perio d of germination and seedling establishment. Removal experiments in co njunction with rainfall manipulation in a phytotron were conducted to test whether competition affects germination and seedling mortality un der different autumn rainfall patterns, in pastures at three successio nal stages after last being ploughed. Early and late autumn rains affe ct the floristic composition as certain species germinate better under certain conditions than others in each successional stage. In general , however, competition is not manifested through the inhibition of new germination once the space has been occupied, and density-dependent m ortality is found only for a few species.