ECOLOGICAL-STUDIES OF THE ENDANGERED RUTIDOSIS LEPTORRHYNCHOIDES .1. SEED PRODUCTION, SOIL SEED BANK DYNAMICS, POPULATION-DENSITY AND THEIREFFECTS ON RECRUITMENT

The seasonal dynamics of the soil seed bank of Rutidosis leptorrhyncho ides F.Muell. were studied by the seedling emergence technique. Seed l ongevity in soil was quantified in a seed burial and retrieval experim ent. The importance of annual seed production to recruitment was also determined over a 2-year-period, as was the impact of conspecific neig hbour density on seed production per inflorescence. Rutidosis leptorrh ynchoides appears to form a transient seed bank with little capacity t o store germinable seeds in the soil from year to year. No seedlings w ere observed in soil sampled after the autumn germination pulse and no viable seed was present in the soil within 16 weeks of burial. The ra te of seed loss was similar when seed was buried under an intact grass land canopy and in 0.25m(2) canopy gaps. It appears that most seeds si mply rot in moist soil or are predated by soil invertebrates. Seedling recruitment was at least 15 times greater in plots where natural seed input occurred than where it was curtailed. Less than 10% of seed she d resulted in seedling emergence. It is suggested that recruitment in the large populations studied was limited by germination rather than b y microsite availability for seedling survival. Population density had an impact on seed production with sparsely distributed individuals pr oducing fewer seeds per inflorescence than plants from denser colonies , although there was much variation. Sparse plants produced significan tly fewer seeds per inflorescence than hand cross-pollinated heads sug gesting reduced pollinator efficacy in these colonies relative to larg er colonies where there was no such difference. Rutidosis leptorrhynch oides is dependent on the maintenance of the standing population for r ecruitment. Any factors that influence flowering and subsequent seed p roduction will limit the ability of the species to regenerate. Over su fficient time, this could lead to the localised extinction of the spec ies and may explain why R. leptorrhynchoides has failed to reappear in remnants where a suitable fire regime has been re-implemented after a period of management unfavourable to the survival, flowering and rege neration of this species.