Soil seed bank dynamics in the rare obligate seeding shrub, Grevillea barklyana (Proteaceae)

Grevillea barklyana is a rare, obligate seeding shrub that occurs in fire‐prone heath and woodland in southeastern Australia. The size and dynamics of the soil seed bank were investigated in populations 2–29 years after fire in order to identify fire frequencies that would threaten population survival. Plants began flowering 2 years after fire (16%), but maximum inflorescence and seed production did not occur until 15–16 years after fire when plants were full size. Seed production declined in older populations. Fruit:flower ratios were very low (0.1–5.3%). Most flowers (> 95%) failed to initiate fruits. Of the initiated fruits, about 60% aborted, 27% were attacked by parrots and 13% matured. An exclusion experiment showed that fruits attacked by parrots would have otherwise matured. Seeds were consumed on the soil surface by mammals, particularly rodents. Post‐dispersal seed losses were consistently high in all months and in all populations (78–100%). Mortality of adult plants increased with time since fire. In the 29‐year‐old population, 30% of plants were dead and 33% were senescent. Recruitment was negligible in the absence of fire, but following fire the seedling to parent ratio was 20:1. Seedling survival was high (90%) following two years of above‐average rainfall. The observed seed bank was small (3–16 seeds irr) and increased during the first 16 years after fire before declining in the 21‐ and 26‐year‐old populations. The size and dynamics of the seed bank may limit population numbers, especially if the intervals between fires are less than 10 years or greater than 25 years.