Seed Longevity of Six Native Forbs in a Closed Themeda triandra Grassland

Abstract

Seeds of six native forbs̵2Arthropodium strictum R.Br., Burchardia umbellata R.Br., Bulbine bulbosa (R.Br.) Haw., Chrysocephalum apiculatum (Labill.) Steetz, Craspedia variabilis Everett & Doust and Leptorhynchos squamatus (Labill.) Less.-were sown on and below the soil surface in a closed, native grassland dominated by Themeda triandra Forsskal. Replicate seed lots were recovered after 2, 4, 6, 9 and 12 months, and viability was assessed. Less than 7% of sown surface seeds of B. bulbosa, B. umbellata, C. variabilis and L. squamatus, and less than 10% of buried seeds of A. strictum, B. umbellata and C. variabilis remained viable after 12 months. Virtually all losses of Liliaceae seeds were due to germination. Fates of Asteraceae seeds were difficult to assess accurately after 6 months, but germination accounted for most seed losses. Burial significantly promoted longevity of B. bulbosa, C. variabilis and L. squamatus seeds. No obvious relationship existed between seed longevity and taxonomic group (Liliaceae versus Asteraceae) or seed mass, for surface or buried seeds; the response of the large-seeded lily, B. bulbosa, was most similar to that of the small-seeded daisy, L. squamatus. Of the six species, C. apiculatum appears to have the greatest potential to accumulate a soil seed bank beneath a closed grass canopy, owing to its small seed size, inhibition of germination beneath a closed canopy, both on and below the soil surface, and sustained viability of buried seeds. Naturally dispersed seeds of the other five species are likely to form smaller, transient or short-term seed banks.