The role of seedbanks in restoration of floodplain woodlands



Plant communities on the River Murray floodplain, South Australia, are degraded by flow regulation and salinization, with up to 95% of eucalypt trees being dead or dying from water stress. This paper describes the floodplain seed bank and its capacity to respond to floods or managed ‘environmental flows’. The soil seed bank contained mainly annual native species, particularly chenopods, whereas the dominant trees, river red gum and black box (Myrtaceae: Eucalyptus camaldulensis, E. largiflorens), retained most of their seeds in a canopy seed bank (‘serotiny’). In healthy trees, seed release peaked in summer (December– February for river red gum, October–March for black box), but variable volumes suggested cyclical patterns in seed crops. Seed release, viability and germination rates did not appear to limit recruitment. In water-stressed trees, however, seed release was up to nine-fold less. Germination requires water from floods or local rainfall. Flow regulation has reduced flood frequencies and delayed timing, so that germination now is likely to be followed by relatively hot, dry conditions (summer). Following managed watering events, seeds accumulated in high-water strandlines, where they germinated readily under a mulch of organic litter, but survival was limited. The importance of local rainfall as a complementary water source was demonstrated, and survival rates were higher for rain-triggered germinants, compared to seedlings germinating in strandlines created by managed watering. Seedling survival would be greater if environmental flows were delivered to complement local rainfall or to extend the effect of short flood events. Copyright © 2008 John Wiley & Sons, Ltd.