When do floodplain vegetation communities need water? Environmental watering projects for red gum, black box and lignum communities on the Lower Murray floodplain are being based on natural phenological cycles, particularly seed fall. If timing of flowering is known, watering can be timed to increase survival of bud and fruit crops, thus increasing flowering volume and seed production, and to provide moist soil to coincide with maximum seed fall to trigger germination.
Monitoring data suggest a continuum in phenological cycles of floodplain eucalypts in response to climatic conditions and water availability. The current working hypothesis is that there is a continuum through three different states in response to drier, average and wetter conditions. In wetter conditions individual trees can support dual alternating biennial crops, with every tree thus producing an annual seed crop with medium to high volumes. In average conditions, a single biennial medium volume crop is produced, with individual trees on opposite cycles in local tree groups, so the group produces an annual seed crop. In drier times, individual trees in local groups produce single biennial cycle crops of much reduced volume, with up to 10 times reduction in seed production.
Watering in late spring-early summer will support flowering and seed production for river red gums and black box at most Lower Murray Valley sites, although a minority of black box trees flower in winter. Watering in other seasons can sustain the bud and fruit crops, which persist for 9-12 months on the trees before flowering or seed fall occurs. Local monitoring allows adjustment for seasonal and annual variations at individual sites.