Using phenology of eucalypts to determine environmental watering regimes for the River Murray floodplain South Australia

Abstract

Trees on the River Murray floodplain in South Australia, particularly river red gum and black box (Myrtaceae: Eucalyptus camaldulensis, E. largiflorens), are increasingly water-stressed as the period since effective overbank flows extends to six years. As a result of declining health and dry conditions, recruitment rates in these species are insufficient to maintain populations. This study examined phenological cycles to determine the potential for timing environmental flows to promote recruitment. Results indicate a relatively consistent pattern in river red gums, which would benefit from watering in summer (December-February) to reinforce bud set, flowering and germination during peak seed rain from aerial seed banks. Present environmental flow programs may not provide water to black box on elevated areas of the floodplain, but this species would benefit from watering to reinforce bud set and flowering either in summer (December- February) or winter (May-July), depending on the phenological cycle of the trees to be watered. The possibility of watering to support seedlings in autumn, following above-average rainfall in the previous spring, warrants more study.