The working hypothesis for black box (Eucalyptus largiflorens) phenology on the South Australian floodplain is that the majority of mature trees flower in summer, geared to soil moisture provided by flood events in late spring-early summer (Jensen et al. 2007). A minority of trees flower in winter, and rely on winter rainfall and the main water source for their flowering cycle.
A major regeneration event occurred for black box at medium elevations on the South Australian River Murray floodplain following the flood sequence of 2010-2012, enhanced by significant summer rainfall in 2012 and 2014. This extensive regeneration highlighted the fact that almost no seedlings have survived from flood events in the 1970s and 1990s. The last mass germination to survive to recruitment was that triggered by the 1955-56 floods.
Environmental watering in the SA Riverland region has focussed on sustaining these black box seedlings to enhance their chances of survival. Monitoring of the ecological response to environmental watering is providing useful data on phenological cycles and crop volume. Early results since March 2015 supported the working hypothesis, until the June 2016 field trip found mass flowering in more than 70% of mature black box trees. Is this a return to ‘normal’, a recovery from 10 years of serious drought 2000-2010? Or is it a new ‘normal’, responding to the very late flood peaks in February 2011 and April 2012 and unusual rainfall patterns? Monitoring continues, to try to answer these questions.