Triple La Niña 2020–2022 revival: river red gum and coolibah recruitment in the Queensland Murray–Darling Basin floodplain, Australia

Floodplain forests in the Queensland Murray–Darling Basin (QMDB) have experienced significant recruitment challenges following multiple droughts, including the Millennium Drought (1997–2009). This study investigated the impact of the rare triple-dip La Niña event (2020–2022) on floodplain tree recruitment patterns for river red gum (Eucalyptus camaldulensis Dehnh.) and coolibah (Eucalyptus coolabah Blakely & Jacobs). Field assessments across QMDB’s three water catchment areas showed recruitment at 34% of plots. Days since last flood (P = 0.04) was significantly associated with recruitment density, whereas bankfull exceedance floods showed a marginally positive effect on recruitment density (P = 0.080), and total days of exceedance had a marginally negative influence on recruitment density (P = 0.06). Open woodland and woodland areas with low canopy cover exhibited significantly higher recruitment rates (P = 0.001 and P = 0.021) compared to forests. Low native fauna grazing pressure showed strong association with increased recruitment (P = 0.007); during wet conditions, abundant grass cover diverted browsing pressure on seedlings. Demographic analysis demonstrated improved reverse J-curve distributions for both species compared with previous assessments, suggesting that this triple-dip event recruitment episode may help restore juvenile cohorts. Findings suggest that although flooding appears to contribute to recruitment through site preparation and seed dispersal, sustained rainfall appears crucial for seedling survival. These results have important implications for environmental water management, highlighting that infrequent but significant recruitment episodes may be sufficient for maintaining sustainable populations over the extended lifespans of these species, while demonstrating the limits of direct management interventions.