Seedling root growth experiments for two Australian dryland riparian eucalypts provide new insights for environmental watering

In dryland environments where rivers have been modified by water resource developments, the use of environmental water provides a management tool to restore or maintain riparian vegetation conditions. Relevant management actions include watering to promote the recruitment of highly valued woody species. However, for many riparian trees, little is known about the watering regimes needed to achieve successful recruitment. We conducted a glasshouse experiment to investigate the early growth of 5-week old seedlings of two Australian dryland riparian tree species, coolibah (Eucalyptus coolabah) and river red gum (Eucalyptus camaldulensis), in floodplain soil cores to provide insights into their requirements for successful establishment in dryland habitats. Both species exhibited similar growth patterns for their above-ground components. E. coolabah root penetration through soil cores was consistent over the 12-week experiment. In contrast, E. camaldulensis root penetration appeared to be considerably slower during the first 6 weeks, but then became more rapid over the following 6 weeks, with similar rooting depths after 12 weeks observed to those of E. coolabah. These findings suggest that coolibah seedlings are more likely to establish under rapidly drying conditions than river red gum seedlings. Such differences in early growth for these iconic species should be considered when determining the provision of environmental water for their management.