The seed bank is an important component of the vegetation of the riverine littoral zone providing a refuge and mechanism for species survival through unfavourable conditions. In particular arid zone rivers where water level fluctuations are large and unpredictable, with conditions generally unsuitable for survival of asexual propagules. In the Lower River Murray this has been further exacerbated by river regulation. The seed bank is also seen as an indicator of resilience as it provides a source of propagules for regeneration following disturbance.
The aim of this study was to gain a baseline of the soil seed bank of the littoral zone of the lower River Murray at three sites in weir pool tailwaters, where vegetation monitoring as part of the Commonwealth Environmental Water Office’s Monitoring, Evaluation and Research Project is being undertaken. The baseline will be used to evaluate the long-term evaluation question: What did Commonwealth environmental water contribute to the resilience of littoral plant communities?
Soil samples were collected from the littoral zone in tailwaters from pool level to 2 m above pool level downstream of Locks 1, 4 and 6 in December 2019. The seed bank was assessed using the seedling emergence technique.
Lock 1 had the highest seedling density (5,489 germinants m-2), followed by Lock 6 (3,703) and then Lock 4 (1,128) with Lock 6 recording the most exotics. Twenty-six taxa (nine exotics) were recorded across all sites. Lock 1 had the highest species richness (18 including five exotics), Lock 6 (16, four exotics) and Lock 4 (13, six exotics). There were no patterns of seed bank composition with respect to site or elevation despite there being patterns in the extant vegetation. Seedling density and species richness in the lower River Murray were depauperate compared to other areas in the Murray-Darling Basin.