Queensland Floodplain Vegetation

  Queensland Floodplain Vegetation
Dr Andrew Biggs installing a sap flow meter into a coolabah (Eucalyptus coolabah) Photo: Bill Senior

Queensland Floodplain Vegetation Water Requirements

The Lower-Balonne region lies south-west of the town of St George and extends across the border about 100 km into New South Wales. Floodplain vegetation is an important component of the ecology of this floodplain system in the northern Murray-Darling Basin. Three tree species: River Red Gum (Eucalyptus camaldulensis), Coolibah (Eucalyptus coolibah) and Black Box (Eucalyptus largiflorens), and the shrub Lignum (Duma florulenta)
are all key landscape components in the area. These species are all believed to depend on occasional river flooding, but have varying tolerances for maximum time between floods and flood duration.

However, almost all of what is known about the requirements of these species comes from research done in the southern Murray-Darling Basin along rivers that are climatically and hydrologically very different to those of the Lower Balonne region. Previous research by the Queensland Government suggests that there are different relationships between flooding and vegetation conditions here, compared with southern parts of the Murray-Darling Basin. These studies have shown that dry spells in this area are longer than in southern region, indicating that the trees may also be being maintained by accessing alternative sources of water such as from rainfall and shallow groundwater.

The EWKR project aims to fill some of the knowledge gaps in this region by:

  • Identifying changes to condition of floodplain vegetation through time, on different soils and positions in the landscape.
  • Comparing the influence of river flooding vs rainfall and shallow groundwater for each species.
  • Identifying and quantifying the influence of river flooding on water availability in shallow aquifers and unsaturated root zones.
  • Identifying the variation in water requirements among vegetation communities with different structural characteristics (such as tree height, tree density and tree girth).

This research is using a combination of on-ground field work and remotely-sensing satellite imagery which can reveal plant condition responses to long-term patterns, such as occurrences of dry spells, river flooding and rainfall events. The team will also model the water cycle characteristics of differing land-systems (a landscape classification based on topography, soil and vegetation types) to analyse how those characteristics influence recharge and the availability and quality of groundwater used by vegetation. The research outcomes aims to significantly improve water managers’ abilities to assess incremental changes in vegetation condition in the medium to long-term, within the context of multiple management interventions, stressors and pressures.

This new scientific information has informed a review of Sustainable Diversion Limits (SDLs) in the northern Basin, adding to the adaptive management of environmental water allocation targets in the Water Resource Plan and annual plans.

The EWKR research is led by scientists from the Queensland Department of Science, Information Technology and Innovation (DSITI) and the Queensland Department of Natural Resources and Mines (DNRM) and includes research collaborations with the University of Queensland and the University of Southern Queensland.

Electrical Resistivity Tomography (ERT) ground-based geophysiscs transect. Equipment in operation. Photo: Andrew Biggs

Coolabah (Eucalyptus coolabah) open woodland with Lignum understorey, Nelyambo on the Lower Balonne Floodplain. Field study site for the QLD floodplain vegetation project. Photo: Bill Senior