5.4 Dryland ecosystems

Dryland ecosystems are extensive in the Cooper GBA region and despite the aridity, the diversity of dryland landscapes and landforms supports a high diversity of ecosystems and grazing on natural pastures. These areas provide habitat for many species, including the kowari, yellow-footed rock-wallaby, and possibly the night parrot. Development activities are likely to amplify existing threatening processes such as habitat degradation, fragmentation and loss; competition and predation; ecosystem burning and soil erosion.

The spatial extent of the dryland vegetation extent and condition endpoint in the Cooper GBA region is 88,538 km², of which approximately 23% overlies areas that are prospective for the development of unconventional gas resources ( Figure 12 ). Dryland vegetation in the Cooper GBA region is relatively undisturbed (less than 1.7% of dryland areas are disturbed), with seismic surveys (571 km²) accounting for 40% of total disturbance (1,442 km²) (Geological and Bioregional Assessment Program, 2021m).

The key distinguishing feature of dryland landscapes is the high dependency on localised rainfall. Dryland ecosystems or ‘rangelands’ are defined as areas that are hyper-arid, arid, semi-arid or dry sub-humid systems. Most of the Cooper GBA region is arid, with a mean annual rainfall of 217 mm/year and evaporation in excess of 1,700 mm/year. As a result, water availability is a major driver of the productivity of these ecosystems.

Despite the aridity, the diversity of landscapes and landforms in the Cooper GBA region supports a high diversity of ecosystems. In Queensland, there are approximately 70 regional ecosystems mapped (Queensland Herbarium, 2018a), and in South Australia, there are 28 ecotypes mapped (Hobbs et al., 2017) within the dryland vegetation extent and condition endpoint. Dominant vegetation communities include the chenopod shrublands, Mitchell grass tussock grasslands, spinifex-dominated hummock grass and Acacia-dominated woodlands and shrublands.

Dryland areas support protected fauna, including the kowari ( Dasyuroides byrnei) found in the gibber pavements of the Sturt Stony Desert and yellow-footed rock-wallaby ( Petrogale xanthopus celeris) found in the tablelands and duricrusts landscape class. Although unconfirmed, the night parrot ( Pezoporus occidentalis) may use long unburnt spinifex for roosting and breeding in dryland areas.

The main land use is grazing on natural pastures represented by the agricultural productivity endpoint. Agricultural productivity is measured as the ratio of outputs produced to inputs used in agricultural production and is defined as land classified as grazing of native vegetation in the catchment scale land use map of Australia (Australian Bureau of Agricultural and Resource Economics and Sciences, 2016).

Soil compaction could increase habitat degradation, fragmentation and loss and soil erosion, which is of ‘potential concern’ in 20% of the agricultural productivity and 23% of the dryland areas. Soil compaction leading to loss of habitat is well studied and the effectiveness of relevant regulations and mitigation strategies is well documented. Knowledge and data available to evaluate materiality thresholds for soil erosion is limited.

Soil compaction in dryland, floodplain and agricultural landscapes can increase soil erosion, depending on the soil properties, ground slope, vegetation, and a combination of the frequency, intensity and duration of wind, rainfall and human activities (Morgan, 2009; Montgomery, 2007). Soil compaction leading to loss of habitat is well studied and documented (Håkansson and Reeder, 1994; Pringle et al., 2019), with mitigation strategies identified by operators (Santos, 2015). Pringle et al. (2019) and Wakelin-King (2013) provide an overview of methods to avoid erosion, including not grading a road down below the ground surface, not leaving road-edge windrows, and properly directed spoon drains. Confidence in pathways related to soil erosion is low as knowledge of materiality thresholds is limited.