Basin-scale evaluation of 2020–21 Commonwealth environmental water: Vegetation.

Strategic management of Commonwealth water for the environment (also known as Commonwealth environmental water) by the Commonwealth Environmental Water Holder (CEWH) is key to achieving the Commonwealth’s (Murray–Darling) Basin Plan 2012 (Basin Plan) environmental objectives. The 3-year Basin-scale Monitoring, Evaluation and Research Program (Flow-MER) aims to demonstrate Basin-scale outcomes of Commonwealth environmental water, support adaptive management and fulfil CEWH legislative requirements under the Basin Plan. This evaluation describes groundcover vegetation outcomes from the use of Commonwealth environmental water for 2020–21, as well as the cumulative outcomes from the use of Commonwealth environmental water since monitoring began in 2014–15. In doing so, the evaluation considers the latest annual (2020–21) and 7-year (2014–21) contribution of Commonwealth environmental water to answer the following questions: • What did Commonwealth environmental water contribute to plant species diversity? • What did Commonwealth environmental water contribute to vegetation community diversity? In addressing these questions, we contribute to evaluating broad expected outcomes for Biodiversity defined within the Basin Plan. The evaluation considers the responses to environmental watering actions that involve Commonwealth environmental water. In many instances, these watering actions also involve the use of state holdings of water. Thus, the evaluation reflects the outcomes of the combined management of environmental water, and not Commonwealth environmental water alone. The evaluation is based on vegetation data collected under the Long Term Intervention Monitoring Project (2014–15 to 2018–19) and Flow-MER (2019–present) from floodplain–wetlands and river channels. Descriptions of the vegetation responses to environmental water are framed in terms of species and community responses and are described in terms of a range of structural and functional attributes. For the purposes of the evaluation: • species diversity encompasses the presence and abundance of individual plant species; here, we use species richness (number of species) • community diversity includes the composition and structure of vegetation assemblages occurring in different habitat types (riverine and floodplain–wetland). Structural and functional attributes include water plant functional groups (submerged, amphibious, damp, woody flood dependent and terrestrial), species growth forms (e.g. forbs, grasses, ferns), native and exotic species, rare and threatened species, and species that are known to be used by Aboriginal people. These attributes are commonly used to describe vegetation community composition, providing information about habitat diversity as well as plants with specific social and cultural values. The data are evaluated in the context of watering history (both natural and managed) and spatial patterns of observed vegetation responses at monitored sites are used to infer responses in vegetation across the Basin. Most of the evaluation focuses on floodplain and wetland vegetation responses to environmental water because we lack in-channel hydrology indices relevant to all riverine sites to support Basin evaluation. Our inference is based on patterns and observations of vegetation at monitoring locations in 2 ways: • comparing locations that received or did not receive environmental water (annual evaluation) • comparing locations that are classified into different hydrological groups reflecting the degree to which they received environmental water (7-year evaluation). The logic is that if environmental water has been provided to a location then it has, in part, contributed to the plant species present at that location. The outcomes from the evaluation are used to infer the contribution of Commonwealth environmental water to Basin Plan objectives and identify adaptive management responses to issues raised in the evaluation.