All chapters of the state of the environment report contain content relating directly or indirectly to biodiversity in its broadest sense. The scope of the ‘Biodiversity’ chapter is focused on content that explicitly speaks to the state and trend of species and ecosystems. Thus, key topics for this chapter are flora and fauna, including threatened species, and ecosystems and habitats, including threatened ecological communities. We include content relating to terrestrial and aquatic (freshwater) species and ecosystems, and cross-reference content in the Coasts, Marine and Antarctic chapters for assessments of species and ecosystems that occur primarily in those domains. The Biodiversity chapter also complements, and links to, content in every other chapter.

The report draws on a wide range of published and grey literature with a focus on changes in the states and trends of species and ecosystems over the past 5 years. We did not conduct original analysis although we have requested specific, sometimes unpublished, content for use in illustrative case studies or where the most up-to-date information was held by agencies such as the Department of Agriculture, Water and the Environment or the Atlas of Living Australia.

We found that, compared with reporting in 2016, there was a much larger base of published literature to draw on for this report. Research funded by the National Environmental Science Program, and research and on-ground work conducted as part of the Australian Government’s Wildlife and Threatened Species Bushfire Recovery efforts and Threatened Species Strategy in particular, have contributed greatly to our knowledge about the threats to, and the status of, threatened species and ecosystems. As a result, there is disproportionately more content about species and ecosystems listed under the Environment Protection and Biodiversity Conservation Act 1999 than for nonlisted species in our report. However, it is also true that our knowledge about biodiversity more generally has improved over the past 5 years as a result of these programs and other research efforts undertaken by a range of agencies and institutions, and in collaboration with Traditional Owners.

Our assessment summaries use the 2016 report as a baseline, and we reflect on changes since 2016 that have led to an improvement or deterioration in state and trend of species and ecosystems, or the magnitude of pressures on biodiversity. Assessment summaries on the state and trend of biodiversity draw on content from across the entire report, rather than solely from the content in the section immediately preceding them. We have endeavoured to consider only where there was some evidence base for claims of management achievement, or for claims of biodiversity decline or loss. However, given that no comprehensive information base is available on which to make objective quantitative analysis for most assessments, elements of this report, including the assessment summaries, are subjective opinions based on our best synthesis and judgement of the multiple lines of evidence, and considering Indigenous and non-Indigenous perspectives and knowledge.