Learn about the main results of the Threatened Plant Index from the TSX Team:
Threatened Plant Index for Australia 2020 for all sites
Interpreting the index graphs
The index shows the average change in populations compared to a base year. It shows a relative change and not population numbers themselves. The base year of this index is 1995, which gets an index score of one. A score of 1.2 would mean a 20% increase compared to numbers in 1995 on average, while a score of 0.8 would mean a 20% decrease compared to 1995 on average.
The Living Planet Index team has produced a blog which illustrates how the numbers are typically crunched to produce an index. This is the same for the calculation of the Threatened Species Index.
Threatened Species Index for Australian Plants 2020
The 2020 index for threatened plants in Australia shows us that between 1995 and 2017 there was a 72% decrease on average in Australian plant populations across all sites for which we have data.
We can also look at how plants are doing at sites with and without conservation management such as herbivore control, weed/disease management, pest control or translocations. At sites where conservation actions have occurred, threatened plants have decreased on average by about 60%, and by about 45% since 2000 for only those sites where translocations have occurred. At sites where no conservation actions have been undertaken (that we know of), populations have decreased on average by about 80%. The separation of plant sites into sites with and without conservation management is based on information communicated by our data custodians.
The overall index is based upon data for many species and subspecies. The 2020 plant index includes data for 112 threatened plants from over 600 time series. As of 2020, this index does not include data on near-threatened plants. As more data is added these numbers will grow.
Within this, some species have decreased a bit more and others a bit less. The grey cloud around the index trend represents some of the variability in the trends of individual species that make up the overall multi-species index. It is created by randomly sampling species trends from all possible trends in the dataset 100 times, and dropping the 5 trends that are furthest from the average, resulting in a 95% “confidence limit”.
In addition to the Australian index, our web visualisation tool allows you to generate indices for individual Australian states and territories and for a range of species groups, such as orchids or shrubs.
More details on the Australian index and all state and territory indices can be found in our research findings factsheets. This project and the factsheets were developed in collaboration with the Commonwealth Department of the Agriculture, Water and the Environment, and all of our major data contributors, including all state and territory governments.
