This report sets out the approach and methods adopted to inform development of the 25 Year Environment Plan Outcome Indicator, D5: ‘Conservation status of our native species’. In scope, it covers conception, development and finalisation of a ‘Red List Index for England’ as the D5 metric, focusing on the creation of a 2022 baseline but also addressing how it will be reported upon in future. An accompanying spreadsheet includes the full list of species in the baseline Red List Index and its calculation.
The Red List Index (RLI) is based on the numbers of species in each Red List category (Extinct, Extinct in the Wild, Regionally Extinct, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern) and how these numbers change over time as species improve or deteriorate in status.
RLI values range from zero to one, where ‘one’ equates to all species assessed as Least Concern and ‘zero’ indicating that all species have gone extinct. The aggregate RLI value for the baseline year (2022) is 0.9070, embracing the status of 8,259 taxa across 23 major taxonomic groups. The RLI values for individual taxonomic groups ranged from 0.7387 (butterflies) to 0.9747 (hoverflies), with a median of 0.8979. Recalculating the RLI at regular intervals will produce trend information.
The index focuses on terrestrial and freshwater taxa in the following groups: 49% invertebrates, 29% vascular plants, mosses & liverworts, 18% fungi and lichens and 4% vertebrates. Most marine taxa have yet to be Red List assessed in GB. Assuming a total of 40,000 native macro-species in terrestrial and freshwater groups in England, c20% are covered by the index.
Red List Indices are best seen a long-term indicators, because there are a number of inherent time lags and trends can be quite subtle. We anticipate the indicator operating over at least a 20-year period (2022-42), encompassing two full update cycles of GB Red Lists.