Information - This Indicator is an official statistic in development and has been published in order to facilitate user involvement in its development – information on how the data have been obtained and how the indicator has been prepared is available via the link(s) in the 'Readiness and links to data' section. We would welcome any feedback, particularly on the usefulness and value of this statistic, via 25YEPindicators@defra.gov.uk.
D4: Relative abundance and/or distribution of species
Short Description
This indicator will use regularly collected data to track changes in relative abundance and/or distribution of species which are characteristic of different broad habitats in England including birds, bats, butterflies, moths, other invertebrates, and plants. The indicator will ultimately have 2 components: (a) changes in the relative abundance of species listed on Schedule 2 of the The Environmental Targets (Biodiversity) (England) Regulations 2023 for which suitable abundance data are available; and (b) changes in the distribution of widespread species for which suitable distribution data are available. The relative abundance of a species will increase when the population of the species grows, and it will decrease when the population of the species declines. The distribution index, also referred to as the occupancy index, measures the number of 1 kilometre grid squares across the country in which species are recorded each year. It will increase when a species becomes more widespread and decrease when a species becomes less widespread.
Readiness and links to data
An interim indicator is presented here which shows composite trends in the relative abundance of species in England.
Further detail about the all-species abundance indicator is available in the annual Indicators of species abundance in England statistics release. This includes taxonomic breakdowns, a technical background section that describes the data sources and methods in greater detail, and a spreadsheet that contains a list of species within the index, together with a more granular breakdown of the data. The data are published as an official statistic in development to gather feedback and facilitate user involvement in the development of the indicator.
Further work is required to develop the distribution measure for this indicator.
Notes on indicator
The relative abundance measure was developed with the aim of producing an index to summarise trends in abundance for the broadest possible set of organisms that are representative of English terrestrial and freshwater biodiversity. The indicator does not represent marine species (with the exception of seabirds and a small number of fish which live in coastal waters) as marine species are highly mobile and widely dispersed, requiring assessments to be done at a much larger scale (e.g. the North East Atlantic). There are existing abundance indicators for marine species in the UK Marine Strategy and in the OSPAR assessments.
Two possible versions of the relative abundance measure are currently presented here, 'option 1' with a greater degree of smoothing applied (using a 10-year timescale) and 'option 2' with a lesser degree of smoothing (using a 3-year timescale). Smoothing is applied to the species abundance indicator to identify long-term trends in otherwise noisy data. A greater degree of smoothing may provide a clearer view of the underlying long-term trend, while a lesser degree of smoothing preserves the shorter-term patterns in the data. The results given in the commentary are based on the values of both trends and are intended to communicate the extent to which reliance of these trends are dependent on methodological decisions. Further details on this methodology are available in the Indicators of species abundance in England statistical release.
Indicator components
Figure D4i: Relative abundance of species in England, 1970 to 2023
Table D4i: Relative abundance of species in England, 1970 to 2023
| Year | Smoothed index (option 1) | 95% credible interval lower bound (option 1) | 95% credible interval upper bound (option 1) | Smoothed index (option 2) | 95% credible interval lower bound (option 2) | 95% credible interval upper bound (option 2) |
|---|---|---|---|---|---|---|
| 1970 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| 1971 | 93.10 | 92.20 | 94.20 | 89.70 | 88.30 | 91.00 |
| 1972 | 88.10 | 86.50 | 89.90 | 84.60 | 82.70 | 86.40 |
| 1973 | 84.60 | 82.60 | 86.80 | 82.80 | 80.50 | 85.00 |
| 1974 | 82.30 | 79.90 | 84.80 | 82.80 | 80.20 | 85.50 |
| 1975 | 80.80 | 78.20 | 83.70 | 83.60 | 80.70 | 86.70 |
| 1976 | 80.10 | 77.30 | 83.30 | 84.30 | 81.00 | 87.50 |
| 1977 | 80.00 | 77.10 | 83.40 | 83.80 | 80.20 | 87.30 |
| 1978 | 80.40 | 77.20 | 84.00 | 82.10 | 78.50 | 85.80 |
| 1979 | 81.00 | 77.70 | 84.90 | 80.10 | 76.40 | 83.80 |
| 1980 | 81.90 | 78.40 | 86.00 | 79.50 | 75.60 | 83.40 |
| 1981 | 82.90 | 79.10 | 87.20 | 81.40 | 77.30 | 85.60 |
| 1982 | 83.90 | 79.80 | 88.50 | 85.10 | 80.70 | 89.90 |
| 1983 | 84.70 | 80.40 | 89.60 | 88.30 | 83.60 | 93.50 |
| 1984 | 85.40 | 80.80 | 90.30 | 89.10 | 84.00 | 94.40 |
| 1985 | 85.80 | 81.10 | 91.00 | 87.40 | 82.30 | 92.90 |
| 1986 | 85.90 | 81.00 | 91.20 | 84.70 | 79.60 | 90.30 |
| 1987 | 85.70 | 80.60 | 91.20 | 82.40 | 77.40 | 87.80 |
| 1988 | 85.20 | 80.00 | 90.80 | 80.90 | 75.90 | 86.40 |
| 1989 | 84.40 | 79.10 | 90.00 | 80.50 | 75.50 | 86.00 |
| 1990 | 83.40 | 78.00 | 89.10 | 80.90 | 75.80 | 86.50 |
| 1991 | 82.10 | 76.70 | 87.80 | 81.70 | 76.30 | 87.30 |
| 1992 | 80.70 | 75.20 | 86.50 | 82.10 | 76.60 | 87.90 |
| 1993 | 79.20 | 73.70 | 85.00 | 81.90 | 76.30 | 87.90 |
| 1994 | 77.60 | 72.00 | 83.30 | 81.40 | 75.60 | 87.50 |
| 1995 | 76.00 | 70.40 | 81.70 | 80.40 | 74.70 | 86.60 |
| 1996 | 74.40 | 68.90 | 80.30 | 78.40 | 72.80 | 84.50 |
| 1997 | 72.80 | 67.50 | 78.70 | 74.60 | 69.20 | 80.60 |
| 1998 | 71.40 | 66.10 | 77.40 | 69.50 | 64.50 | 75.20 |
| 1999 | 70.20 | 64.90 | 76.10 | 65.00 | 60.20 | 70.30 |
| 2000 | 69.10 | 63.80 | 75.00 | 62.80 | 58.00 | 68.00 |
| 2001 | 68.20 | 63.00 | 74.00 | 63.40 | 58.50 | 68.70 |
| 2002 | 67.50 | 62.30 | 73.30 | 65.90 | 60.70 | 71.40 |
| 2003 | 67.00 | 61.70 | 72.80 | 68.40 | 63.00 | 74.30 |
| 2004 | 66.60 | 61.40 | 72.50 | 69.90 | 64.30 | 76.10 |
| 2005 | 66.50 | 61.20 | 72.50 | 70.20 | 64.50 | 76.60 |
| 2006 | 66.40 | 61.00 | 72.50 | 69.70 | 63.90 | 76.10 |
| 2007 | 66.40 | 60.90 | 72.60 | 68.80 | 63.10 | 75.30 |
| 2008 | 66.50 | 60.90 | 72.70 | 68.30 | 62.50 | 74.60 |
| 2009 | 66.60 | 60.90 | 72.90 | 68.10 | 62.30 | 74.50 |
| 2010 | 66.60 | 60.80 | 73.00 | 68.20 | 62.20 | 74.70 |
| 2011 | 66.70 | 60.80 | 73.10 | 67.80 | 61.70 | 74.50 |
| 2012 | 66.70 | 60.70 | 73.20 | 66.60 | 60.60 | 73.30 |
| 2013 | 66.60 | 60.70 | 73.10 | 65.00 | 59.10 | 71.80 |
| 2014 | 66.50 | 60.60 | 73.10 | 63.70 | 57.80 | 70.30 |
| 2015 | 66.40 | 60.40 | 73.20 | 63.00 | 57.20 | 69.50 |
| 2016 | 66.40 | 60.30 | 73.10 | 63.00 | 57.20 | 69.50 |
| 2017 | 66.30 | 60.20 | 73.10 | 63.80 | 57.80 | 70.40 |
| 2018 | 66.30 | 60.00 | 73.10 | 65.00 | 58.80 | 71.80 |
| 2019 | 66.40 | 59.90 | 73.30 | 66.10 | 59.80 | 73.00 |
| 2020 | 66.50 | 60.00 | 73.50 | 66.90 | 60.50 | 74.00 |
| 2021 | 66.70 | 60.10 | 73.60 | 67.20 | 60.70 | 74.30 |
| 2022 | 67.10 | 60.50 | 74.00 | 67.00 | 60.60 | 74.20 |
| 2023 | 67.50 | 60.90 | 74.60 | 66.60 | 60.10 | 73.70 |
Trend description for D4i
By 2023, the index of change in the relative abundance of species in England had declined to around 67% of its baseline value in 1970, with the majority of these changes taking place in the last 3 decades of the 20th century. More recently, between 2018 and 2023, the relative abundance index showed no meaningful change over the latest 5 years for which data are currently available.
Assessment of change
The composite ‘all-species’ relative abundance measure is also reported in Indicators of species abundance in England. This statistical release presents a short-, medium- and long-term assessment for the same time periods used in this Outcome Indicator Framework assessment. These assessment results were reused here as the method in the source publication is tailored to the specific composite abundance index and it factors-in information on confidence. The assessment found little or no change in the abundance of species in England over the short- and medium-term periods and a decline (deterioration) over the long-term.
Details on the assessment methodology used for this indicator can be found in the ‘assessment of change’ section of the Indicators of species abundance in England statistical release. Further information on the standard assessment used in the Outcome Indicator Framework, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table D4i: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| D4i | Smoothed index (options 1 and 2) | Short term | 2018 to 2023 | 1.8 to 2.5 | Smoothed data | Little or no change |
| D4i | Smoothed index (options 1 and 2) | Medium term | 2013 to 2023 | 1.4 to 2.5 | Smoothed data | Little or no change |
| D4i | Smoothed index (options 1 and 2) | Long term | 1970 to 2023 | -32.5 to -33.4 | Smoothed data | Deterioration |
Note that smoothed data presented in Figure D4i were used for percentage change calculations. The smoothing method is specific to this indicator and differs from the default Loess smoothing approach adopted for most indicators for the Outcome Indicator Framework assessment. Percentage change refers to the difference seen between the first and last years in the specified date range.
Figure D4ii: Long-term and short-term changes in the relative abundance of individual species in England, 1970 to 2023
Table D4ii: Long-term and short-term changes in the relative abundance of individual species in England, 1970 to 2023
| Period | Strong decrease | Weak decrease | Little or no change | Weak increase | Strong increase |
|---|---|---|---|---|---|
| Long term (1970–2023) | 22.20 | 17.30 | 27.70 | 12.80 | 20.00 |
| Short term (2018–2023) | 30.50 | 9.50 | 14.70 | 7.80 | 37.40 |
Trend description for D4ii
The long-term decline in the overall abundance of species in England shown in D4i masks the trends of the individual species within the index, 39% of which have shown a strong or weak decrease and 33% of which have shown a strong or weak increase in abundance since 1970. Over the short-term period (2018 to 2023) 45% of species showed a strong or weak increase and 40% showed a strong or weak decrease in abundance over the latest 5 years for which data are currently available.
Assessment of change
No assessment of change was undertaken for this indicator component as it is based on the same underlying data that are already assessed in D4i.