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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.

Indicator Metadata