D6: Relative abundance and distribution of priority species in England

Short Description

Priority Species are those identified as the most threatened or declining species in the UK. They were identified to support UK conservation planning and are published and maintained by the Joint Nature Conservation Committee. Priority species are used as the reference source to produce statutory species lists of principal conservation importance. Such lists are published by the Secretary of State under Section 41 of the Natural Environment and Rural Communities Act 2006. There are over 940 priority species recognised in England.

This indicator has 2 components: (a) changes in the relative abundance of those priority species for which suitable abundance data are available; and (b) changes in distribution (the number of 1 km grid squares in which species are recorded in any given year) of those priority species for which distribution data are available. The relative abundance of a species will increase when the population of the species grows; it will decrease when the population of the species declines. The occupancy index will increase when a species becomes more widespread; it will decrease when a species becomes less widespread.

The taxonomic coverage of this indicator is limited at present. The relative abundance measure includes priority birds, butterflies, some mammals (one hare and 5 bats) and moths but does not currently include plants, fungi, amphibians, reptiles, fish or invertebrates other than butterflies and moths; the distribution measure includes priority species of bryophytes, lichens, insects and other invertebrates but does not currently include amphibians, reptiles, birds, fish or mammals.

Readiness and links to data

This indicator is not available for reporting in 2023 in a finalised form. Trends for the relative abundance and distribution of priority species at an England-level were presented here for the first time in 2021 as a revised interim indicator, but there were no new data available to update this indicator in 2022 or 2023. Further details about this indicator, including a technical background document that describes the data sources and methods in detail, and spreadsheets that contain a list of species within each index together with the data behind the indices are published annually as England Biodiversity Indicators 4a and 4b – Status of priority species: relative abundance and distribution. Methods are being developed to refine the future reporting of this indicator and to expand the taxonomic coverage.

These methods are still undergoing peer review and user feedback is invited via 25YEPindicators@defra.gov.uk.

Notes on indicator

While the currently available data mostly predate the 25 Year Environment Plan, they provide the most recently available assessment of the relative abundance and distribution of priority species in England. They enable a better understanding of a baseline from which to measure progress towards the goals of the 25 Year Environment Plan when the indicator is next updated.

Indicator components

Figure D6ai: Relative abundance of priority species in England, 1970 to 2018

Table D6ai: Relative abundance of priority species in England, 1970 to 2018

Year 95% credible interval lower bound 95% credible interval upper bound Smoothed index
1970 87.39 114.49 100.00
1971 74.52 97.77 85.40
1972 67.12 87.63 76.76
1973 65.00 83.95 73.95
1974 64.17 81.68 72.38
1975 65.51 82.44 73.48
1976 69.08 86.42 77.23
1977 65.48 81.58 73.10
1978 62.12 76.66 69.00
1979 58.40 71.38 64.50
1980 53.53 65.63 59.20
1981 51.15 62.17 56.35
1982 52.81 63.43 57.87
1983 52.78 63.19 57.78
1984 52.38 62.32 57.12
1985 48.23 56.97 52.42
1986 45.64 53.68 49.54
1987 43.45 50.87 47.00
1988 41.44 48.16 44.66
1989 41.45 47.97 44.58
1990 41.23 47.42 44.24
1991 39.86 45.63 42.66
1992 38.11 43.45 40.69
1993 35.55 40.18 37.79
1994 34.02 38.33 36.12
1995 33.46 37.60 35.46
1996 31.67 35.30 33.44
1997 28.50 31.67 30.02
1998 25.14 27.64 26.36
1999 23.29 25.53 24.38
2000 22.43 24.71 23.54
2001 23.21 25.35 24.25
2002 24.24 26.43 25.30
2003 25.24 27.77 26.49
2004 25.18 27.51 26.32
2005 23.95 26.04 24.98
2006 22.64 24.80 23.71
2007 21.24 23.17 22.18
2008 21.50 23.44 22.46
2009 22.64 24.69 23.65
2010 23.43 25.47 24.43
2011 23.05 25.10 24.05
2012 21.01 22.93 21.96
2013 20.47 22.24 21.34
2014 19.73 21.43 20.57
2015 18.66 20.36 19.49
2016 17.56 19.13 18.33
2017 17.05 18.58 17.80
2018 16.62 18.79 17.68

Trend description for D6ai

By 2018, the index of relative abundance of priority species in England had declined to 17.7% of its base-line value in 1970, a statistically significant decrease. The majority of this change took place between 1970 and 2000; since then, declines in the indicator have slowed. More recently, between 2013 and 2018, the relative abundance index declined from 21.3 to 17.7 (by 17% of the 2013 value), again a statistically significant decrease.

Assessment of change

An indicator for relative abundance of priority species in England is also reported in the England Biodiversity Indicators, which presents a short and long-term assessment for the same time periods used in this Outcome Indicator Framework assessment. These assessment results were reused here as the England Biodiversity Indicators method is more tailored to the specific dataset and factors-in information on confidence. The assessment found a decrease (deterioration) in the relative abundance of priority species in England over the short and long-term time periods. No results are currently available for the medium-term assessment period using the England Biodiversity Indicators methodology, although this will be considered for future publications.

Change since 2018 has not been assessed for this indicator as sufficient data are not yet available.

Details on the England Biodiversity Indicators assessment methodology for this indicator can be found in section 4a of the latest England Biodiversity Indicators report. 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 D6ai: Assessment of change

Component Period Date range Percentage change Smoothing function Assessment of change
D6ai Short term 2013 to 2018 -17.14 Smoothed data Deterioration
D6ai Medium term N/A N/A N/A Not assessed
D6ai Long term 1970 to 2018 -82.32 Smoothed data Deterioration

Note that smoothed data presented in the indicator charts were used for percent 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. Percent change figures in Tables D6ai may differ from unsmoothed values quoted elsewhere. Percent change refers to the difference seen between the first and last years in the specified date range.

Figure D6aii: Long-term and short-term changes in the relative abundance of individual priority species in England, 1970 to 2018

Table D6aii: Long-term and short-term changes in the relative abundance of individual priority species in England, 1970 to 2018

Time period Little or no change Strong decrease Strong increase Weak decrease Weak increase
Long term (1970–2018) 10.07 65.77 1.34 17.45 5.37
Short term (2013–2018) 23.49 44.97 14.09 11.41 6.04

Trend description for D6aii

Over the long-term period, 7% of species showed a strong or weak increase, 83% showed a strong or weak decline and 10% showed little or no change. Over the short-term period, 20% of species showed a strong or weak increase, 56% showed a strong or weak decline and 23% showed little or no change.

Figure D6bi: Distribution of priority species in England, 1970 to 2016

Table D6bi: Distribution of priority species in England, 1970 to 2016

Year 95% credible interval lower bound 95% credible interval upper bound Smoothed index
1970 100.00 100.00 100.00
1971 98.65 102.18 100.37
1972 97.80 102.56 100.14
1973 97.02 102.47 99.71
1974 96.56 102.20 99.33
1975 96.37 102.16 99.28
1976 96.07 101.77 98.93
1977 94.60 100.27 97.46
1978 93.50 99.20 96.36
1979 92.60 98.47 95.56
1980 91.72 97.52 94.62
1981 90.95 96.74 93.78
1982 91.20 97.06 94.06
1983 91.42 97.32 94.34
1984 91.12 96.93 93.96
1985 89.99 95.71 92.79
1986 89.16 94.70 91.89
1987 88.92 94.37 91.61
1988 88.59 94.06 91.32
1989 89.00 94.58 91.79
1990 89.60 95.21 92.35
1991 89.65 95.11 92.32
1992 89.24 94.62 91.92
1993 88.97 94.26 91.56
1994 89.43 94.73 92.10
1995 90.72 96.14 93.39
1996 91.45 96.86 94.13
1997 91.79 96.98 94.33
1998 90.73 95.94 93.25
1999 90.65 95.77 93.14
2000 90.98 96.23 93.61
2001 91.97 97.24 94.55
2002 92.67 97.90 95.21
2003 93.33 98.64 95.95
2004 92.91 98.14 95.49
2005 92.80 97.97 95.31
2006 92.51 97.81 95.12
2007 89.12 94.42 91.74
2008 88.20 93.47 90.79
2009 89.32 94.67 91.90
2010 89.50 95.20 92.29
2011 89.49 95.13 92.26
2012 86.24 92.12 89.06
2013 86.96 93.05 89.86
2014 85.28 91.52 88.24
2015 82.71 89.65 86.15
2016 79.39 87.94 83.68

Trend description for D6bi

By 2016, the index of distribution of priority species in England decreased to 84, a statistically significant decrease of 16% of the 1970 value. More recently, between 2011 and 2016, the distribution index declined from 92.3 to 83.7 (9% of the 2011 value), again a statistically significant decrease.

Assessment of change

An indicator for the distribution of priority species in England is also reported in the England Biodiversity Indicators, which presents a short and long-term assessment for the same time periods used in this Outcome Indicator Framework assessment. These assessment results were reused here as the England Biodiversity Indicators method is more tailored to the specific dataset and factors-in information on confidence. The assessment found a decrease (deterioration) in the distribution of priority species in England over the short and long-term time periods. No results are currently available for the medium-term assessment period using the England Biodiversity Indicators methodology, although this will be considered for future publications.

Change since 2018 has not been assessed for this indicator as sufficient data are not yet available.

Details on the England Biodiversity Indicators assessment methodology for this indicator can be found in section 4b of the latest England Biodiversity Indicators report. 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 D6bi: Assessment of change

Component Period Date range Percentage change Smoothing function Assessment of change
D6bi Short term 2011 to 2016 -9.31 Smoothed data Deterioration
D6bi Medium term N/A N/A N/A Not assessed
D6bi Long term 1970 to 2016 -16.32 Smoothed data Deterioration

Note that smoothed data presented in the indicator charts were used for percent 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. Percent change figures in Tables D6bi may differ from unsmoothed values quoted elsewhere. Percent change refers to the difference seen between the first and last years in the specified date range.

Figure D6bii: Long-term and short-term changes in the distribution of individual priority species in England, 1970 to 2016

Table D6bii: Long-term and short-term changes in the distribution of individual priority species in England, 1970 to 2016

Time period Little or no change Strong decrease Strong increase Weak decrease Weak increase
Long term (1970–2016) 37.57 17.13 14.92 20.99 9.39
Short term (2011–2016) 28.18 31.49 4.97 27.07 8.29

Trend description for D6bii

Over the long-term period, 24% of species showed a strong or weak increase, 38% showed a strong or weak decline and 38% showed little or no change. Over the short-term period, 13% of species showed a strong or weak increase, 59% showed a strong or weak decline and 28% showed little or no change.

Indicator Metadata