Provision of evidence statements to accompany the UK and England species trend indicators and an overview of the causes of biodiversity change. Final report

Isaac, Nick; Eaton, Mark; Burns, Fiona; Rob, Dyer; Gregory, Richard; Peyton, Jodey; Roy, David. 2016 Provision of evidence statements to accompany the UK and England species trend indicators and an overview of the causes of biodiversity change. Final report. Defra, 13pp. (CEH Project no. C05522, Defra Project no. BE0112)

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The set of “UK Biodiversity Indicators” includes 11 indicators which show changes in the status of wildlife through a series of species trend assessments. We have produced a set of Evidence Statements (Annex 1) to ensure that interpretation of trends, causal factors and relationship to policy interventions is rigorous, objective and reflects scientific consensus. The Evidence Statements for each of the 11 indicators have a common format with five sections: 1) a background section describing the underlying datasets and the species they contain; 2) sets of bullet points stating what the indicator represents and placing limits on how the line should be interpreted; 3) a description of how the indicator has changed over time, and the strength of evidence linking changes in the indicator with changes in the species that contribute; 4) the wider relevance to ecosystem services, where known, and biodiversity targets; and 5) a review of evidence about the factors driving change in the indicator line. The eleven species indicators report on a broad range of organisms, but the taxonomic coverage remains biased towards charismatic vertebrates: five of the eleven indicators contain only birds and a sixth contains only bats. There are three indicators for insects, of which two contain only butterflies. The other two indicators are for species categorised as conservation priorities,comprising some birds and mammals, a large number of moths and other terrestrial insects, and a small number of plants. There are substantial differences in the trends of the eleven indicators, suggesting that no one taxon can represent the whole of biodiversity adequately. Thus, the broadened taxonomic coverage of the current indicator set presents a fuller but more complex picture of how biodiversity has changed over recent decades. The datasets that contribute to the indicators contain a range of biases. Many of these biases are well-known, such as the spatial bias caused by schemes that allow volunteers to select the locations of monitoring sites. In general, we find that indicators based on data with the fewest biases also contain the most complete forms of bias correction. At one extreme, the Breeding Bird Survey contains the lowest overall spatial bias, but the wild bird indicators to which it contributes are the only indicators that contain a correction for spatial bias. There are substantial differences in how the indicators are constructed from raw data. In part these differences reflect the biases in the underlying data, and the decisions on choices about which species should be included. However, the biggest differences lie in whether the headline indicator is statistically smoothed and, if so, how the smoothing is conducted. These and other differences mean that confidence intervals around the indicator line represent different aspects of the overall uncertainty in different indicators. Harmonising the production of species indicators around a set of common standards would therefore make it easier to communicate what the indicators represent. One feature that the indicators share is that uncertainty is measured relative to the index value in the first year (typically set at 100). This has the peculiar property that confidence intervals tend to become progressively wider over time. This is both undesirable and counter-intuitive, because the quantity of data generally increases over time and the first year is typically the one with the least data. A variety of alternative statistical treatments exist, each of which has different implications for how uncertainty in the headline indicator can be presented and interpreted. There is little published evidence linking changes in species populations at a national scale, to changes in the provision of ecosystem services, and so the current indicators, with the exception of pollinating insects, cannot be used as service indicators. The indicators show how some aspects of the natural environment are changing, but would need to be supplemented with additional data or qualitative assessment to draw conclusions about progress to international targets such as those in the CBD Strategic Plan. We conducted a structured review using expert opinion to score the relative importance of putative drivers of biodiversity trends. We assessed a representative sample of 398 species that contribute to the indicators using a peer-reviewed framework for assessing drivers of change and their impacts (both positive and negative). We collated these scores to identify the principle drivers for each of the eleven species trend indicators. Across all indicators, our review found that agricultural intensification has been the principle driver of change in UK biodiversity. This review, covering drivers of change across the eleven species trend indicators, is presented as Annex 2. We used a modified Delphi technique to determine whether the Evidence Statements are an adequate reflection and synthesis of the available evidence. A panel of independent experts scored their level of agreement with 139 assertions within the Evidence Statements. Assertions for which there was no consensus were discussed, rewritten and rescored at a workshop. The mean agreement score and the consensus among delegates were used to assign confidence ratings to each assertion. The Delphi technique provided a transparent way to synthesize a large body of evidence without being overly influenced by the opinions of individual experts. In this way, we were able to review and fine tune the Evidence Statements for each indicator.

Item Type: Publication - Report
UKCEH and CEH Sections/Science Areas: Pywell
Funders/Sponsors: Defra
Additional Information. Not used in RCUK Gateway to Research.: This report, together with its appendices and Executive Summary, are freely available via the Official URL link.
NORA Subject Terms: Ecology and Environment
Date made live: 27 Mar 2018 09:49 +0 (UTC)

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