Today (22nd April) sees the publication of a new Scottish Government marine and terrestrial biodiversity indicator. Mark Eaton, RSPB Principal Conservation Scientist explains how this indicator will help progress towards national biodiversity commitments (such as the National Outcome for the Environment, which is to ‘value, enjoy, protect and enhance our environment’) to be measured.

This is important – we want the state of nature and the environment to be measured, and treated as just as important for national wellbeing as are measures of economic performance, crime and health, for example.

RSPB expertise

The RSPB Centre for Conservation Science has led the creation of this new indicator, in consortium with scientists from the UK Centre for Ecology & Hydrology, James Hutton Institute, and University of Sheffield, under contract to the Scottish Government. This involved a process of reviewing the options used elsewhere and scoping the availability of suitable data on Scottish biodiversity, as well as consultation across many partners involved in the collection and reporting of biodiversity data in Scotland. The initial requirement from the Government was to produce a single line indicator to encompass change in both marine and terrestrial biodiversity – an extremely challenging task.

Pine marten at RSPB Abernethy (c) Paul Turner (rspb-images.com)

Whilst we identified how this might be done (see here), we stated repeatedly that while possible, such an indicator would be technically flawed, and virtually impossible to interpret in a meaningful way. We were very pleased that subsequently the Scottish Government decided against the original intention of publishing a single line to report on all of Scottish biodiversity. Instead, it was agreed that change in biodiversity should be measured using three separate lines – although a single assessment of overall progress will be derived from these three lines. We then worked on a second contract to provide revised indicators, as published today.

The indicators

Trends in abundance (how many individuals there are of a species) and occupancy (how widely a species is found) may vary in different ways and at different rates within the same species, and so the two measures are reported separately. This indicator provides two lines measuring change in terrestrial biodiversity, one for species’ abundance and one for species’ occupancy – note that the species compositions for these are very different. Trends in marine biodiversity are represented by a separate indicator based on seabird abundance; trends in abundance for other marine species’ groups are shown as additional contextual information.

In total the new indicators include the trends in 3,049 species in Scotland, from all regions and habitats, and including Scotland’s seas. The trends in abundance (for 583 species) come from a range of established monitoring schemes, and trends in occupancy (2,466 species) from analyses of biological records held by the Biological Records Centre.

They are broadly similar to the indicators published in the State of Nature Scotland report in 2019, but there are some notable differences. In particular, the desire for a standard start date means that the terrestrial occupancy indicator starts in 1994, not in 1970 as in the State of Nature. As a result, it misses the decline in occupancy that the State of Nature indicator showed in the 1970s and 80s. In addition, the species composition is different, most notably with vascular plants omitted from this new version.

Twinflower (Linnaea borealis) is a small delicate flower, native to pinewoods in Scotland, but one which will not be included in these new indicators (c) Cairngorms Connect

There are considerable biases in the availability of species trends for incorporation in the indicator. For example, vertebrates are over-represented in the terrestrial abundance indicator in comparison to invertebrates, and vascular plants are absent entirely. Thus, these indicators are not perfect representations of change in all of Scotland’s biodiversity and have considerable biases; they are, however, the best possible based upon current knowledge.

And, of course, we must remember that by only measuring change since 1994, while the indicators are valuable for measuring current progress in protecting and restoring nature, they tell us nothing about the previous loss of Scotland’s wildlife on a broad and massive scale. While we lack robust, quantitative trend data prior to the period of modern biodiversity monitoring, the sweeping changes to the Scottish landscape that has occurred over centuries undoubtedly came with an accompanying loss of nature. At the beginning of the UN Decade on Ecosystem Restoration, such wider, long term losses of nature are framing global thinking on how we must tackle the crisis facing species and habitats across the world.

What do the indicators tell us?

The marine abundance indicator has shown a statistically significant decrease of 35%, the terrestrial abundance indicator a statistically significant decline of 31%, and the terrestrial occupancy indicator a statistically significant increase of 24%, all since the start year of 1994.

 

Figure 1: Marine abundance indicator, derived from data for 11 seabirds. The shaded ribbon shows 95% credible intervals.

Figure 2: Terrestrial abundance indicator, derived from data for 133 birds, 25 butterflies, 9 mammals and 204 moths. The shaded ribbon shows 95% credible intervals.

Figure 3: Terrestrial occupancy indicator, derived from data for bryophytes (218 species), lichens (650 species), freshwater invertebrates (151 species), terrestrial insects (1,104 species), and terrestrial invertebrates (excluding insects) (343 species). The shaded ribbon shows 95% credible intervals.

An assessment of change in these three indicators is made over the final year in order to assess current performance e.g. towards the National Outcome on the Environment. While this may be a sensible timeframe for looking at issues such as economic change, it unfortunately makes little sense for a biodiversity indicator.

Firstly, as the estimate of error around our indicators mean that there is rarely a significant between-year change, but more importantly because meaningful changes in biodiversity (as opposed to short-term fluctuations, due to the weather, for example) do not happen over a single year. It would be more appropriate to look at change since the start of the indicators, and over a short-term period such as five years (as was done for State of Nature, and is used for UK’s biodiversity indicators). The three measures of change are used to produce a single overall assessment of performance, which is ‘performance maintaining’ (i.e. stable) for this first publication.

Further detail

In addition, we should remember that all such species’ trend-based indicators amalgamate data, and thereby hide a wealth of information on how individual species, and groups of species, are faring. In addition to the three ‘headline’ indicators, the indicator report published by NatureScot today includes breakdowns by major taxonomic groups, giving some ideas of the patterns within the headline indicators as well as providing a discussion of the drivers of change in Scottish biodiversity.

Thanks to thousands

The new indicator was produced in collaboration with Nick Isaac and Rob Cooke (UK CEH), Robin Pakeman (James Hutton Institute) and Tom Webb (University of Sheffield), and my RSPB colleagues Andy Stanbury and Fiona Burns. We worked closely with John Landrock (Rural & Environmental Science and Analytical Services, Scottish Government) and David O’Brien and Simon Foster (NatureScot), and benefited from the input from many experts in governmental and non-governmental organisations.

The great majority of the data sources contributing to the new indicator are collected through the efforts of expert and dedicated volunteer surveyors and recorders, without whom our knowledge of biodiversity in Scotland would be much poorer, and this indicator would not be possible. Data for the indicators comes from a wide range of recording and monitoring schemes, listed in the report.

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