How does Scotland’s biodiversity measure up?

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This blog explains the findings of a recent report from the Natural History Museum and RSPB that ranks Scotland and the rest of the UK poorly for biodiversity ‘intactness’ compared to most other countries and territories. It also discusses other research on the state of Scotland’s biodiversity. The blog is published the day before World Environment Day on 5 June 2021 which marks the launch of the UN Decade on Ecosystem Restoration and associated calls for urgent action to revive the world’s damaged ecosystems.

Biodiversity – and why we measure it

Biological diversity – or biodiversity – is the variety of life on earth. It includes genetic diversity within species and variation between species and ecosystems. Scotland’s biodiversity includes a variety of marine and land-based ecosystems – where living organisms interact with each other and their non-living environment. Scotland is home to an estimated 90,000 animal, plant and microbe species. Some species, like the Scottish primrose and the Fair Isle wren, are found nowhere else in the world. Some of Scotland’s habitats are also very rare, like coastal machair found only in Scotland and Ireland.

“Scottish Primrose” by Kristel Jeuring is licensed under CC BY 2.0

Biodiversity is fundamental to the ability of humans to survive and thrive. We depend on nature’s diversity: from the soil microbes that sustain our crops, to the forests that absorb and store atmospheric carbon, mitigating climate change. Our lives have always been, and modern economies remain, embedded in nature. Yet, accelerating rates of biodiversity loss since the Industrial Revolution now exceed limits considered safe for humanity. This is often termed the ‘nature crisis’ or the ‘ecological crisis’ and is closely connected with the climate crisis.

The vertebrate species extinction rate has accelerated since the Industrial Revolution and is now up to 100 times higher than it would be without extinctions caused by humans.

This figure from Ceballos et al. (2015) shows biodiversity loss by one measure: the cumulative vertebrate species recorded as extinct or extinct in the wild by the IUCN. The dashed black curve represents the background extinction rate – the number of extinctions expected without extinctions caused by humans.

The nature crisis is complex and aspects of it are invisible to many people, partly because our reference points for measuring biodiversity loss can be misleading. If we think back to how nature looked when we were children and compare it to now, we might not think that much biodiversity loss is occurring. This is an example of what researchers have termed ‘shifting baseline syndrome’, where each new generation come to see a degraded environment as a new baseline. Moreover, if we live somewhere where there have been recent conservation successes, we might think that nature is doing really well.

Measuring biodiversity over long timescales (greater than living memory and historical records) and large areas can tell a different story. Assessments and estimates of biodiversity are therefore important for establishing trends, understanding how biodiversity is changing across different parts of the world and what that could mean for the future.

Scotland’s biodiversity – 56% remains intact

Biodiversity is vast and complex – so how do we measure it? There isn’t a single metric that can measure all of biodiversity, but there are several good indicators available. A recent report headed by the Natural History Museum, collaborating with the RSPB, used an indicator called the biodiversity intactness index (BII) to compare biodiversity intactness in the UK with other nations and territories.

BII measures the change in abundance (number of individuals of the same species) of a wide variety of species, usually plants and animals, in a given place. BII indicates the proportion of nature that remains following human activities on land, such as converting forest to cropland, including historical losses. This is usually done by comparing sites with similar places where there has been minimal human use. It is often expressed as a percentage, where 100% indicates that nature is fully intact. BII can be greater than 100% for some organisms if human activities have led to an increase in their abundance.

The report finds that the UK’s biodiversity intactness is 50%: it has retained half of its historic land-based biodiversity. Scotland has a BII of 56%, with slightly more biodiversity intact compared to other parts of the UK. The report ranks the countries and territories assessed from 240 (the country/territory with the most biodiversity intact) to 1 (least biodiversity intact). The UK as a whole and UK territories separately are amongst the 240 countries and territories included in the ranking.

This figure is based on data presented in the report by the Natural History Museum in collaboration with the RSPB ranking biodiversity intactness as measured by BII for 240 countries and territories, where each point represents a country or territory.

It is important to note that the state of Scotland’s biodiversity – by any measure – doesn’t tell a full story of Scotland’s role in biodiversity loss. For example, resource extraction for export is a major cause of biodiversity loss in developing countries. Scotland’s BII indicates biodiversity intactness on Scottish land only, not Scotland’s impact on global biodiversity, including via consumption of resources extracted abroad.

How to measure biodiversity intactness

BII was developed by researchers in 2005 and since then has been adopted by major international organisations like the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services and used in assessments such as the recent Dasgupta Review on the Economics of Biodiversity, in combination with other indicators.

The Natural History Museum and RSPB used estimates of BII based on data from a project called PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems). The PREDICTS database is publicly available and incorporates biodiversity data from over 29,000 sites worldwide. Instructions on how to use the data to calculate BII are also publicly available. The team behind PREDICTS have published research estimating that biodiversity intactness, as measured by BII, has reduced by 10% or more across 58.1% of the Earth’s land area.

Recent biodiversity trends in Scotland

Much biodiversity loss in Scotland as reflected in its BII score is likely the result of historic declines. Evidence from elsewhere explores nuances in recent Scottish biodiversity trends. For example, the State of Nature Scotland 2019 report found that between 1994 and 2016, 49% of Scottish species decreased and 28% increased in abundance. It reported that some pressures on biodiversity, such as freshwater pollution, have decreased in recent decades but that the most harmful human pressures continue to cause biodiversity declines.

The report highlights some conservation successes, such as the relative recovery of corncrake populations since the 1990s following severe historic declines, though this species remains at the highest level of conservation concern for UK birds. However, overall the abundance and distribution of Scotland’s species have declined, including in the last 10 years and the pressures that drive biodiversity loss are collectively continuing to have a negative impact on nature. The report says, “there has been no let-up in the net loss of nature in Scotland”.

What about marine biodiversity?

The PREDICTS data and BII analysis don’t measure biodiversity trends in the ocean. The area of Scotland’s seas is about six times larger than its land area, so it’s important to monitor biodiversity change here too. The State of Nature Scotland 2019 report identifies recent trends in marine environments. For example 12 breeding seabird species have declined in abundance by an average of 38% between 1986 and 2016. Plankton communities have changed in response to climate change which impacts fish and birds higher up the food chain. There has been recent recovery of some fish stocks following improved fisheries management, but the impacts of unsustainable fishing persist.

Scotland’s response to the nature crisis

A full exploration of Scotland’s response to the nature crisis is outside the scope of this blog but there have been important recent announcements. For example, the Scottish Government announced intentions for a post-2020 biodiversity strategy, including committing to protecting 30% of land areas by 2030. In her Priorities of Government Statement, the First Minister announced the aim to “protect and enhance our natural habitats”, increase woodland creation by 50% and invest £250 million in peatland restoration this decade.

SPICe plans to publish more on the nature crisis in a research briefing ahead of the upcoming Convention on Biological Diversity COP15.

Ellie Wood

Environment, Rural, Constitution and International Research