Terrestrial insects and other invertebrates have continued to decline in Great Britain over the past 30 years, particularly in intensively farmed areas, a new study has found. This is despite the introduction of some agri-environment schemes to try to protect biodiversity, which provides important services for humans, ranging for pollination to pest control.
The study by the UK Centre for Ecology & Hydrology (UKCEH) found that bees and spiders are the worst-affected invertebrates, possibly because they rely more heavily on semi-natural habitats for food and shelter.
The researchers analysed citizen science data from 1990-2019 for 1,535 species of bees, hoverflies, ground beetles, ladybirds, true-bugs and spiders. They divided mainland Britain’s rural landscape into 1km square grids, each classified as high-, low- or no- cropland cover. They then looked at how the proportion of these grid squares occupied by each species changed over time.
The study found there were continuing general reductions in the distribution of invertebrates in Britain throughout this timeframe but declines were greater in regions with a high proportion of arable or horticultural crop cover.
The way we farm our land has transformed since the Second World War. Intensive agricultural practices, such as mechanisation, chemical use and farming land that was previously wildflowers or hedgerows, have successfully increased food production to feed a growing population at relatively affordable prices. But this has come at a high cost to biodiversity, say authors of the new study, which has been published in the journal Proceedings of the Royal Society B.
UKCEH ecological modeller Dr Francesca Mancini led the research, which was funded by the Natural Environment Research Council. She says: “Invertebrates are one of the most diverse groups in agricultural landscapes but they are also particularly sensitive to intensive farming practices. There have been attempts to mitigate negative impacts since the 1990s and the fundamental question has been what effect these have had.
“Despite successful conservation at individual farms where farmers have successfully implemented sustainable practices, our study shows that more needs to be done to conserve and restore invertebrate populations at a national scale.”
“Changes in agricultural policies and philosophy provide opportunities to restore invertebrate populations across the UK, though given current trends, we are facing a significant challenge.”
The study found:
• Overall, across all species groups, there was an average 5% decline in areas of high cropland cover over the 30-year period studied, while in areas of low cropland cover declines were around 2%.
• The spiders were the group with the most severe declines - 7% in areas of high cropland cover and 3% in areas of low cropland cover.
• Bees declined by around 4% in areas of high cropland cover and around 1% in areas of low cropland cover.
The researchers point out that it is difficult to make comparisons with no cropland areas because these are largely concentrated in northern Britain, with different climate and land use.
They say that the extent of these declines is significant in ecological terms if they are part of a continuing trend. It is likely that reductions in populations were greater prior between the 1940s and 1990s when there was intensive agriculture and few agri-environment schemes, though there are few relevant species data in the post-war years for comparison.
However, it is possible to reverse these declines. Dr Mancini points to UKCEH’s long-term Defra-funded experiment at Hillesden estate in Buckinghamshire, where 5% of the 1,000-hectare commercial farm was set aside for wildlife habitats. This resulted in increases in local bird and butterfly populations without affecting the farm’s overall food production.
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Notes to editors
Mancini F, Cooke R, Woodcock BA, Greenop A, Johnson AC, Isaac NJB. 2023. Invertebrate biodiversity continues to decline in cropland. Proceedings of the Royal Society B. DOI: 10.1098/rspb.2023.0897. Open access.
The research was funded as part of two UKCEH-led projects supported by the Natural Environment Research Council, part of UK Research and Innovation. These were ChemPop (grant number NE/S000100/1), which investigated the impact of chemicals on wildlife populations and the GLiTRS project (NE/V007548/1), which looked at how human activities cause global insect declines.
The species trends for the new paper were based on data collected by volunteers from the Bees, Wasps and Ants Recording Society, the Hoverfly Recording Scheme, the UK Ladybird Survey, the Spider Recording Scheme, the Ground Beetle Recording Scheme and the Terrestrial Heteroptera Recording Scheme.
About the UK Centre for Ecology & Hydrology (UKCEH)
The UK Centre for Ecology & Hydrology is a world-leading centre for excellence in environmental sciences across water, land and air. Our research makes a major contribution to the development of sustainable, productive farming systems that are resilient to climate change and protect biodiversity. We identify key drivers of biodiversity change, develop tools and technologies for monitoring biodiversity, and provide robust socio-economic and environmental solutions for restoring biodiversity.
The UK Centre for Ecology & Hydrology is a strategic delivery partner for the Natural Environment Research Council, part of UK Research and Innovation.