The effects of a decade of agri-environment intervention in a lowland farm landscape on population trends of birds and butterflies
Author(s): Redhead, J.W., Hinsley, S.A., Botham, M.S., Broughton, R.K., Freeman, S.N., Bellamy, P.E., Siriwardena, G., Randle, Z., Nowakowski, M., Heard, M.S. & Pywell, R.F.
Published: August 2022
Journal: Journal of Applied Ecology
Digital Identifier No. (DOI): 10.1111/1365-2664.14246
Food production and wildlife conservation are often thought of as incompatible goals, and it is rare that conservation studies consider both economics and long-term changes in ecology. However, a decade-long study at a commercial arable farm in Buckinghamshire has found that agri-environment schemes significantly increased local bird and butterfly populations without damaging food production, offering hope for the UK’s farmland birds and butterflies.
Declines in farmland biodiversity remain evident despite over three decades of research and implementation of agri-environment schemes (AES). Although positive effects of AES are often demonstrated locally or in the short term, studies exploring longer-term trends in biodiversity often show contradictory results. Evidence for the potential of AES to drive beneficial changes in populations remains sparse, especially for mobile taxa such as birds and butterflies.
We analysed the abundance of 12 widespread bird and 9 butterfly species from a 10-year study of AES intervention in a farmland landscape in southern England. We compared estimates of annual population growth rates from our study landscape with rates derived from large-scale national monitoring schemes in equivalent landscapes without substantial AES.
Species trends in our study landscape were frequently stable or increasing, in contrast to concurrent declining trends in equivalent landscapes without AES. These differences were significant for total abundance of granivorous species and for chaffinch Fringilla coelebs, blue tit Cyanistes caeruleus and great tit Parus major individually. For butterflies, differences in trends were significantly more positive for gatekeeper Pyronia tithonus and green-veined white Pieris napi, while small white P. rapae showed a trend that was significantly more negative in our study landscape.
Our results demonstrate that, for some bird and butterfly species, the higher abundances associated with areas of AES uptake within a typical commercial farmland landscape can co-occur with positive or stable population trends over long time scales and that these trends can show significant differences from those in equivalent landscapes without substantial AES interventions. Our results suggest that previously observed inconsistencies in AES benefits may in part reflect a lack of long-term studies with accurate data on AES uptake and quality (i.e. successful implementation and management). Our results, thus, affirm the importance of delivering and monitoring high-quality AES options if the design and implementation of the next generation of AES is to achieve significant benefits for biodiversity.
The widespread expansion and intensification of farming practices over the 20th century has brought about well-known declines in farmland biodiversity. A key mechanism for attempting to reverse these declines has been agri-environment schemes (AES), which offer financial compensation for taking land out of agricultural production or changing farming practices to achieve environmental targets. AES have been established in many countries for over three decades, with a corresponding history of research into their effectiveness. However, there is still debate regarding their true potential to reverse population declines, especially for more widespread and mobile species of farmland birds and butterflies, which continue to show declines despite over 20 years of AES aiming to support their recovery.
Long-term studies of population trends on farms with known levels of high-quality AES, compared with spatially separated controls, are rare, and limited almost entirely to birds. The study reported here is important in this respect, providing valuable insight for both birds and butterflies from a long-term (10 years) experiment in southern England, within a large, well-characterised farm landscape with high-quality AES.
The study set out to explore whether the results of previous studies demonstrating higher abundances of widespread farmland bird and butterfly species in the parts of the study landscape with higher AES uptake were associated with positive population trends over the 10-year time series following establishment of AES. These trends were then compared with concurrent trends from national monitoring schemes in equivalent control landscapes (i.e. similar climate, soils, topography, land cover composition and landscape structure but without substantial AES).
Monitoring data collected within the study landscape were compared with comparable national data derived from the BTO/JNCC/RSPB Breeding Bird Survey and the Wider Countryside Butterfly Survey. Population trends were analysed by using generalised linear models, revealing that species trends within the study landscape were frequently stable or increasing, in contrast to concurrent declining trends in equivalent landscapes without AES. These differences were found to be statistically significant for the total abundance of granivorous bird species, and for Chaffinch, Blue Tit and Great Tit individually. For the butterfly species, differences in trends were significantly more positive for Gatekeeper and Green-veined White, while the reverse was the case for Small White.
The results demonstrate that, for some bird and butterfly species, the higher abundances associated with areas of AES uptake within a typical commercial farmland landscape can co-occur with positive or stable population trends over long time scales, and that these trends can show significant differences from those in equivalent landscapes without substantial AES interventions. The results underline the importance of delivering and monitoring high-quality AES options if the design and implementation of the next generation of AES is to achieve significant benefits for biodiversity.
The authors are extremely grateful to the Hillesden Estate, especially Robin Faccenda, Richard Franklin and Jamie Orpwood. Thanks to Sarah and Lucy Hulmes, Jodey Peyton, Nadine Mitschunas, Bjorn Beckmann, Marta Maziarz and Mark Jitlal for undertaking field surveys and to Lucy Ridding and Ben McCrindle for assistance with digitising data. UK Wider Countryside Butterfly Survey data are copyright and database right Butterfly Conservation, the UK Centre for Ecology & Hydrology, British Trust for Ornithology, and the Joint Nature Conservation Committee (JNCC), 2020. The UK Breeding Birds Survey is jointly funded by the BTO, JNCC and the Royal Society for the Protection of Birds (RSPB). The authors are indebted to the thousands of volunteers who contribute data to the WCBS and BBS. Both phases of the Hillesden experiment were funded by the Department for Environment, Food & Rural Affairs (Defra). Thanks to all reviewers who gave constructive feedback on an earlier version of this manuscript.
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