In order to mitigate the effects of climate change, the UK government has set a target of achieving net zero greenhouse gas (GHG) emissions by 2050. Agricultural GHG emissions in 2017 were 45.6 million tonnes of carbon dioxide equivalent (CO2e; 10% of UK total GHG emissions). Farmland hedgerows are a carbon sink, storing carbon in the vegetation and soils beneath them, and thus increasing hedgerow length by 40% has been proposed in the UK to help meet net zero targets. However, the full impact of this expansion on farm biodiversity is yet to be evaluated in a net zero context. This paper critically synthesises the literature on the biodiversity implications of hedgerow planting and management on arable farms in the UK as a rapid review with policy recommendations. Eight peer-reviewed articles were reviewed, with the overall scientific evidence suggesting a positive influence of hedgerow management on farmland biodiversity, particularly coppicing and hedgelaying, although other boundary features, e.g. field margins and green lanes, may be additive to net zero hedgerow policy as they often supported higher abundances and richness of species. Only one paper found hedgerow age effects on biodiversity, with no significant effects found. Key policy implications are that further research is required, particularly on the effect of hedgerow age on biodiversity, as well as mammalian and avian responses to hedgerow planting and management, in order to fully evaluate hedgerow expansion impacts on biodiversity.

Conventional farming in the UK has had adverse effects on farmland biodiversity, particularly during post-war intensification of agriculture. Efforts have been made in the reversal of these effects, with much of the literature reporting a mixture of findings. At a localised scale, these efforts have been noticeable with RSPB Hope Farm observing a 200% increase in bird territory numbers from 2000 to 2012, achieved with the wide implementation of agri-environment schemes (AES) on the farm. We aimed to investigate the spatio-temporal drivers of territory density in four hedgerow specialist bird species using a thirteen year (2000–2012) dataset of hedgerow management, in-field cropping and field boundary habitat records. Territory maps were used to calculate territory counts for each hedgerow across the time period. Generalised Linear Mixed Models were used to model territory counts for each habitat variable. These findings demonstrate that for Emberiza citrinella, Carduelis cannabina and Sylvia communis, presence of oilseed rape (OSR) is a strong predictor of higher territory numbers, leading to a doubling in territory density compared to absence of OSR. However, tree presence in hedgerows was a negative predictor of territory numbers for these species. Opposing trends were observed for Carduelis chloris, which exhibited significantly greater territory numbers in roadside hedgerows, hedges with trees and when adjacent fields were not sown with a main crop. Management of hedges was a weak predictor of S. communis territories. This demonstrates that crop type, AES features, tree presence and location of hedgerows are drivers of farmland bird territory numbers. These findings validate the usefulness of more sustainable, wildlife-friendly farming under previous CAP rules and have important implications for post-Brexit farming policy, such as the Agriculture Bill.