Impacts of Agricultural Change on Farmland Biodiversity in the UK

NIGEL D. BOATMAN, HAZEL R. PARRY, JULIE D. BISHOP AND ANDREW G.S. CUTHBERTSON

1 Introduction

Over the past 50 years, there has been a marked decline shown by many species closely associated with lowland farmland in the UK, which is widely considered to be a key issue in British nature conservation. Increased availability of survey data has meant it is now possible to quantify changes in biodiversity for some groups. Changes have occurred in many farming practices and these have affected biodiversity in a variety of ways. Mixed agriculture in Britain has been lost and farms have become specialised; traditional crop rotations have declined and pastoral and arable farming have become polarised. Farming has intensified; for example, wheat yields in Scotland increased by 201% during the period 1967–1999 due to more effective tillage, application of fertilisers and pesticides and plant breeding. Field sizes have increased, reducing non-crop habitat at field margins. Other changes include more autumn sowing of crops and more efficient harvesting, more non-inversion tillage, drainage and reseeding of grassland, a switch from hay to silage, increased stocking rates and the use of avermectin wormers. This has all impacted upon wildlife species that inhabit lowland farmland landscapes. Upland farming and livestock grazing has also intensified during this time. High grazing pressure, especially by sheep, has had a negative impact upon vegetation and wildlife in many upland regions of Britain.

Much of the focus on biodiversity conservation within agricultural landscapes has been on the conservation of rare or rapidly declining species, driven in part by the UK Biodiversity Action Plan, the Government's response to the 1992 Convention on Biological Diversity, and also by the adoption of a commitment as part of the Government's Public Service Agreement to "care for our natural heritage, make the countryside attractive and enjoyable for all and preserve biological diversity by reversing the long-term decline in the number of farmland birds by 2020, as measured annually against underlying trends; and bringing into favourable condition by 2010 95 per cent of all nationally important wildlife sites'. However, other issues of importance in the context of agriculture include whether or not increased biodiversity or species richness enhances ecosystem functions such as primary productivity and nutrient retention or ecosystem services such as pollination and biological control. Non- crop habitats on farmland are usually more species diverse than cropped fields or intensive grasslands, and the areas of non-crop habitat may even become islands of species richness if dispersal across suitable habitat is limited. However, over-zealous "tidying" of non-crop areas can reduce value for biodiversity and there may be a conflict here between the concept of an attractive (which for many equates with 'tidy') countryside and the wish to see it populated by diverse fauna and flora.

A review of changes in biodiversity on arable farmland concluded that around half of plant species, a third of insect species and four-fifths of bird species characteristic of farmland have declined. This chapter reviews the key changes that have occurred in agriculture during the second half of the twentieth century, set in the context of evolving policies on agricultural support and their impact on the characteristic fauna and flora of the farmed landscape. It concludes by considering the most recent reform of the EU Common Agricultural Policy and the implications of the shift away from production support and towards greater provision of incentives for environmentally sustainable management. A.D. Watt et al. present additional related and complementary material in Chapter 6 of this volume, with particular emphasis on the wider European aspects of land use change.

2 The Post-war Intensification of Agriculture

During and following the Second World War, agricultural policy focused on maximising food production. This resulted in an unprecedented level of change and intensification accompanied by subsidies ensuring prolonged price stability throughout the second half of the twentieth century. Although highly successful, this policy has been blamed for large declines in biodiversity within both the UK and Europe. Farming practices became polarised, where arable farming dominated the east of the UK and grassland/livestock farming the west, whilst mixed farming and the use of grass leys declined.

The key changes in both arable and grassland landscapes have been identified. In arable landscapes, the key changes that took place in the last forty years include simpler rotations and block cropping; a switch from spring to autumn cropping; more efficient harvesting and sealed grain storage; and recently, more non-inversion tillage. On grasslands, key changes in the last forty years include more drainage and reseeding; a switch from hay to silage; a move away from dicotyledonous fodder crops and barley grown for fodder to intensive grass and forage maize; increased stocking rates; and the introduction of avermectins. In the lowlands, there was a trend to larger, specialised farms with large fields and fewer hedgerows and increased use of pesticides and fertilisers.

2.1 Land Drainage

Land drainage grants were introduced in 1940 and abolished in 1987. The area of land drained reached a peak of 100 000 ha year in the 1970s. Most land drainage was undertaken to improve extensively managed or rough grassland but 40% was carried out for conversion to arable cropping. Remaining wet grassland habitats have also been affected by the drainage of adjacent arable land. Wet grasslands support distinctive plant communities and often contain rare species that are adapted to local conditions. Land drainage has also impacted...