Ruth E. Feber

Benefits of organic farming to biodiversity vary among taxa

Habitat and biodiversity differences between matched pairs of organic and non-organic farms containing cereal crops in lowland England were assessed by a large-scale study of plants, invertebrates, birds and bats. Habitat extent, composition and management on organic farms was likely to favour higher levels of biodiversity and indeed organic farms tended to support higher numbers of species and overall abundance across most taxa. However, the magnitude of the response varied; plants showed larger and more consistent responses than other taxa. Variation in response across taxa may be partly a consequence of the small size and isolated context of many organic farms. Extension of organic farming could contribute to the restoration of biodiversity in agricultural landscapes.

The effects on butterfly abundance of the management of uncropped edges of arable fields

1. The abundance and species richness of butterflies on expanded-width uncropped arable field edges, which were subject to 10 contrasting, experimental management regimes, were measured using transects in 1989, 1990 and 1991. The effects of the management regimes on a number of botanical variables, likely to be of importance to butterflies, were measured. 2. On the experimental field edges, butterfly abundance and species richness fluctuated between years and peaked at different times each year. 3. Butterfly abundance and species richness differed between experimental treatments. Plots which were either cut in the spring and autumn, or not cut at all, attracted more individuals and species of butterfly than did plots cut in the summer. Sowing with a grass and wild flower seed mixture increased butterfly abundance. Butterfly abundance declined on swards sprayed once annually with herbicide. 4. Mowing, sowing and spraying had significant effects on mean flower abundance, on the annual and perennial components flowering in the sward, and on the abundance of commonly used nectar sources and larval host-plants. 5. Stepwise multiple regression analyses on butterfly and plant data showed that the abundance of adults of most butterfly species was most closely associated with the abundance of flowers of key nectar source species. 6. The results are discussed in relation to resource provision for larval and adult butterfly stages. Recommendations (emboldened in the text) are made for the conservation management of butterflies on arable farmland.

The effects of organic farming on pest and non-pest butterfly abundance

Butterfly transects were conducted on eight pairs of organic and conventional farms in the UK in 1994, and ten pairs of farms in 1995. Each transect included areas of conventional and organic farmland. All species seen, and the abundance of each species, were recorded separately for the uncropped field boundary and the crop edge. In both years, significantly more non-pest butterflies were recorded on organic than on conventional farmland, and more non-pest butterflies were recorded over the uncropped boundary habitat than over the crop edge habitat in both systems. By contrast, there was no significant difference in either year in the abundance of two pest species, Pieris brassicae (the large white) and Pieris rapae (the small white) between the two systems. Implications of the results for the conservation of butterflies within agricultural systems are discussed.

Integrating the environmental and economic consequences of converting to organic agriculture: evidence from a case study

In the current debate about the future of food quality, the merits of organic agriculture are frequently championed, but few studies have sought to integrate the changes in soil conditions, biodiversity and socio-economic welfare linked to the conversion from non-organic to organic production. This article aims to undertake this approach with respect to one case study. Its conclusions may not be representative for all organic conversions, but the findings are of relevance at a time of debate over changing patterns of subsidies and other incentives in agricultural policy. The study showed that there were demonstrable differences in overall environmental conditions in the comparison of organic and non-organic farming, with field evidence of increased species diversity, and an eventual improvement in the profitability of the organic farming regime. The broad conclusion is that there are definite environmental and economic advantages arising from organic agriculture that are not fully reflected in the present pattern of agricultural incentives. The study also showed that variations in farm management practice strongly influence the notion of on-farm and off-farm environmental consequences. The implications of these findings for the future of sustainable agriculture and for interdisciplinary science are also discussed.

Mammals, agri‐environment schemes and set‐aside – what are the putative benefits?

1. The impacts of agricultural intensification on farmland wildlife have been the subject of increasing concern, particularly over the last two decades. Population declines have occurred for a number of mammalian species, sometimes drastically so, and changes in farming practice are believed to be significant contributory factors. 2. The major policy instruments for delivering environmental benefits on farmland are agri-environment schemes. These encourage farmers to adopt more environmentally sensitive farming practices to promote farmland biodiversity. Additionally, compulsory set-aside, which reduces agricultural surplus, could also have positive impacts on wildlife. In this paper we consider some of the putative benefits of agri-environment schemes and set-aside for mammals. 3. We review how establishment and management options within agri-environment schemes and set-aside might affect habitat resources for mammals. For example, conservation headlands increase plant and invertebrate resources within the crop edge for mammals such as wood mice. Grassy field margins can support communities of smaller mammals, and hedgerows may act as important commuting and hunting routes. Their potential will depend on factors such as seed mixtures used, timing and severity of cutting, and length of time they have been in place. 4. At a farm level, habitat heterogeneity may be increased through organic agriculture, which is supported by some agri-environment schemes. Studies suggest significant benefits to mammals, including wood mice and bats. However, it is increasingly recognized that effective conservation of farmland mammals must seek solutions at the landscape scale, addressing such issues as habitat connectivity between farms. One approach may be the better targeting of scheme agreements. 5. We suggest that agri-environment schemes and set-aside can contribute to the conservation of mammals on farmland. Recent policy changes are likely to have further positive impacts on farmland wildlife but appropriate mammal monitoring programmes must be developed rigorously to assess their effects.

Habitat use by wood mice ( Apodemus sylvaticus ) in a changeable arable landscape

Wood mice Apodemus sylvaticus are potentially useful indicators of change in arable ecosystems. Here we focus on changes resulting from removal of land from arable production under the set-aside scheme. Wood mice were radio-tracked to compare: (a) their use of set-aside, crop and hedgerow before and after harvest; (b) set-aside configured as margins and as a 3 ha block; (c) cut and uncut 20-m wide set-aside margins. Males had larger home ranges, and were more mobile than females. Ranges were larger, and animals more mobile, before harvest than afterwards. There were no differences in range sizes of breeding and non-breeding animals after harvest, suggesting that changes in habitat use were not a function of cessation of breeding. Before harvest, wood mice used habitats within their ranges at random, and their ranges contained a high proportion of cropped area. After harvest they preferred hedgerow and avoided margin set-aside within their ranges, but did not similarly avoid the set-aside block. The proportion of cropped area within their ranges decreased after harvest, and the proportion of margin increased. Our evidence suggests wood mice avoided using the area adjacent to the hedgerow, perhaps to avoid predators. Uncut set-aside patches were favoured and cut patches avoided, possibly in response to differences in food availability and levels of protection from predators. These results confirm that wood mice are useful indicators of change in arable landscapes.

Does organic farming benefit farmland birds in winter

The generally higher biodiversity on organic farms may be influenced by management features such as no synthetic pesticide and fertilizer inputs and/or by differences in uncropped habitat at the site and landscape scale. We analysed bird and habitat data collected on 48 paired organic and conventional farms over two winters to determine the extent to which broad-scale habitat differences between systems could explain overall differences in farmland bird abundance. Density was significantly higher on organic farms for six out of 16 species, and none on conventional. Total abundance of all species combined was higher on organic farms in both years. Analyses using an information-theoretic approach suggested that both habitat extent and farm type were important predictors only for starling and greenfinch. Organic farming as currently practised may not provide significant benefits to those bird species that are limited by winter food resources, in particular, several declining granivores.

Identifying high-quality pond habitats for Odonata in lowland England: implications for agri-environment schemes

Abstract.  1. Agricultural intensification has contributed to severe declines in odonate (dragonfly and damselfly) populations. The objective of our study is to benefit current measures for the conservation of odonates by establishing the conditions favourable to Odonata and focusing on ponds within agricultural land.

Habitat preference and mobility of Polia bombycina: are non-tailored agri-environment schemes any good for a rare and localised species?

General agri-environment schemes (AES) have been shown to benefit widespread species, but there is little information on the extent to which rare, more localised, species may also benefit. We tested whether AES options aimed at increasing general biodiversity also benefit a highly endangered moth, Poliabombycina, without species-specific tailoring. We assessed effects on its abundance of two AES options, wide field margins and hedgerow trees, using light traps at the landscape-scale and for mark-release-recapture at the farm-scale. We hypothesized that abundance would be highest at wide field margins and at hedgerow trees, and that if hedgerow trees conferred a positive effect, individuals would be more likely to follow hedgerows than crossing exposed fields while on the move. The results showed that significantly more individuals were captured at sites with a hedgerow tree. Numbers were also higher at wide margins, but this was not statistically significant, and no individuals were caught at field centres. Our study suggests that general options within appropriately designed and implemented AES aimed at increasing overall biodiversity in intensive agricultural landscapes have the potential to not only benefit common, widespread habitat generalists, but some rare and more endangered species as well. P. bombycina serves as an example of how general AES options, existing and novel ones alike, might cater for the needs of rare and localised species. As the precise ecological requirements of most invertebrate species remain unknown, we urge scientists and governments to address the challenge to research and design truly general AES, which options should be able to deliver not only for widespread species but also for the less-widespread counterpart of farmland biodiversity.

Manipulating the abundance of Lepthyphantes tenuis (Araneae: Linyphiidae) by field margin management

Populations of the linyphiid spider Lepthyphantes tenuis were sampled in field margins in May, July and September in 1990–1991 and 1995–1996. Field margins were subjected to 10 grassland management regimes, which included the effects of spraying the herbicide glyphosate, cutting, leaving vegetation in situ after the cut, sowing and a control. These treatments were randomised within six complete blocks at the University of Oxford’s farm at Wytham. Cutting vegetation had an immediate effect on number of L. tenuis in both spring and summer. Cutting margins in summer had a more persistent effect on populations of L. tenuis than did cutting margins in spring. The effect of cutting was not mitigated by leaving cut vegetation in situ, but no cutting ensured higher number of L. tenuis in margins, an indication that height and structural complexity of grassland vegetation were important in determining population size. Significantly fewer spiders were found in July and September plots which had been sprayed with herbicide in late June/early July. However, spider numbers were not affected by glyphosate application when samples were taken nearly a year later. Sowing a wildflower seed mixture had no significant effects on number of this generalist predator although other invertebrate groups did benefit. Field margins provided an excellent source habitat for L. tenuis. Habitats that border crop fields acted as a refugia for many other beneficial invertebrates and should be retained as an important component of the agricultural landscape.