Will Manley

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.

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.

Managing set-aside for field voles (Microtus agrestis)

Abstract Set-aside is a potentially important habitat for field voles, ( Microtus agrestis ), populations of which may have declined in lowland Britain. We hypothesized that field vole abundance would increase with the length of time set-aside was left in situ. To test this we monitored development of field vole populations in the first 2 years after set-aside establishment, and on older set-aside we related abundance to set-aside age and vegetative characteristics. Voles were not recorded on set-aside until 9 months after establishment, and populations only began to increase after nearly 2 years. In set-aside fields 2–9 years old, vole abundances were not related to age, but increased with the proportion of grasses and litter in the sward. Management practices such as sowing with a grass seed mix, mowing at least once annually and leaving set-aside in place for >2 years are likely to benefit field voles.

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.