Action: Provide or retain set-aside areas in farmland
- We found 34 studies comparing use of set-aside areas with control farmed fields. Two were reviews, none were randomized, replicated, controlled trials. Of these, 20 (from Austria, Finland, Germany and the UK) showed benefits to or higher use by all wildlife groups considered. Twelve (from Finland, Germany, Ireland, Sweden and the UK) found some species or groups used set-aside more than crops, others did not. Two studies (all from the UK) found no effect, one found an adverse effect of set-aside.
- Three of the studies, all looking at skylarks, went beyond counting animal or plant numbers and measured reproductive success. Two from the UK found higher nest survival or productivity on set-aside than control fields. One from the UK found lower nest survival on set-aside.
- Fifteen studies (from Belgium, Germany, Sweden and the UK) monitored wildlife on set-aside fields, or in landscapes with set-aside, without directly comparing with control fields or landscapes. Three looked at set-aside age and found more plants or insects on set-aside more than a year old. Two compared use of different non-crop habitats and found neither insects nor small mammals preferred set-aside. Two showed increased bird numbers on a landscape scale after set-aside was introduced, amongst other interventions. Eight looked at effects of set-aside management such as use of fertilizer and sowing or cutting regimes.
- A systematic review from the UK found significantly higher densities of farmland birds on fields removed from production and under set-aside designation than on conventionally farmed fields in both winter and summer.
Allocation of some farmland to set-aside (fields taken out of production) was compulsory under European agricultural policy from 1992 until 2008. The idea was to reduce production. However, set-aside has also been promoted as a method of enhancing biodiversity within farmland. Set-aside can be rotational (in a different place every year or two) or non-rotational (same place for 5-20 years) and fields can either be sown with fallow crops or left to naturally regenerate. Unlike fallow land left for the benefit of ground-nesting birds or arable plants, set-aside is not ploughed or harrowed except for the purpose of sowing.
Set-aside is often managed by cutting and/or spraying. In some cases, set-aside land has had strips of wildflowers or grasses sown on it. Evidence for the effects of this management has been included under the following interventions: ‘Plant nectar flower mixture wildflower strips’ and ‘Plant grass buffer strips margins around arable or pasture fields’.
Supporting evidence from individual studies
A replicated, controlled study of 44 fields on five farms over two years in Hampshire and Wiltshire, UK (Moreby & Aebischer 1992) found that, overall, chick food was three times higher on fallow set-aside than on wheat. Significantly higher numbers of leafhoppers (Auchenorrhyncha) were found on first and second-year set-aside (53 vs 9/sample) and true bugs (Heteroptera) in second-year set-aside than wheat (24 vs 6). In contrast, ground beetles (Carabidae; 0.3 vs 0.8), rove beetles (Staphylinidae; 6 vs 14), leaf beetles (Chrysomelidae; 0.7 vs 1.4), aphids (Aphididae; 31 vs 74) and flies (Diptera; 38 vs 67) were all significantly less abundant on set-aside than crops (respectively). Numbers in set-aside and wheat did not differ for spiders (Araneae; 13 vs 10/sample), springtails (Collembola, 855 vs 661) or larvae of butterflies, moths and sawflies (Lepidoptera and Symphyta; 0.4 vs 0.7). Fields in the first year of the UK’s five-year set-aside scheme (left fallow or drilled with grass) were sampled in June 1990. In 1991, 15 fields at two of the five farms were re-sampled to evaluate second-year fallow set-aside. Invertebrates were collected using a D-Vac suction sampler in the headlands of fields, 3 m from the field edge. Five samples of 0.5 m² were taken at each site.
A replicated site comparison study in 1990-1991 on 1-year-old and permanent set-aside fields in a small-scale arable region in Germany (van Elsen & Gunther 1992) found higher weed cover on permanent set-asides (89.3 – 94.1%) than on 1-year-old set-asides (74.2 - 78.5%). The number of weed species was somewhat higher along the edge of 1-year-old (average 35.1 species) than of permanent set-asides (30.7 spp.), but no such difference was found in the field centre (28.2 spp. vs 27.8 spp.). Effects of set-aside age were strongly trait and species-dependent. For example, declining, rare and threatened weed species were more common in 1-year-old (122 to 154 recordings) than on permanent set-asides (91 to 110 recordings). Most of the investigated permanent and 1-year-old set-aside fields were left uncultivated, but occasional fields were sown. In each field, two 2 m x 50 m long transects (one along the field edge and one 10 m away towards the field centre) were surveyed repeatedly. Cover estimates for each plant species and total vegetation cover were recorded. No statistical analyses were performed on the data.
A replicated, controlled site comparison study from May to October 1990 in 40 farmland sites (10 field types, four replicates each) near Karlsruhe, south Germany (Gathmann & Tscharntke 1993) found significantly more species of solitary bee in artificial reed stem nests in unsown sites with naturally developed vegetation (average 7.9 species) than in sown fields, including crops and sown grass/clover fields (average 4.6 spp.). Bee species richness increased with increasing age of the unsown set-asides and with increasing plant diversity. Wasp diversity was similar in the different field types (1 to 4 spp./field type). Smaller bee and wasp species inhabited fields with high plant diversity but were absent in fields with low plant diversity. Foraging flights took twice as long in fields with low plant diversity (35 min) than in fields with high plant diversity (15 min) for two investigated bee species (leaf-cutter bee Megachile versicolor, blue carpenter bee Osmia caerulescens). No such effect was found for the European potter wasp Ancistrocerus gazella (ca. 21 min in both sites). Unsown sites with naturally developed vegetation included one- and two-year old mown and unmown set-asides and old meadow orchards. Crops on sown fields were peas, barley, rye, clover-grass mixture and Phacelia tanacetifolia. Mowing of set-asides took place in late June-early July. Three artificial nests (each with two 750 ml cans filled with 180 reed stems) were located in each field centre. Female body length of bees and wasps was measured. For Ancistrocerus gazella, Megachile versicolor and Osmia caerulescens, the time spent on foraging flights was measured on four one-year old set-asides and four old meadows. Plant surveys were conducted in May, July and October.
A replicated site comparison study of 24 one-year-old set-aside fields and 24 cereal fields in Uppland, central Sweden (Berg & Part 1994) found that four of 17 bird species sampled showed a significant positive association with set-aside fields: skylark Alauda arvensis, whinchat Saxicola rubetra, whitethroat Sylvia communis and linnet Carduelis cannabina. Other species showed greater association with unfarmed habitats, roads and houses, forest edges or open habitat. The study plots were of similar size, edge and habitat structure. Each was sampled seven times for 28 species of breeding bird from April-June 1992. Species with at least 10 territories were examined.
A replicated, controlled site comparison study with four replicates of each treatment (Gathmann et al. 1994) - the same study as (Gathmann & Tscharntke 1993) - found that naturally regenerated set-aside fields had significantly more cavity-nesting bee and wasp nests, and more nesting species than fields sown with fallow or arable crops. The study compared bees and wasps nesting on set-aside land managed in six different ways with crop fields and old meadows in Kraichgau, southwest Germany. It used reed Phragmites australis stem nest boxes and recorded nesting only, not foraging activity. Set-aside fields were either sown in the year of study, with a grass-clover mix or phacelia Phacelia tanacetifolia, or were in their first or second year of natural regeneration, with or without mowing.
A replicated, controlled site comparison study 1989-1991 in up to 65 arable sites in the Kraichgau region, Germany (Greiler 1994; same study as Gathmann & Tscharntke 1993) found more plant species but fewer invertebrates on naturally developed set-aside fields than on control crop fields. There were more plant species in orchard meadows (50 species/49m2) and naturally developed set-asides (37-45 species/49m2) than in sown set-asides (10-15 species/49m2) and cereal fields (10-17 species/49m2). Plant species richness was also higher in mown than in unmown set-asides. Invertebrate numbers from suction samplers were highest in set-asides sown with clover-grass-mixes (1500 individuals/5 m2), intermediate in naturally developed set-asides and cereal fields (ca. 1000 individuals/5 m2) and lowest in Phacelia-sown set-asides (500 individuals/ 5m2). Invertebrate numbers caught in Malaise-traps were highest in rye fields and clover-grass-mixes (around 3000 individuals) and lowest in naturally developed set-asides (1000 individuals). The effect of field type and set-aside age was strongly species- or family-dependent. Up to 11 field types (four to five replicates each) were investigated: one, two and three-year-old naturally developed set-asides (mown and unmown), 1-year-old set-asides sown with either Phacelia tanacetifolia or a clover-grass mix, conventionally managed cereal fields (rye and barley) and low-intensity orchard meadows (>30 years old). Plant surveys (three visits) were conducted in May to October 1990-1991 on one 49 m2 permanent quadrat (meadows and sown fields) or on 120 m2 (naturally developed fields). Insects were sampled on four to five visits in April to October using Malaise-traps (20 fields) and suction samplers (61 fields; 3 minute suctions of five 0.25m2 plots).
A replicated site comparison study from April to August 1993 at 21 farmland sites in Kraichgau, Germany (Steffan-Dewenter & Tscharntke 1995) (same study as Gathmann & Tscharntke 1993) found that naturally regenerated set-asides and orchard meadows held more wild bee species and more individual bees than set-aside fields sown with phacelia Phacelia tanacetifolia (averages of 27, 28 and 10 bee species; 120, 100 and 75 bees, respectively). Also the numbers of Red-listed bee species and specialist species were higher in naturally developed than in Phacelia-sown set-asides. Seven field types (four replicates each) were investigated: one, two, three, four and five-year-old naturally regenerated set-asides, 1-year-old set-asides sown with phacelia and orchard meadows. Wild bees were monitored for 30 minutes on each of six visits to each site. Along one 100 m long transect in the field centre, bees were caught using sweep nets (100 sweeps/transect). In addition, flower-visiting bees were caught.
A replicated site comparison study of four arable, 10 mixed and three pastoral farms within the South Downs Environmentally Sensitive Area, UK (Wakeham-Dawson 1995) found that rotational set-aside tended to be used more than arable crops by skylarks Alauda arvensis, but used less or a similar amount by hares Lepus euroaepus. Rotational set-aside was used significantly more than arable crops during the first skylark brood period (22 vs 3-15 males/km²). During the second brood, once set-aside had been topped or cultivated, use of set-aside by skylarks was more similar to their use of arable crops (topped: 16; cultivated: 8; arable: 9-14). Hares used winter sown cereals more than rotational set-aside in October-January (0.2-0.3 vs 0.1 hares/ha), but in February set-aside was used the same amount as crops (0.1 hares/ha). Hares were sampled by spotlight counting over an average of 26% of the area of each farm between November and March (1992-1993, 1993-1994). Skylarks were sampled by mapping breeding males during two counts along representative transects on 12-17 farms in April-June (1992-1993).
A small replicated, randomized study of set-aside on a farm west of Moray, Scotland (Ford 1996) found that vegetation of conservation value can develop within set-aside provided species occur in the seed bank. The abundance of the dominant species false oat grass Arrhenatherum elatius, Yorkshire fog Holcus lanatus and cock’s-foot Dactylis glomerata varied across the set-aside. Some variations were explained by sub-plot location, others by management; removing cuttings reduced false oat grass abundance. No further results are provided as the study was ongoing at time the paper was written. A 25 m wide strip of set-aside was established in 1989 and divided into three plots of 25 x 28 m in three randomized blocks. Treatments were: cut in July, cut in September and cut in July and September to 6 cm. Each plot was divided into two sub-plots: cuttings removed or left in situ. Plant species composition was recorded in June-July 1993.
A small, controlled study of an arable and set-aside field on a farm near Braunschweig, Germany (Buchs et al. 1997) found that arthropod numbers and species richness tended to increase with a reduction in management intensity. More species of spider were found in set-aside than arable plots with four levels of management intensity (set-aside: 33-36; reduced intensity: 10-22; conventional: 11-13). The effect on spider abundance was less clear. Set-aside also had a greater density of wolf spiders (Lycosidae; set-aside: 68/trap; arable 10-22) and a lower proportion of pioneer species (set-aside: 8%; reduced inputs: 49-75%; conventional: 81%). Beneficial species, such as Carabus auratus, were more abundant in set-aside (97-148/trap) than arable plots (1-18/trap); their activity periods were also longer in set-aside. Similar effects were seen for juvenile spider abundance (set-aside: 108/trap; reduced intensity: 50-55; conventional farming: 21). In 1992-1995 a long-term set-aside was compared with four plots within an arable field that differed in the input of fertilisers and pesticides (high, 30-50% reduced, none), crop rotation (three/four course), tillage, weed control (mechanical/chemical), cultivars, drilling technique and catch crops. Six to eight emergence traps and pitfall traps sampled arthropods within each treatment. Traps were collected every 2-4 weeks throughout the year. Results for pest species are not included here.
A replicated, controlled study in summer 1991-94 on three to six arable farms and two experimental sites in the Province of Bayern, Germany (Hilbig 1997) found more plant species on rotational set-asides (17.4 species) than on control fields (10.8 species). Moreover, naturally regenerated set-asides held more plant species (range 18.3 to 32.2 spp.) than set-asides with sown clover-grass mixtures (range 16.0 to 18.9 spp.). This effect was still visible the following year, when cereal was grown on the former set-aside fields (range 13.3 to 14.2 spp. on cereal after natural regenerated set-aside vs 12.0 to 12.4 spp. on cereal after sown set-aside). Rotational set-asides were taken out of production for one year and either left to regenerate naturally or sown with a clover-grass-mix. Controls were often cereal fields. Vegetation was surveyed between June and September on total areas between 100 and 400 m2. Cereal crops were surveyed yearly, cut set-asides several times a year. Note that no statistical analyses were performed on these data.
A replicated, controlled study of set-aside at four sites on two Royal Agricultural College farms, Gloucestershire, UK (Tattersall et al. 1997) found that small mammals showed no preference for first-year set-aside over crops. Trapping success was significantly lower in set-aside (0.6%) than the adjoining unharvested cereal crop (13%) and hedgerow (30%). Wood mice were the only species caught in set-aside. There was no significant difference in trap success between set-aside in blocks (0.6%) or strips (0.6%) or between sown (0.4%) or naturally regenerated (1.0 %) set-aside, although sample sizes were very low (six captures). Following harvest, trap success in the crop decreased (4.5% to 0.5%) and significantly increased in set-aside (0.1 to 2.5%). Set-aside was either sown with a mix of wheat and rape (three sites) or left to regenerate naturally. A grid of 50 Longworth live-traps was set at each site covering a hedgerow, a 20 m strip of set-aside and a block of either set-aside or cereal crop. Trapping was undertaken for five nights/month from June-August 1995.
A replicated, paired sites before-and-after study on seven pairs of fields in northeast Scotland in 1989-1991 (Watson & Rae 1997) found that 1-year-old set-aside fields held significantly more species of bird than similar, non-set-aside fields (average of 11.9 species/10 ha for first year set-aside vs 4.8 species/10 ha for control fields). There were no differences in the years before or after set-aside. In addition, there were higher breeding densities of grey partridge Perdix perdix, skylark Alauda arvensis and Eurasian curlew Numenius arquata in set-aside compared with control fields. Densities of curlew, partridge, northern lapwing Vanellus vanellus and Eurasian oystercatcher Haematopus ostralegus were higher in set-aside years than before set-aside (passerine densities were not recorded before set-aside was used). Wader breeding success appeared higher on set-aside, but numbers were too small for statistical tests. The densities and number of species declined over time in set-aside fields. Set-aside fields were previously arable fields but were not cropped for at least one year.
A replicated study in summers of 1993-5 on seven farms in southern England (Wilson et al. 1997) found significantly higher densities of skylark Alauda arvensis territories on set-aside fields than on conventionally or organically-managed crop fields (0.26-0.56 territories/ha for set-aside fields vs a maximum of 0.38 territories/ha for cropped fields). Estimated nest survival was significantly higher on set-aside fields than conventionally-managed cereal fields (44% survival to fledgling on set-aside vs 11% for conventional cereals). Set-aside was both naturally regenerated from crop stubble or sown with grass.
A site comparison study of set-aside in southern Germany (Steffan-Dewenter & Tscharntke 1997) found that numbers of plant and butterfly species were higher in naturally regenerated set-aside than cereal or set-aside sown with Phacelia tanacetifolia, but that number of plant species decreased and butterfly species composition changed with set-aside age (1-4 year-old). Numbers of plant species were higher in four naturally regenerated set-aside fields (20-30 species) than in a cereal field (1) or 1-year-old set-aside sown with P. tanacetifolia (3). The number of species decreased significantly with age of naturally regenerated set-aside fields from one (30 plant species) to three-years-old (20 species). Cover of annual herbs declined rapidly in the 3rd to 4th year of set-aside. The number of butterfly species was higher in naturally regenerated set-aside (11-13 species) than cereal (4) or sown set-aside (7). Butterfly species richness did not differ with set-aside age (11-13 species), but species composition changed greatly. Butterfly body size tended to decrease with set-aside age (from 24 mm to 23 mm) and mean life-span of caterpillars increased (from 61 days to 105 days). Plant species and cover were sampled in 49 m² plots in September 1992 and flowering plant abundance was estimated nine times from May-October. Adult butterflies were counted along transects, nine times per field (May-October 1992) and caterpillars were sampled twice in September 1992 by sweep-netting.
A small site comparison study in Belgium (Desender & Bosmans 1998) found 53 species of ground beetle (Carabidae) during one year of sampling in three set-aside fields, including eleven species in the Red Data Book for Flanders. The most notable species were Amara tricuspidata and Harpalus froelichi. Thirty-five of the species were considered to be breeding within the fields. The set-aside fields contained more ground beetle species than were found in previous years on cultivated arable fields (numbers not given). Two of the fields were set-aside in 1994, sown with grasses and annually mown once. These were managed without fertilizers or pesticides for two years before becoming set-aside. The other field had been left to naturally regenerate since 1992, and was partly grazed by sheep. Beetles were sampled between May 1994 and April 1995 in three pitfall traps per site, emptied fortnightly or monthly throughout the year.
A replicated controlled study of former arable fields at six sites in Sweden (Hansson & Fogelfors 1998) found twice as many plant species in unfertilized compared to fertilized set-aside after 10 years (30 species in the least fertile site; 10 in the most fertile). Annual cutting resulted in an increased number of species over the years. The competitive success of plant species was related to management practices but there were also interactions between management and site conditions. At each site, two plots (10 x 20 m) were sown with a grass cover crop and two were left bare. Each year, one of each pair had fertilizer added (equivalent to 150 kg N/ha) and half of every plot was cut and cuttings removed (late July). Vegetation cover was assessed in the centre of each plot (8 x 1 m²; 1975-1986).
A site comparison study from April to August 1992 on three farms in south England (Poulsen et al. 1998) found that skylarks Alauda arvensis had significantly higher productivity in set-aside fields, compared to spring-sown cereals or grass (0.5 fledglings/ha in set-aside vs 0.21 fledglings/ha in spring cereals and 0.13 fledglings/ha in silage grass). This difference was largely due to higher densities of territories (2-3 times higher in set-aside and grass, compared to cereals), more successful nests (highest on grass, but twice as high in set-aside as in cereal crops) and larger clutches in set-aside (3.9 eggs/clutch for nests in set-aside vs 3.3 eggs/clutch for spring cereals and 3.4 eggs/clutch in grass, eleven nests in each habitat type). Fledging success did not vary between habitats. No nests with chicks were found in winter-sown cereals. Set-aside consisted of 4-year-old permanent fallow sown with red fescue Festuca rubra, perenial ryegrass Lolium perenne and white clover Trifolium pratense.
A literature review (Sotherton 1998) looked at the effect of agricultural intensification and the role of set-aside on the conservation of farmland wildlife. It found one study that demonstrated a three-fold increase in insect density on rotational set-aside compared to conventional cereals, mainly due to increases in plant hoppers and beetle families (Carabidae, Staphylinidae and Chrysomelidae; described above (Moreby & Aebischer 1992)).
A replicated study of wood mice Apodemus sylvaticus in arable habitats at two Royal Agricultural College farms at Cirencester, UK (Tattersall et al. 1998; following on from Tattersall et al. 1997), found that wood mice showed no preference for first-year set-aside over crops. Wood mouse numbers were lowest on whole field set-aside (0-16), followed by hedgerow with set-aside margins (5-40) and crop (3-27). Numbers were significantly higher in woodland apart from in July (18-73). There were two replicate 5 ha blocks of set-aside and adjacent 20 m wide set-aside margin strips of a similar area. A grid of 49 live traps was set in each replicate covering the four habitats. Trapping was undertaken monthly for a year from December 1995.
A replicated site comparison study in summer 1995 on 89 fields in the South Downs, southern England (Wakeham-Dawson et al. 1998) found that the density of singing Eurasian skylarks Alauda arvensis was higher on set-aside fields than on any other field type, except undersown spring barley fields (approximately 15 birds/km2 on six set-aside fields vs 22 birds/km2 on four spring barley fields and 2-12 birds/km2 on 79 other fields). Other field types were: arable fields reverted to species-rich grassland or permanent grassland, downland turf, permanent grassland, winter wheat, barley and oilseed rape.
A randomized, replicated site comparison in the winters of 1992-1993 and 1993-1994 on 40 farmland sites in Devon and East Anglia, England (Buckingham et al. 1999) found that only one taxonomic group (finches, sparrows and buntings, seven species) showed a significant selection of set-aside habitats in both years, preferentially using sown set-aside less than one year old. Conversely, thrushes (four species) and hedge-dwelling species (European robin Erithacus rubecula, wren Troglodytes troglodytes and dunnock Prunella modularis) avoided regenerating set-aside less than one year old in Devon. At a species-level, a preference for set-aside was seen in both winters by one species in Devon (cirl bunting Emberiza cirlus selected sown set-aside more than one year-old) and two species (plus one introduced species not considered here) in East Anglia (grey partridge Perdix perdix preferred older sown set-aside and yellowhammer Emberiza citrinella selected one year-old sown cover). A further 13 species in both East Anglia and Devon preferentially selected set-aside in one winter. Blackbird Turdus merula and five other species avoided some set-aside in at least one year in Devon, no native species did so in East Anglia. The same 40 plots (50-100 ha) were surveyed each winter, although the amount of set-aside they contained varied due to rotation schemes.
A replicated, randomized site comparison study of 27 arable fields on a farm in southern Finland over one year (Kinnunen and Tiainen 1999) found that the abundance of ground beetles (Carabidae) was significantly higher in set-aside than crop fields. Set-aside contained 1,442 beetles/site compared to 334-524/site in crop fields. Of 21 species compared in set-aside and cereal fields, two were significantly more abundant in set-aside (Trechus secalis, Dyschirius globosus) and two in cereal (Asaphidion pallipes, Bembidion quadrimaculatum). The ground beetle community differed between set-aside and crop fields. Autumn breeding species dominated set-aside (70% in June), whereas spring breeders tended to use crops tilled in spring (56-80%). Twenty-seven of 150 fields were randomly selected. Six were permanent set-aside, sown with perennial grass and left for 5-10 years. The others were barley, oats, sugar beet, oilseed rape and potato. Beetles were sampled using 20 pitfall traps (7 cm diameter) at each site. These were emptied every two weeks for 10 consecutive weeks from June-August 1995.
A site comparison study monitoring the behaviour of individual wood mice Apodemus sylvaticus on two arable farms in England (Tattersall et al., 1999a; following on from Tattersall et al. 1997) found that set-aside established using species-rich mixes of grasses and native forbs was preferred and set-aside established using a simple grass/clover mix avoided by the mice. On average, wood mice at Jealott's Hill preferred set-aside (species-rich mixes; preference index: 0.12) and avoided crop (-0.12); at Eysey they avoided set-aside (simple mix; -0.16) and preferred other habitats (0.12). However, only at Eysey was there a significant deviation from random habitat use overall. Vegetation at Jealott's Hill contained more species but was shorter and provided less cover than that at Eysey. Set-aside was established in the 10 m next to the crop and the hedge at Jealott's Hill (1996) and on 20 m wide margins and an adjoining 5 ha block at Eysey (1995). Nine wood mice were radio-tracked continuously for three nights at each farm (May-July 1996-1997). Vegetation data were obtained using a quadrat survey (1 m²).
A small, replicated study of set-aside on two Royal Agricultural College farms in Gloucester, England (Tattersall et al. 1999b; same study as Tattersall et al. 1999a) found that set-aside established as margins (20 m wide; 5 ha) next to hedgerow had a more abundant and species rich small mammal community than larger (5 ha) blocks. Set-aside margins had more mammals (21 animals, 8 species caught/trap session) than larger blocks (11 animals, five species caught/trap session). Wood mice dominated (76% on margins; 50% on blocks). Species richness, but not diversity, was significantly greater on margins (richness: 2.4; diversity: 0.3) than blocks (richness: 2.1; diversity: 0.2). Both parameters increased from 1996 to 1997. The abundances of species changed with time and season on set-aside margins and blocks. Set-aside was established by sowing a grass/clover mix in 1995, which was cut annually in July or August. Grids of 49 traps were set in the centre of set-aside blocks and spanning the set-aside margin and adjacent hedgerow and crop. Traps were set for five nights in March, June, September and December 1996-1997 and a mark recapture technique followed.
A 2000 literature review from the UK (Aebischer et al. 2000) found that the populations of grey partridge Perdix perdix, Eurasian thick-knee Burhinus oedicnemus and cirl bunting Emberiza cirlus all increased following multiple measures including the provision of set-aside. Partridge numbers were 600% higher on farms with conservation measures aimed at partridges (including conservation headlands, planting cover crops, using set-aside and creating beetle banks), compared to farms without these measures. The UK thick-knee population increased from 150 to 233 pairs from 1991 to 1999 (interventions were set-aside provision and uncultivated plots in fields). The UK cirl bunting population increased from 118-132 pairs in 1989 to 453 pairs in 1998, with a 70% increase on fields under schemes (with overwinter stubbles, grass margins, and beneficially managed hedges and set-aside), compared to a 2% increase elsewhere.
A replicated, randomized site comparison study of non-rotational set-aside up to nine years old at 50 farms in the eastern arable region and 50 in the western mixed farming region in the UK (Critchley and Fowbert 2000) found that plant communities differed between region, establishment method (natural regeneration or sown cover) and site age. Succession continued after five years, with number of plant species increasing over time (7-8 species on older sites, 4-6 on younger sites) along with proportions of perennials and plants characteristic of non-arable habitats. Species richness declined with increasing distance from the field boundary (1 m: 6-8 species; 32 m: 4-7 species). A stratified sample of farms was selected from the Integrated Arable Control System database of the Ministry of Agriculture, Fisheries and Food. One set-aside site was randomly selected per farm and one field boundary was randomly selected for vegetation sampling. Six quadrats (0.5 x 0.5 m) were sampled along five randomly located transects at distances of 1, 2, 4, 8, 16 and 32m from the boundary.
A replicated site comparison study with paired sites in 1996-1997 across 92 arable farms in England (Henderson et al. 2000a) found five of six bird functional groups at higher densities on set-aside fields, compared to winter cereals or grassland (although thrushes only showed this preference in one year). On ten farms with rotational and non-rotational set-aside, all groups except crows were found at higher densities on rotational fields. All groups except gamebirds (which showed no significant field preferences) were more likely to be found on set-aside than other field types. Functional groups of birds were gamebirds, pigeons, crows, skylarks Alauda arvensis, thrushes and seed-eating songbirds (sparrows, buntings and finches).
A replicated paired sites comparison study in 1996-1997 on 11 farms in east and west England (Henderson et al. 2000b) found that set-aside fields supported more species and higher densities of birds than adjacent crop fields (1.4-7.1 birds/ha and 7-21 species for 11 set-aside fields vs 0.2-0.8 birds/ha and 2-5 species on 11 crop fields). Between 78% and 100% of species found on both field types were more abundant on set-aside. These preferences were stronger (although not significantly so) for rotational set-aside, compared to non-rotational.
A replicated, controlled, paired sites comparison study of 51 set-aside and wheat fields on 30 farms in southern and eastern England (Moreby & Southway 2000) found that stubble set-aside had more spiders (Araneae) and leafhoppers (Auchenorrhyncha), higher weed cover and greater plant species diversity, whilst wheat had more beetles (Coleoptera). Set-aside fields had 16 spiders, 16 leafhoppers, 0.7 leaf beetles (Chrysomelidae), 0.5 ground beetles (Carabidae) and 0.4 soldier beetles (Cantharidae)/sample on average. Wheat fields had 11 spiders, 9 leafhoppers, 0.3 leaf beetles, 0.3 ground beetles and 0.3 soldier beetles/sample on average. Numbers did not differ between set-aside and wheat for true bugs (Heteroptera; 5-6/sample), larvae of butterflies, moths (Lepidoptera) and sawflies (Tenthredinidae; 0.2-0.5 larvae/sample) or weevils (Curculionidae) (0.2 vs 0.1). Cutting set-aside (to 10-15 cm) tended to decrease invertebrate numbers compared to topping (to 25 cm) or leaving it uncut. Weed cover and diversity were significantly higher on set-aside (cover: 32%; species: 99) compared to wheat (cover: 3%; species: 41). Set-aside fields were naturally regenerated after harvest. Wheat fields received pesticides. Invertebrates were sampled using a D-Vac suction sampler in each set-aside and adjacent wheat field in June-July. Weed cover was sampled in 10 random quadrats (0.25 m²) per field.
A replicated, controlled site comparison study in summer 1995 on 10 sites of three different arable habitats in the biosphere reserve Schorfheide-Chorin, northeast Germany (Schmitt & Roth 2000) found significantly more individuals (but not families) of parasitic wasps (Hymenoptera: Parasitica) on set-aside land (>160.7 wasps/ m2) than on cereal fields (<107.5 wasps/m2). The age of set-aside did not affect wasp numbers. There was no significant difference between numbers of parasitic wasps on set-asides and extensively managed grasslands (178.7 wasps m2). Four winter cereal fields, four set-asides (1 to >10 years old) and two extensively managed grasslands (one meadow, one grassland grazed by sheep) were monitored. Hymenoptera were sampled from March to July 1995 using six photo-eclectors on each site. The eclectors were placed randomly and emptied every four weeks. Insects were identified to family level.
Another analysis (Henderson et al. 2001) as part of the same study as Henderson et al. 2000a, found that skylark Alauda arvensis densities on set-aside fields ranged from zero to approximately 2.7 birds/ha. A total of 74 set-aside fields (36 rotational and 38 non-rotational) were examined, each from a different farm. Fields with approximately 30% bare earth, straw and litter had the highest densities of skylarks.
A replicated site comparison study near Karlsruhe, south Germany (Steffan-Dewenter & Tscharntke 2001) examined the abundance and species richness of foraging bees, both solitary and social, on annually mown set-aside fields of different ages and management. The number of bee species increased with the age of set-aside fields, from 15 species on 1-year-old fields to 25 species on 5-year-old fields. Two-year-old set-aside fields had the most bee species – 29 on average, compared to 32 species for old meadows, including an average of around five oligolectic species (specializing on pollen from a small group of plant species). One-year-old set-aside fields sown with phacelia had an average of 13 bee species, mainly common, generalized species of bumblebee Bombus and Lasioglossum.
As part of the same study of wood mice Apodemus sylvaticus on an arable farm in England as that described in Tattersall et al. 1997, (Tattersall et al. 2001) found that after harvest, mice preferred hedgerow to set-aside. Before harvest, wood mice tended to use habitats (crop, margin set-aside, block set-aside and hedgerow) at random. After harvest, set-aside was avoided. Margin and cut set-aside were avoided significantly more than block and uncut set-aside. A three ha block of set-aside adjoining a 20 m wide set-aside field margin was sown (grass/clover mix) in 1995 between two arable fields. Twenty-four alternate 50 x 6 m wide patches of cut and uncut set-aside were created either side of the central hedgerow. The remaining 14 m width of the margin was cut as normal. Thirty four wood mice were radio-tracked continuously for at least three nights (June-July and September-November 1996-1997).
A replicated site comparison in 1996-1998 on 22 farms in southern England (Donald et al. 2002) found that skylark Alauda arvensis nests had significantly lower survival in set-aside, compared to in cereals (22% overall survival for 525 nests in set-aside vs 38% survival for 183 nests in cereal fields). There were no differences between set-aside and other crop types (19% survival for 173 nests in grass fields, 29% survival for 60 nests in other field types) or between rotational and non-rotational set-aside. On one intensively-studied farm, over 90% of 422 skylark nests were found on ten fields of well-established, non-rotational set-aside.
A replicated site comparison study carried out in June 2000 in ten edge habitats at the arable Loddington Estate in Leicestershire, England (Moreby, 2002) found a higher density of weevils (Curculionoidea) in edges of non-rotational set-aside than all the other habitats studied. Spider (Aranae) and rove beetle (Staphylinidae) densities were lower in set-aside than in edges of un-grazed pastures. Beetle banks, brood cover, one- and two-year-old wild bird cover, hedge bottoms, sheep-grazed pasture edges, grass/wire fence lines and winter wheat headlands were also included in the study. Invertebrates were sampled with a vacuum suction-sampler in June 2000.
A study of different set-aside crops at Loddington farm, Leicestershire (Murray et al., 2002) found that skylark Alauda arvensis, but not yellowhammer Emberiza citrinella used unmanaged set-aside more than expected compared to availability. Skylarks used unmanaged set-aside more than expected, but significantly less than set-aside sown with kale-based wild bird cover, wild bird cover strips and beetle banks. Cereal (wheat, barley) and broad-leaved crops (beans, rape) were used less than expected. Yellowhammer used unmanaged set-aside as expected compared to availability, but significantly less than cereal and set-aside with cereal-based wild bird cover or wild bird cover strips. Field margin and midfield set-aside strips were sown with kale-based and cereal-based mixtures for wild bird cover, and beetle banks. Other habitat types were: unmanaged set-aside, cereal (wheat, barley), broad-leaved crop (beans, rape) and other habitats (including permanent pasture, woodland, hedgerows, tracks and riparian areas). Thirteen skylark and 15 yellowhammer nests with chicks between 3-10 days old were observed. Foraging habitats used by the adults were recorded for 90 minutes during three periods of the day.
A replicated, randomized site comparison study of 200 farms in England with set-aside (Firbank et al. 2003) found that set-aside supported a range of biodiversity. Rotational set-aside supported 12 plant species/site and one nationally rare species (corn marigold Chrysanthemum segetum). On non-rotational set-aside, plant species richness and cover of annuals was greater on naturally regenerated than sown grass sites (27 vs 20 species/site); cover by perennials showed the opposite trend. Older naturally regenerated sites had more perennial species, but plant communities did not appear to be developing into those considered of conservation value. Twenty percent of farmers reported an increase in wildflowers, and 47% reported an increase in bird numbers on rotational set-aside. Fifty-one percent of farmers reported an increase in wildflowers and 69% an increase in bird numbers on non-rotational set-aside. Bird density in set-aside was nine times higher than in crops for rotational set-aside and seven times higher for non-rotational sown grassland set-aside. Management of set-aside had minimal effect on bird abundance. Significantly more invertebrates were found in set-aside than in the adjacent crop. Vegetation was assessed on 100 rotational (spring 1996-1997) and 100 non-rotational set-aside sites (summer 1996-1997). Breeding bird territories were mapped on 63-92 farms (1996-1997). More intensive surveys were undertaken for: vegetation (8+ per year) on six farms, habitat use by birds and invertebrates (pitfall trapping, May-June) on 11 farms (1996-1997). Pest data are not presented here.
A replicated, controlled study in May to September 2000-2001 on six farmland sites near Vienna, Austria (Kromp et al., 2004) found a higher number of ground beetle (Carabidae) species in set-aside areas than in arable fields. Sowing wildflower seed mixtures on set-aside land further increased the number of ground beetle species. The community composition of ground beetles differed between the three types of habitat. No statistical analyses were presented. Two unsown set-aside fields were >50 and six years old and cut regularly. Wildflower strips (four sites) were sown on set-aside land with the Voitsauer seed mix containing 25 species of herbs and weeds between 1998 and 2000. Typical crops for the region were sown on five arable fields. One of the arable fields was under conservation contract growing a wildflower seed mix undersown in rye. Ground beetles were sampled using four pitfall traps 10 m apart in each habitat and site. There were five sampling periods each year, each lasting two to three days (2001) or seven days (2000).
A replicated, controlled site comparison study from November-February in 2000-2001 and 2001-2002 on 20 arable farms in eastern Scotland (Parish & Sotherton 2004) found that, of 23 species recorded, only skylarks (Alauda arvensis) were significantly denser in fields with set-aside than fields with wild bird cover crops or conventional crops. Bird density was up to 100 times higher in wild bird cover crops than on set-aside fields. The wild bird cover crops attracted 50 % more species than set-aside fields. Of eight species with sufficient data for individual analysis, seven were consistently more abundant in wild bird cover than in set-aside fields. Set-aside fields were those in which cereal stubble was left to regenerate naturally. Between 6.2 and 28.3 ha were sampled on each farm annually.
A review and meta-analysis of 127 studies comparing set-aside and conventional land (Van Buskirk & Willi 2004) found that species richness and population densities of plants, birds, insects and spiders and harvestmen were significantly higher on set-aside land than on nearby conventional fields in Europe and North America. Positive effects were greatest on larger and older areas of set-aside, when the comparison conventional field contained crops rather than grasses, in countries with more arable land under agri-environment schemes and with less intensive agriculture. Overall, variation in establishment methods and types of set-aside made little difference to the positive effect on biodiversity, although species richness was increased more when set-aside was naturally regenerated rather than sown.
A replicated, controlled, paired sites comparison in summer 2003 in County Laois and County Kildare, Ireland (Bracken & Bolger 2006) found that 18 set-aside fields had significantly higher bird species diversity and richness than 18 adjacent agricultural fields (an average of 12.8 species on set-aside vs 9.2 species on control fields). Three species - meadow pipit Anthus pratensis, skylark Alauda arvensis and woodpigeon Columba palumbus - were significantly more abundant on set-aside. Six species (whitethroat Sylvia communis, goldcrest Regulus regulus, blackcap Sylvia atricapilla, stonechat Saxicola torquata, tree sparrow Passer montanus and treecreeper Certhia familiaris) showed a preference for non-set-aside fields, but these were not statistically significant and were considered likely to be based on field margins, rather than field management. Six species were associated with non-rotational set-aside, two with rotational set-aside, one with long-term grazed pasture set-aside and three with first year pasture set-aside.
A controlled trial in Jokioinen, southern Finland (Huusela-Veistola & Hyvanen 2006) from 2003 to 2004 found more spiders (Araneae) and flying insects in set-aside than in a control cereal crop, but not more plant species or ground beetles (Carabidae). Spiders were significantly more abundant in two-year fallows, regardless of the sowing treatment (28-55 spiders/trap) than in one year fallows, in which spider numbers did not differ from the control cereal crop (less than 10 spiders/trap). Numbers of flying insects in the vegetation followed a similar pattern, with fewer insects in first year fallows than in stubble or two -year fallows. Numbers of ground beetles and numbers of plant species were similar across all fallow treatments and in the case of beetles, also in the control cereal crop (5-25 beetles/trap, 2-14 unsown plant species/m2). Two-year fallow plots sown with red clover had fewer plant species (around 2 species/m2) than control cereal fields, which had around 16 plant species/ m2. Fallow treatments were established in 2003 or 2004, each on a 44 x 66 m plot. The treatments were: one- and two-year fallow sown with either grasses, or a grass- red clover Trifolium pratense mix; two-year rotational fallow established by undersowing spring cereal with either grasses, or a grass-red clover mix. The control was a spring barley crop. Insects were sampled using a yellow sticky trap and three pitfall traps in the centre of each plot for a week in June, July and August 2004. Unsown plant species were counted in four 50 x 50 cm quadrats in each plot in late August 2004.
A replicated controlled site comparison in 1999 and 2003 on 256 arable and pastoral fields across 84 farms in East Anglia and the West Midlands, England (Stevens & Bradbury 2006) found that only two of twelve farmland bird species analysed were positively associated with the provision of set-aside, wildlife seed mixtures or overwinter stubble. These were skylark Alauda arvensis (a field-nesting species) and linnet Carduelis cannabina (a boundary-nesting species). The study did not distinguish between set-aside, wildlife seed mixtures or overwinter stubble, classing all as interventions to provide seeds for farmland birds.
A replicated site comparison study of agri-environment scheme habitats in arable farmland in England (Askew et al. 2007) found that set-aside tended to have lower numbers of small mammals than sown grass margins. Numbers of small mammals caught in permanent set-aside (fallowed for five years or more, annual cutting of at least 90%: 1.6-2.0 mammals/plot) were lower than in 2 m grass field margins (2.9-4.4 mammals/plot) and 6 m margins (2.5-3.6 mammals/plot). In 2003, significantly fewer common shrew Sorex araneus and wood mouse Apodemus sylvaticus were captured in set-aside (shrews: 0.6; mice: 0.5) than grass margins (shrews: 0.9-1.4; mice: 0.7-1.1). The trend was similar for bank voles Myodes glareolus in 2004 (set-aside: 0.5 voles/plot; margins: 1.4-1.6 voles/plot). Species richness did not differ significantly between treatments (1.7-2.0 species). Twelve small mammal traps were set within 20 plots per treatment (1 m from the habitat boundary) for four days in November-December 2003-2004. Mammals were individually fur-clipped and released. Results from farm woodlands are not included here.
A review of the effects of agri-environment scheme options and set-aside on small mammals in the UK (Macdonald et al. 2007) found that results tended to depend on the management of set-aside. Studies have found that after harvest wood mice Apodemus sylvaticus avoided cut set-aside and crops and preferred uncut set-aside and hedge (Tattersall et al. 2001); that wood mice tended to avoid set-aside land relative to crop and hedgerow habitats (Tattersall & Macdonald 2003); that wood mice used set-aside with species-rich mixes of grasses and native forbs more, and tended to avoid set-aside established using a simple grass/clover mix (Tattersall et al. 1999a) and that set-aside established as margins next to hedgerow had a more abundant and diverse small mammal community than larger blocks (Tattersall et al., 1999b). Although small mammal abundance did not increase as set-aside aged, a study found that species composition changed and species diversity and species richness increased (Tattersall et al. 2000).
Tattersall F.H., Avundo A.E., Manley W.J., Hart B.J. & Macdonald, D.W. (2000) Managing set-aside for field voles (Microtus agrestis). Biological Conservation, 96, 123–128.
Tattersall F.H. & Macdonald D.W. (2003) Wood mice in the arable ecosystem. Pages 82–96 in: F.H. Tattsersall & W.J. Manley (eds.) Conservation and Conflict: Mammals and Farming in Britain. Linnean Society Occasional Publications, Westbury Publishing, West Yorkshire, UK.
A replicated site comparison study of 31 rotational set-aside fields in England (Moreby, 2007) found that invertebrate numbers tended to be higher in uncultivated field boundaries than within set-aside fields. There were significantly lower numbers of the following groups within set-aside compared to at field edges: harvestmen (Opiliones; 0 vs 3/m²), leafhoppers (Auchenorryncha; 10 vs 60), true bugs (Heteroptera; 2-10 vs 25), parasitic wasps (14 vs 20), beetles (Coleoptera; 7 vs 22), flies (Dipteral; 38-42 vs 63), ‘chick food items’ (20-30 vs 85) and ‘highly ranked predators’ (1 vs 5). Aphids were more numerous in set-aside than at the field boundary (100-112 vs 10/m²). There was no significant difference in numbers of spiders (Araneae), lacewing (Neuroptera) larvae, butterfly and moth (Lepidoptera) larvae, sawfly (Tenthreadinidae) larvae and aphid predators between the margin and the field. Invertebrates were sampled in the uncultivated field boundary (0 m) and at 3 m and 50 m in to each field in mid-May. Total invertebrates (excluding springtails (Collembola) and thrips (Thysanoptera)) and those in 12 groups known to be food for farmland birds were recorded.
A 2007 systematic review (Roberts & Pullin 2007) identified 11 papers investigating the effect of set-aside provision on farmland bird densities in the UK. In both winter and summer surveys there were significantly higher densities of farmland birds on fields removed from production and under set-aside designation than on conventionally farmed fields. The meta-analysis included experiments conducted between 1988 and 2002 from eight controlled trials and three site comparison studies.
A before-and-after study examining data from 1976 to 2003 from farms across southern Sweden (Wretenberg et al. 2007) found that four locally migrant farmland birds showed less negative (or positive) population trends during a period of agricultural extensification, which included an increase in the area of set-aside. The authors suggest that the two could be causally linked.
A before-and-after site comparison study in 2000-2005 in Bedfordshire, England (Henderson et al. 2009) found that set-aside fields sprayed in May or June supported higher densities of grey partridge Perdix perdix, seed-eating songbirds and skylark Alauda arvensis, compared to set-aside sprayed in April or crop fields (although seed-eating songbirds were equally numerous on oilseed rape Brassica napus fields). Early-sprayed set-aside had consistently lower densities of all species, compared to all land uses except winter-sown wheat.
A site comparison study of seven arable fields over two years in Devon, UK (Woolley 2009) found that in set-aside, spider abundance was higher, but number of species was similar to other arable fields. Numbers of species in set-aside (14) were similar to winter wheat (14-15) and maize (13), but higher than in winter barley, temporary grass ley (10-11) or permanent grass ley (9). Abundance was highest in set-aside (2,490 spiders), followed by wheat (2,009-2,039), maize (1,325), temporary ley (1,280), barley/temporary ley (1,087) and permanent ley (1,067). In set-aside, non-linyphiid spiders (money spiders; 1236) accounted for a greater proportion of the total spiders sampled than in other field types. The total number of linyphiids in set-aside (1,254) was similar to numbers in ley (1,039-1,268) and maize fields (1,253). Spider numbers decreased once set-aside was cut. The set-aside field was established the year before the study and previously received low intensity management and occasional sheep grazing. Set-aside was cut once in August and was grazed over winter. A D-Vac suction sampler was used to take six sub-samples in each field at 2-3 week intervals from June 2001 to October 2002.
A site comparison study in 2002-2009 on mixed farmland in Hertfordshire, England (Aebischer & Ewald 2010) found that the estimated population density of grey partridge Perdix perdix was significantly higher on set-aside land than on conventional arable crops. The difference was strongest for rotational set-aside, with non-rotational set-aside not having a significant positive impact on partridge densities.
A site comparison study on four farms in Aberdeenshire, northeast Scotland, in summer 2005 (Douglas et al. 2010) found that yellowhammers Emberiza citrinella from ten nests preferentially foraged on set-aside land, compared to cereal fields, but that this preference was not significant (set-aside comprising 23% of available habitat but used for 42% of foraging flights vs cereals comprising 42% of habitat and being used 25% of the time). The authors suggest that the lack of significance may be due to small sample sizes.
A replicated controlled site comparison in summer 2008 in northwest Scotland (Redpath et al. 2010) found that croft sections in fallow had nine times more foraging bumblebees than croft sections grazed by sheep and cattle in July. In August there were more foraging bumblebees in fallow sections than sections with a silage crop, but fewer than in sections sown with a bird and bumblebee conservation seed mix. Red clover Trifolium pratense and greater knapweed Centaurea nigra were two of few plant species favoured by bumblebees and were predominantly found in the fallow sections July-August. Thirty-one crofts located on Lewis, Harris, the Uists and at Durness were included in the study. In addition to the four management types mentioned, arable crops, unmanaged, sheep-grazed and winter-grazed pastures were surveyed for foraging bumblebees and bumblebee forage plants along zigzag or L-shaped transects in each croft section in June, July and August 2008. Foraging bumblebees 2 m on either side of transects were identified to species and recorded together with the plant species on which they were foraging. Inflorescences of all plant species were counted in 0.25 m2 quadrats placed at 20 or 50 m intervals along the transects.
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