Action: Leave headlands in fields unsprayed (conservation headlands)
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- Twenty-two studies from 14 replicated, controlled experiments (of which two randomized) including two reviews, from a total of 32 studies from 20 experiments (of which 17 replicated, controlled) including three reviews from Finland, Germany, the Netherlands, Sweden and the UK that investigated species richness and diversity of farmland wildlife found that conservation headlands contained higher species richness or diversity of invertebrates or plants than other habitat types. Twelve studies (including a review) from ten replicated experiments (of which eight controlled and three controlled and randomized) found that some or all invertebrates or plants investigated did not have higher species richness or diversity on conservation headlands compared to other habitat types. This included both replicated, controlled studies investigating bee diversity. Two replicated studies from the UK found that unfertilized conservation headlands had more plant species than fertilized conservation headlands.
- Positive effects of conservation headlands on abundances or behaviours of some or all species investigated were found by 27 studies from 15 replicated experiments (of which 13 controlled) including five reviews out of a total of 36 studies from 20 experiments (17 replicated, controlled) including five reviews from Finland, Germany, the Netherlands, Sweden and the UK that investigated birds (some studies looked at number of visits), mammals (some studies looked at number of visits), invertebrates and plant abundance/cover. One review from the UK found a positive effect on grey partridge populations but did not separate the effects of several other interventions including conservation headlands. Nineteen studies from 13 replicated (12 controlled) experiments and a review from Finland, Germany, the Netherlands and the UK found that some or all species of birds, invertebrates or plants investigated were at similar, or lower, abundances on conservation headlands compared to other management. One review from the UK and a study in Germany found conservation headlands had a positive effect on plants and some, but not all invertebrates, or rare arable weeds but did not specify how.
- All eight studies from the UK and Sweden that investigated species’ productivity, from three replicated (two controlled) experiments including two reviews found that grey partridge productivity or survival was higher in conservation headlands (or in sites with conservation headlands), compared to other management. One replicated study from the UK found that conservation headlands did not increase the proportion of young grey partridges in the population. A before-and-after study from the UK found that some invertebrates in conservation headlands survived pesticide applications to neighbouring fields. A review found crop margins reduce the effects of spray drift on butterflies.
- A replicated study from Germany and a review found that conservation headlands appeared to prevent or reduce the establishment and spread of pernicious weeds.
Conservation headland management involves restricted fertilizer, herbicide and insecticide spraying in a 6 m margin of sown arable crop. The prescription allows selected herbicide applications to control injurious weeds or invasive alien species.
Supporting evidence from individual studies
A replicated, controlled study of cereal headlands on an arable farm in north-east Hampshire, UK (Rands et al. 1984) found that grey partridge Perdix perdix brood size, abundance of invertebrates (chick food and pest predators) and weed density tended to be greater on unsprayed compared to sprayed headlands. Grey partridge brood size was significantly larger on plots with unsprayed (6.4) compared to sprayed headlands (2.2). Abundance of chick food species (true bugs (Heteroptera), caterpillars (Lepidoptera) and sawfly (Hymenoptera: Symphyta) larvae, leaf beetles (Chrysomelidae) and weevils (Curculionidae)) was significantly higher and aphid predators (spiders (Araneae), ground beetles (Carabidae), rove beetles (Staphylinidae)) tended to be greater in unsprayed (chick food: 180/50 sweeps, predators: 7.8) compared to sprayed headlands (chick food: 62/50 sweeps, predators: 4.6). Weed densities tended to be higher on unsprayed (5/m²) compared to sprayed headlands (3/m²), but only one of 21 species was significantly higher. Three areas were split into two treatment plots: sprayed with conventional pesticides or 6 m headlands left unsprayed. Grey partridge brood size was recorded from August-September 1983. Insects were sampled using a sweep net (50 sweeps in June) and weed species were recorded within 10 quadrats in each headland. This study was part of the same experimental set-up as (Rands 1985, Rands 1986, Rands & Sotherton 1986, Dover et al. 1990, Sotherton 1991, Dover 1997).
A replicated, controlled study in 1980-1983 in arable fields on a farm in Hampshire, UK (Rands 1985) found that grey partridge Perdix perdix broods were significantly larger in 1983 on plots with conservation headlands, compared to control headlands sprayed with fungicides and herbicides (averages of 5.1-10.3 chicks/brood for 29 broods in unsprayed areas vs 1.8-2.4 chicks/brood for 39 broods on controls). No differences were found in 1980-1981, before conservation headlands were implemented. However, more broods were found on conventional fields, reflecting more pairs (49 vs 37) in the spring. Areas with conservation headlands had significantly higher abundances of true bugs (Heteroptera), leaf beetles (Chrysomelidae) and weevils (Curculionidae) than sprayed headlands (1.9 individuals/50 net sweeps vs 1.4 individuals/50 sweeps for true bugs, 1.0 individuals/50 sweeps vs 0.7 individuals/50 sweeps for leaf beetles and weevils). Sawflies (Hymenoptera) and butterfly/moth (Lepidoptera) larvae abundance did not vary significantly. The author argues that larger broods were the result of higher chick survival, due to more food insects being present. This study was part of the same experimental set-up as (Rands et al. 1984, Rands 1986, Rands & Sotherton 1986, Dover et al. 1990, Sotherton 1991, Dover 1997).
A replicated, controlled study in 1984 on the same farm in Hampshire as in (Rands 1985) and on eight sites in East Anglia, UK (Rands 1986), found that grey partridge Perdix perdix broods had significantly higher survival, and were significantly larger on plots with conservation headlands, compared to control plots with conventionally-sprayed headlands (average of 75% survival and 7.8-10.0 chicks/brood for five broods on conservation headland plots vs 60% and 4.7-7.5 chicks/brood for four broods on conventional plots, 196 broods surveyed). This paper also describes similar, although less conclusive effects on two non-native gamebirds (red-legged partridge Alectoris rufa and ring-necked pheasant Phasianus colchicus). This study was part of the same experimental set-up as (Rands et al. 1984, Rands 1985, Rands & Sotherton 1986, Dover et al. 1990, Sotherton 1991, Dover 1997).
A replicated, controlled, paired study in 1984 of headlands of 14 arable fields in Hampshire, UK (Rands & Sotherton 1986) found that butterfly (Lepidoptera) abundance was greater on conservation (unsprayed) headlands than on sprayed headlands. Twenty-two species of butterfly were recorded, 21 of which were on conservation and 17 on sprayed headlands. Significantly more individuals were found on conservation (868) than on sprayed headlands (297). Of the seventeen species recorded on more than one transect section, 13 were significantly more abundant on the conservation (11-140) than sprayed headlands (0-59). For half of the 14 fields, a 6 m strip around the edge (headland) was left unsprayed, the remainder received conventional pesticide applications. Butterflies were sampled along a transect at least once a week from 9 May to 15 August 1984. Sprayed and conservation headlands were paired with similar adjacent habitats. This study was part of the same experimental set-up as (Rands et al. 1984, Rands 1985, Rands 1986, Dover et al. 1990, Sotherton 1991, Dover 1997).
A study of cereal fields on 20 farms in Germany between 1978 and 1981 (Schumacher 1987) found that unsprayed field margins had a positive effect on rare and endangered arable weeds. Results are not provided, but authors note that the project was such a success, particularly on the calcareous soils of the Eifel Mountains and intensively farmed soils of the Lower Rhine, that various states in the Federal Republic began providing financial support to protect biodiversity. Farmers made a total of 15 km, later 20 km of 2-3 m wide unsprayed field margins within their cereal fields to protect arable weeds.
A continuation of the same replicated, controlled, paired study as in (Rands & Sotherton 1986) in Hampshire, UK, (Dover et al. 1990), found that butterfly (Lepidoptera) abundance was greater on conservation headlands than on conventional headlands over a further three years (1985-1987). Between 1984 and 1987, 29 species of butterfly were recorded, of which 13-21 were on conservation and 13-17 on conventional headlands each year. Significantly more individuals were found on conservation headlands (222-472/km) than on conventional headlands (80-259/km) in all years. This study was part of the same experimental set-up as (Rands et al. 1984, Rands 1985, Rands 1986, Rands & Sotherton 1986, Sotherton 1991, Dover 1997).
A replicated, controlled study of the headland of a wheat field in Hampshire, UK (Chiverton & Sotherton 1991) found that plots not sprayed with herbicides had significantly higher densities of arthropods than sprayed plots. This was particularly the case for non-pest species which are important for feeding birds and predatory arthropod groups. No significant between-treatment differences were found in the total pitfall trap catch of the two most common ground beetles (Carabidae), Pterostichus melanarius and Agonum dorsale. However, a significantly greater proportion of female A. dorsale were caught in treated plots than in untreated plots. Unsprayed headland plots had greater weed species, densities, biomass and cover. Along one field boundary the headland crop was divided into eight 100 x 12 m plots, which were alternately sprayed and unsprayed with herbicides in April 1988. Five vacuum-suction samples were taken (0.5 m²) before and five times (up to 90 days) after spraying. Five pitfall traps (7 cm diameter) were placed within gaps in enclosure boundaries (6 x 10 m) within plots and were emptied twice weekly from 20 June to 29 July. Weeds were assessed in 10 quadrats/plot (0.25 m²) in June.
A replicated, controlled study of two headlands over two years 1989-1990 in England (Cowgill 1991) found that in 1990, there were significantly higher proportions of some species of hoverfly (Syrphidae) adults (marmalade hoverfly Episyrphus balteatus, Metasyrphus spp.) in conservation headlands (20-24%) compared to fully sprayed headlands (9-12%). There were also higher proportions of E. balteatus adults feeding and lower proportions inactive in conservation (feeding: 15-90%, inactive: 0-85%) compared to fully sprayed headlands (feeding: 0-35%, inactive: 0-100%). Behaviour of Metasyrphus corollae did not differ with treatment. There were no significant differences in 1989. Weed density and floral area tended to be higher in conservation compared to sprayed plots. Headlands were divided into three or five replicate plots of 75-100 m x 12 m wide, each containing the two pesticide treatments. A set route was walked to record hoverflies encountered during a fixed time period. Weekly counts of weeds and hoverfly eggs on wheat were made in 15-21 quadrats/plot from May-July. Aphids (Aphidoidea) were also recorded but results are not included here.
A paired, replicated, controlled study in the 1980s in cereal fields in southern and eastern England (Sotherton 1991) found higher plant species richness (on average 7 vs 2 species/0.25 m2), biomass (10 vs 1 g/0.25 m2) and percentage weed cover (14% vs 3%) in conservation headland plots compared with fully sprayed headland plots on one Hampshire farm. Several species of rare arable weeds occurred more frequently and in higher abundance in conservation headlands. Total numbers of chick-food items, true bugs (Heteroptera), sawflies (Tenthredinidae) and butterfly/moth (Lepidoptera) larvae, and beetles (Coleoptera) were higher in conservation headlands on the Hampshire farm ((Rands 1985), Sotherton 1989), and butterfly/moth abundance was higher in field margins adjacent to conservation headlands with 2-4 more species observed there ((Rands & Sotherton 1986), (Dover et al. 1990), Dover 1991). Examination of the digestive tract of polyphagous beetles (beetles that feed on many types of food) revealed that a higher proportion of beetles were better fed in conservation headlands. In every year 1983-1986 in southern and eastern England, the brood size of grey partridge Perdix perdix was higher on blocks of cereal fields with conservation headlands (6-10 chicks respectively) compared with conventionally sprayed headlands (3-8 chicks) (Sotherton & Robertson 1990). Breeding density of grey partridges on the Hampshire farm increased from 4 to 12 pairs/km2 between 1979 and 1986. No such increases were recorded on adjacent farms where pesticide regimes remained unchanged. The yield of grain from conservation headlands was 6-10% lower than that from fully sprayed headlands. Grain moisture levels were around 1% higher and weed seed contamination was also higher in conservation headlands. The Hampshire part of this study was part of the same experimental set-up as (Rands et al. 1984, Rands 1985, Rands 1986, Rands & Sotherton 1986, Dover et al. 1990, Dover 1997).
Sotherton N.W. (1989) Farming methods to reduce the exposure of non-target arthropods to pesticides. Pages 195–212 in: P.C. Jepson (ed.) Pesticides and Non-target Invertebrates. Intercept Ltd., Wimborne.
Sotherton N.W. & Robertson P.A. (1990) Indirect impacts of pesticides on the production of wild gamebirds in Britain. Pages 84–102 in: K.E. Church, R.E. Warner & S.J. Brady (eds.). Perdix V, Gray Partridge and Ring-necked Pheasant Workshop. Kansas Department of Wildlife and Parks, Emporia.
Dover J.W. (1991) The conservation of insects on arable farmland. Pages: 293–318 in: N.W. Collins & J. Thomas (eds.) The Conservation of Insects and their Habitats. Academic Press, New York.
A replicated, controlled study of headlands (outer 6 m) of eight barley fields over one year 1988 at three locations within the Breckland Environmentally Sensitive Area in East Anglia, UK (Hassall et al. 1992) (same study as (Cardwell et al. 1994)) found that ground beetles (Carabidae) and true bugs (Heteroptera), but not spiders (Araneae), were more abundant in conservation headlands (restricted pesticides) than sprayed headlands. Ground beetles and true bugs were significantly more abundant in conservation headlands (ground beetles: 160, true bugs: 30) than sprayed headlands (ground beetles: 70, true bugs: 25), spiders did not differ significantly (110 vs. 100). Ground beetles were twice as abundant in crops adjacent to conservation headlands than adjacent to sprayed headlands. There were significantly more ground beetle and true bug species in conservation headlands (ground beetles: 18, true bugs: 3 species) than in sprayed headlands (ground beetles: 15, true bugs: 2), species diversity did not differ significantly (ground beetles: 5-8, true bugs: 2, spiders: 2-3). Spider diversity and biovolume increased with age of site. True bug nymphs (for example field damsel bug Nabis ferus) penetrated further into the crop adjacent to conservation headlands than sprayed headlands. Thirty-five pitfall traps were set up in 6 x 50 m grids at each site (in headlands and crops) and emptied after 14 days in June-July 1988. A Dietrick Vacuum sampler was used along five transect lines (0-15 m into the crop), two samples were taken each of five subsamples (each 0.4 m²).
A replicated, controlled study in summer 1988 in four headlands, adjacent arable fields and field margins in western Germany (Raskin et al. 1992) found that vascular plants, hoverflies (Syrphidae) and ground beetles (Carabidae) all benefited from extensive management in unsprayed headlands. Species richness of all three taxa, as well as abundance and diversity of hoverflies and ground beetles and vegetation cover were higher in the unsprayed margins than in the adjacent fields and the conventional control edge. Field margins adjacent to conservation headlands also held higher numbers of plant, hoverfly and ground beetle species than the margins next to the control edge. Three unsprayed headlands (up to seven years old) and one conventional field edge were compared to three adjacent conventional cereal fields and four field margins next to the headlands. Plants were surveyed in May to September. Ground beetles were sampled weekly from April to August in six pitfall traps (9.5 cm diameter) on each site. Hoverflies were monitored between May and August. Visual observations were made along a 100 m transect in each site. In addition, six yellow bowls (23 x 16 x 5 cm) were placed in the field margins and one in the field centre.
A replicated, controlled study in 1986-1988 of two wheat fields in Oxfordshire, UK (Tew et al. 1992) found that conservation and unsprayed headlands were used more frequently by wood mice Apodemus sylvaticus than sprayed headlands and mid-field. Preference indices for wood mice were 6 for conservation headlands, 6-7 for unsprayed headlands, 2-4 for sprayed plots and 3 for mid-field. Mice showed a significant preference for the mid-field over sprayed headlands. Conservation and unsprayed headland plots contained significantly higher densities of black-grass Alopecurus myosuroides, wild oats Avena spp., sterile brome Bromus sterilis and forget-me-not Myosotis arvensis. Abundance did not differ between the sprayed headland and mid-field for any weed species. In 1986, four of 15 orders of invertebrate were significantly more abundant in unsprayed than sprayed headlands (springtails (Collembola): 6 vs 1 m², true bugs (Hemiptera): 23 vs 8 m², flies (Diptera): 142 vs 24 m², parasitoid wasps (Parasitica): 18 vs 5 m²). In 1987 there was no significant difference between invertebrate abundance in sprayed, unsprayed or conservation headland plots. In one field, alternate plots (20 x 10 m) along the headland were either conventionally sprayed or unsprayed, or in 1987 conservation headland plots. Vegetation was sampled in 5-10 quadrats (0.25 x 0.25 m) in 8-11 plots/treatment in July. In the conventionally sprayed control field, plants were sampled in quadrats of 0.06 m² at 1, 5 and 8 m from the hedge and in the centre of the field. Invertebrates were sampled at 3-5 random positions within 3-8 plots/treatment using a D- Vac sampler in July 1986-1987. Wood mice were radio-tracked at 10 min intervals at night in May-August.
Further results for ground beetles (Carabidae) from a replicated, controlled study of headlands of eight barley fields in 1988 in East Anglia, UK (Hassall et al. 1992) are presented in a second paper (Cardwell et al. 1994). As shown by (Hassall et al. 1992), ground beetles tended to be more abundant in conservation headlands (3-14/trap) than sprayed headlands (3-6/trap) and the main crop (3-9/trap). Species richness was greater on conservation headlands (32 species) than fully sprayed headlands (24), but similar to the main crop (31). Significantly higher numbers of ground beetles were found in headlands than field verges (0-4/trap). There was no significant difference between numbers in verges adjacent to different treatments. There was no significant difference between the vegetation cover under different treatments or in the crop. Plant cover was measured in five 25 x 25 cm quadrats in each grid.
A replicated, controlled study in 1992-1993 of arable fields on eight farms in the Netherlands (de Snoo et al. 1994) found that unsprayed field margins had a higher abundance of blue-headed wagtail Motacilla flava flava than sprayed edges. Blue-headed wagtails made 1.5-2.4 visits/km to unsprayed margins compared to just 0.5 visits/km for sprayed margins. Numbers of Eurasian skylark Alauda arvensis and meadow pipits Anthus pratensis did not differ significantly in sprayed and unsprayed margins (skylark: 0.4 vs 0.2-0.4, meadow pipit: 0.1 vs 0.1). Blue-headed wagtails and skylarks visited field margins more than field centres and sprayed edges bordering ditches more than sprayed edges adjacent to a second plot. Strips 6 m-wide along field edges were left unsprayed by herbicides and insecticides (total length 2560-3790 m/year) and were compared to sprayed edges in the same field and to the sprayed field in 1992-1993. Farmland birds were sampled using a linear transect census, with all birds visiting field margins recorded and a similar size strip in the centre of each field recorded. Birds were sampled 10-12 times between April and mid-July. This study was part of the same experimental set-up as (de Snoo 1996, de Snoo & de Leeuw 1996, de Snoo 1997, de Snoo et al. 1998, de Snoo 1999).
A replicated, controlled study in 1992-1994 of headlands of spring cereal fields on four farms in central and southern Finland (Helenius 1994) found that arable weed density and the abundance of some insect groups were higher in unsprayed headlands compared to sprayed headlands, weed diversity did not differ. Weed density was significantly higher in unsprayed conservation headlands (275-420/m) than sprayed headlands (160-371/m). However, numbers of species were similar in both treatments (31-38 vs 31-36). The following insect groups were more abundant in conservation headlands than sprayed headlands: leafhoppers/planthoppers/aphids (Homoptera) 112-1401 individuals vs 85-706, flies (Diptera) 77-80 vs 69-74, bees/wasps/ants (Hymenoptera) 34-58 vs 29-46, true bugs (Heteroptera) 9-109 vs 7-43 and beetles (Coleoptera) 7-14 vs 5-7. In contrast, thrips (Thysanoptera) were more abundant in sprayed headlands (746-1846 vs 591-960). Twelve conservation (no pesticides) and control headlands (herbicide and insecticides) 4-6 m wide and 100-200 m long were established. Weed abundance was sampled in three pairs (0.5 and 3 m from the crop edge) of 0.25 m² quadrats per headland in late July. Insects were sampled using a D-Vac (five x 10 s per sample) at the same locations as plant quadrats in early July. A sweep net sample (2 x 15 sweeps) was also taken from each headland.
A replicated site comparison study of cereal fields in the Lower Rhine area of Germany (Lösch et al. 1994) found that plant species diversity was higher in fields with unsprayed margins than sprayed margins. Plant diversity (Shannon index) was higher in fields with unsprayed margins (-2.1 to -2.4 vs-1). The average number of species was also higher in unsprayed margins compared to sprayed centres of fields in winter (4-10 species vs 0-2) and summer crops (3-7 species vs 1-3). By the end of the study, there were 100 species recorded within the study site (mean 44 species/field), including nine categorized as highly endangered by the red data book, which had recovered in the local area. Fields were either managed according to the regulations of the government field margins programme (5 m margins, no pesticides, limited fertilizer) or were managed conventionally with intensive pesticide and fertilizer use. Plant species diversity and floristic richness were sampled along transects within cereal fields.
A replicated, controlled study in 1991-1993 of cereal fields on 10 pairs of farms in central and southern Sweden (Chiverton 1994 ) found that grey partridge Perdix perdix brood size, chick survival and abundance of invertebrates tended to be higher on farms with unsprayed headlands (6 m-wide) compared to those sprayed conventionally. Mean brood size tended to be higher on experimental farms (half headlands unsprayed: 7-9 chicks) than on control farms (sprayed: 3-8). Numbers of broods (10-19 vs 4-16), chick survival rate (26-54% vs 11-47%) and numbers of partridge pairs in the spring (20-30 vs 15-24) also tended to be higher on experimental farms. However, none of these differences were statistically significant. Mean density of chick food insect groups (true bugs (Heteroptera), aphids/leafhoppers/planthoppers (Homoptera), weevils (Curculionidae), leaf beetles (Chrysomelidae), larvae of butterflies/moths (Lepidoptera) and sawflies (Tenthredinidae)) was significantly higher on unsprayed (25-74) compared to sprayed headlands of wheat (5-32). Farm pairs (control and experimental) were within 5 km of each other and of similar size, cropping and agricultural practice. On the experimental farm, the headlands left unsprayed (50%) were swapped each year (1991-1993). Partridge counts were undertaken in spring and after harvest using dogs to flush birds. Ten invertebrate samples (0.5 m²) were taken from each headland during the first week in July using vacuum-suction.
A small replicated, controlled study from 1990 to 1992 of the headland (outer 6 m) of a wheat field at Ixworth Thorpe, on the southern edge of Breckland in East Anglia, UK (Hawthorne & Hassall 1995) found that ground beetles (Carabidae) were more abundant in conservation headlands (no herbicides or insecticides) than sprayed headlands (as main field). Conservation headlands had a significantly greater abundance of ground beetles (1474) than sprayed headlands (938). Species diversity was higher in conservation headlands (41) than sprayed headlands (35). Different species reacted differently to treatments. There were a number of species that were restricted to conservation headlands and one restricted to sprayed headlands. Numbers of species and overall abundance varied with season. Two 120 m strips of each treatment were established in a randomized block design along one headland of the 19 ha field. Ground beetles were sampled using 3-5 pitfall traps in the middle of each plot, 3 m from the field boundary. Catches were collected every 1-2 weeks from February-August. Aphid (Aphidoidea) numbers were also sampled but are not presented here.
A replicated, controlled, paired study of arable field edges from 1990 to 1992 in the Netherlands (de Snoo 1996) found that unsprayed field margins had greater plant cover, broad-leaved species, butterfly (Lepidoptera) abundance and insect groups than sprayed margins. Plant cover was significantly higher in 6 m (outer 3 m: 35%, inner 3 m: 26%) and 3 m unsprayed margins (36%) than sprayed margins (outer 3 m: 6%, inner 3 m: 3%). Numbers of broad-leaved species were also higher in 6 m (outer 3 m: 13 species, inner 3 m: 11) and 3 m (12) unsprayed strips than sprayed edges (outer 3 m: 3, inner 3 m: 2). Grass species did not differ (2-3). Numbers of butterfly species were significantly higher in unsprayed margins (6-7/300 m²) compared to sprayed margins (1-2/300 m²). Density did not differ between 3 m (6/300 m²) and 6 m (7/300 m²) unsprayed margins. Numbers on adjacent ditch banks were also higher for unsprayed (18-20) than sprayed margins (9-11). The number of insect groups in the upper vegetation was higher in the unsprayed (12-14) than sprayed margins (8-11). The predominant groups were flower-visiting insects, such as hoverflies (Syrphidae) and ladybirds (Coccinellidae). Insect density was also significantly higher in unsprayed (3 m: 53/100 m, 6 m: 31/100m) compared to sprayed margins (3 m: 20/100m, 6 m: 12/100m). Margins 3 m x 100 m and 6 m x 400 m were left unsprayed by herbicides and insecticides and compared to sprayed edges in the same field. Plant species were sampled in 75 m² plots within margins in June. Butterflies were sampled on 3 m (eight farms) and 6 m (six farms) margins 11 times between mid-May-July. Insects in the upper parts of plants were sampled twice/plot at the end of June with a sweep net. This study was part of the same experimental set-up as (de Snoo et al. 1994, de Snoo & de Leeuw 1996, de Snoo 1997, de Snoo et al. 1998, de Snoo 1999).
A replicated, controlled, paired study of wheat field edges on 10 farms from 1992 to 1993 in the Netherlands (de Snoo & de Leeuw 1996) found that unsprayed field margins had greater insect diversity and abundance in the upper parts of plants than sprayed margins. The average number of insect groups was higher in the unsprayed margins (12-14) than sprayed margins (8-11). Insect density was also significantly higher in the unsprayed winter wheat margins (31-41 vs 10/100 m). Of the 18 groups found on 50% of the sites, 11 in 1992 and 9 in 1993 were significantly more abundant on unsprayed edges. The greatest effect was on flower-visiting insects and aphid predators (unsprayed: 62-73% of all insects, sprayed: 24-32%). Only three groups (long-legged flies (Dolichopodidae), crane flies (Tipulidae) and moths (Heterocera)) were less abundant in the unsprayed edges. Strips 6 m x 450 m along field edges were left unsprayed by herbicides and insecticides and were compared to sprayed edges in the same field. Insects were sampled once or twice in June. Ten sub-samples, 1.5 m from the field edge, were taken using a sweep net (total area sampled 20 m²/100 m). Aphid (Aphidoidea) abundance and dispersal was also recorded, but results are not presented here. This study was part of the same experimental set-up as (de Snoo et al. 1994, de Snoo 1996, de Snoo 1997, de Snoo et al. 1998, de Snoo 1999).
A replicated, controlled study in 1990-1994 of arable fields on 15 farms in the Netherlands (de Snoo 1997) found that unsprayed field margins contained higher plant diversity, abundance and more important/rare plant species than sprayed margins or fields. Species diversity was significantly higher in unsprayed edges than in sprayed edges (sugar beet: 24 vs 16 species/75 m², potatoes: 17 vs 8, winter wheat: 17 vs 6). Field centres had the lowest diversity (2-10 species/75 m²). Thirteen, nine and 30 species were found only in the unsprayed edges in sugar beet, potatoes and wheat respectively. Unsprayed edges had significantly higher floristic values (scoring system based on the importance of different plant species in terms of rarity) than sprayed edges: by a factor 5.2 in sugar beet, 2.8 in potatoes and 7.2 in winter wheat, values were lowest in field centres. The cover (biomass and height) of farmland plants was significantly higher in unsprayed compared to sprayed edges (8-52% vs 1-13%) and lowest in field centres (0-3%). A total of 5-20 fields were studied from 1990-1994. Strips 3-6 m x 100 m long along field edges were left unsprayed by herbicides and insecticides and were compared to sprayed edges in the same field and to the sprayed field. Vegetation was sampled in 75 m² plots in mid June to mid July. This study was part of the same experimental set-up as (de Snoo et al. 1994, de Snoo 1996, de Snoo & de Leeuw 1996, de Snoo et al. 1998, de Snoo 1999).
A replicated, controlled study in summer 1995 in five different field margin types and one control (winter wheat field) in an intensively farmed, homogenous landscape near Göttingen, Germany (Denys 1997) (same study as (Denys et al. 1997, Denys & Tscharntke 2002)) found higher arthropod species richness on potted mugwort Artemisia vulgaris plants placed in unsprayed cereal strips (headlands) compared to the cereal field, but not compared to other margin types. The predator-prey-ratio in the headland did not differ from the control but was significantly lower than in a six-year-old uncultivated field margin. The effect of unsprayed headlands on individual arthropod numbers was species-dependent with some species (e.g. the aphid Macrosiphoniella oblonga and the fly Oxyna parietina), but not all, being found in higher individual numbers in the headlands than in the control. Investigated margin types apart from the unsprayed cereal headlands were wildflower strips (wildflower seed mixture or Phacelia spp. only) and uncultivated margins (one and six-years-old). There were four replicates of each margin type. Potted mugwort plants were placed in all margin types and the control. All herbivores feeding on the plant and their predators were recorded during six visits in June and July. In September, all mugwort plants were dissected in the lab to assess numbers of arthropods feeding within the plants.
A replicated, controlled study in summer 1995 investigating five field margin types plus controls in intensively managed farmland near Göttingen, Germany (Denys et al. 1997) (same study as (Denys 1997, Denys & Tscharntke 2002)) found higher species richness of arthropods colonizing potted mugwort Artemisia vulgaris plants in fertilized but unsprayed cereal strips than in the unsprayed cereal control edges. However, arthropod species numbers on mugwort did not differ between cereal strips and any of the other established margin types. Besides the cereal strips, one- and six-year-old naturally regenerated margins, wildflower strips (19 species sown), phacelia strips (Phacelia tanacetifolia plus three species), and cereal control edges were investigated. Potted mugwort plants (four pots) were placed in all margin types and the controls. Mugwort plants were visited six times in June and July to count all herbivores feeding on the plants and their predators before being taken to the lab in September to assess all arthropods feeding within the plants. Vegetation of all margins was surveyed in June.
A replicated, controlled, paired study in 1985-1987 of butterfly (Lepidoptera) behaviour in headlands of 14 cereal fields in north-east Hampshire (Dover 1997) found that flight speeds tended to be slower and more time was spent resting, interacting and foraging in conservation headlands (no broadleaved herbicides) than those with conventional herbicide applications. Flight and transit speeds of male Pieridae and transits of female green-veined white Pieris napi were significantly slower in conservation headlands. In contrast gatekeeper Pyronia tithonus males (in 1986) were significantly slower in the sprayed headlands, sample sizes were too small for other species. In fields with sprayed headlands, spring emerging large white P. brassicae, green-veined white and small white P. rapae were principally associated with the hedgerow, whilst in fields with conservation headlands they were associated with the headlands. In sprayed headlands, the principal activity was flight, whereas in conservation headlands there was an increase in time spent resting, interacting and particularly foraging. Butterflies that emerged in the summer tended to have less of an association with conservation headlands than spring-emerging butterflies. Limited data were available for meadow brown Maniola jurtina and gatekeeper. Half of the 14 fields were sprayed with conventional pesticides and the other half had conservation headlands. The behaviour and location (hedgerow or headland) of five species of butterfly were observed during the middle of the day along 4-8 headlands. This study was part of the same experimental set-up as (Rands et al. 1984, Rands 1985, Rands 1986, Rands & Sotherton 1986, Dover et al. 1990, Sotherton 1991).
A replicated, controlled study in 1992-1994 of cereal headlands in Sweden (Fischer & Milberg 1997) found that numbers of plant species, including species of conservation interest, were higher in margins without herbicide and pesticide applications at one of two sites. On Öland, there were significantly more species in field margins with no herbicides (6 species) and with no herbicides or fertilizers and reduced sowing rates (5.0) than in conventional plots (3.0). The same pattern was seen for cover per species (no herbicides: 8%, no herbicides/pesticides: 6%, conventional: 4%). Numbers did not differ significantly in Uppland (species: 5, 4 and 3, cover: 4%, 5% and 4% in the different treatment plots respectively). On Öland, frequencies of rare species increased, particularly in plots with no herbicides (1992: 8-10 rare species, 1994: 45-50) compared to conventional plots (1992: 2, 1994: 28). Red list species established in all Öland plots over the study (1992: 0, 1994: 9-12), with higher cover in plots with no herbicides (1994: 3-6% vs 1%). No rare or Red list species occurred at Uppland. On Öland, four fields with two to four treatment blocks and in Uppland, two fields with two blocks were established with treatment plots of 6 x 20 m within margins. Plant species were recorded in each plot on two or three visits each year.
A replicated, controlled, randomized study of cereal headlands on 26 farms in East Anglia, UK (Hodkinson et al. 1997) found no significant difference in plant species richness or density between conservation and sprayed headlands, but plant composition did differ. Although figures tended to be higher in conservation headlands (6-12 m-wide, restricted pesticide applications, selected herbicides only), there was no significant difference between conservation and conventionally sprayed headlands in terms of species richness (10 vs 5), plant density (99 vs 47) or grass tiller count (73 vs 69). Conservation headlands had a significantly greater proportion of annuals and biennials to perennials (0.7 vs 0.5) and ratio of broadleaves (dicotyledons) to grasses (monocotyledons) (0.8 vs 0.6). On nine farms within the Breckland Environmentally Sensitive Area, three conservation headlands and one sprayed headland were selected. One conservation headland was randomly selected from each of an additional 17 farms. Three transects 50 m apart were located within randomly selected 100 m sections of headlands. Along these, three quadrats (0.5 x 0.5 m) at 1, 3 and 5 m from the field boundary in 6 m headlands and 2, 6 and 10 m from the boundary in 12 m headlands were surveyed.
A replicated, controlled study of headlands of three winter rye fields in 1991 in the Netherlands (Kleijn & van der Voort 1997) found that weed species richness, abundance and biomass was higher in unfertilized crop edges than those that had received fertilizer. Species richness (17 vs 14 species/m²), abundance (276 vs 170 plants/m²) and biomass (88 vs 35 g/m²) were higher in unfertilized headlands. Species richness, plant numbers and total weed biomass decreased significantly with distance from the field boundary in fertilized plots. Some individual species followed the same trend, others were more abundant in the fertilized plots and some showed no overall effect of treatment. Thirty-six plots were established within headlands, half were fertilized and half unfertilized, no herbicides were applied. Above-ground weed biomass and the number of individuals of each species were sampled in quadrats (0.5 x 2 m) at distances of 0.25, 1.25 and 2.25 m from the boundary in August.
A study of habitat use by yellowhammers Emberiza citrinella in 1994 and 1995 on a mixed farm in Leicestershire, UK (Stoate & Szczur 1997) found that conservation headlands were not used significantly more than adjacent crops (1.0 vs 0.7 yellowhammers flushed). The outer tramline of each field was walked three times in June 1994 and 1995. Yellowhammers flushed from the conservation headland and equivalent area in the adjacent crop were recorded.
A replicated, controlled, paired study from 1990 to 1992 of arable field edges on 12 farms in the Netherlands (de Snoo et al. 1998) found that unsprayed field margins had greater butterfly (Lepidoptera) abundance than sprayed margins. Butterfly numbers were significantly higher in the unsprayed edges of winter wheat in both years (10-12 butterflies/100 m²) and potatoes in 1992 (5/100 m²) compared to sprayed edges (wheat: 2-3, potato: 1). The same was true for numbers of species: unsprayed winter wheat (3-4 species/100 m²) and potatoes in 1992 (3/100 m²) compared to sprayed edges (wheat: 1-2, potato: 1). In all six individual species, abundance was greater in unsprayed compared to sprayed edges (in one or both years and crops). Strips 6 m x 100 m or 400 m long along field edges were left unsprayed by herbicides and insecticides and were compared to sprayed edges in the same field. Butterflies were sampled once a week on the crop edges and adjacent ditch banks nine times from mid-May to July in 1990 and 1992. This study was part of the same experimental set-up as (de Snoo et al. 1994, de Snoo 1996, de Snoo & de Leeuw 1996, de Snoo 1997, de Snoo 1999).
A 1998 literature review (Sotherton 1998) looked at the effect of agricultural intensification and the role of set-aside on the conservation of farmland wildlife, particularly gamebirds and endangered annual arable wildflowers. It found a replicated study on farms in three English counties showing that there were greater numbers of arable weed species in headland plots of winter cereals that received no herbicide and fertilizer (23 species) compared to those that received fertilizer (no herbicide, 20 species) and the controls (normal fertilizer and herbicide applications, 6-8 species) (Wilson 1994). A further three studies were found, two in the UK (Rands 1985, Rands & Sotherton 1986) and one in Sweden (Chiverton 1999) showing that gamebird (grey partridge Perdix perdix) chick survival rates were significantly higher in conservation headlands with reduced pesticide inputs compared to controls receiving the usual pesticide application.
Wilson P.J. (1994) Botanical diversity in arable field margins. British Crop Protection Council Monographs, 58, 53-58.
Chiverton P.A. (1999) The benefits of unsprayed cereal crop margins to grey partridges Perdix perdix and pheasants Phasianus colchicus in Sweden. Wildlife Biology, 5, 83–92.
A replicated, controlled study from 1990 to 1993 of 16 arable fields on farms in the Netherlands (de Snoo 1999) found that unsprayed field margins had greater plant and insect diversity and abundance, and more visits by blue-headed wagtails Motacilla flava flava and field mice Apodemus spp. than sprayed margins. Results for vegetation, butterflies (Lepidoptera), insects in the upper parts of the vegetation and birds are presented in (de Snoo et al. 1994, de Snoo 1996, de Snoo & de Leeuw 1996, de Snoo 1997, de Snoo et al. 1998). Unsprayed margins contained greater diversity and abundance of ground-dwelling invertebrate species (14-17 vs 12-14) and ground beetle (Carabidae) activity density tended to be significantly higher than in sprayed margins. Orb-weaving spiders (Araneida) (in winter wheat) and beetles (Coleoptera) (in sugar beet) were more abundant in unsprayed edges than in sprayed edges (in one year), other ground-dwelling groups did not differ with treatment. More field mouse visits were recorded in unsprayed (38 visits) than in sprayed cereal edges (27). Strips 3-6 m x 100-450 m long along field edges were left unsprayed by herbicides and insecticides and were compared to sprayed edges in the same field. Floristic value was sampled in 75 m² plots (mid-June to mid-July). Insects were sampled by: sweep netting in wheat (June), butterfly transects along crop edges (mid-May to July) and pitfall traps (11cm diameter, May-July). Blue-headed wagtail, Eurasian skylark Alauda arvensis and meadow pipit Anthus pratensis visits were recorded in 6 m winter wheat edges using a linear transect census and small mammals were live trapped in winter wheat.
A 1999 review of research on unsprayed field margins in north-west Europe (de Snoo & Chaney 1999) found that both plants and invertebrates were enhanced in areas with unsprayed margins. Three studies reported that numbers of plant species and abundance were higher in or adjacent to unsprayed margins (e.g. Fischer & Milberg 1997, de Snoo & van der Poll 1999). One study also found that rare arable weeds returned (Schumacher 1984). Three studies reported that buffer strips of 8-23 m were necessary for caterpillars of the large white butterfly Pieris brassicae for more toxic insecticides, whereas strips of 1 m were sufficient for other insecticides (Sinha et al. 1990, Davis et al. 1991, de Jong & van der Nagel 1994). An additional study reported that a buffer strip 3 m-wide strongly decreased the effects on aquatic species next to a sprayed field (de Snoo & de Wit 1998).
Schumacher W. (1984) Gefährdete Ackerwildkräuter können auf ungespritzten Feldrändern erhalten warden [Endangered wild herbs can be protected/conserved on unsprayed field margins]. Mitteilungen der LÖLF, 9, 14-20.
Sinha S.N., Lakhani K.H. & Davis B.N.K. (1990) Studies of the toxicity of insecticidal drift to the first instar larvae of the Large White Butterfly Pieris brassica (Lepidoptera: Pieridae). Annals of Applied Biology, 116, 27-41.
Davis B.N.K, Lakhani K.H., Yates T.J. & Frost A.J. (1991) Bioassays on insecticide spray drift: the effects of wind speed on the mortality of Pieris brassica larvae (Lepidoptera) caused by diflubenzuron. Agriculture, Ecosystems and Environment, 36, 141-149.
de Jong F.M.W. & van der Nagel M.C. (1994) A field bioassay for side-effects of insecticides with larvae of the large white butterfly (Pieris brassica L.). Medical Faculty Landbouww. University of Gent, 59/2a, 347-355.
de Snoo G.R. & de Wit P.J. (1998) Buffer zones for reducing pesticide drift to ditches and risks to aquatic organisms. Ecotoxology and Environmental Safety, 41, 112-118.
A replicated, controlled, paired study in 1991-1992 of ditch banks on arable farms in the Netherlands (de Snoo & van der Poll 1999) found that plant diversity and the value of the vegetation in terms of species rarity was significantly higher on ditch banks along unsprayed edges of winter wheat (65 species, floristic value: 2201) than those sprayed with pesticides (50 species, floristic value: 1181). There was no significant difference on banks along unsprayed and sprayed edges of sugar beet (species: 48 and 41, floristic values: 3616 and 3029 respectively) and potato crops (species: 46 and 41, floristic values: 1961 and 1864 respectively). Frequency and cover of species and floristic value of vegetation (scoring system based on the importance of different plant species in terms of rarity) was recorded in two plots on each ditch, one along a sprayed and one an unsprayed edge of sugar beet (seven), potato (eight) and winter wheat (20) fields in June-July.
A replicated, randomized study in Oxfordshire, UK (Haughton et al. 1999) found that from 1995 to 1996 spraying naturally generated margins with herbicides resulted in significantly lower numbers of invertebrates than leaving them unsprayed (650 vs 1275 invertebrates respectively). The same was true for spiders (Araneae) in all seasons (56-138 vs 107-392), true bugs (Heteroptera) in September (8 vs 27) and leafhoppers (Auchenorrhyncha) in July and September (39-60 vs 112-171). Existing field margins (0.5 m-wide) were extended by 1.5 m in October 1987. These were rotavated and left to naturally regenerate or sown with a wildflower seed mix. Six management treatments were applied with six replicates in a randomized block design. Fifty metre-long plots received one of six treatments: sprayed once a year in summer, uncut, cut once in summer, cut spring and summer, cut spring and autumn, cut spring and summer (hay left lying). Invertebrates were sampled using a D-Vac suction sampler at 10 m intervals along each plot in May, July and September in 1995-1996.
A replicated, controlled, randomized study in 1996-1997 of a silage field in Scotland (Haysom et al. 1999) found that ground beetle (Carabidae) abundance and diversity was not consistently higher in headlands (no fertilizers or pesticides) than in main fields (fertilizers, no pesticides). Total abundance of ground beetles was higher mid-field (128-278 individuals) than in the headland (43-201). The field boundary had an intermediate abundance in 1996 (77 individuals) and a higher abundance in 1997 (612). In 1996, species diversity was higher mid-field (13) than in the headland (9-12). This trend was reversed in 1997 (headland: 10-14, mid-field: 6), the field boundary had the highest diversity both years (16-32). The headland received three treatments: uncut, annual cut (August) and three annual cuts (May, June, August). These were assigned randomly within blocks to three 10 x 10 m plots. Cattle were excluded April-October and plots were intermittently grazed by sheep October-February. Ground beetles were sampled using pitfall traps in late May to mid-July and late August to early October. There was a line of three pitfall traps in the centre of each plot, within the field boundary and three rows in the main field, 80 m from the field edge. Results from 1997 are also presented in (Haysom et al. 2004).
A replicated, controlled study from 1989 to 1991 of headlands of two arable fields in England (Moreby & Southway 1999) found that plant and invertebrate diversity was greater in unsprayed plots compared to those receiving autumn herbicide applications. Thirty-two of 34 broadleaved plant species (dicotyledons) were found in unsprayed plots compared to 19 in sprayed plots, total dicotyledon species cover and total cover were also significantly greater in unsprayed plots. Numbers of true bugs (Heteroptera) (unsprayed: 29, sprayed: 23 species), leafhoppers (Auchenorrhyncha) (unsprayed: 1-13 groups/0.5 m², sprayed: 0-9), total beetles (Coleoptera) (10-55 vs 2-40), weevils (Curculionidae) (0.3-5.0 vs 0-1.3), rove beetles (Staphylinidae) (0-30 vs 0-22), total flies (Diptera) (40-280 vs 20-240), chick-food insects (7-33 vs 2-25), total arthropods (80-1175 vs 40-1165) and spiders (Araneae) (2-40 vs 2-28) were significantly greater in the untreated plots compared to sprayed plots. Aphids (Aphididae), sawflies (Symphyta) and butterfly/moth (Lepidoptera) larvae did not differ between treatments. Field headlands were divided into (6-8) plots (100 x 6 m), half (and crops) were sprayed with herbicides in autumn and half were unsprayed. No insecticides or fungicides were applied. Plants were sampled in 10 quadrats (0.25 m²) per plot in May and late June/early July (1989-1991). Arthropods were sampled on five occasions (May-July), five samples were collected per plot using a D-Vac insect sampler.
A 2000 literature review from the UK (Aebischer et al. 2000) found that populations of grey partridge Perdix perdix were 600% higher on farms with conservation measures aimed at partridges in place, compared to farms without these measures (Aebischer 1997). Measures included the provision of conservation headlands, planting cover crops, using set-aside and creating beetle banks.
Aebischer N.J. (1997) Gamebirds: management of the grey partridge in Britain. Pages 131-151 in: M. Bolton (ed.) Conservation and the Use of Wildlife Resources. Chapman & Hall, London.
A before-and-after study of two winter wheat fields over one year in Dorset, UK (Holland et al. 2000) found that some arthropod taxa survived within the unsprayed headland and appeared to recolonize the mid-field surrounded by the headland more extensively compared to when there was no headland. Ground beetle (Carabidae) species (Pterostichus melanarius, P. madidus), spiders (Araneae: money spiders (Linyphiidae), wolf spiders (Lycosidae)), parasitic wasps (Aphidius spp.) and total predatory arthropods showed the greatest decline immediately after application of the insecticide dimethoate; rove beetles in the sub-family Aleocharinae did not decline. Numbers of the ground beetle P. madidus, money spiders and parasitic wasps Aphidius spp. decreased within the field and unsprayed headland. Numbers of P. madidus recovered faster within the field edge than mid-field and particularly within the unsprayed buffer zone and the mid-field area it enclosed. Money spiders were present across most areas of both fields 19 days after spraying, although in lower numbers than pre-spraying, parasitic wasps Aphidius spp. had not recovered 20 days after spraying. A grid of 75 and 29 pitfall traps were used in each field, over two days on five occasions May-July 1997 and then 6, 20 and 34 days after spraying with the pesticide dimethoate (0.86 l/ha). A 6 m headland around half of one field was unsprayed. A D-Vac suction sampler was also used three times pre-spraying and at 6 and 20 days after treatment.
A replicated controlled trial in 1999 on five arable farms in the West Midlands, UK (Kells et al. 2001) found fewer bees (Apidae) on conservation headlands compared to naturally regenerated margins (average less than three bees/transect in conservation headlands vs averages of 10-50 bees/transect in naturally regenerated margins. Bumblebees Bombus spp. and honey bees Apis mellifera were counted on 50 m transects in five 6 m-wide field margins managed as conservation headlands, and ten naturally regenerated, uncropped field margins between 29 June and 9 August. Two unsown margins and one conservation headland were created on each farm.
A replicated study from April to September 1995 in five types of field margin around four cereal fields near Göttingen, Germany (Denys & Tscharntke 2002) (same study as (Denys 1997, Denys et al. 1997)) found that unsprayed margins sown with cereals (conservation headlands) suppressed the colonization of aggressive weeds. However, abundance of predators (mainly spiders (Araneae)) and predator prey ratios in cereal sown margins were lower than in six-year-old naturally developed margins. Arthropod abundance, diversity and predator-prey ratios in the cereal margins did not differ from the rest of the studied margin types. The following margin types (3 m-wide, 100-150 m long) were studied: one-year old naturally developed, six-year old naturally developed, sown with mixture of 19 wildflower species, sown with phacelia Phacelia spp. mixture, and control strips sown with winter wheat or oats. Potted plants of mugwort Artemisia vulgaris (four pots per margin) and red clover Trifolium pratense (three pots per margin) were used to study plant-arthropod communities. Mugwort pots were set out in May and visited weekly to count all arthropods living on the plants, leaf miners and galls that had colonized the plants. In September, the plants were dissected and all larvae and pupae living inside the plants were individually reared in the lab to estimate parasitization rates. Red clover pots were set out in April. At five visits in June and July, flower heads were sampled, dissected and larvae and pupae were reared in the lab for species determination.
A 2002 review (Evans et al. 2002) of two reports (Wilson et al. 2000, ADAS 2001) evaluating the effects of the Pilot Arable Stewardship Scheme in two regions (East Anglia and the West Midlands) in the UK from 1998 to 2001 found that conservation headlands with restricted use of fertilizers, insecticides or both, benefited plants and true bugs (Hemiptera), but not bumblebees Bombus spp., ground beetles (Carabidae) or sawflies (Symphyta). There were total areas of 605 and 1085 ha of conservation headlands in East Anglia and the West Midlands respectively. The effects of the pilot scheme on plants and invertebrates were monitored over three years, relative to control areas.
Wilson S., Baylis M., Sherrott A. & Howe G. (2000) Arable stewardship project officer review. Farming and Rural Conservation Agency report.
ADAS (2001) Ecological evaluation of the Arable Stewardship Pilot Scheme, 1998-2000. ADAS report.
A 2003 literature review in Europe (Bat Conservation Trust 2003) found three studies that showed that unsprayed crop margins reduce the effects of spray drift on butterflies (Lepidoptera) (Longley et al. 1997, Longley & Sotherton 1997, de Snoo 1999). One study suggests that a 6 m buffer is not sufficient to eliminate spray drift (Longley & Sotherton 1997), whereas other research suggests that a 6 m buffer provides no more protection than a 3 m buffer (de Snoo 1999). One study reported that hoverflies (Syrphidae) were more abundant in unsprayed headlands (Cowgill et al. 1993).
Cowgill S.E., Wratten S.D. & Sotherton N.W. (1993) The effect of weeds on the numbers of hoverfly (Diptera: Syrphidae) adults and the distribution and composition of their eggs in winter wheat. Annals of Applied Biology, 123, 499-515.
Longley M., Cilgi T., Jepson P.C. & Sotherton N.W. (1997) Measurements of pesticide spray drift deposition into field boundaries and hedgerows: 1. Summer applications. Environmental Toxicology and Chemistry, 16, 165-172.
Longley M. & Sotherton N.W. (1997) Measurements of pesticide spray drift deposition into field boundaries and hedgerows: 2. Autumn applications. Environmental Toxicology and Chemistry, 16, 173-178.
A replicated study in the summers of 1999-2000 comparing ten different conservation measures on arable farms in the UK (Critchley et al. 2004) found that conservation headlands without fertilizer appeared to be one of the three best options for the conservation of annual herbaceous plant communities. Wildlife seed mix (sown for birds and bees) and uncropped, cultivated margins were the other two options. Conservation headlands with fertilizer use had fewer plant species. The average numbers of plant species in the different conservation habitats were no-fertilizer conservation headlands 4.8, conservation headlands 3.5, wildlife seed mixtures 6.7, uncropped cultivated margins 6.3, undersown cereals 5.9, naturally regenerated grass margins 5.5, spring fallows 4.5, sown grass margins 4.4, overwinter stubbles 4.2, grass leys 3.1. Plants were surveyed on a total of 294 conservation measure sites (each a single field, block of field or field margin strip), on 37 farms in East Anglia (dominated by arable farming) and 38 farms in the West Midlands (dominated by more mixed farming). The ten habitats were created according to agri-environment scheme guidelines. Vegetation was surveyed once in each site in June-August in 1999 or 2000, in thirty 0.25 m2 quadrats randomly placed in 50-100m randomly located sampling zones in each habitat site. All vascular plant species rooted in each quadrat, bare ground or litter and plant cover were recorded.
A continuation of the same replicated, controlled, randomized study in Scotland as in (Haysom et al. 1999), (Haysom et al. 2004) found that ground beetle (Carabidae) species diversity and abundance was significantly higher in the headland (no fertilizers or pesticides) than in the main field (fertilizers, no pesticides) in 1997-1998. The total abundance of ground beetles was significantly higher in the headland (927-1053 individuals) than main field (631-910). This was also the case for species diversity (headland: 38 species, main field: 23).
A replicated controlled paired-sites comparison in 2003 in East Anglia and the West Midlands, UK (Pywell et al. 2005) found no significant difference in bumblebee Bombus spp. species richness and abundance when 16 conservation headlands were compared with paired conventional field margins. In both types of field margin, a few species of plant contributed to the vast majority of foraging visits by bumblebees, mainly creeping thistle Cirsium arvense and spear thistle C. vulgare. Nineteen farms were surveyed in East Anglia, and 17 farms in the West Midlands. Three agri-environment scheme (Arable Stewardship Pilot Scheme (ASPS)) options were studied: field margins sown with a wildlife seed mixture (28 sites), conservation headlands with no fertilizer (16 sites), naturally regenerated field margins (18 sites). Fifty-eight conventional cereal field margins were used as a control, and paired with ASPS sites. Bumblebees were surveyed along 100 x 6 m or 50 x 6 m transects twice, in July and August. Vegetation was surveyed in twenty 0.5 x 0.5 m quadrats.
A replicated study in 1999 and 2003 on farms in East Anglia and the West Midlands, UK (Stevens & Bradbury 2006) found that five of 12 farmland bird species analysed were positively associated with conservation headlands and a general reduction in herbicide use. These were corn bunting Miliaria calandra (a field-nesting species), chaffinch Fringilla coelebs, greenfinch Carduelis chloris, whitethroat Sylvia communis, and yellowhammer Emberiza citrinella (all boundary-nesting species). The study did not distinguish between conservation headlands and a general reduction in herbicide use, classing both as interventions reducing pesticide use. A total of 256 arable and pastoral fields across 84 farms were surveyed.
A replicated controlled trial from 2001 to 2004 across central and eastern England (Carvell et al. 2007) found that unsprayed conservation headlands did not support more bumblebee Bombus spp. individuals or species than conventional cropped field margins. The number of flowers and flower species in conservation headlands was not significantly different from cropped field margins or margins sown with a tussocky grass mix. Six sites were studied and two experimental plots (50 m x 6 m) established in each cereal field along two margins. Six treatments were assigned to plots: wildflower mixture (21 native wildflower species and four fine grass species), pollen and nectar mixture (four agricultural legume species: red clover, Alsike clover T. hybridum, bird’s-foot trefoil and sainfoin Onobrychis viciifolia and four fine grass species), tussocky grass mixture, conservation headland, natural regeneration, crop (control treatment). Foraging bumblebees were counted from May to late August, on 6 m-wide transects between six and 11 times in each margin. Flower abundance was also estimated along the bumblebee transects in 2002, 2003 and 2004.
A replicated, controlled study in 2000-2003 of five grassland headlands on four intensively managed pastoral farms across Scotland (Cole et al. 2007) found that aphids/leafhoppers/planthoppers (Homoptera) and true bugs (Heteroptera) were more abundant in conservation headlands (no fertilizers, pesticides or grazing April-August) than conventional headlands and open fields. Homoptera had higher activity densities in conservation headlands (2.1) and field edges (conventional: 2.0, conservation: 1.9) than in conventional headlands (0.8) and open fields (0.6). Roundback slugs (Arionidae) showed the same pattern (2.3 conservation headlands, 2.1 conventional field edges, 2.4 conservation field edges, 0.7 conventional headlands, 0.3 open fields). True bugs were more abundant in conservation headlands (0.7) and field edges (1.1-1.2) than in open fields (0.2). Keelback slug (Limacidae) activity density was greater in both headlands (conventional: 1.9, conservation: 2.8) and field edges (2.3-2.7) than in open fields (1.1). Butterfly/moth (Lepidoptera) and sawfly (Symphyta) larvae showed a similar trend, whereas ground beetle (Carabidae) abundance did not differ with treatment (3.5-3.6). Ground beetle activity density was highest in open fields (4.0). One headland in each field was divided into two areas of 6 x 100 m, a conventional and conservation headland. In each field, invertebrates were sampled with five pitfall transects of nine traps in the conservation headland, conservation field edge, conventional headland, conventional field edge and open field. Traps were set for 3–4 weeks in May-June and July-August 2000-2003.
A replicated site comparison study in 2004 and 2005 in the UK (Critchley et al. 2007) found that conservation headlands without fertilizer had more plant species (17 species/margin) than standard conservation headlands (reduced pesticide only, 11 species/margin) and significantly more species than control margins in all plant groups except grasses. Standard conservation headlands did not have significantly more plant species than control margins (11 and 8 species/margin on average), but they did have a higher percentage of spring germinating plant species (63% of plant species were spring germinating, compared to 48% in control margins). Thirty-nine of each type of conservation headland managed under the Countryside Stewardship Scheme, were surveyed in 2005, and compared with 72 conventionally cropped field margins surveyed in 2004 or 2005. Margins were randomly selected from eight UK regions. Plants were surveyed in thirty 0.025 m2 quadrats within a 100 m sampling zone of each margin and percentage cover across all quadrats estimated.
A 2007 review of published and unpublished literature (Fisher et al. 2007) found experimental evidence of benefits of conservation headlands to plants (four studies: Helenius 1994, Chiverton 1994, Kleijn & van der Voort 1997, Critchley et al. 2004), rare arable plants (when fertilizer also reduced, one study: Kleijn & van der Voort 1997), invertebrates (some groups, five studies: Hassall et al. 1992, Helenius 1994, Chiverton 1994 , Dover 1997, de Snoo et al. 1998) and mammals (three studies not summarized here, showed potential value through increased food resources).
A review of the effects of agri-environment scheme options on small mammals in the UK (Macdonald et al. 2007) found one study that reported that 12 radio-tracked wood mice Apodemus sylvaticus preferred unsprayed and conservation headlands (sprayed only with herbicides to control grasses) over sprayed headlands and mid-fields (Tew et al. 1992). Another study found that conservation headlands have higher abundances of insects and arable weeds, both of which are eaten by wood mice (Sotherton 1991).
A replicated, controlled, randomized site comparison study in 2005 of field margins at 39 sites in England (Walker et al. 2007a), (same study as (Walker et al. 2007b)), found no significant difference in the number of rare arable plants in conservation headlands and the crop. No-fertilizer conservation headlands had higher numbers of rare arable plants (0.7/sample zone) than conservation headlands (reduced insecticides/pesticides) or the crop (0.1), but the difference was not significant. In total 18 species were found on no-fertilizer conservation headlands. There were no significant differences in diversity at 1, 3 or 5 m from the field edge within margins, although it tended to decline. There were significant regional differences in diversity. One of each margin type and an adjacent control was randomly selected in thirty-nine 20 x 20 km squares in England. Rare arable plants were sampled in 10 quadrats (0.5 x 0.5 m) at three distances (1, 3 and 5 m) from the field edge within a 100 x 6 m sample zone in June-July 2005.
A replicated, controlled, randomized site comparison study in 2005 of Countryside Stewardship scheme field margin options across England (Walker et al. 2007b), (same study as (Walker et al. 2007a)) found that arable plant species diversity was higher in no-fertilizer conservation headlands (4.1 species) and spring fallow (4.3) than in fertilized conservation headlands (2.4 species, reduced pesticide use) and cereal crop controls (1.4). A total of 39 randomly selected 20 x 20 km squares throughout England were visited to sample four Countryside Stewardship scheme options: uncropped margins, spring fallow and conservation headlands with and without fertilizer. A conventionally managed cereal crop (control) was also sampled at each of the farms visited. A total of 195 field margin agreements were surveyed during June and July 2005. All plant species and 86 rare arable plants were investigated.
A 2008 review of control methods for competitive weeds in field margins managed to maintain uncommon arable plant populations in the UK (Critchley & Cook 2008) found that specific management regimes can reduce abundance of pernicious weeds in margins. One study found pernicious weeds were more likely in uncropped cultivated margins than in conservation or conventional headlands (Critchley et al. 2004), two studies found the latter two did not differ in weed abundance (Pinke 1995, Fischer & Milberg 1997, Critchley et al. 2004). Three studies found lower weed abundance in fertilized conservation headlands (Pinke 1995, Wilson 2000). In naturally regenerated margins, fertilizer increased one grass species and decreased 10 out of 14 rare plant species (Wilson 2000, Meek et al. 2007).
Pinke G. (1995) The significance of unsprayed field edges as refugia for rare arable plants. Acta Agronomica Ovariensis 37, 1-11.
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Critchley C.N.R., Fowbert J.A. & Sherwood A.J. (2004) Botanical assessment of the Arable Stewardship Pilot Scheme, 2003. ADAS report to the Department for Environment, Food and Rural Affairs April 2004.
Meek W.R., Pywell R.F., Nowakowski M. & Sparks T.H. (2007) Arable field margin management techniques to enhance biodiversity and control barren brome, Anisantha sterilis. Pages 133-141 in: C. Britt, A. Cherrill, M. le Duc, R. Marrs, R. Pywell, T. Sparks, I. Willoughby (eds.) Vegetation Management (Aspects of Applied Biology 82).
A 2009 literature review of agri-environment schemes in England (Natural England 2009) found evidence that grey partridge Perdix perdix broods were significantly larger in cereal fields with a 6 m unsprayed margin around them, compared to conventional fields. Two studies showed that more butterflies (Lepidoptera) were found in conservation headlands than in pesticide-sprayed areas (Dover 1997, Longley & Sotherton 1997). One study (Walker et al. 2007b) found that 264 plant species typically found in disturbed or arable habitats, including 34 rare and uncommon arable plants, were recorded in three agri-environment scheme options: uncropped cultivated margins (highest diversity), spring fallow, conservation headlands (lowest diversity).
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A 2009 literature review of European farmland conservation practices (Vickery et al. 2009) found that rare annual flowers were more abundant in conservation headlands than in adjacent crops, but less abundant than in uncropped field margins. Invertebrates were also more common in conservation headlands than in crops, but less diverse than in uncropped margins. Gamebirds made frequent use of conservation headlands, for shelter and foraging. The authors note that the effects on non-gamebirds are less certain.
A replicated site comparison study from 2004 to 2008 in England (Ewald et al. 2010) found that grey partridge Perdix perdix overwinter survival was positively correlated with the proportion of a site under conservation headlands in 2007-2008, and with year-on-year density changes in 2006-2007. There was no relationship between the proportion of a site under conservation headlands and brood size or the ratio of young to old birds. Spring and autumn counts of grey partridge were made at 1031 sites across England as part of the Partridge Count Scheme.
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