E. J. P. Marshall

Field margins in northern Europe: their functions and interactions with agriculture

Abstract Most agricultural landscapes are a mosaic of farmers’ fields, semi-natural habitats, human infrastructures (e.g. roads) and occasional natural habitats. Within such landscapes, linear semi-natural habitats often define the edges of agricultural fields. This paper reviews the role and interactions within and between the flora of these elements. In temperate, intensive agriculture, such field margin habitats, which historically had true agricultural functions, now are important refugia for biodiversity. As manmade habitats, field margins may also have important cultural roles as part of our landscape heritage, e.g. hedges in Britain. Whilst field margins are not usually specific habitat types, they contain a variety of plant communities in a variety of structures. These may range from aquatic elements to ruderal and woodland communities. Studies demonstrate a variety of interactions between fields and their margins. Agricultural operations, such as fertiliser and pesticide application, have effects on the flora. Some margin flora may spread into crops, becoming field weeds. Margins also have a range of associated fauna, some of which may be pest species, while many are beneficial, either as crop pollinators or as pest predators. The biodiversity of the margin may be of particular importance for the maintenance of species at higher trophic levels, notably farmland birds, at the landscape scale. Margins contribute to the sustainability of production, by enhancing beneficial species within crops and reducing pesticide use. In northwestern Europe, a variety of methods to enhance diversity at field edges have been introduced, including sown grass and flower strips. The impact of these on weed flora and arthropods indicate mostly beneficial effects though conflicts exist, notably for the conservation of rare arable weed species.

On the relationship between farmland biodiversity and land-use intensity in Europe

Worldwide agriculture is one of the main drivers of biodiversity decline. Effective conservation strategies depend on the type of relationship between biodiversity and land-use intensity, but to date the shape of this relationship is unknown. We linked plant species richness with nitrogen (N) input as an indicator of land-use intensity on 130 grasslands and 141 arable fields in six European countries. Using Poisson regression, we found that plant species richness was significantly negatively related to N input on both field types after the effects of confounding environmental factors had been accounted for. Subsequent analyses showed that exponentially declining relationships provided a better fit than linear or unimodal relationships and that this was largely the result of the response of rare species (relative cover less than 1%). Our results indicate that conservation benefits are disproportionally more costly on high-intensity than on low-intensity farmland. For example, reducing N inputs from 75 to 0 and 400 to 60 kg ha−1 yr−1 resulted in about the same estimated species gain for arable plants. Conservation initiatives are most (cost-)effective if they are preferentially implemented in extensively farmed areas that still support high levels of biodiversity.

Arthropod abundance and diversity in differently vegetated margins of arable fields

Abstract Field margin strips, sown with either the main field crop, rye grass (Lolium perenne), a grass and wild flower mixture, or left to natural regeneration, were established in replicated plots along three hedgerows and field edges. Pitfall traps were used to assess the carabid beetle fauna in mid-summer between 1993 and 1996. Suction sampling was used to assess a wider range of arthropod taxa in June 1994. Pitfall data showed no significant overall effects from plot-type although significant differences in carabid activity-density were found between fields and years. In contrast, suction sampling showed marked differences between the crop, the hedge and the plots with different vegetation structures. There was a significant positive correlation between faunal and floral diversity, with arthropod diversity lowest in the crop, low in the crop edge, higher in the more diverse sown plots and highest in the hedge. Studies of over-wintering arthropods from soil samples revealed similar trends, confirming that arthropods colonised sown margin strips within 11–15 months of establishment. The results indicate that the appropriate scale for using pitfall traps is at the field rather than the plot scale. The introduction of botanically diverse field margin strips is shown to be an important method of increasing the arthropod diversity of semi-natural habitat in farmland.

DISTRIBUTION PATTERNS OF PLANTS ASSOCIATED WITH ARABLE FIELD EDGES

SUMMARY (1) Distribution records of the flora within arable field boundaries and the associated crop indicated that most species in field boundaries did not occur in the crop area. About 30% of the species recorded in the boundary were found also at varying distances into the crop. Many of these were found only within 2 5 m of the undisturbed field edge, though some important field weeds appear to originate in the margins, e.g. Bromus steriis L., Elymus repens and Galium aparine. (2) Four types of plant distribution were found on two farms, one in Cambridgeshire and the other in Hampshire. Plants were (i) limited to the margin, (ii) limited to the crop but occasionally found in the hedge-bottom, (iii) occurring at the boundary and at decreasing density into the crop, and (iv) distributed through the headland with highest densities between 1 0 m and 5 m from the field edge. (3) A number of annual arable weeds, e.g. Veronica persica, were recorded at low densities within the field boundary and were present in the boundary seed bank. (4) The distribution of the viable buried seed flora from samples taken at different distances from the field boundary were similar to those of the plants above ground.

Isolating the components of activity-density for the carabid beetle Pterostichus melanarius in farmland

Abstract The activity and density of the carabid beetle, Pterostichus melanarius, were studied over 10 weeks in a continuous mark-recapture experiment using a grid of pitfall traps spanning a hedgerow and extending approximately 30 m into two cereal fields; 1777 beetles were individually marked. The recapture rate was approximately 60% and 40% for males and females, respectively. Activity-density rose and fell four times between early June and mid August. Jolly-Seber estimates of density showed population density increasing to a single peak in late July. The mean population density in late July and August was relatively stable at approximately 0.26 m−2. Activity varied over the 10 weeks and was significantly higher during August than in June or July. The daily displacement distance frequencies, calculated from 750 male and 485 female recaptures of individually marked beetles, were distributed exponentially. Mean displacement distances were approximately 2.6 m day−1 during June and July, and 5.3 m day−1 during August. A diffusion model provided diffusion coefficients of 23.7 and 27.9 m2 day−1 for female and male beetles, respectively. The spatial distribution of P. melanarius was aggregated in patches. Spatial analysis by distance indices showed the spatial distribution of counts between successive periods of activity-density to be significantly associated. Approximately 5.75% of recaptures were from releases on the opposite side of the hedgerow. Approximately 20% of recaptures were from releases in opposite halves of the grid within the same field. The hedgerow acted as a significant barrier to dispersal between fields, with implications for the metapopulation structure of the species.

The influence of sown margin strips, management and boundary structure on herbaceous field margin vegetation in two neighbouring farms in southern England

Field margins are refugia for many species in arable landscapes, but are also affected by adjacent farming operations and by margin management. Botanical diversity in 117 hedge-bottoms on two neighbouring farms in Yatesbury, Wiltshire, UK, were studied in relation to boundary structure, hedge management practices and adjacent features on the farm to which they belong. The farms differed with regard to field margin and hedge management practices, but soil type and cropping patterns were very similar. Attention was also paid to effects of sown grass strips, coppicing and gapping-up of hedges and different approaches towards field margin management. Results indicated that there were no significant differences in woody species richness between the two farms, with hedges of similar composition. There was significantly higher herbaceous species diversity on the farm with grass strips. Multivariate analyses indicated that community differences were present, with a number of annual and biennial plant species predominating on the farm without grass margins. Principal components analysis (PCA), redundancy analysis (RDA) with forward selection and associated Monte-Carlo permutation tests, and stepwise linear regression showed the following. (1) Sown grass and/or wildflower strips adjacent to the hedge-bottom have a positive effect on species richness of the hedge-bottom vegetation. They also reduce the abundance in the hedge-bottom of Anisantha sterilis, Galium aparine, Poa trivialis and Urtica dioica, all four considered to be pernicious weed species. (2) Coppicing in combination with gapping-up of hedges increases species richness of the hedge-bottom vegetation and has a positive effect on floral diversity in the landscape. (3) Diversity in management, boundary structure and adjacent features within one farm increases the floral diversity at the farm scale. Diversity in management, boundary structure and adjacent features between farms increases the floral diversity on a landscape scale.

Factors affecting field weed and field margin flora on a farm in Essex, UK

Abstract Field margins, particularly hedgerows, are important refuges for many species in intensively managed arable landscapes. Their management is influenced by the perception that weed species colonise adjacent crops. Mobile species, such as beetles, are able to use field margins as corridors to recolonise suitable habitat. This study examines whether field margins influence adjacent weed flora, and if there is evidence of the corridor effect of adjacent woodland in margin plant communities. The higher plants present in 51 field margin sites on a large farm in Essex, UK, were recorded. The weed flora in the adjacent arable crops was also assessed in 41 of the sites at 5 and 50 m into the field. Field margin floras were much more diverse than the weed flora, though 25% of species in the margins were also found in the adjacent crops. Most species of the margin were perennials, while arable weeds were dominated by annual species. There was little correlation between field margin and crop flora. The margin flora was correlated with margin structure, which ranged from woodland edge, to shelterbelt, to tall and short hedgerows. Principal component analysis of species indicated woodland sites and those close to woodland were differentiated from hedgerows. Site scores were positively correlated with distance from woodland, possibly indicating site history or colonisation along hedges were important in determining plant communities of field margins.

Biomonitoring of genotoxic risk in agricultural workers from five Colombian regions: Association to occupational exposure to glyphosate

In order to assess possible human effects associated with glyphosate formulations used in the Colombian aerial spray program for control of illicit crops, a cytogenetic biomonitoring study was carried out in subjects from five Colombian regions, characterized by different exposure to glyphosate and other pesticides. Women of reproductive age (137 persons 15–49 yr old) and their spouses (137 persons) were interviewed to obtain data on current health status, history, lifestyle, including past and current occupational exposure to pesticides, and factors including those known to be associated with increased frequency of micronuclei (MN). In regions where glyphosate was being sprayed, blood samples were taken prior to spraying (indicative of baseline exposure), 5 d after spraying, and 4 mo after spraying. Lymphocytes were cultured and a cytokinesis-block micronucleus cytome assay was applied to evaluate chromosomal damage and cytotoxicity. Compared with Santa Marta, where organic coffee is grown without pesticides, the baseline frequency of binucleated cells with micronuclei (BNMN) was significantly greater in subjects from the other four regions. The highest frequency of BNMN was in Boyacá, where no aerial eradication spraying of glyphosate was conducted, and in Valle del Cauca, where glyphosate was used for maturation of sugar cane. Region, gender, and older age (≥35 yr) were the only variables associated with the frequency of BNMN measured before spraying. A significant increase in frequency of BNMN between first and second sampling was observed in Nariño, Putumayo, and Valle immediately (<5 d) after spraying. In the post-spray sample, those who reported direct contact with the eradication spray showed a higher quantitative frequency of BNMN compared to those without glyphosate exposure. The increase in frequency of BNMN observed immediately after the glyphosate spraying was not consistent with the rates of application used in the regions and there was no association between self-reported direct contact with eradication sprays and frequency of BNMN. Four months after spraying, a statistically significant decrease in the mean frequency of BNMN compared with the second sampling was observed in Nariño, but not in Putumayo and Valle del Cauca. Overall, data suggest that genotoxic damage associated with glyphosate spraying for control of illicit crops as evidenced by MN test is small and appears to be transient. Evidence indicates that the genotoxic risk potentially associated with exposure to glyphosate in the areas where the herbicide is applied for coca and poppy eradication is low.

Similarities in vegetation development of newly established herbaceous strips along contrasting European field boundaries.

Abstract In France, the Netherlands and the UK, arable field boundaries were extended with four metres of crop edge. Plots with perennial, herbaceous vegetation were established by natural regeneration or by sowing grass, both annually cut. Vegetation development was monitored in the first three years after establishment in the original boundary and in the new boundary strip. Species composition, species-richness and biomass production in the new strip were related to those in the original boundary to examine the potential of predicting vegetation development in extended field boundaries from the vegetation composition of the original boundary. Within three years species-richness, biomass production and monocot:dicot ratio in both the grass and regeneration plots converged to the levels of the original boundary in all three countries. Species composition in the new strip was not closely related to the original boundary, however, since only 20–50% of the species encountered in the original boundary at the onset of the experiment had managed to colonise the new boundary strip in the final year. The low similarity was mainly due to low establishment rates of annual and woodland species in the new strip while mobile, perennial grassland species were generally very successful. Sowing grass, which may be preferable with respect to weed control, had adverse effects on species-richness. These relationships, which were found to apply in a broad geographical area and in different boundary types, may aid efforts to restore botanical diversity in arable field boundaries.

Microsatellite analysis of the inbreeding grass weed Barren Brome (Anisantha sterilis) reveals genetic diversity at the within‐ and between‐farm scales

Nine microsatellites were used to screen 131 samples of Barren Brome (Anisantha sterilis: synonym Bromus sterilis) collected from within the fields of three English farms [from Oxfordshire (Oxon), Leicestershire (Leics) and Wiltshire (Wilts)] and eight seeds taken from samples of each of 10 farms across England, UK. Most individuals (~97%) were homozygous. Polymorphism occurred at all nine loci in all three farms sampled at the field scale, and at most loci for nine of the other 10 farm samples. Between three and 11 alleles were found per locus. Gene diversity (D = 1 − ∑pi2) ranged from 0.088 to 0.760. Polymorphism occurred among individuals within and among fields, and farms. Some alleles were found in only one farm. On the basis of the alleles at all nine loci in the 211 sampled plants, a total of 92 (44%) different genotypes was identified. Clustering analysis using the unweighted pair group method with arithmetic averages (upgma) for the combined Oxon, Wilts and Leics samples did not cluster them into their respective farms. Similarly, a phenogram of samples from all 10 farms showed considerable mixing of individuals with respect to farm origins. Identification of genotypes on field plans showed evidence of both spatial localization and mixing. Previous reports have suggested that A. sterilis is strictly inbreeding with little intrapopulation variation at the genetic level. Our data reveal that A. sterilis exists as numerous separate and genetically different lines, which are maintained by inbreeding but which very occasionally outcross. Possible explanations for this pattern of high genetic diversity are discussed.