Field Margin Strips Research Articles

Quantifying trade‐offs between butterfly abundance and movement in the management of agricultural set‐aside strips

Abstract Agri‐environment schemes (AES) create small areas of habitat within agricultural landscapes to support biodiversity. Here, we study butterfly flight behaviour within linear AES features and examine whether differences in resource availability affect the speed, linearity, or directionality of local movements, thereby affecting their contribution to landscape connectivity. We surveyed butterflies within three basic (naturally regenerating) and three wildflower‐sown linear field margin strips (0.09–0.15 ha) on a farm in North Yorkshire, UK, and mapped butterfly flight paths to quantify local displacement (movement speed), efficiency (linearity, turning angles), directionality (step orientation), and behaviour (time spent flying, nectaring). Butterfly species richness was similar between margin types {estimated asymptotic species richness of 21.9 [confidence interval (CI): 15.0–77.7] for basic margins and 14.2 (CI: 14.0–18.7) for wildflower‐sown margins}, but abundance was 78% higher in wildflower‐sown margins. For the three most common species [meadow brown, Maniola jurtina (L.); ringlet, Aphantopus hyperantus (L.); and small white, Pieris rapae (L.); n = 233 paths], movements within both margin types were highly linear (median turning angle 45°) and generally oriented along the length of the margin strip (median step orientation 27°). Movements in basic margins were slightly more orientated along the length of the margin but we found no differences between margin types in speed, path linearity, turning angles or the proportion of time spent flying or nectaring. We found strong channelling of movements along field margin strips regardless of management type, potentially aiding landscape connectivity. Providing field margin strips with additional foraging resources through wildflower‐sowing increases butterfly abundance without impeding local movement rates or efficiency.

Assessing non-intended effects of farming practices on field margin vegetation with a functional approach

To assess the unwanted side effects of farming practices on non-target plants, we used a nationwide survey of the vegetation of arable field margin strips. The vegetation was surveyed during two years (2013, 2014) in 430 field margins distributed over all agricultural regions of France. We used two complementary multivariate, trait-based approaches to examine how ten plant traits were related to ten environmental variables describing abiotic conditions, landscape factors, field margin management and in-field practices. Generalized additive mixed models were also developed to assess how the same environmental variables correlated with species richness, functional diversity and relative richness of agrotolerant versus hemerophobic species. Traits responded primarily to an environmental gradient of landscape diversity and field margin management. For instance, narrow field margin strips, frequent management and presence of a ditch favoured annual plants, small size at maturity and perennial plants, respectively. The second environmental gradient affecting plant traits was related to field size and intensity of in-field farming practices. On this gradient, fertilizer drift appeared to have a much stronger effect on plant trait composition of field margin strips than herbicide drift. The relationship between species richness, or functional diversity, and environment was consistent with the trait-based approach: the two former variables were negatively correlated with agriculture intensification (e.g. field size). However, this analysis also highlighted new covariates, such as a negative relationship between frequency of herbicide use and species richness. Some of the observed patterns seemed to be driven by differential responses of agrotolerant versus hemerophobic species, with the latter being more species-rich under organic than under conventional farming. Despite efforts to reduce nitrogen inputs since the 2000s, our results shows that N-fertilization still has significant non-intended effects on field margin vegetation. More generally, increasing the width of field margin strips, keeping or restoring semi-natural elements (ditches, hedges) in the field boundary, and lowering the number of management events may promote grassland plant species more typical of semi-natural habitats.

Nectar accessibility determines fitness, flower choice and abundance of hoverflies that provide natural pest control

Summary In modern agricultural landscapes, many organisms providing ecosystem services such as pollination and natural pest control are likely constrained by shortage of nectar and/or pollen required for adult nutrition. More and more flower‐rich field margin strips and other habitats are created to eliminate these constraints. For most target organisms, however, it is not well known which (types of) flowers are effective in providing suitable pollen and nectar. We studied the suitability of a wide range of flowers as a food source for zoophagous hoverflies (hoverflies with predatory larvae) at five different levels: nectar accessibility (based on flower morphology), realized adult fitness, flower choice (both based on cage experiments), flower visitation and hoverfly abundance in mixed vegetation (both based on field observations). Realized survival of Episyrphus balteatus is related to effective flower depth by a sigmoid function. The critical flower depth is 1·6 mm, which is less than the proboscis size of the hoverfly. For Asteraceae, the critical floret depth is even less than 1·0 mm, which – in contrast to common knowledge – rules out most species within this family. Both flower choice in the laboratory and flower visitation rates in the field are well correlated with nectar accessibility and realized adult survival. In mixed floral vegetation, the number of zoophagous hoverflies is highly correlated with the abundance of only those flowers that have accessible nectar for these hoverflies. Synthesis and applications. This comparative study demonstrates that nectar (and not pollen) accessibility is the main driver determining flower resource suitability, flower choice and abundance of zoophagous hoverflies in arable field margins. The study identifies the limited range of plant species that can effectively support these beneficial insects. Preserving the right flowers in and around agricultural fields could enhance local populations and the pest control and pollination services they provide.

Earthworm assemblages as affected by field margin strips and tillage intensity: An on-farm approach

Earthworm species contribute to soil ecosystem functions in varying ways. Important soil functions like structural maintenance and nutrient cycling are affected by earthworms, thus it is essential to understand how arable farm management influences earthworm species. One aim of arable field margin strips and non-inversion tillage is to enhance agrobiodiversity, however their influence on earthworm species assemblages remains unclear. In particular, on-farm studies conducted over multiple years that capture variability across the landscape are rare. The current study monitored earthworm species assemblages on 4 farms in Hoeksche Waard, The Netherlands, from 2010 to 2012. It was hypothesised that arable field margin strips (FM) and non-inversion tillage (NIT; a reduced tillage system that loosens subsoil at 30−35 cm depth) would have higher earthworm species abundances (epigeics and anecics in particular), soil organic matter, and soil moisture than adjacent mouldboard ploughing (MP) fields, and that earthworm numbers would decrease with distance away from FM into arable fields (MP only). FM contained a mean total earthworm abundance of 284 m−2 and biomass of 84 g m−2 whereas adjacent MP arable fields had only 164 earthworms m−2 and 31 g m−2. Aporrectodea rosea, Lumbricus rubellus, Lumbricus terrestris, and Lumbricus castaneus were significantly more abundant in FM than adjacent arable soil under MP. However, no decreasing trend with distance from FM was observed in earthworm species abundances. A tillage experiment initiated on the farms with FM showed that relative to MP, NIT significantly increased mean total earthworm abundance by 34% to 275 m−2 and mean total earthworm biomass by 15% to 51 g m−2 overall sampling dates and farms. L. rubellus, A. rosea, and L. terrestris were significantly more abundant overall in NIT than MP. FM and NIT positively affected earthworm species richness and abundances and it is noteworthy that these effects could be observed despite variation in environmental conditions and soil properties between samplings, farms, and crops. Higher top-soil organic matter and less physical disturbance in FM and NIT likely contributed to higher earthworm species richness and abundances. The anecic species L. terrestris (linked to water infiltration and organic matter incorporation) was more abundant in FM, but densities remained very low in arable soil, irrespective of tillage system.

Permanent and new arable field margins support large earthworm communities but do not increase in-field populations

The maintenance of uncultivated field margins and the creation of new field margin strips are standard agri-environmental measures aimed at enhancing above-ground biodiversity, but their effects on below-ground biodiversity (in margins and also in-field) are insufficiently known. This study compared earthworm communities in permanent (grassy) margins, newly created field margin strips (unsown) and in-field in five arable fields in Ireland over a 3-year period. Permanent field margins initially supported highest earthworm abundance, biomass and species richness compared to the newly created margin strips and in-field at three conventional and two minimum (conservation) tillage sites. However, after three years, mean earthworm populations in the newly created margin strips (371±181individualsm−2 and 91.9±41.7gbiomassm−2) approached those observed in the permanent margins (470±47individualsm−2 and 126.5±14.7gbiomassm−2) in the three conventional tillage field sites. By contrast, overall mean population sizes inside conventionally tilled fields were 155±46individualsm−2 and 38.3±12.5gbiomassm−2. Similar trends were observed at the two minimum tillage sites. Permanent field margins supported somewhat larger mean species numbers compared to in-field at conventional and minimum tillage field sites, but most species still occurred, at significantly lower abundances, inside fields. Spatially defined transect sampling (at 1, 3, 10 and 50m in-field) at all study sites did not provide evidence for increased populations nearer to the margins or margin strips, even under reduced cultivation. It is concluded that permanent and newly created margin strips in arable systems support larger earthworm populations than are found in-field, but field margins did not appear to enhance in-field populations through colonisation or spill-over effects documented for more mobile, above-ground invertebrate taxa.

Spatial autocorrelation in honeybee foraging activity reveals optimal focus scale for predicting agro-environmental scheme efficiency

A substantial honeybee decline is being observed worldwide. Agricultural intensification and loss of wild floral resources rank among the main factors contributing to this decline. Landscape enhancement of floral resources has been proposed as an agro-environmental scheme intended to provide honeybees with compensatory food sources in intensive agrosystems. Floral scheme efficiency has rarely been evaluated with respect to landscape context. In this study, we developed and validated a modeling tool to delineate the landscape areas likely to be associated with higher efficiency of floral enhancement schemes. In particular, the proximity of some landscape elements used by honeybees, either as foraging habitat or as visual landmark for orientation, may partly determine floral scheme efficiency. We investigated this issue using resource selection functions (RSFs), i.e. models that aim to predict the occurrence of foraging honeybees at floral patches as a function of the presence of keystone landscape elements in their proximity. However, deciding which landscape elements are effectively in the proximity or not is mostly a matter of subjectivity. The novelty of our approach resides in its use of a distance-weighting function to explicitly account for the spatial location of surrounding landscape elements. In that respect, a distance function should be scaled on movement patterns of foraging organisms. Herein, we inferred movement patterns from the autocorrelative properties of honeybee foraging activity. This modeling approach was developed on Phacelia ( Phacelia tanacetifolia) field margin strips, a typical “honeybee-friendly” floral scheme. A foraging survey conducted on 170 Phacelia plots (2 m × 2 m) from 17 Phacelia strips, all positioned within the foraging range of an experimental apiary, revealed that (i) the floral scheme efficiency is positively influenced by the presence of linear landscape elements such as hedgerows and forest edges, but negatively affected by the presence of alternative floral resources, and that (ii) weighting the relative importance of those landscape elements by incorporating a distance function into models considerably improved their predictive power. This modeling tool has the potential to help land managers optimizing their financial investment by avoiding low-efficiency landscape areas, or favoring high-efficiency ones, at the time of planning floral enhancement schemes.

Environmental-friendly farming in Switzerland is not hornwort-friendly

Traditionally managed arable fields host a specialised flora adapted to regular disturbance through tillage. Agricultural intensification during the 20th century resulted in a pronounced biodiversity decline in European agroecosystems. Anthoceros agrestis and Phaeoceros carolinianus, both largely confined to cultivated land in Central Europe and the only representatives of hornworts in northern Switzerland, are examples of species that decreased in Central Europe during the last century. A repeated survey of 28 arable fields in the Swiss Plateau from 1989 to 1995 demonstrated that crop type and associated farming routines were critical in determining hornwort occurrences. During the 10 years following the completion of this survey, agri-environment schemes were introduced aiming at a more environmental-friendly agricultural production. We re-investigated the selected sites in 2005–2007 to examine whether these programmes favoured hornworts. We found a significant decrease of untilled autumn stubble-fields, which accounted for a decline of hornworts. High relative summer air humidity positively affected hornwort occurrence. Gametophytic populations of both taxa regenerated from the persistent diaspore bank after years of unfavourable conditions. To ensure the long-term persistence of hornworts in the Swiss Plateau, we recommend three alternative modifications of current Swiss agri-environment schemes to be implemented in cereal fields with known hornwort occurrences: (1) Tailored conservation headlands, (2) Autumn stubble-fields and (3) Field margin strips sown with arable flora but without crop plants. The proposed practices will promote other typically ephemeral arable bryophytes and seed plants and are likely to be advantageous also for other organisms, such as farmland birds.

Spatial aggregation facilitates coexistence and diversity of wild plant species in field margins

Abstract European agri-environment schemes encourage farmers to establish sown field margin strips to protect and enhance wild plant diversity. However, plant diversity in such wild plant sowings based on seed mixtures is often low due to the high competitiveness of few, common species. Here we analysed whether intraspecific aggregation could enhance the performance of less competitive species, and how plant performance is influenced by the number of species in a mixture. We focused on inter- and intraspecific competition between six agricultural wild plant species (Centaurea cyanus, Calendula arvensis, Melilotus officinalis, Poa annua, Bromus mollis, Medicago lupulina), and tested (i) two different seeding patterns (intraspecifically aggregated vs. randomly dispersed) and (ii) three different species mixtures (monocultures, three-species, and six-species mixtures). Plant performance was measured in terms of number of individuals, biomass per individual, and biomass per m2. Intraspecific aggregation resulted in higher numbers of individuals of all species, while mixtures generated lower numbers of individuals. The performance of plant species differed depending on their position in the competitive hierarchy. Competitively weak species suffered much less from intraspecific than interspecific competition in terms of biomass, and the competitively weakest species became even excluded in the most species rich and randomly dispersed sowings with high interspecific competition. In conclusion, the performance of wild plant species was influenced by both seeding pattern and number of species in a mixture. Intraspecific aggregation enabled the coexistence of competitively weak species by reducing interspecific competitive exclusion processes. Consequently, agri-environmental schemes designed to preserve and enhance biodiversity should consider small-scale processes influencing the distribution and abundance of plants, and develop new agricultural sowing technologies to cultivate competitively weak and endangered wild plant species.

Dry matter yield and herbage quality of field margin vegetation as a function of vegetation development and management regime

Dry matter (DM] yield and herbage quality of unfertilized mown field margin strips were studied during early succession in a field experiment over a period of three years. The experiment aimed to maximize botanical diversity and was conducted at two different locations with contrasting soil type and comprised four vegetation types (spontaneously regenerated versus sown vegetation) and three herbage removal strategies (herbage left versus herbage removed). The experimental factors investigated were location, vegetation and herbage removal. Margin strips were mown twice a year with a late first cut around 15 June and a regrowth cut around 15 September to meet nature conservation objectives. Average DM yield over the first three years was not significantly affected by herbage removal but increased significantly over time, irrespective of vegetation or herbage removal. Initially, sown margin strips significantly outyielded unsown margin strips, but differences in DM yield converged over time. The mid-June cut yielded significantly more than the regrowth cut but its herbage quality was significantly lower. Herbage from the unsown margin strip had a significantly better forage quality than herbage from sown margin strips. Forage quality decreased over time, irrespective of location or vegetation. Changes over time in DM yield and quality were attributed to changes in species composition. The herbage quality of field margins was lower than the herbage quality of intensively managed grassland, limiting its use in rations for highly productive livestock.

A 3-year field-scale monitoring of foliage-dwelling spiders (Araneae) in transgenic Bt maize fields and adjacent field margins

Abstract Concerns have been raised that genetically modified Bt maize may harm non-target organisms, and there is a general call and need for a risk assessment of Bt maize. Spiders are important pest predators in agroecosystems and in maize, and can be exposed to the Bt toxin by herbivorous or pollen-collecting prey, by active Bt maize pollen feeding, and by ingesting their pollen-dusted webs. The foliage-dwelling spider fauna of Bt maize fields and adjacent margins was monitored and compared to non-transgenic maize fields. The study took place during the vegetation seasons of 2001–2003 in Bavaria, South Germany. Maize fields and adjacent nettle field margins were colonized by a typical spider assemblage, dominated by space-web spiders (Theridiidae and Linyphiidae). Abundance and species richness of spiders was higher in nettle margins than in maize fields. The proportion of hunting spiders tended to be higher in nettle margins, whereas space-web spiders tended to be more frequent in maize fields. Bt maize showed no consistent effect on individual numbers, species richness and guild structure of spiders in maize fields and adjacent nettle field margin strips. The spider abundance was higher in Bt treatments in 2003, whereas in 2001 and 2002 no significant differences were found. The results provide an important contribution for the implementation of case-specific and general surveillance of transgenic plants to be employed due to the regulations of the European Community.

Effect of margin strips on soil mineral nitrogen and plant biodiversity

We studied the effects of two- to three-year-old unfertilized field margin strips, installed between the pre-existing field boundary and the field crop, on soil ammonium N and nitrate N, and on the botanical composition of the adjacent semi-natural vegetation in the field boundary. Margin plots were regenerated spontaneously or were sown to grass/forb mixtures and were managed under a cutting regime with removal of cuttings. In general, soil nitrate N, soil ammonium N and soil mineral N losses were significantly affected by distance from the field crop edge and not by plant community type. The further away from the crop edge, the lower soil nitrate (up to fivefold lower than in the crop) was found in the margin strip, but soil ammonium N was approximately 50% higher close to nearby trees and shrubs. Inside the margin strip, total soil mineral N as well as N loss during winter was minimal at a distance of 5 m from the crop edge. The reduction of soil nitrate N near the boundary by the presence of a margin strip was responsible for the increase in abundance of less competitive species and for an up to 20% higher species-richness within the field boundaries. In summary, our results show clearly that margin strips both decrease N pollution of groundwater and increase botanical diversity. A minimal margin width of 5 m is recommended.

Effect of light and botanical species richness on insect diversity

Composition and diversity of flying insects was assessed within and along one-year-old sown/unsown field margin strips installed along both the shaded and unshaded side of an old lane of beeches. Investigated factors were light regime, plant community and monitoring position. Both insect composition and spatial preference of insect families was strongly dependent on light regime, field margin type and monitoring position. The number of insect families preferring the shaded side was fivefold higher than the number of families preferring the unshaded side. Particularly, insect families associated with moist conditions (Haliplidae, Dolichopodidae, etc.) were preferably or exclusively found on the shaded side characterised by higher soil moisture content. Some families (Bibionidae, Scatopsidae, Proctotrupoidea, etc.) showed higher abundance in the unsown field margin whilst others (Cicadellidae, Chalcidoidea, etc.) preferred the sown field margins. Similarly, some families (Lygaeidae, Cantharidae, etc.) occurred preferably in the field margin strip whilst others (Chironomidae, Empididae, Cicadellidae, etc.) preferred the adjacent field crop. Differential habitat preference might be explained by differences in botanical composition and structure of the vegetation. Insect diversity was significantly higher near the margin strip richest in botanical species (i.e. the unsown margin strip), reflecting the highest Shannon diversity index (2.57). Furthermore, insect diversity was significantly higher on the shaded side, irrespective of monitoring position, with Shannon diversity indices between 2.59 and 2.70.

Disturbance effects on early succession of field margins along the shaded and unshaded side of a tree lane

Effects of light and disturbance on species diversity and vegetation succession were assessed during early succession of newly created sown and unsown field margin strips installed along the sunny and shady side of a tree lane. During succession, disturbance by farming operations was simulated by a single rotocultivation of the margin strip. Two years after the disturbance event, species richness was not significantly determined by light regime or disturbance level. However, shortly after the disturbance event, disturbance caused a temporary increase in species richness on the unshaded side due to introgression by annual species in created gaps. On the shaded side, species richness was significantly lower in disturbed plots. Disturbance caused a temporary increase in importance of spontaneous annuals, which were quickly replaced by perennial sown and unsown monocotyledons and to a lesser extent by perennial unsown dicotyledons. The importance of spontaneous species within functional groups increased, resulting in higher similarity between sown and unsown vegetation.

An indicator of plant species richness of semi-natural habitats and crops on arable farms

Abstract As a straightforward method of assessing on-farm biodiversity, plant species numbers were compared in a fixed sampling area for each type of habitat distinguished independent of farm size and applicable for comparing different farm strategies. Using the species–area relationship, the minimum sampling areas were determined. For ditch banks, crops and field margin strips sampling areas of 400 m2 (independent of the ditch bank width), 100 and 25 m2, respectively, were proposed. Indicator threshold values for conventional farms were defined based on the best 10% of the variation in species richness among farms. With appropriate farm management these targets could be achieved. In comparison to ditch banks, crops and sown field margin strips were relatively poor in plant species. The respective numbers of naturally occurring plant species found in crops and field margin were both significantly smaller than those found in ditch banks. In contrast, ecological management of ditch banks appeared to be a promising means of increasing species richness.

Agricultural Landscapes

SUMMARY 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 and fauna of these elements. In temperate, intensive agriculture, such field margin habitats, which historically had true agricultural functions, now are important refugia for biodiversity. As man-made habitats, field margins may also have important cultural roles as part of landscape heritage, e.g., hedges in Britain. Although field margins are not usually specific or characteristic 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, with combinations of them over small spatial scales. Studies demonstrate a variety of interactions between fields and their margins. 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. Agricultural operations, such as fertilizer and pesticide application, can have adverse effects on the margins. 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 can also contribute to the sustainability of production, by enhancing beneficial species within crops and reducing pesticide use, though further research on the predictability of these effects is needed. In northwestern Europe, a variety of methods to enhance diversity at field edges have been introduced, including sown grass and flower strips. While minor conflicts exist, notably for the conservation of rare arable weed species and the spread of some pests and weeds, the impacts of well-managed field margins on weed flora and arthropods indicate mostly beneficial effects. Thus field margin strips offer a practical means of providing on-farm biodiversity and enhancing more environmental and sustainable production.

Plant-insect communities and predator-prey ratios in field margin strips, adjacent crop fields, and fallows.

The management of field margin strips for the enhancement of biodiversity of plant-insect communities and natural-enemy populations was studied on experimental farms near Göttingen (Germany). Young and old, sown and naturally developed field margin strips were compared and differences to large fallows established. The five types of field margin strips (around cereal fields) were: (1, 2) 1- or 6-year-old naturally developed strips, (3) strips sown with a Phacelia mixture, (4) strips sown with a mixture of 19 wild flower species, and (5) strips sown with winter wheat or oat as a control. The naturally developed vegetation of the field margin strips was dominated by aggressive weeds, presumably due to the intensive farming practices and the fertile soils. Cirsium arvense populations decreased, while Elymus repens populations increased with age of habitat. Sowings were suitable to suppress these aggressive weeds. Potted plants of mugwort (Artemisia vulgaris) and red clover (Trifolium pratense) were exposed in the field margin strips to study arthropod colonization of these experimentally standardized plant patches. Arthropod species richness did not differ between field margin types, reflecting the overall similarity in floristic diversity, but sprayed and strip-free edges of cereal fields had a reduced diversity. Dispersal of insect populations of red clover into the cereal fields decreased with increasing distance, but benefited from adjacent field margin strips. Populations of predators (mainly spiders) as well as predator-prey ratios were significantly larger in 6-year-old than in 1-year-old strips emphasizing the importance of habitat age for natural enemies and possible biological control. Predator-prey ratios were also higher on old than young fallows. Large fallows had greater predator-prey ratios than small field margin strips emphasizing the trophic-level hypothesis of island biogeography in that the relative importance of natural enemies increased with habitat area. Insect species richness was only marginally influenced by area and not by age. As species richness of predators did not increase with area and age, species diversity and the possible biological-control function did not covary.

Landscape structure and biological control in agroecosystems

Biological pest control has primarily relied on local improvements in populations of natural enemies, but landscape structure may also be important. This is shown here with experiments at different spatial scales using the rape pollen beetle (Meligethes aeneus), an important pest on oilseed rape (Brassica napus). The presence of old field margin strips along rape fields was associated with increased mortality of pollen beetles resulting from parasitism and adjacent, large, old fallow habitats had an even greater effect. In structurally complex landscapes, parasitism was higher and crop damage was lower than in simple landscapes with a high percentage of agricultural use.

Arthropod abundance and diversity in differently vegetated margins of arable fields

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.

The effects of organic and integrated farming on rare arable weeds on the Forschungsverbund Agrarökosysteme München (FAM) research station in southern Bavaria

Since the compensation for unsprayed field margin strips was recently reduced in Germany, the area used in this way has rapidly declined. These experiences show that management restrictions for the sake of species conservation are only accepted when high compensation is paid and efficiency is regularly controlled. The aim of the present investigation was to determine if conservation of arable weeds could be reached by management systems without imposing such restrictions. Therefore, 110 ha farmland, situated in the Tertiärhügelland in southern Bavaria, was investigated to compare the effects of a change from conventional farming to an organic and an integrated cultivation system. Four years after the change to the integrated farming system, the number of rare species had decreased at 90% of all sampling points where they occurred. This development seems mainly to be caused by minimum tillage, which was applied to prevent soil erosion. In the organic management area, rare weed species were observed at 94 grid points. At 33% of them weeds decreased, at 41% they remained unaffected, and at 26% weeds increased in number. Among the species occurring often enough for a statistical analysis, four did not change significantly, while Legousia speculum-veneris was found more frequently. Investigations in the population development at selected points showed a differing response of individual species to these management changes. Nevertheless, frequencies as well as densities of the rare weeds stayed constant within the fields under organic management. This and the respective literature lead to the conclusion that the influence exerted on rare weed species by the organic cultivation system is neutral to positive. Thus, organic management could be at least a way to prevent further decline in rare weeds.

Impact of Nitrogen and Organic Manures on Yield, Botanical Composition and Herbage Quality of Two Contrasting Grassland Field Margins

ABSTRACT Grassland field margin strips, including hedge bottoms, may support a high diversity of wild flower and grass species. This diversity is threatened by applications of fertilizer nitrogen. Organic fertilizer, in the form of farm-yard manure and rain-diluted liquid slurry which only slowly release nitrogen for plant uptake, might prove less damaging. A 5-year experiment on two contrasting sheep grazed, species-rich grassland field margin sites adjoining a mature hedgerow in mid-Wales compared three levels of fertilizer N (0, 100 and 300 kg N ha−1 year−1) with farm yard manure (FYM) and rain-diluted slurry containing an average annual equivalent of 30–42 kg N ha−1 and 27–72 kg N ha−1 respectively. The aim was to assess the impact of treatments on the plant communities of the hedge bottom and field margin strip ecosystems, and to establish whether the species diversity contained within the strips could be encouraged without significantly undermining the quantity and quality of the herbage. By the end of the experiment, the forb component of both ecosystems had been drastically reduced by the high N treatment, to less than half of their original level. The organic treatments on the other hand, particularly FYM showed signs of developing species-rich communities, while at the same time providing a relatively high yielding and nutrient-rich field margin sward of high mineral content. The implications of FYM deposition, particularly in terms of nature conservation considerations are highlighted.