Summary of the AIR3 Project "Field Boundary Habitats for Wildlife, Crop and Environmental Protection"

Field Boundary Habitats For Wildlife, Crop And Environmental Protection

AIR3 - CT 920476
AIR3 Project Publications
Field Margin Network

Summary

Contractors:
01 IACR - Long Ashton Research Station, University of Bristol, UK
02 Agricultural University, Wageningen, The Netherlands
03 Université de Rennes I, France

Sub-contractors:
04 Georg-August-Universität, Göttingen
05 Universitā degli studi di Padova

Introduction

Agricultural landscapes across Europe are diverse, ranging from small-scale hedged landscapes, such as the bocage in France, to large-scale open landscapes of intensive arable production. Bearing in mind that well in excess of 50% of the European land surface is managed by farmers, the effects of that management has significant impact on the flora, fauna and environment of the Community. These landscapes are a mosaic of cropped land (fields) and areas of semi-natural habitat, including watercourses, woodland, hedgerows and field margins. All fields have margins and these margins are often the major component of semi-natural habitat in the landscape. As such, they have been shown to be important refugia for many plants and animals and thus a key to maintaining biological diversity in farmland. That diversity may be of particular importance in the development of more sustainable farming systems.

As well as importance for biodiversity, field margins often have cultural and historical importance. The structure of field margins is variable, lending a particular sense of place to many locations and are important for regional character. However, changes in agriculture impact on these traditional features. Field margins are the interface between intensive farming practices and the wider environment. They may be influenced by farming operations and they may also affect the adjacent fields. The rapid change from one habitat to another can form an ecotone, which may support particular species and may buffer the movement of agrochemicals, water and soil erosion. Thus the field margin can have agricultural, environmental and wildlife functions. The objective of this study was to further our understand the function of field margins in order to better exploit them for agricultural, environmental and wildlife benefits.

The objectives of this project were to understand the processes at work across the field boundary ecotone and the factors influencing these semi- natural features within the mosaics of farmland landscapes, with the aim of developing appropriate management to benefit farm wildlife, environmental protection and more sustainable crop production. The project has taken place at a time of considerable interest in field boundaries, both from research and policy fields, and there have been a number of complimentary research initiatives relevant to biodiversity and agri-environmental development in Europe which continue.

The programme centred on three common tasks, a collaborative experiment on introducing new margin habitat (Task A), a comparative study of the factors affecting the flora of semi-natural habitat at larger scales (Task B) and a research co-ordination exercise, involving representatives from all Member States, to produce a Newsletter, databases and to assess the feasibility of a code of good practice for field margins (Task K). The common tasks were underpinned by a series of separate tasks undertaken by the three major participants (Tasks C, D, E, F, G, H, I and J).

The project has had a number of successes and has generated some important findings. New insights into the functions of margins have been gained, techniques of increasing botanical and invertebrate diversity at field edges have been developed, we have a reasonable understanding of the factors affecting botanical composition of margins at the landscape scale, models of plant-plant interactions relevant to margins have been constructed and a European Network continues to foster links between researchers. Following extensive discussion, we came to the conclusion that diversity of structure and management of boundaries is important for maintaining species and landscape diversity and that a code of good practice was beyond the scope of this project, though it could usefully be developed further. The results of the project are summarised below taking an holistic approach to the many tasks carried out.

Field margins in European landscapes Studies of the flora and fauna of field margins in a range of European countries, farming systems and landscapes demonstrated that a range of factors are important in influencing the abundance and diversity of species. Consistently, the structure of the margins is important. Margins can contain a range of structural components and therefore a range of species and communities associated with them. Field utilisation (cropping) is important and farm type affects field margins. Farmers are particularly important in affecting margins, via their perceptions and requirements for farming and thus management. The level of disturbance associated with adjacent farming and management also have profound influences. High disturbance, by both physical and chemical means, can reduce abundance and diversity of species. The location of margins within the landscape is also influential, mediating the opportunities for species dispersal and thus colonisation and recolonisation of habitats. Hedges connected to woodland are more likely to support woodland species, but other elements, such as roads, may isolate habitats.

Effects of flora and fauna are found at both site level and at landscape scales. There is a general trend for a reduction in diversity and abundance with increasing landscape simplification and increasing disturbance via farm inputs, cultivation and management. There are also changes in the species compositions of field margins along such gradients. However, these changes are not simple or linear and simple generalisations do not apply to all species within groups of both faun and flora. Further, certain groups and species react to landscape at different scales. Thus, the implementation of general management prescriptions, e.g. for set-aside, should take account of scale effects as appropriate for the groups under consideration.

A field survey of two farms, one with sown grass strips and one without, showed that introduced margins at arable field edges, together with accurate fertiliser application, could result in less disturbance in the field margin and increase botanical diversity. The technique of introducing field margin vegetation strips thus can increase biodiversity on farms.

Where strips were introduced into a field-scale comparison of conventional arable production with a low-input integrated system, there was little evidence of an effect of the farming system on the successional development of the strip flora in four years.

Processes affecting field margins

Small-scale experimentation shows that plants are affected by addition of fertiliser, herbicide and by management, including cutting. Fertiliser additions favour the establishment and growth of tall plant species, typically those with a ruderal habit. Such species, including perennials, can colonise margin habitats early on in secondary succession and may dominate the community. In the crop edge, fertiliser effects on the arable flora are modified via the canopy and the light climate. Fertiliser promotes poorer light under the canopy, by favouring the taller crop. Detailed studies of the flora of the field boundary show that plants at the edge, within 20 cm of the tilled soil, are able to exploit the fertility of the crop, producing significantly more biomass than plants further into the margin. Thus, nutrients are "harvested" from the field into the boundary. This favours taller species while low-growing species are reduced. Further into the margin, reduced fertility allows greater species diversity.

The effects of herbicides on plants are less predictable, partly as there are many chemicals with varying spectra of activity. Some herbicides have direct impacts on species, while others cause changes in plant communities indirectly, by allowing unaffected species to increase. In general, herbicide application or drift from field operations has negative effects on botanical diversity.

Management, in the form of vegetation cutting, can also have impacts on the flora of field margins. Cutting and removal, as in hay harvesting, can remove nutrients and ameliorate the adverse effects of fertiliser additions. Cutting has been shown to reduce populations of a perennial weed in sown meadow patches, and over a period of years, increases in desirable subordinate species, particularly of legumes, were recorded.

There is evidence that dispersal is important for the size of annual plant populations and that herbivores can have a highly significant impact on annual plant population establishment. Dispersal and successful colonisation of new habitat varies between species. A knowledge of dispersal may be essential in designing successful schemes for the conservation of rare plants of arable fields, and for maintaining diverse perennial flora in field margins. A specific study of a rhizomatous weed, Elymus repens, shows that it is able to exploit bare ground within margins. A perennial ground cover, without disturbance, would limit its success.

The inter-plant interactions that occur in field margins have been successfully modelled, using a range of species with differing life-history strategies. The model builds on studies made within the project on establishment, competition and fate of plants, so that patterns of successional change in field margins are simulated. The model includes effects of fertiliser, herbicide and cutting. Clearly, fertiliser additions lead to loss of subordinate species. Herbicides cause species loss and reduced diversity. Vegetation removal by cutting modifies competition and mortality, allowing species and therefore diversity to be maintained.

Introducing vegetation strips at field edges

Sown margin strips have been successfully established in a variety of situations in five European countries. These strips have compared, under experimental conditions, sowing perennial grasses, grasses and wild flowers, wild flowers and naturally regenerating flora, with the field crop. Sown strips show successional changes, typically with annual weed plant species common in the first year which largely disappear in the second and subsequent years after sowing, except on regeneration plots.
Successional patterns were similar between sites, indicating that soil fertility was a poor predictor of outcome. In general, few plants of the pre-existing margin colonise the new strips. The sown strips showed some convergence towards grass margins with colonisation by more mobile species of grassland. In general, the species present showed low dispersal capabilities and seedbanks were often impoverished. Colonisation by species not previously recorded in the above-ground flora was very low, indicating that the use of seed mixtures is likely to be essential in most farm situations.

The sown plots significantly reduced weed species populations. This was particularly apparent where the perennial Cirsium arvense achieved high populations where grasses were not sown in strips. The productivity of the strips was lower than might be expected on land taken out of arable production. Nevertheless, fertiliser use in the adjacent field affected plant growth, increasing biomass in the 10-20 cm nearest the crop. With the exception of some spread of the sown grasses, there was little evidence of the sown strips themselves causing weed problems in the adjacent crop.

In a survey of margins on two farms, it was shown that sown grass margins were associated with less disturbed and more species-rich field margin flora, indicating that such strips would give some protection to the pre-existing margin flora, with farming operations taking place further from the margins.

Invertebrates of field edges

Field margins were shown to increase the diversity and abundance of insects, especially if they were both botanically and structurally diverse. In experiments using pitfall trapping, a technique which measures activity-density, no significant differences were found between different field margin strips. However, it was demonstrated that the technique is unsuitable for comparing different vegetation structures, and unsuitable for small plots. Many invertebrates move significant distances and studies should be made at the field scale, rather than the plot scale. Alternative sampling methods showed that the more structurally complex and botanically rich plots supported the most abundance and diversity of invertebrates.

A novel field technique of marking individual ground beetles was developed, in order to study the dispersal characteristics of these invertebrates. These species are often polyphagous predators, implicated in the control of aphid and slug pest populations. Many species were particularly mobile, moving from the field margin into the crop over short time intervals. Introduced field margin strips were rapidly colonised, so that over- wintering populations were similar to pre-existing margin habitat with 12 to 14 months of establishment. Mark-recapture techniques were deployed with pitfall trapping to assess total population size and dispersal characteristics of species. Behaviour of species varied considerably. Some species were ubiquitous, while others were dependent on field margins for over-wintering sites. One species used margins during a summer aestivation period, before dispersing into the crop in late summer/early autumn. Other species were part of a diverse community found within the arable crops. Mark-recapture studies provided quantitative results on dispersal for use in subsequent modelling, for example, maximum (c. 100 m day-1) and average daily displacement. Other significant findings were that patterns of occurrence were not uniform. Some species were found in consistently high densities in certain locations, the reasons for which are unknown, but which might be manipulated to reduce pest populations. Another finding was that field margins, particularly a hedge, may act as a barrier to dispersal between fields.

Studies in Germany using mark-recapture methods demonstrated that ground beetles will move into adjacent crops in spring. A significant local influence of the field margin was recorded in the crop on populations of aphids. The reduction of aphids up to 5 m or more from the margin is likely to have resulted from a complex of predator species associated with the margin.

The results demonstrate that field margins can support a diverse invertebrate fauna, some of which can contribute to the agricultural control of pest species. Suitable manipulation of the field margin may enhance the diversity and abundance of insects.

Managing field margins

The project has shown that disturbance, particularly in the form of fertiliser and herbicide contamination, has adverse effects on the diversity of the perennial flora of field margins. Data indicates that significant herbicide drift will occur over 3 m form the crop and up to 4 m for fertiliser applied by spinning disk machinery. Sown margin strips 3 to 4 m wide, extending pre-existing boundaries, have the capability of reducing such disturbance by buffering drift. Such strips would be best managed by cutting and removal of clippings at a time of year when ground-nesting birds would be least disturbed.

In areas with a history of intensive agrochemical use, it is likely that the existing flora of field margins has adapted to high fertility conditions and is species-poor and unlikely to recover significant diversity without species introductions. Sown grass and wild flower strips would be suitable under such conditions. The seed used may need to be of local provenance.

Sown perennial vegetation strips located at field edges would not be suitable for the encouragement of rare arable weed species, many of which are threatened with extinction in modern arable farming. Such species are often found in soil seed banks at field edges. Where such species are know to exist, the technique of no-input crop edges (conservation headlands, ackerrandstreifen) is suitable. Studies indicate no significant increase in pest and disease problems and minor increases in weeds under some conditions and on some soils. Studies on some species show that fertiliser in the crop has a significant adverse effect on rare weeds, mediated by a poorer light climate created by a competitive crop. Fertiliser should also be omitted from no-input crop edges for rare weed conservation.

Conclusions

At the plot scale, field margin floras are affected by adjacent management. Plants of the margin can forage into the arable area over short distances. Sowing seed mixtures of grasses and flowers as a field margin strip is a practical means of increasing local diversity and can protect adjacent pre-existing boundary flora. There is evidence that the technique can reduce the abundance of competitive annual hedgerow weeds, while increasing available habitat for invertebrates. There is evidence of limited seed spread from sown margins into crop areas, but this is not likely to be of economic significance.

At the field scale, impacts of field operations, particularly fertiliser application, are likely to be important for field margin flora. Contrasting results were shown in the development of margin flora: in sown strips, there was little evidence of farming system effect on the flora; in contrast, a farm with grass margins had significantly more diverse herbaceous hedge flora, compared with an adjacent farm without strips. Fauna studies show that species-specific spatio-temporal behaviour occurs in Coleoptera.
Margins are important as over-wintering or aestivation sites. They may also be barriers to movement between fields for some species, which may have implications for re-colonisation and population recovery after field operations. Invertebrate abundance and diversity is encouraged by structural complexity and botanical diversity in margins.

At the landscape scale, boundary structure, land-use (farming type), location and the management of the boundary affect the shrub and herbaceous flora. Disturbance and eutrophication from adjacent farming are important in affecting margins. These various factors are in fact a resultant of many specific environmental and physical processes, which require further understanding. However, it is clear that local diversity of structure and land use favour diversity in margins. With a diversity of land use in Europe, and a range of overlying climatic differences, margins are variable features of agricultural landscapes. In those landscapes examined, field margins are an important contributor to biological diversity, but they are sensitive to the farming operations practised.

Recommendations

1. Sown margin strips at least 3 m wide should be introduced at arable field edges, to buffer the effects of fertiliser and pesticide drift and to create new habitat on farmland. The technique will make significant contributions to the maintenance of biological diversity in agricultural systems.

2. The structural diversity of field margins should be maintained at farm, field and landscape scales.

3. Implementation of agri-environmental measures, changes to farming support and landscape planning should take account of their effects at the appropriate scales for different fauna and flora.

AIR3 Project Publications are listed

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Email: jon.marshall@agroecol.co.uk
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Last changed - 17 October 1997