Field Margins & Boundary Habitats

Local Biodiversity Action Plan

Field margins and boundary habitats include a range of linear features of importance to biodiversity and landscape, including drystane dykes, hedges, ditches, and burns. Dyking has been used by farmers to dispose of unwanted stone and provides a permanent field barrier and shelter that needs little maintenance. Dykes are important wildlife habitats for lichens, mosses, ferns and flowering plants. Small holes within walls form sheltered nesting sites for birds such as wheatear, wagtail and wren. Lizards and small mammals also use dykes as places to forage or hide. Dykes also contribute to the character of the local landscape and are often of archaeological interest.

Many field boundaries are formed by small burns and drainage channels. Burns and the vegetation along their banks are of considerable wildlife interest. Vegetation strips form important buffers between agricultural activity and water courses, helping to prevent soil erosion, nutrient run off and pesticide drift. Hedgerows support a great variety of species but are less common in North East Scotland as they are not traditionally part of the landscape.

If the outermost zone of an arable crop is managed to control weeds rather than eliminate them, plants and invertebrates can co-exist with the crop. If margins are sown with tussock-forming grasses and broad-leaved plants they can help suppress pest species and reduce the spread of troublesome weeds. Grass margins also encourage populations of agriculturally beneficial invertebrates (e.g. money spiders and ladybirds) and can be used to straighten field edges.

Over recent decades, the promotion of intensive farming methods has resulted in a great reduction in the extent and quality of boundary habitats. Various initiatives have been established to replace lost boundary features. Within the North East area the local priorities of the Countryside Premium Scheme include the conservation management of field margins. Alternatively, farmers can meet their set-aside obligations by the non-cultivation of field margins of 20m minimum width.

The UK Action Plan for cereal field margins has set a target of maintaining, improving or restoring the biodiversity of 15,000 hectares of margins on appropriate soils in the UK by 2010. This is equivalent to a target of maintaining or restoring 765 hectares of field margins in North East Scotland.

Field margins and boundary habitats include a range of linear features of differing local abundance and importance for biodiversity and landscape. These include: drystane dykes, hedges, field edges, ditches, verges, burns and banks. Within the context of North East Scotland, the predominant features from this list are burns, drystane dykes and field edges.

Many field edges are routinely sprayed with broad action herbicides. Designed to suppress weeds, this activity is frequently a vicious circle, which creates fertile disturbed ground. This is ideal for pernicious weeds, rather than the less competitive and more desirable rough grassland species.

Dyking has been used by farmers to dispose of otherwise unwanted stone. Drystane dykes offer a permanent field barrier and shelter for stock, which needs little in the way of maintenance. The farmed landscape of North East Scotland is predominantly a mixture of arable fields and grassland, or rotations thereof. Within completely farmed landscapes, the field boundaries may offer the only opportunity for semi-natural habitat to develop. These habitats can be managed in the interests of biodiversity.

From a biodiversity perspective dykes provide an important wildlife habitat for lichens, mosses, ferns and flowering plants. Small holes within walls can form sheltered nesting sites for birds such as wheatear, wagtail and wren. Lizards and small mammals also use dykes as places to forage or hide. Dykes contribute to the local landscape and often are of archaeological interest, providing evidence of previous settlement and land management.

Hedges may support greater species diversity than do dykes, but they are not a traditional field boundary in much of the North East. The most recent figures from the late 1980s record the amount of hedgerow in North East Scotland as only 2,128 km (about 0.5 % of the UK total). Important species are associated with hedges, including the UK priority listed bird species yellowhammer and tree sparrow.

Many field boundaries are formed by small burns and drainage channels, and their riparian habitats can be of considerable wildlife interest. Strips of water margin vegetation can form important buffers between agricultural activity and water courses, helping to prevent soil erosion, nutrient run off and pesticide drift. Unfortunately, water fringe vegetation is frequently sensitive to over-grazing and agro-chemicals, resulting in either poaching or rank species poor vegetation, respectively.

In conservation headlands, the outermost zone of the arable crop is managed to control weeds rather than eliminate them. The limited selective use of agrochemicals on headlands allows annual plants and the invertebrates that they support to co-exist with the crop. This more diverse habitat can improve survival of some gamebird chicks.

Grass margins are sown strips of tussock-forming perennial grasses, sometimes including broad leaved species. Many agriculturists have regarded these as reservoirs for weeds. However, managed well they can help suppress pest species and reduce the ingress of troublesome weeds. Additionally, grass margins encourage populations of agriculturally beneficial invertebrates (e.g. money spiders) and can be used to straighten field edges. They form habitats for invertebrates and small mammals, especially important in providing over wintering sites. These small mammals are preyed upon by owls and weasels, both of which use field margins as corridors to cross farmed land. In summer wild flowers within grass margins provide nectar, so encouraging movement of wildlife through the countryside.

There is little information regarding the distribution or abundance of boundary habitats within North East Scotland. Very few farmers are thought to manage cereal margins for the benefit of wildlife. As stated above, however, there is a large network of field edges, which could be converted into valuable wildlife habitats. The Countryside Premium Scheme (CPS) encourages farmers to establish grass margins, but there is no information available as to the uptake of this option.

Over the last 50 years there has been a great reduction in the number and quality of boundary habitats. The main factors responsible for this are listed below.

3.1 A trend towards increased field sizes. This accommodates modern farm machinery and has resulted in removal of dykes and hedges and the piping of watercourses under fields.

3.2 The intensification of crop production. Increased use of chemical pesticides and fertilisers has resulted in the decline of many species or created high fertility habitats less able to support high diversity. Similar effects have resulted from the practice of burning hedge bottoms to control weeds.

3.3 A reduction in the size of the rural labour force, increased labour costs and loss of traditional skills. This has resulted in no or poor maintenance of both dykes and hedges many of which have been replaced by fencing.

3.4 Changes in farming practice. Increased stocking rates and larger breeds of cattle have caused damage to dykes, erosion of water margins and overgrazing of hedges. The shift to winter cropping, reduction in cereal rotations and reductions in amount of undersowing of cereals, have all reduced the conservation value of farmed land.

3.5 Introduction of invasive plants. Many boundary habitats (especially water margins) have become dominated by a few species, e.g. giant hogweed and rosebay willowherb. Such alien species tend to support a lower invertebrate diversity.

Within the North East area the local priorities of the CPS include the conservation management of field margins. The Scheme offers cash incentives to establish margins around fields that are free of chemical sprays. Alternatively, farmers can meet their set-aside obligations by the non-cultivation of field margins of 20m minimum width. They are also provided with information on managing set-aside for the benefit of wildlife, but this is rarely acted upon. SNH provides funding through local groups such as Aberdeenshire and East Moray Conservation Programme, which may include hedge planting and conservation management of boundary features.

The CPS provides financial assistance to help farmers establish new and/or renovate old dykes and hedges (or sections there of). In addition to material and labour cost these schemes also provide moneys towards fencing to protect dykes and establishing hedges. FWAG, the Game Conservancy Trust and SAC all employ Field Advisers to provide farmers with information covering the conservation management of boundary habitats.

SEPA promote the use of buffer strips and Best Management Practice for farm watercourses. Action points described in other biodiversity action plans, e.g. Daubenton’s Bat also may be relevant to boundary habitats.

The benefits of fulfilling the identified targets are likely to occur at several levels.

• Help maintain biodiversity in the farmed landscape. Over 2,000 species of invertebrates and 300 species of plants are known to inhabit cereal field margins. Within North East Scotland field margin habitats contain species that are locally rare and visually attractive, e.g. scarlet pimpernel and corn marigold. This helps improve the aesthetics of the countryside. Within North East Scotland, water margins and grass margins in arable fields may be more important in supporting species diversity.

• Improve farm economics, by controlling weeds, encouraging beneficial invertebrates, preventing soil erosion and providing shelter for stock. Conservation headlands also encourage gamebirds and thus increase potential revenue from shooting.

• Help employment in rural areas by providing opportunities for skilled dykers and hedge layers.

• Improve the appearance of the countryside through ensuring traditional landscape features are well maintained.

• Improvement to water quality and water courses through the interception of fertiliser run off from agricultural land and reduction in soil erosion, particularly if riparian field boundaries are targeted. This can provide considerable benefits to the fishing and tourist industries.

On the less positive side, field margins are seen by farmers as providing habitat for weeds and rabbits. While it is possible to argue that weeds such as cleavers and couch may be less problematic in field margins managed for conservation; the fact that hedges can encourage rabbits and consequently result in soil erosion is more of an issue.

The UK costed action plan for cereal field margins alone has set a target of maintaining, improving or restoring the biodiversity of 15,000 hectares of margins on appropriate soils in the UK by 2010. On a pro rata basis this translates to a target for North East Scotland of 765 hectares of cereal margins created or managed in the interests of biodiversity by 2010.

The national target for hedgerows is to halt the net loss of species-rich hedgerow by 2000 and to halt all loss of ancient and species-rich hedgerow by 2005. The favourable management of 25% of species-rich and ancient hedges is to be reached by 2000, a target of 50% to be reached by 2005. These targets for hedgerows can be utilised directly as local goals.

There is no national costed action plan for drystane dykes, however, the national habitat statement’s conservation directions states that targets similar to those for hedges should be aspired to. Measures to be considered include:

• Protection of all drystane dykes of wildlife or historic importance.

• Construction of new dykes and renovation of old ones, where they connect isolated fragments of habitats, or add significantly to the landscape.

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