THE ROLE OF FIELD MARGINS IN CONSERVATION AND AS HABITATS FOR SPECIES USEFUL TO THE FARMER

Introduction
Field margins come in many forms; fences, walls, ditches, raised banks, etc., but the most common is the hedgerow. My task was to consider the usefulness of field margins as habitats mainly for insects, the benefits to the farmer of field margins, the habitat requirements of insects and the management and establishment of hedgerows. I was also to include information on small mammals and birds. Most work has been done on hedgerows, and hedgerows were used on the poster, but in this essay I have included some information about walls.
Hedges, walls and uncultivated strips of vegetation around the edges of fields serve many purposes not only agricultural, but also environmental, landscape and sporting. An ideal field margin should:-
1. clearly define the field boundary;
2. provide a stock-proof barrier;
3. provide shelter for stock;
4. provide protection to crops and soil by preventing soil erosion by acting as a windbreak or snow barrier;
5. provide shelter, nest sites, overwintering and hibernation sites, and food to beneficial insects, game and other useful animals;
6. field margins may also provide a screen against the drift of sprayed chemicals.
Many beneficial predatory invertebrates thrive in field margins. These invertebrates may move into the cultivated area once the crop provides suitable cover, and hunt harmful insects such as aphids, or they may play a part in pollinating the crop. Some field margins can also provide good habitat for game species, e.g., grey partridges, red-legged partridges, pheasants and hares.
Most British native small mammals have evolved in woodland habitats. In many intensively farmed areas hedgerows and field margins may be the only semi-natural habitats left available. Shrews and voles will only stray from the field margin into the fields when there is enough cover.
It has been shown that some butterflies preferentially make use of field margins as flight corridors. Males of territorial species such as the small tortoiseshell and peacock prefer to take up territories along stretches of field margins, as such areas increase their chances of meeting a female looking for oviposition sites.
Hedges
The past
For over a hundred years many farmers have seen hedges as being unproductive, but necessary as stock-proof barriers. In the east of the country cereal growing greatly increased since the Second World War, so hedges were no longer needed for their stock-proofing and sheltering abilities, and they were a hindrance to the larger farm machinery. So miles of hedgerows were removed and small fields were joined together. Until 1974 grants for the removal of hedges were still available to farmers. In intensively cultivated areas many of the hedges had become island habitats. Once the hedge was removed there would be no other suitable habitat available to populations with limited dispersal abilities, so they would die out.
Variety of habitats
Within a very short area a hedge and uncultivated strip can provide a large number of habitats:-
1. a linear habitat of shrubs and bushes;
2. isolated trees;
3. a herbaceous verge, relatively undisturbed;
4. ditches providing a temporary or permanent aquatic habitat.
In the U.K. about 1000 plant species have been recorded in hedgerow habitats, and about 250 are closely associated with it, so there is great structural and foodplant variety. Hedges are often dismissed as "edge" habitats, and they do contain more "edge" species than "interior" species. However a good thick hedge can be considered an "interior" habitat to some insects, and even to some small mammals such as the dormouse, which rarely strays out of the cover of the hedge. If a hedge has a ditch with water this can provide a habitat for dragonflies, mayflies, stoneflies and water beetles, as well as frogs, newts and toads.
Hedgerow animals
Hedgerows with grassy verges and raised banks are important overwintering habitats for and aphid eating carabid and staphylinid beetles, e.g. Tachyporus hypnorum. Of the 35 carabids found in agricultural settings 24 overwinter in and around hedgerows. Hedgerows are also important nesting and hibernating sites for bumblebees. Bumblebees require south facing banks for their nests, and colder north or north-west facing banks for hibernation sites for the queens. The long-tongued bumblebee Bombus pascuorum suffers when grass is cut right up to the edge of the hedge as this destroys its nest which is found in tussocky grass. This bee is particularly valuable in pollinating red clover. B. sylvarum, a bumblebee found only in the south, which has similar habitat requirements to B. pascuorum, has decreased in numbers to such an extent that captive breeding and re-introductions have been considered.
It has been found that increasing the number of flowers in the hedge bank and grassy strip of cereal fields, and allowing them to flower leads to an increase in numbers and diversity of hoverflies and parasitic wasps. Hoverfly adult females need to eat pollen in order for their ovaries to develop, then they lay their eggs in the middle of groups of aphids, which the larvae eat. The numbers of overwintering spiders will also increase in untreated grassy and clover strips.
Some of the herbaceous plants that grow at the bottom of the hedge overwinter as rosettes, e.g. foxglove; these provide valuable hibernation sites for insects such as ladybirds. Ladybirds in both the larval and adult stages consume large numbers of aphids.
Hedges provide sheltered nesting and breeding sites for a wide variety of vertebrates including, the linnet, yellowhammer, whitethroat, and the dormouse. In a study 84% of whitethroat and 97% of yellowhammer nests were found in field margins, and both were significantly more numerous in hedges with ditches.
Ditches
Plots of arable land containing ditches were found to contain twice as many species of bird, and three times the density than plots without ditches. Many of these are game birds whose young eat the insects found in the grassy verges of hedges.
Hedges as corridors
Hedges can provide links between what would otherwise be isolated populations; some capture-recapture studies have shown considerable movement, and probably genetic exchange in some butterfly species, e.g. the gatekeeper, ringlet and meadow brown. However studies in Norway have shown that hedges can act as a barrier to butterfly movement, as some butterflies will not fly over obstacles of a certain height. The best type of hedge for some butterflies would be one with large gaps in it.
Shape and size
It is stated throughout the literature that for most types of hedge an "A" shape is better than a hedge with parallel sides, though there does not seem to have been any real scientific study to justify this. The best height for a hedge is about 2 m by 1.5 m wide. However in 1992 The Institute of Terrestrial Ecology found that the best type of hedge for birds, invertebrates and small mammals was an unmanaged hedge about 5 m high and 4 m wide. This may take up more space and cause more shading of crop than the farmer would wish.
A hedge is like a wood, there will be no one "best" shape and size, and there will probably be a whole range of management regimes that will suit different groups of insects and different sites. The study of hedges and their contribution to conservation is still in its infancy, and there may be a danger that increasing legislation will produce a standard hedge for the whole country.
Hedge management
Insects often have different habitat requirements at the different stages in their life-cycle, the requirements of each stage must be met, if they are not then the insects will die. The current methods of trimming and cutting hedges can lead to the loss of habitat for some stages in the life cycle of some insects.
If the hedge is allowed to flower and is cut on a rotational two or three year basis, the flowers will provide out-of-season pollen and nectar to pollinating insects until the crop flowers. Also the berries and nuts are a valuable food source for rodents and birds.
For some insects that survive as eggs or pupae on twigs and branches over winter, yearly hedge cutting can lead to serious population reductions. Insects or eggs on the branches that are cut off will almost certainly die, others may have lost the shelter and protection they need, and others may become dislodged by the violence of the operation. Annual hedge trimming is thought to be the cause of the decrease in numbers of the brown hairstreak butterfly which lays its eggs on blackthorn twigs in August, and they hatch the following spring. Also the small eggar moth which overwinters as a cocoon on twigs. This moth is listed in the Red Data Book as being vulnerable; indiscriminate hedge trimming, destruction of hedgerows and pollution by agricultural sprays and motor vehicles are the threats to the reduced populations that remain.
It is recommended that hedges be trimmed every two or three years, preferably on one side at a time, and no more than one third of the length of the hedge should be trimmed in any one year. The best time for trimming is said to be late winter. It has also been found that trimming with a mechanical flail causes great damage to the hedge itself as the branches are not cut cleanly; this encourages diseases and fungal infections.
Establishing new hedgerows
Grants are now available for the establishment of new hedgerows; however these should not be planted at the expense of existing herb-rich field margins. Ditches should not be dug if they might drain existing damp or marshy areas of meadow. And at all times native shrub and tree species should be used, as these will best provide for the local fauna. A raised bank will provide overwintering sites for beetles, and nest and hibernation sites for bumblebees.
Conservation headlands
Conservation headlands is a management technique where pesticide input to the outer 6 m or 12 m of cereal fields is reduced and selective. This technique has been shown to benefit butterflies. Ideally such an expanded field margin can act as a buffer zone between the hedge and the crop.
Walls
The main difference between walls and hedges as far as insects and small mammals are concerned is that a badly neglected and damaged wall will still provide a perfectly good habitat. Stone walls, especially dry stone walls with lots of spaces are excellent nest sites for Bombus lapidarius (a bumblebee) and many solitary bees. In fields bordered by walls it was found that the highest density of carabid beetles and spiders was in the tussocky grass at the sides of walls. Some Linyphiidae spiders are only found next to walls and require stones for hunting, shelter and support for their webs. Also in areas of low pollution the lichens on walls may provide a background for cryptic insects to rest and bask.
Conclusions
In some areas field margins are the only semi-natural habitats left. With agricultural over production farmers are being encouraged to set aside land, this could be used as an opportunity to expand the field margin area, or even to allow whole fields to revert to woodland. Field margins provide habitats to many useful insects, their populations could be increased with just a little more knowledge about their requirements, particularaly their life-cycles. This would decrease the neccesity for pesticides and some herbicides, leading to savings in finances and labour.
References
Boatman, N. (Ed.) (1994). Field margins: integrating agriculture and conservation. British Crop Protection Council, Monograph No. 58.
Brodie, L. (1996). Bumblebee foraging preferences: species and individuals. BSc. Thesis Aberdeen University.
Chinnery, M. (1993). Insects of Britain and Northern Europe. Collins.
Jones, S., Fry, R. & Lonsdale, D. (1991). Hedgerows and arable field margins. In: Habitat conservation for insects - a neglected green issue. The Amateur Entomologists' Society.
Marshall, J. (1994). Life on the edge: managing field margins. Enact. 2: 7-9. Park, J.R. (Ed.). (1988). Environmental Management in Agriculture. Belhaven Press.
Robb, K. (1996). The invertebrate assemblage of a dry stone wall and adjacent field systems. BSc. Thesis Aberdeen University.
Roberts, M.J. (1995). Spiders of Britain and Northern Europe. Collins.
Shirt, D.B. (Ed.). (1987). British red data books; 2 insects. Nature Concervancy Council.
Sladen, F.L.W. (1912). The humble bee. MacMillian.
Way, J.M. & Greig-Smith, P.W. (Eds.). (1987). Field margins. British Crop Protection Council, Monograph No. 35.
Wolton, R. (1994). Hedges in decline. Enact. 2: 18-20.

The planning of buffer zones around tropical forest reserves

1 Introduction
Buffer zones are, "Areas peripheral to National Parks or reserves which have restrictions placed on their use to give an added layer of protection to the nature reserve itself and to compensate villagers for the loss of access to strict reserve areas".
Tropical forests probably harbour over 50% of the world's species of animals and plants, but they are being opened up by logging, and converted to agriculture so rapidly that there is widespread concern that the entire biome will be irredeemably damaged in the next few decades. The conservation of these ecosystems requires the establishment of protected areas. The problem in the past however, has been that legal protection alone has not maintained the integrity of these areas as conservation zones. The view often held by the local people in the region surrounding the parks and reserves was that such protected zones were an infringement on their traditional rights. Despite the demarcation of boundaries, inadequate patrolling by guards and minimal management all too often resulted in illegal hunting, the gathering of forest products and the encroachment of agriculture. It soon became clear that laws without support cannot be enforced and it was this realisation that prompted the MAB/UNESCO Biosphere Reserves Action Plan adopted in Minsk, in the USSR, in 1984. The purpose of the Action Plan was to incorporate "buffer zone" activities that involve the interaction with local communities into the management of protected areas.
2 Planning buffer zones
2.1 The two main kinds of buffer zone are: Extension buffers, this extends the habitat of the reserve, allowing the animals and plants a larger area. There may also be selective logging, hunting and firewood collection by the local villagers. Socio-buffering is where the main importance of the buffer zone is to provide the locals with cash crops etc. This involves the planting of species that the animals in the reserve would find unattractive in order to keep them within the reserve itself.
2.2 Requirements and restrictions When planning a buffer zone the following should be taken into consideration:
The natural history of any species within the reserve.
The need for protection against fire, soil erosion, water conservation etc.
The need to contain species that may wander out of the reserve, e.g. elephant.
The needs of the locals for forest products and cash crops.
The amount of land available and its current use.
The suitability of particular crops for the soil and climatic conditions, and also whether the animals in the reserve would find the crop attractive, e.g. bananas or maize near elephants and monkeys.
The following restrictions should be considered:
No permanent settlement within the zone.
No burning of vegetation except where species are adapted to a regular fire regime.
No hunting of endangered species or species that may threaten the food acquisition of endangered species.
No planting of crops likely to entice wildlife out of the reserve.
2.3 Types of buffer zone
Traditional Use Zones. Where no suitable land exists or is available outside the reserve, some part of the reserve is made available to the locals to satisfy the need for forest products, e.g. fishing, traditional hunting, fruit gathering, firewood collection, rattan cutting, some grazing of animals if it does not conflict with the grazing of wild animals.
Economic buffers. These reduce the need for the locals to take resources from the reserve itself, and may include, cash crops, wildlife hunting permits for use outside the reserve, or even a share of the income from the reserve.
Forest buffers. These provide the locals with firewood. The area may be a part of the reserve, or secondary forest, or even plantations to maximise growth.
Physical buffers. Where there is no land available, or no suitable buffer area fences, ditches, canals etc. discourage wildlife from leaving the reserve and people and domestic animals from entering.
Therefore it can be seen that several types of buffer zones exist and involve the consideration of many aspects of conservation in their planning. Two case studies will now be examined to demonstrate firstly the different types of buffer zone used in practice. And secondly to assess their relative success or failure.
3 Case study - Lake Manyara National Park
3.1 Introduction
Lake Manyara National Park is part of the Tarangire-Simanjro ecosystem situated south of the Tanzania/Kenya border. The area of the national park is very small, only 110km2 of park land. It has been awarded "Biosphere Reserve Status" due to its unique qualities.
3.2 Environment
Wildlife. The park has high animal diversity with the highest animal biomass in Africa. Migratory species include zebra, wildebeest, Grant's gazelle, buffalo, as well as elephants and lions.
Physical. Rift escarpments, saline lakes and hot springs.
3.3 Society. Rural area dwellers and tourists. Land uses include agriculture, pastoralism, wildlife, conservation, grazing, there is also a phosphate mine and game controlled areas.
3.4 Problems Population increase. In 1976 the study area had 6.5 persons/km2, which by 1988 had increased to 37.9 persons/km2, with a total population of 25,985. The population growth rate is 3.4% (much higher than the national average), due to an increase in immigration into the area, especially Mtowambu.
Low returns from agriculture. As the returns from agriculture are low crop land has been greatly increased. In 1958 cropland accounted for 36km2, and by 1988 185km2 (Mowambu cropland increased from 218ha in 1957 to 1093 ha in 1980, a difference of 401% in 23 years).
Game migration and crop destruction. Game migration after the rains coincides with crop ripening (May - June), this leads to crop destruction which creates conflict and tension with local people.
3.5 Impact
Game movement is restricted. this is caused by increased human numbers and therefore settlements with expansion of agriculture.
Elimination of grazing and water resource. Enlargement of settlements has meant encroachment onto dry season grazing land and water resources for the wild animals. The area is also used as an escape route when the lake floods along the shoreline.
The blocking of this area has also meant there is a risk of populations being wiped out if a natural catastrophe hits the area, e.g. rinderpest epidemic in buffalo in 1959; severe flooding of the lake in 1970 which led to the death of many wildebeest and zebra through drowning of marooned animals.
3.6 Responses
Game corridor. This will enable migratory species to have a route for dispersion, and allow a connection between Lake Manyara National Park and Tarangire National Park.
Buffer zone. To minimise conflict on boundaries with partly restricted land use, which will protect the national park and gives benefits to the villages.
3.7 Proposed plan for Lake Manyara National Park A 2km wide buffer zone between Lake Manyara Hotel and Marang forest reserve, within which fuel wood and livestock grazing will be allowed. The existing park boundaries will serve as a buffer strengthened by trenches, electrical fences and spike barriers to a) discourage animals from destroying crops, b) prevent people and livestock from entering the reserve. And plans to convert part of the whole forest reserve into a National Park.
3.8 Conservation incentives Rural populations to be involved in decision making on such issues as game corridors, buffer zones, anti-poaching and prevention of fires. Public awareness, information and education. Programmes for sustainable utilisation of wildlife within village boundaries, some allowance to exploit some resources of the park, and compensation for damage to crops and property caused by wild animals.
The case study highlights proposed plans made in 1991 by R. Mwalyosi. An original plan was proposed in 1987 by H. Prins, "Nature conservation as an integral part of optimal land use in E. Africa: The care of the Masai ecosystem of northern Tanzania". After the 1987 plan it was decided that more field data were necessary. The 1991 plan was produced, but again it has been decided that more field data are necessary.
3.9 Conclusion
It can be seen that the buffer zone planned around lake Manyara National Park does not fall into just one classification of a buffer zone, in fact it relates to three types; economic, physical and forest buffer zones. The continuation of livestock grazing within the buffer zone reduces the need for locals to take resources from the reserve and in this respect it is an economic buffer zone. The introduction of trenches, electrical fences and spike barriers introduces the physical aspect to this buffer zone. Lastly the collection of fuel wood within this buffer also implies that it is a forest buffer. Therefore it can be seen that in practice buffer zones often incorporate a number of factors. The second case study examines some problems that may occur in the implementation of a National Park and buffer zone, the location of this case study is Korup National Park in the Cameroon.
4 Case study- Korup National Park.
4.1 Introduction
The Korup national park in Cameroon is situated in the south west province near the border with Nigeria. It covers 1,250km2. The park was established in 1986 after preliminary surveys in the early 1980's identified the ecological potential of the forest.
4.2 Resources and processes
Environment Wildlife, 17 tree species previously unknown, were discovered. Korup emerged as potentially the richest and most diverse forest yet studied in the whole of Africa. A chemical screening programme identified ninety substances of potential economic value, 38 of which were new to science. Land uses are agriculture, logging, wildlife, conservation, fuel wood gathering.
Society Inhabitants include the indigenous population and employees of logging companies.
4.3 Aims of Korup National Park
The aims of Korup National Park were to protect 8000 species of plant, animal and insects, whilst providing the local population with space for sustainable rural development in the buffer zone. 1042 people living in six villages would have to be resettled in the buffer zone.
4.4 Implementation of Korup National Park Project
The project needed financial backing and in April 1988 the World Wildlife Fund pledged to raise £2.5 million, the Overseas Development Agency pledged a further £500 000 and the West German government pledged a further £600 000 to the project. The W.W.F. signed a contract with the Cameroon government to establish a protected core area of 1 200 km2 surrounded by a 4 000 km2 buffer zone. The contract included helping farmers in the buffer zone to identify the better land and offer advice on farming techniques. Tree nurseries would be established to provide seedlings of indigenous food crops, cash crops, fruit trees and fuel wood. The Cameroon government also agreed to establish guard posts off the buffer zone to stop illegal hunting.
4.5 Problems
Population re-settlement. 1042 people living within the boundaries of the proposed National Park would have to be resettled within the buffer zone.
Illegal logging. The Cameroon government sees Korup National Park as a prime source of foreign exchange to help alleviate the country's severe economic crisis. Due to ineffective surveillance and policing mechanisms along the park's boundaries, illegal logging continues. As well as this, the government have granted logging concessions since February 1990 to international timber companies in areas bordering the park. It has been alleged that some companies have removed species other than those they have declared. Directives to consult local agricultural officials and communities before applying to cut timber are being ignored.
4.6 Impact
Disruption of indigenous population. In the creation of the National Park several villages will have to change location and alter their lifestyles.
Loss of biodiversity. As a result of illegal logging involving bad management policies the rich biodiversity is under threat.
Therefore in this case study it can be seen again that the buffer zone falls into several categories, not just one. These are traditional use zone, economic buffer, forest buffer, and physical buffer. Korup National Park has been regarded as a model for the conservation of threatened rain forests world wide. However it has been demonstrated that despite careful management of the buffer zone many problems still exist, such as illegal logging and slack implementation of rules. Problems such as these are difficult to resolve unless the government gives full support to a project.
5 Conclusion
In conclusion it can be seen that buffer zones represent an example of resources and processes in environment and society. Diagram 1 summarises these resources and processes. Buffer zones demonstrate how conservation problems in the tropics such as deforestation and loss of biodiversity, are directly related to economic activities such as agro-forestry, livestock production, and logging. For example in the case of Lake Manyara the buffer zone not only serves to protect the National Park and therefore preserve conservation but also to aid the economic development of the local population by allowing fuelwood collection and livestock grazing. In the case study of Korup National Park it can be seen that trying to satisfy both economic and conservation needs is not easy and many problems can occur. Examples are illegal logging and governmental regulations allowing concessions for international timber companies, these pose threats for the natural resource. Short term benefit may initially be brought to the local economy, but in the long term the results may be highly detrimental.
LITERATURE CITED
INTRODUCTION HALL, J. B. and RODGERS, W. A. 1992. Rural development forestry network. Overseas Development Institute, U. K.
OLDFIELD, S. 1988. Buffer zone management in tropical moist forests. IUCN, U. K.
PLANNING BUFFER ZONES MacKINNON, J. and MacKINNON, K. (Eds.). 1986. Managing protected areas in the tropics. IUCN, U.K.
LAKE MANYARA NATIONAL PARK
MWALYOSI, R. B. B. 1991. Ecological evaluation for wildlife corridors and buffer zones for Lake Manyara National Park, Tanzania, and its immediate environment. Biological conservation 57:171-186.
PRINS, H. H. T. 1987. Nature conservation as an integral part of optimal land use in East Africa: The case of the Masai Ecosystem of Northern Tanzania. Biological conservation 40:141-161.
KORUP PROJECT PARK, C.C. 1992. Tropical rainforests. Routlege, U.K.