The Convention on Biological Diversity "encourages the development of technologies and farming practices that not only increase productivity, but also arrest degradation as well as reclaim, rehabilitate, restore and enhance biological diversity and monitor adverse effects on sustainable agricultural diversity. These could include, inter alia, organic farming, integrated pest management, biological control, no-till agriculture, multi-cropping, intercropping, crop rotation and agricultural forestry" (Decision III/11, 15 e).
While several agricultural approaches make sustainability claims, organic agriculture is the only well-defined agricultural management system, including recommended and restricted practices that aim at environmental protection and food production. The decades-long implementation of organic agriculture, including inspection and certification to ensure compliance, as well as the steady growth of organic food sales on the global market, offer a living example of a viable system that reconciles conservation and production needs.
The Codex Alimentarius Commission defines organic agriculture as "a holistic production management system which promotes and enhances agro-ecosystem health, including biodiversity, biological cycles, and soil biological activity. It emphasises the use of management practices in preference to the use of off-farm inputs, taking into account that regional conditions require locally adapted systems. This is accomplished by using, where possible, agronomic, biological, and mechanical methods, as opposed to using synthetic materials, to fulfil any specific function within the system" (WHO/FAO, 2001).
All definitions of organic agriculture converge in recognizing that this food system is based on ecological principles and that it relies on using adaptive management for building long-term farm productivity. As such, the principles behind organic agriculture are in line with the Ecosystem Approach advocated by the CBD (Decision V/6) and its application focuses on functional relationships and processes within ecosystems; enhances benefit sharing; uses adaptive management practices; carries management actions at all level, and where a legislative framework exists, it ensures intersectoral cooperation1.
For practical purposes, organic agriculture guidelines and norms specify minimal requirements to label foods as "organic". These requirements contain mandatory and voluntary practices for organic management. Therefore, throughout the world, the contribution of organic agriculture to biodiversity has different levels of achievements, depending on whether the mandatory requirements only are implemented to obtain certification or whether the broader voluntary requirements are also adopted. As such, biodiversity achievements of organic farms range from pollution reduction (of systems based on agro-chemical substitution) to fully-fledged holistic systems that harbour semi-natural habitats and a wide range of biodiversity.
Generally, farm habitat quality in organic farms is enhanced through practices that build below- and above-ground diversity, with a view to establish ecological processes that serve agricultural production. It must be understood that no single organic agriculture practice alone will sufficiently serve to enhance biodiversity but it is the result of the suite of practices, used in concert, that have the net effect of increasing farm habitat heterogeneity and thus, biodiversity.
Building of soil fertility and avoiding the use of synthetic agricultural inputs (including fertilizers, pesticides and genetically-modified organisms) is common to all organic agriculture norms (e.g. EU Regulation 2092/91, USDA National Organic Programme, the WHO/FAO Codex Alimentarius Guidelines on Organically Produced Foods, IFOAM International Basic Standards). In order to ensure the agro-ecosystem productivity, a set of practices are adopted. The main strategies and their benefits on biodiversity are outlined below.
Biological control and least-toxic approaches to pest management. Pest management in organic systems is achieved through a number of general and site-specific physical, biological and accepted biological pest control methods. The primary strategy for pest management in organic agriculture is preventative, where the use of sound soil fertility management serves to improve the physical, chemical and biological properties of soils, leading to elevated soil fertility and optimal conditions for plant growth. Crops grown in healthy soils tend to be more resistant and resilient to pest and pathogens and require little to no applications of pest control materials (Flint, 1998). The reduction or absence of synthetic soil fumigants, insecticides, herbicides, fungicides, etc. serves to prevent exposure of agricultural and surrounding ecosystems to the toxic effects of pesticide pollution. Because pesticides have a direct suppressive effect on many organisms within the agro-ecosystem, the elimination of pesticide use removes a major obstacle to the diversification process of agro-ecosystems (Gliessman, 1999). In protected area landscapes, the avoidance of pesticide use by organic farmers is conducive to wildlife conservation (see Examples 1 to 4 in Annex).
The use of natural soil amendments. The rational use of soil amendments is a critical aspect of organic system management. The use of soil analysis and nutrient budgets matches agricultural inputs with the nutrient demands of crops in order to make more efficient use of available resources and avoid the pollution problems resulting from the over application of agricultural nutrients. The use of naturally occurring mineral soil amendments (e.g. rock phosphate, sulphate of potash) serves to supply essential plant nutrients while reducing nutrient leaching and/or runoff. Compost is used to improve and maintain soil organic matter levels and, when combined with an appropriate legume/grass cover crop and the incorporation of crop residues, it helps support larger and more diverse populations of soil organisms. Higher soil biodiversity has shown to increase the rate of nutrient cycling, improve soil aggregation and aggregate stability and improve the disease suppression of agricultural soils (Tugel, 2000; Mader, 2002).
Use of adapted genetic resources. While there are no, as yet, specific requirements for the use of genetic resources in organic certification systems, the restriction on use of synthetic inputs and genetically-modified organisms leads organic farmers to use and regenerate locally adapted landraces and genotypes resistant to climatic stress and diseases. It is also economically advantageous for organic farmers to use traditional varieties that are productive under low-input conditions, that can survive adversities and that can grow in marginal environments. The organic market often valorises endangered under-utilized and threatened species, including varieties and breeds that have specific nutritional characteristics (e.g. gluten-free crops). Research on selection, improvement and distribution of open-pollinated varieties is at early stage of development2.
Polycultures (intercropping and strip-cropping). Polyculture is the intentional cropping of multiple species within a farm, in a planned spatial sequence. Intercropping is a direct way of increasing the diversity of an agro-ecosystem by introducing much more structural and chemical variation to smaller areas of the agricultural landscape and thereby encourages more complex interactions between crops and other organisms (Gliessman, 1999). Strip cropping, where strips of one crop are planted next to strips of another is a less management intensive form of multi-cropping. When compared to monocultures, polycultures have consistently shown lower populations of pest insects and weed populations. Increases in the variety of food sources, the creation of micro-habitats as well as the increased difficulty of pest populations within polycultures to locate dispersed patches of crop hosts serve to limit the growth of pest populations and stabilize predator-prey and parasitoids-host population dynamics (Vandermeer, 1989; Altieri, 1999).
Crop rotation. Crop rotation is the intentional planting of crops in different areas within a farm, in a planned temporal sequence. Crop rotations serve to provide new above- and below-ground habitats, as each new crop has a distinct chemical and biological make-up, introducing new vegetation types to the landscape and eventually, crop residues to the soil ecosystem. Different crop residues promote or inhibit different soil organisms which may have inhibitory or growth promoting effects to subsequent crops or pests. By interrupting the continuous presence of a crop host, crop rotation serves to break the build-up phase in the cycles of weeds, insects and diseases, thus eliminating the need for pesticide application. Fallow periods, where ground is left uncultivated for an extended period of time (a few months to one year), allow a limited amount of secondary succession to advance and hence, the recovery of the diversity of both terrestrial and below-ground species.
Cover cropping. Cover cropping is a type of non-crop cover grown specifically for soil improvement purposes. Both annual and perennial cover crops may be used, with varying benefits to above- and below-ground biodiversity (Sustainable Agriculture Network, 2001). Cover crops may provide a physical temporary habitat for many different species of ground-nesting birds and small mammals as well as nectar and pollen sources for many species of insects. The habitat value of cover crops varies by species and variety; therefore, cover crops must be carefully selected to meet specific management objectives. Cover crops root system improves water penetration and prevents soil erosion. Cereal cover crops planted as an over-wintering rotation may also capture plant available nitrogen, thus preventing nutrient leaching into sensitive water ways. Cereal and legume cover crop mixes can be an important source of organic matter when incorporated into the soil. The use of perennial cover crops in orchards and vineyards is an effective means of enhancing the biodiversity and productive capacity of cropping systems and avoiding the labour and environmental risks associated with herbicide use. In Mediterranean climates, economic and agronomic advantages may be gained through the use of native perennial grass species in vineyards having a summer dormant growth cycle. As a result, they provide the advantages of a perennial cover crop without the disadvantage of excessive competition or water use (Costello, 1999).
Minimum tillage. Although reduced tillage is not a required practice in certified organic agriculture, it is a practice that is consistent with the objectives of organic system management and encouraged by most certifying programmes. The minimization of tillage will often lead to increased earthworm abundance and activity, increased populations and diversity of decomposer organisms and an associated increase in the organic matter content and aggregate stability of soils. When compared to conventionally tilled soil, low and no-till systems exhibit improved nutrient and water holding capacities, improved nutrient cycling and more desirable physical properties. The enhanced biodiversity of these systems lend themselves to improved cropping performance and greater resistance and resilience to various kinds of disturbances. Farming systems using no and low-till approaches are also less likely to incur soil erosion and require less inputs of energy (Vakali, 1999; Magdoff, 2000).
Impact of organic agriculture on biodiversity
Numerous studies have provided evidence of the positive role organic farming plays in both above and below-ground biodiversity, reduction of agricultural pollutants and the preservation and restoration of on-farm biodiversity. Long-term comparisons with conventional agriculture systems demonstrated that organically farmed soils showed higher biological activity (30-100 percent) and higher total mass of soil micro-organisms (30-40 percent). Nitrate leaching rates on organic farms were shown to be significantly lower (40-64 percent) and energy use to be more efficient (30-50 percent) on a per hectare basis (FAO, 2002). Studies taking place between 1988-2001, comparing conventional and organic agricultural practices in both the US and UK have repeatedly shown higher levels of wild biological diversity (e.g. birds, arthropods, weedy vegetation and soil organisms) in organically managed farms (Benton, 2003; Stolton, 1999). The influence of organic agriculture and landscape diversity was further illustrated in over 30 separate studies contrasting organic and conventional farms in the UK between 1983 and 2000. The findings showed that organic systems consistently had higher levels of: wild plants (5 times more biomass and 57 percent more species); arthropods, non-pest lepidoptera and spiders; and birds. In particular, 25 percent more birds were found at field edges, with 44 percent more in-field birds in the fall-winter, and higher numbers of breeding pairs of rare bird species (Soil Association, 2000).
Although biodiversity conservation is implicit in most national and international organic standards, explicit biodiversity conservation requirements for non-agricultural purposes remain under-developed at this time. In recognition of the need to establish standards for biodiversity conservation in organic agriculture, the 2002 revision of the IFOAM3 Basic Standards for Organic Production and Processing outlines a set of recommended practices that may serve as a foundation for establishing certification standards for biodiversity conservation in agriculture. These standards' section on "Organic Ecosystems" requires measures for maintaining and improving landscape and enhancing biodiversity quality as well as prohibition on clearing of primary ecosystems. General recommendations are made on the maintenance of an appropriate portion of the farm as wildlife refuge habitat through, inter alia: the establishment of hedges, hedgerows and ecologically diversified field margins as well as areas with ruderal flora and wildlife corridors that provide linkages and connectivity to native habitats (IFOAM, 2002).
Agro-ecosystem heterogeneity (and therefore biodiversity of the landscape) may be increased through the conservation, management and/or restoration of various on-farm landscape features such as soil, water and native non-crop vegetation. The techniques outlined below require varying degrees of modifications of current agricultural practices. Not all organic systems implement habitat enhancement practices and there is scope for improving organic standards for biodiversity conservation. Additional research in restoration ecology will be necessary to make specific recommendations on how to best restore native vegetation to altered landscapes in particular areas. Also, the cost implications of restorative measures need to be compensated for the effective uptake of truly holistic systems, especially in the neighbourhood of protected areas.
Minor farm habitat enhancement strategies. A number of on-farm management techniques may be used to protect or enhance on-farm habitat for wild biodiversity. Leaving natural snags and the erecting of artificial perches or houses for native song birds, raptors and bats may provide on-farm roosting, nesting sites and refuges to support populations of wildlife (Imhoff, 2003). Where mechanical equipment is used for on-farm vegetation management, harvest or clearing of land, the postponing of such operations until after ground-nesting fledge lings have emerged may significantly decrease nesting losses (Edge, 2000).
Development of wetlands and multi-purpose farm ponds. The extensive loss, worldwide, of natural wetlands makes agricultural wetlands most important to wildlife. In particular, flooded rice fields have an enormous significance in creating temporary wetlands for reproduction and feeding of migrant birds and other wildlife (e.g. reptiles, amphibian). These important agriculture wetland functions are best addressed by organic management that avoids using synthetic pesticides and fertilizers (see Example 2 in Annex). In other environments, the development of farm ponds may serve to attract diverse wildlife and may be an economical source of water for small farmers. Planted with native aquatic vegetation, farm ponds provide food and cover, resting and breeding areas for wildlife. Migratory waterfowl may be attracted to these ponds for food resources and may become occupied year around with salamanders, turtles, shorebirds and certain species of ducks. Wide ranging animals may also use small farm ponds for watering holes. In agricultural areas reliant on furrow irrigation, tail water pond systems are an effective way of recycling irrigation water, trap and filter sediments and provide year around water habitat for wildlife (Imhoff, 2003; WFA, 2003).
Organic rice cultivation and migratory waterfowl conservation, California, USA
Three to five million ducks, geese and swan winter in California. During their annual cycle, large number of shorebirds, cranes, pelicans, egrets, herons, ibises and songbirds utilize the Central Valley wetlands. The total annual water bird count (including migrants) in the region has been estimated as high as 10-12 million. In the Central Valley of California, over 95 percent of the wetland ecosystems have been lost to agriculture and other forms of development in the last 100 years. The agricultural wetlands created by rice cultivation have provided an important mitigation for the extensive loss of natural wetland habitats. California rice fields provides for over 141 species of birds, 28 species of mammals and 24 species of amphibians and reptiles. Thirty of these species (27 birds, 2 reptiles and 1 amphibian) are listed as endangered, threatened or species of special concern by the California or federal government. No other crop comes close to providing this level of benefit to such a vast array of wildlife. Since 60 percent of all the waterfowl on the Pacific Flyway winter in the Central Valley, both natural and agricultural wetlands are indispensable to them. Some 230 000 shorebirds winter annually in the Central Valley and, during fall migration, their numbers can swell to over 400 000. Rice fields provide feeding habitat for nearly 70 percent of these migrant shorebirds during their journey south (Page et al. 1994). Without rice farming, wetland habitats would be reduced by as much as 45 percent, with disastrous effects on waterfowl and a host of other wetland-dependent species. Equally important, the waste grain left after the rice harvest is a major source of food for a number of waterfowl species. Rice farmers also benefit by receiving large amounts of natural fertilizer left behind in the droppings of these feeding flocks. In addition to the wetland conservation and the leaving of crop stubble for wildlife forage, many rice growers in the region have adopted organic farming practices in order to capture a price premium for their products and protect the habitat value of these artificial wetlands.
Source: California Rice Commission, 1997
Leaving strips of unharvested crops for wildlife. Leaving some unharvested portion of fields for wildlife forage has proven a highly effective means of maintaining or enhancing population levels of many species. Food plots provide over winter food for wildlife which is particularly useful during times of stress or in areas when habitat modification has been significant. Location, size and spacing are several factors to consider when planning food plots. Although plot size and shape may vary according to the type of planting and the intended wildlife use, it is commonly recommended that wildlife lots be scattered over the entire property if possible. Corn is the most common forage plant for wildlife, but annual rye, millet and buckwheat are also beneficial for both mammals and waterfowl. In temperate climates, perennial crops such as clover, alfalfa and other legumes can be planted to provide food for turkeys, songbirds, rabbits and deer in the summer. In addition, sunflower beds along field edges provide more food for birds and small animals (Mississippi Fish and Wildlife Foundation, 2003; Edge, 2000). Constraints of this method of wildlife habitat enhancement may include unintended attraction of animals to production areas, leading to crop losses and artificially elevating the carrying capacity of lands resulting in population declines upon discontinuance of practice.
Native hedgerows. Intentional plantings of complex assemblages of native trees and herbaceous and woody perennials along field margins and areas of marginal or highly erosive soils is an effective means of enhancing biological diversity and the production capacity of agro-ecosystems. Hedgerows introduce greater micro-habitat diversity to agriculture lands and can reduce the velocity of winds and runoff when planted along field margins. As a result, hedgerows reduce soil degradation, increase crop yields by conserving soil moisture, increase livestock productivity by buffering extreme temperature variations (Le Coeur et al., 2002). The functional role of hedgerows is being researched to enhance biological control of agricultural pests through specific hedgerow species assemblages (Bugg and Picket, 1998; Landis et al., 2000). Complex hedgerows provide shelter and food (e.g. a diversity of pollen, nectar and seeds) which serve to elevate the carrying capacity for wildlife in an otherwise simplified agricultural landscape. They also serve as a corridor for the movement of animals between intact patches of habitat that have been interrupted by agricultural development (Le Coeur et al., 2002). When hedgerows are planted between natural ecosystems and agricultural lands, they can also help to reduce the potential impacts of agriculture on native plant and animal communities by modifying winds, moisture levels, temperature levels and solar radiation (Gliessman, 1999).
Biodiversity associated with ancient hedgerows in the United Kingdom
Hedgerows are the most significant wildlife habitat over large stretches of lowland in the UK and are essential refuge for a great many woodland and farmland plants and animals. Over 600 plant species (including some endemic species) 1 500 insects, 65 birds and 20 mammals have been recorded at some time living or feeding in hedgerows. Currently 77 percent of the land area of the UK is under some form of agricultural land use where ancient hedgerows play a central role in supporting wildlife species through providing food, shelter, breeding grounds and migratory pathways to other patches of native vegetation. Hedgerows in these areas are preferred habitat for numerous birds, insects, small mammals and amphibians. The loss of species abundance in the UK is positively correlated with the intensification of agriculture and the removal of historic hedgerows. They are a primary habitat for at least 47 extant species of conservation concern in the UK, including 13 globally threatened or rapidly declining ones, more than for most other key habitats. They are especially important for butterflies and moths, farmland birds, bats and dormice. In recognition of the important role hedgerows play in the preservation of biodiversity in the UK, the Environment Act 1995 introduces an enabling power to protect important hedgerows throughout Britain.
Source: Scottish Executive, 2003
Vegetative buffer strips. Vegetative buffer strips are mixed native vegetation of various widths that are planted along field margins, irrigation and drainage ditches, tail water ponds or between agricultural areas and sensitive native habitats to serve both an environmental protection and biodiversity enhancement function. Being climate adapted, regionally specific native grasses and woody perennials will need only minimal care until they become established (many perennial native grasses and shrubs will also re-seed themselves). Grass species often have extensive root systems that may serve to prevent erosion and catch sediment and nutrients, thereby filtering runoff and improving water quality. Such forms of vegetation management serve to increase the complexity of vegetation in agricultural landscapes, providing diverse pollen and nectar and micro-habitat for native species of insects, birds and small mammals. In organic agriculture, vegetative buffer strips also function to protect from the negative impacts of neighbouring conventional farms, as they catch sediment and excess nutrients or agricultural chemicals. Vegetative buffer strips can also serve to reduce the spread of fire from the agricultural areas to the native vegetation. Planting complexes of regionally specific native perennial grasses and other herbaceous and wood perennial species in buffer strips can be an effective and inexpensive way to address the common management problem of weed control in these areas.
Riparian corridors. Due to the fragmentation of habitat common in agricultural areas, the maintenance or re-establishment of corridors between intact habitat remnants is an important component of enhancing the habitat value of agricultural areas. Riparian vegetation connects terrestrial and aquatic ecosystems creating extensive ecotone areas and serve as corridors for the movement of plants and animals between areas of undisturbed habitats. Riparian corridors are considered to be one of the most diverse and complex terrestrial habitats on earth (Naiman, 1993). Riparian corridors play a critical role in filtering sediments, providing organic matter to aquatic organisms, regulating water temperatures and dissolved oxygen levels, sequestering excess nutrients and absorbing surface runoff and preventing or reducing flood damage (ISU, 2001). Loss of riparian vegetation can significantly alter the function of these systems leading to loss of migration corridors, colonization of invasive exotic plant and animal species, stream bank erosion, alteration of streambed habitat, reduced ability to assimilate chemical and soil losses from agriculture lands and associated degradation of water quality (Wild Farm Alliance, 2003b). Maintaining the quality of the water mitigates the need for watercourse clean-up, and encourages wildlife and aquatic life. The UK Soil Association standards for riparian buffer zones for water quality protection recommend a minimum of 2 metres buffer of riparian vegetation on each side of a stream (Soil Association, 2003). In Northern California agricultural areas, a minimum of 30 metres on both sides of the stream is often recommended to provide significant ecological values such as wildlife corridors and biological control of agricultural pests (Imhoff, 2003).
The role of riparian corridors in agricultural areas, California, USA
The results of a recent study comparing the species abundance and diversity of mammalian predators in three types of riparian corridors adjacent to California vineyards indicate that both the number and composition of mammalian predators change based on different widths of natural vegetation along creeks. A greater diversity of all mammalian predators and more native mammal predators were found in wide riparian corridors (more than 30 metres of natural vegetation on each side of the creek), compared to narrow corridors (vegetation ranging from 10 to 30 metres on each side of the creek) or denuded corridors (very little natural vegetation along the creek). A separate study also indicated that overall levels of vineyard use by these mammal predators was very low compared to riparian corridor use, a result which indicates the preferential use and importance of these riparian zones for wildlife movement between undisturbed patches of habitat.
Source: Hilty et al., 2002
Buffer zones. Buffer zones link protected areas to one another through the preservation of habitat. By definition, these areas are intended to remain under wild cover or be managed in such a way as to ensure that human land use is compatible with the maintenance of a high degree of biological connectivity. Buffer zones are used in protected areas to delineate areas where human activities such as grazing, non-extractive agroforestry, under-story cropping, hunting and gathering may occur. Depending on the species selected and how the area is managed, buffer zones may serve to reduce the pressures placed on intact native vegetation for the production of foods and fuels for human consumption. Buffer zones play an essential ecosystem function by allowing for the dispersal of plants and the movement and migration of animals between intact habitat types. To be effective, buffer zones must offer suitable habitat to wildlife and therefore the preservation of such environments free of pollutants along such pathways is of critical importance.
Under-story cropping. Under-story cropping is one the most effective ways to conserve native habitats and biological diversity of tropical forest areas that are used for agricultural production. Many traditional cropping systems integrate crops into the under-story vegetation of thinned primary or old secondary forests for the production of coffee, cacao, yerba mate and some tea varieties (Rice, 1996). Those traditional systems, which minimally modified the native habitat, are currently replaced by intentionally planted polyculture systems composed of native and non-native species that serve various ecologic, economic and cultural functions. In the last decade, the biodiversity value of shade cropping and its role in the sustainable management of protected area landscapes has emerged and a return to traditional polycultures is being achieved through organic agriculture and other biodiversity-friendly approaches. Under-story cultivations present enormous opportunities for the conservation and enhancement of protected areas and buffer zones while securing food and livelihoods for millions of people living in tropical forests (see Examples 3 and 4 in Annex).
Organic and shade-grown coffee in El Triunfo Biosphere Reserve, Mexico
Coffee plantations that are designed to mimic natural systems may have even higher numbers of species than natural forest. Central American coffee agroforests are second only to moist tropical forests for species diversity (Perfecto, 1996). Studies of the Smithsonian Migratory Bird Centre indicate that at least 180 species of birds live in Mexican shade coffee and cocoa fields and that 90 percent fewer bird species live in Colombian sun coffee plantations where original forest cover has been reduced or removed. The biodiversity of shade coffee ecosystems is currently under threat as a result of changes in production practices. In response to low coffee prices, many of the traditional shade coffee plantations are now intensifying production with the use of higher-yielding sun-tolerant coffee varieties that do not require the native tree canopy. In transitioning to sun tolerant varieties, forest canopy is thinned or removed, plantation life is reduced, use of agricultural chemicals is greater, and the risk of erosion is higher. In the highlands of the El Triunfo Biosphere Reserve in Sierra Madre Occidental of Mexico, Conservation International is supporting a Conservation Coffee Programme. The purpose of the project is to protect forest biodiversity while supporting economic development for local producer cooperatives through the encouragement of understory and certified organic coffee production in the buffer zone of the Reserve. Currently 1 250 farmers (working approximately 3 500 ha of organic coffee) are involved in the project (GEF, 2002).
1 For an analysis of the application of the ecosystem approach in organic agriculture, see Settle, 2003.
2 For a study on the contribution of organic agriculture to genetic resources, see El-Hage Scialabba et al., 2003.
3 International Federation of Organic Agriculture Movements (IFOAM).