Agriculture Benefits of Biodiversity to

People depend on biodiversity for healthful, sustainable agricultural systems. Biodiversity is the ultimate source of all cultivated plants and domesticated animals, and it provides essential assistance in maintaining crops and pastureland. Farmers save billions of dollars each year thanks to the services of pollinators, microbes that help create productive soil, and natural predators that reduce the need for pesticides.

For thousands of years humans have used the natural diversity of plants and animals to increase the productivity of crops and livestock. Traditionally, at the end of a harvest the farmer will select seeds from the "best" plants—those that grow well in the farmer's fields (that is, those adapted to the local climate or those most resistant to prevalent pests or disease). Livestock ranchers make a similar effort, breeding animals, say, for faster growth or leaner meat. This "selective breeding" depends upon the existing genetic diversity of individuals in a species to create better strains or livestock. As agriculture has modernized over the last fifty years, new methods have developed to achieve these goals.

Genetic engineering enables scientists to create new breeds rapidly by inserting specific genes into a plant or animal to obtain a desired trait. Unlike selective breeding, however, genes can be selected from any species. For example, "Bt corn" is modified by adding a gene from the soil bacteria Bacillus thuringien-sis, which allows it to produce Bt toxins, an insecticide against the European corn borer. Geneticists look to nature for inspiration when creating new breeds, and biodiversity is their genetic library. Despite these new techniques, existing crop strains and domesticated animals, their wild counterparts, and closely related plants or animals are still essential for breeding. Unfortunately, we are rapidly losing these sources of genetic inspiration. As agriculture has become industrialized, we are sacrificing the diverse cultivars (or landraces) and breeds that have developed around the world. Habitat loss threatens the regions where domesticated crops and animals originated. Conserving this biological heritage is critical to future agricultural production.

Biodiversity acts as insurance for agriculture. Changing climates may require drought-resistant or salt-tolerant crops, and biodiversity helps ensure that crops can adapt to future environments. Although humans have used more than 12,000 wild plants for food (Burnett, 1999), today 20 species support much of the world's population. Although there are 235 species of potatoes, only seven are cultivated. Those other species may one day become a major source of food. There are also many cases in history when a widely grown crop has failed because of disease, with devastating consequences. One famous example is the Irish potato famine, which led to the deaths of a million people. In the mid-nineteenth century, a blight (or funguslike pathogen) destroyed much of the crop. European potato crops were particularly susceptible to infection, since they had all originated from only a few sources and thus were genetically very similar. To combat the disease, a long search began to find a plant resistant to the blight. By the early twentieth century a related plant in Mexico provided the solution, and hybridizing that plant with potatoes produced a resistant strain. Unfortunately, it was not a permanent solution. Today potato blight is once again a concern, and the solution likely lies in existing biodiversity. As the world's crops become increasingly homog enized, it is important to remember the lessons we have learned: systems with higher biodiversity are more resilient, and ultimately biodiversity may solve these crises.

Biodiversity provides many services to agriculture, such as pollination, soil microbes, and natural predators. Approximately 90 percent of flowering plants depend on pollinators to reproduce, and pollination is critical to most major crops around the world (Buchmann and Nabhan, 1996). Pollinators play such a key role for crops that their loss is considered a threat to the security of the world's food supply. Insects—especially beetles, bees, and wasps—are the largest group of pollinators; however, some birds and bats are also important pollinators. Studies have shown that as pollinators disappear there is a loss in yield and harvest quality in many crops, from blueberries to pumpkins. Even crops that don't need pollination to reproduce, such as cotton, produce increased yields when pollinated. Economic losses to crop yields in the United States from the decline of honeybees alone are estimated at $5.7 billion a year (Southwick and Southwick, 1992). Replacing pollination with other methods is virtually impossible. For instance, greenhouse tomatoes were originally hand-pollinated, but that tedious process has been mostly replaced by commercially raised bees.

Successful farming depends on healthy soils, too, and it is biodiversity that helps form soil and improve it for crop production (Pimental et al., 1995). Bacteria, algae, fungi, worms, and an array of invertebrates living in soils help recycle and redistribute nutrients. They aerate soil, keep nutrients close to the surface, moderate water flow, and as a result, enhance plant productivity. Among these organisms, nitrogen-fixing bacteria are particularly important to agriculture, as nitrogen is essential to plant growth and is often a limiting factor. These bacteria are the only organisms that can convert atmospheric nitrogen into forms that plants can use. Certain plants (such as soybeans) harbor these bacteria in their roots as symbionts. During fallow periods, these plants are still used to help naturally enrich soils. Fertilizer, the human equivalent of nitrogen fixation, is highly inefficient compared with the natural process. It is expensive to produce and much of it doesn't reach its target, washing away instead and polluting aquatic systems.

Like natural fertilizers, natural pest control is important to agriculture. Pests destroy an estimated 25 to 50 percent of the world's crops each year (Pimentel 1991). Without the natural predators that control agricultural pests, these figures would be even higher (Nay-lor and Erlich, 1997). Natural pest control also has many advantages over chemical controls such as pesticides and herbicides. Pesticides are usually nonselective, killing both the pest and helpful organisms such as pollinators. Pesticides can create a "new problem," as pests may develop resistance over time, forcing farmers to change to another chemical to combat the same pest. Like fertilizers, application of pesticides and herbicides is inefficient. Realizing their limitations, farmers are turning to biological methods of controlling pests.

—Melina Laverty

See also: Agriculture and Biodiversity Loss: Industrial Agriculture; Agriculture, Origin of; Bacteria; Nitrogen Cycle; Soil; Topsoil Formation Bibliography

Buchmann, Stephen L., and Gary P. Nabhan. 1996. The Forgotten Pollinators. Washington, DC: Island; Burnett, John. 1999. "Biodiversity, Agricultural Productivity, and People." In The Living Planet in Crisis: Biodiversity Science and Policy, edited by Joel Cracraft and Francesca T. Grifo, pp.173-196. New York: Columbia University Press; Naylor, Rosamond, and Paul Erlich. 1997. "The Value of Natural Pest Control Services in Agriculture." In Nature's Services:

Societal Dependence on Natural Ecosystems, edited by G. Daily, pp. 151-174. Washington, DC: Island; Pimental, David, et al. 1995. "Environmental and Economic Costs of Soil Erosion and Conservation Benefits. Science 267: 1117-1123; Pimentel, David, ed. 1991. "Introduction." In Handbook of Pest Management in Agriculture, 2d ed., vol. 1, pp. 3-11. Boca Raton, FL: CRC; Southwick, Edward E., and Lawrence Southwick, Jr. 1992. "Estimating the Economic Value of Honey Bees as Agricultural Pollinators in the United States." Economic Entomology 85, no. 3: 621-633; Vietmeyer, Noel. 1986. "Lesser-known Plants of Potential Use in Agriculture and Forestry." Science 232: 1379-1384.

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