Agroecosystems are the living communities of soil, plants, and animals that constitute our farms, croplands, orchards, pastures, and rangelands. More than 90% of all the crops and livestock we consume as well as livestock feed is produced by agroecosystems. They also contribute fiber crops such as cotton, flax, hemp, and jute, which we use for clothing and textile manufacturing.

Unlike other ecosystems, agroecosystems do not occur naturally; they are created and maintained by humans. They are former prairies or forests or even arid areas that people converted to produce crops or raise livestock. No matter how they came about, our lives depend on agroecosystems.

Population Trend, 1950-2150 (click on image to enlarge)

For the past 40 years, as the global population doubled, agroecosystems kept pace with our demands for food, feed, and fiber. In fact, agroecosystems provide, on average, 24% more food per person today than they did in 1961. But by 2020 agroecosystems will have to supply food for an estimated 1.7 billion more people. Can agroecosystems continue to keep up? What about the years beyond 2020 — are today's farming methods sustainable into the future?

How much land do we farm globally?

Agroecosystems are defined as "areas where at least 30% of the land is used for cropland or highly managed pasture." They cover approximately 28% of Earth's land area, excluding Greenland and Antarctica — a total of 4.92 billion hectares. Of this, about 30% is cropland and 70% is pasture. Irrigated agroecosystems comprise little more than 5% of the total, but produce about 40% of the world's crops.

The Global Extent of Agriculture (click on image to enlarge)

Between 1966 and 1996, the total amount of agricultural land worldwide increased about 8%. But, in many industrialized regions — the United States, Canada, and Europe, for example — suburban sprawl and industrial development engulfed farm land, shrinking the area covered by agroecosystems in these areas by 49 million hectares.

Agriculture isn't just a rural activity. It takes place in urban areas, too. Approximately 800 million city-dwellers around the world are actively involved in urban agriculture, planting crops in back yards, vacant lots, on rooftops and roadsides — anywhere they can find space. In developing countries particularly, urban agriculture often provides a subsistence income.

What are some of the most important goods and services agroecosystems provide?

What’s the environmental cost of growing more food?

Since the 1950s, especially in industrialized countries, use of intensive agricultural methods (adding chemical pesticides, herbicides, and fertilizers as well as irrigating and using heavy machinery and genetically engineered seeds) has become widespread. Intensive cultivation techniques are generally credited for the 24% increase in food supply per person since 1961, despite world population growth from 3 to 6 billion people during that period. With the population expected to increase by another 1.7 billion people in the next 20 years, however, we'll need more food.

But intensive agriculture is depleting the richness of our soils and polluting our water. Soil erosion and nutrient depletion in particular may be undermining the long-term productivity of more than 50% of the worlds' agricultural lands. Competition for water (expected to increase as unpolluted freshwater supplies diminish) will only magnify problems that constrain food production.

And food production levels depend greatly on the condition of the soil in which crops are grown. Productivity has already been reduced on 16% of agricultural land, mostly in Africa and Central America. Even in the United States, more than 20 tons of topsoil may be lost from a single Great Plains agroecosystem yearly. And global warming increases the threat of desertification, especially on severely degraded agricultural lands.

The chance of a crop failure that could detrimentally affect nutrition on a wide scale in the United States is unlikely. We may not need to worry about widespread hunger in the United States — a country rich enough to import the food we need — but we do worry about people in other countries and those in our own who cannot afford to buy the available food.

If food shortages drive up prices, how can we ensure that all U.S. citizens are able to afford more expensive food? If the solution to the higher global demand for food is more intensive agriculture, can we live with more agricultural pollution in our freshwater supplies?