For each plant species grown as a crop we eat, untold numbers of other species participate in its success. A cubic meter of soil houses an enormous abundance of life, on the order of several billion living organisms. One function of these microbes is to help fix nitrogen, an essential plant nutrient, into the soil. Mycorrhizae, a group of fungi that create vast underground scaffoldings (the length of mycorrhizal strands contained in a cubic meter of soil would measure more than a thousand miles if stretched out end to end (Pennisi 2004)) provide an additional service. The fungal strands attach to plant roots from which they draw nutrients and water. In so doing, they prevent soil erosion and have been shown to be capable of binding toxic heavy metals such as cadmium, thus preventing their absorption into the edible parts of crops. Soil organisms are not all microscopic of course. That same cubic meter of soil also holds tens of thousands of insects, worms, and burrowing vertebrates, all of which shape and renew the soil.
The diversity that nurtures crops extends above ground as well. Beneficial insects, such as Green Lacewings whose larvae eat a variety of plant parasites, protect crops against infestations. Another 100,000 species, including insects, birds, and other animals, serve as pollinators. Each year about $15 billion of crops rely on bees for pollination in the U.S. and studies show that the percentage of food crops depend on pollination is rising (Aizen 2008). Yet, populations of pollinators, particularly honeybees, are in sharp decline. In 2006, losses of up to 70 percent of hives were reported in 24 states across the U.S.
