Healthy agriculture and ecosystems ultimately depend on preserving biodiversity at the base of the food chain, where a billion organisms can live in a handful of soil.

Ask most people about biodiversity and they will most likely talk about endangered birds, mammals and fish. But the concerns we share for preserving diversity on a grand scale should also apply to soil macro- and microfauna, including microbes.

Researchers, farmers and policymakers have long sought to develop agricultural systems that are self-sustaining, low input, diversified and energy efficient. Maintaining soil biodiversity is essential to that goal, and soil macrofauna are increasingly recognized for their positive effects on nutrient cycling, regulating pest populations and encouraging plant growth.

Soil macrofauna include the full range of "creepy-crawlies" most of us know by their vernacular names as earthworms, termites, ants, spiders, grasshoppers, centipedes, millipedes and beetles. Common microfauna are nematodes and rotifers (tiny wormlike organisms), mites, and single-cell protozoa. Another level down is the realm of soil fungi and bacteria. Altogether, more than a billion organisms can live in a handful of soil.

While not nearly as photogenic as the noble elk, the soaring eagle or the leaping salmon, soil is where life on earth is generated. Using the energy absorbed from the sun to combine water with carbon dioxide drawn from the air, soil populations produce the sugars, starches and proteins that sustain all life on the planet. Healthy soil regulates the flow, storage and quality of water. It supports the crops that produce 99% of our fiber and food. Maintaining healthy diversity in soil macro- and microfauna is no less important that protecting habitats for river dolphins, rehabilitating mangrove forests or saving critically endangered saiga antelopes. The fact is, the base of the food chain that supports earth's millions of species is in soil.

As Chutinan Choosai, an entomologist at Khon Kaen University, and her coauthors explained in Termite mounds and dykes are biodiversity refuges in paddy fields in north-eastern Thailand, which was published in Environmental Conservation in 2009, rice lands illustrate how this complex interaction of organic life and inorganic matter works.

Rice paddy is one of the most common land uses across Asia and in expanding parts of Africa. In northeastern Thailand, 35% of the landscape is paddy field. Rice paddy in general does not encourage soil biodiversity, and northeast Thailand is a particularly harsh environment for organisms in the soil. It is sandy and often saline, with very low fertility. It cycles through a cool dry season, an extremely hot dry season and a rainy season during which most of the landscape is flooded. What research shows, however, is that these radically altered landscapes provide refuges in the form of bunds (soil embankments with an average height of 40 centimeters) and termite mounds. Bunds and termite mounds provide a safe haven for soil macrofauna during the rainy season, when paddy fields are flooded, as well as the shade and humidity necessary for their development and survival during the dry season.

As ecosystem engineers, termites play a prominent role in maintaining biodiversity. They modify soil properties by displacing soil organic and mineral compounds from one site to another, and by producing biogenic structures with specific physical, chemical and biological properties. Soil ecologists sometimes refer to these structures as "fertility islands," which create spatial variability in soil properties at the ecosystem scale.

Ants and earthworms modify soil particle size and the dynamics of soil organic matter, and other soil macrofauna play important roles in promoting litter decomposition and mineral nitrogen dynamics. Termite mounds and bunds provide a haven in which soil macrofauna predators like ants and spiders can shelter and thus constitute a sustainable resource for controlling certain rice pests. Finally, insects are themselves consumed as food by people in many parts of the world. In northeast Thailand some species of ants, grasshoppers and crickets are common culinary ingredients or side dishes and valuable sources of protein.

Because soil fauna provide important ecosystem functions and services, their conservation must be integrated into sustainable agricultural systems. In an important step toward that end, the Tropical Soil Biology and Fertility (TSBF) Institute of the International Center for tropical Agriculture (CIAT) recently completed an 8-year major global initiative, which was aimed at finding ways to enhance agricultural productivity through improved management of below-ground biodiversity.

Meanwhile, in the course of its work on agricultural water-management solutions, the International Water Management Institute incorporated the International Board for Soil Research and Management in 2001, further strengthening its expertise in soil research. Also, the newly proposed CGIAR Mega Program Durable Solutions for Water Scarcity and Land and Ecosystem Degradation integrates the work of CGIAR Centers and their partners on soil into a comprehensive research program addressing the intersection of land, water and ecosystems.