Recent archaeological evidence of Hohokam land-use practices may provide insight into how large populations can live sustainably in dry lands. The Hohokam did it from at least 500 to 1450 A.D. by being farmers and environmentalists at the same time. As farmers, they adapted their subsistence strategies to specific environmental conditions. As environmentalists, they used resources conservatively and minimized their impact on the ecosystem on which they depended.

Hundreds of miles of prehistoric canals in the Salt, Gila, and Santa Cruz river basins are the most dramatic evidence of the Hohokam's sophisticated management of their crucial water resource. These canals are located in the Sonoran Desert of southern Arizona in the United States (see map). Irrigated fields along these canals, however, are just part of a complex agricultural system that adapted its land- and water-use strategies to a range of environmental conditions to assure food, fiber, fuel, and building materials for a growing population.

The Hohokam used a complex network of canals to irrigate fields surrounding the area's permanent rivers. Further from the permanent water sources, farmers diverted seasonal flood waters to irrigate their fields, or used dams, terraces, rock walls, and rock mulches to concentrate and retain runoff in cultivated areas.

In addition to growing crops, such as corn, cotton, and tepary beans, the Hohokam also gathered a variety of plants from the surrounding desert. The line between cultivated crops and wild plants was indistinct. Weeds, including chenopods, amaranths, and spiderling, flourished in Hohokam fields, partly because of the improved moisture conditions of the fields, and partly because the Hohokam protected them and probably even sowed or transplanted them. The greens and seeds of these plants would have provided an alternative source of food, especially in years where other crops performed poorly. In marginal fields that received little water, the Hohokam cultivated drought-hardy agave, a wild desert plant that provided food, fiber, and building materials. The Hohokam also transplanted and tended cholla and prickly pear cacti in field borders, fallow ground, and marginal fields. They also trapped or hunted many small mammals that would have been attracted to the fields.

Many Hohokam land-use practices amounted to a sort of environmental protection plan. Cultivating and protecting wild native plant species in irrigated fields helped preserve those in surrounding wild areas by reducing the likelihood that people would need to harvest them heavily. Since the Hohokam did not keep domestic animals, they further pro-tected wild areas from the pressures of grazing.

The Hohokam seem to have recognized the value of trees in their landscape, due at least in part to the nutritious beans produced by many leguminous desert tree species. They protected trees in fields and allowed them to grow densely in hedgerows in irrigated areas. They minimized fuelwood consumption (thereby protecting trees) by cooking food slowly with heated stones in covered pits, often shared by several households.

Finally, Hohokam irrigation systems provided a sustainable source of soil fertility. The irrigation canals and runoff catchment systems harnessed the fertile sediment carried by the running water. The fine sediment added essential nutrients and improved the texture of soil for retaining water and nutrients. This sediment was both added to fields along with irrigation water, and manually spread on the fields during periodic cleaning and clearing of the irrigation canals.

Well-adapted strategies for producing and gathering a wide variety of crops in diverse conditions and zones provided the Hohokam a stable basis to assure subsistence and reduce risks in an unpredictable environment. If flooding from excessive rains destroyed some fields, or if drought prohibited some crops from maturing, the Hohokam would have had others to fall back upon. In order to sustain this diversity of strategies, the Hohokam had to be organized to spread enough people over various zones to implement land-use strategies and maintain canals, while not overpopulating any given area. Organization also would have allowed for sufficient specialization and cooperation to exploit the different zones while spreading the risks. By using agricultural practices that minimized destructive impact on their delicate environment, by conservative use of plant resources, and by having a built-in system for replenishing soil fertility, the Hohokam were able to sustain their civilization for more than 1,000 years in a marginal environment.