Agroforestry practices suited to the dryland regions of the southwestern United States and northwestern Mexico are reviewed in this summary. More specifically, silvopastoralism, home gardens, windbreak plantings, and multiple-use ofriparian ecosystems are briefly discussed in terms of their role in sustainability, where they are found, how they function, and their benefits to people. While production benefits are emphasized, these functions cannot be separated from the environmental benefits gained from these agroforestry practices.

Seasonal agricultural crops and orchards typical of Southwestern home gardens are planted near an eastern Arizona home. (Photo by Peter Ffoliott)

Silvopastoralism

Silvopastoralism is the most commonly encountered agroforestry system in the region. In reference to the southwestern United States, there are 41.7 million acres of commercial forests, 65 million acres of pinyon-juniper woodlands, 10.2 million acres of oak woodlands, and 1.3 million acres of mesquite-dominated ecosystems; comparable information in northwestern Mexico is incomplete.

Timber harvesting o­n large tracts of commercial forest land has been restricted in response to environmental concerns; the tree and shrub component of many woodlands has comparatively little value to people; and not all of the rangelands are grazed by livestock each year. As a consequence, less than the nearly 120 million acres potentially available for silvopastoralism are managed for such at any o­ne time.

The most common form of silvopastoralism is integrated forest grazing, which occurs when livestock graze o­n mostly native forage plants as part of a ecosystem-based multiple-resource management system. Cattle is the primary livestock component in the southwestern United States, while larger numbers of sheep and goats are found with cattle in northwestern Mexico. Cow-calf and yearling operations are the focus of most of the cattle production practices.

Managers and practitioners need to appreciate the relationships between forest or woodland overstories and associated herbaceous understories in managing the rangelands to optimize the joint production of these outputs in the future. A number of relationships have been and continue to be established for this purpose. Many of the relationships show competition between wood and forage; that is, o­ne output increases while the other decreases. Appropriate models of production-economic relationships are employed to identify the optimal combination of outputs in these instances.

Home Gardens

Planting of home gardens has a long tradition in the southwestern United States and northwestern Mexico. Products of these home gardens are obtained from a tree layer at the upper levels, an herbaceous layer near, o­n, or in the ground, an intermediate shrub or vine layer, or combinations thereof. Home gardens are found in close proximity to people's homes or communities. Home gardens in the southwestern United States are mostly privately owned and maintained, while home gardens in northwestern Mexico are grown o­n ejido and other communal lands.

A diversity of trees, shrubs, vines, and annual and perennial herbaceous plants yield a variety of vegetable crops, fruits and nuts, forage and fodder, poles and posts, firewood, and flowers for the home or sale; the trees also provide shade for people, their homes, and their livestock. The home gardens are most commonly planted in blocks, rows (alley cropping), or random arrangements.

Developmental trials are developing to improve the design of the "traditional" home gardens common to the region for energy conservation, food products, and the variety of specialty products that could be cultivated or collected. An inventory of useful plants (such as traditional medicinal plants) and home gardening practices that are appropriate to the region and their climatic analogs would be useful. Small-scale irrigation and water harvesting systems that meet the requirements of minimal water losses in applications, prevention of site degradation (such as waterlogging), and sustained economic efficiency would likely expand the planting and cultivation of home gardens.

Windbreak Plantings

Scattered windbreaks are planted throughout the semi-deserts of the southwestern United States and northwestern Mexico to protect pastures, homesteads, and other structures. These windbreaks are generally shorter in length, narrower in width, and more simple in design than those found in the Great Plains and Upper Midwest. Multiple-row and multiple-species windbreaks are found o­n the higher-precipitation sites, while o­ne or two rows of o­ne species are common where precipitation is more limiting, approaching 150-300 millimeters annually. The extent of windbreaks in the region is unknown, although plantings are increasing.

Trees comprising the windbreaks are often harvested o­n a local scale for fuelwood and poles when they attain maturity. Forage in the protected zone can increased in production up to 10 percent, depending largely o­n the plant species involved, precipitation regime, and soil features. The increase in forage has been translated into weight gains of livestock (mainly cattle) by 15-to-20 percent because the environmental stresses o­n the livestock are decreased, allowing more energy to be converted into body weight. Many windbreaks in the region are planted simply to improve the scenic values of homesteads and associated landscapes.

Findings from plant-materials testing centers have shown that there are opportunities to increase the current level of windbreak plantings by incorporating easily-established, fast-growing hybrid tree and shrub species into these plantings. Although the performance of these species in the "long-run" is not always known, preliminary listings of species suitable for many of the fragile sites in the region are becoming available. Along with species considerations, alternative planting configurations and other design criteria developing to improve o­n the success of the windbreak plantings.

Riparian Ecosystems

Riparian ecosystems are important to people in the region because of the diversity of plants and animals found in these comparatively wet environments within otherwise arid or semi-arid landscapes. In contrast to riparian ecosystems in the eastern United States, emphasis in the southwestern United States and northwestern Mexico is placed less o­n planting trees, shrubs, or herbaceous plants and more o­n managing the naturally regenerated vegetation for limited amounts of wood for specialty products (including many of those also obtained from home gardens), controlled livestock grazing, habitats for wildlife and fish species (including some species that are listed as threatened or endangered), and recreational opportunities. Some of the riparian ecosystems at lower elevations are used to grow maize, barely, sorghum, and other agricultural crops. Agricultural production extends outward o­nto adjacent flood plains in many of these instances.

A major management emphasis is presently placed o­n assessment of the condition of the riparian resources in the region and, when necessary, the restoration of riparian ecosystems that are dysfunctional and, as a consequence, demonstrating a trend toward degradation. While millions of dollars have been spent in the past o­n riparian restoration and fish habitat improvement, healthy riparian ecosystems continue to be lost at an alarming rate. Fortunately, current research efforts are showing than many of the degraded (but resilient) riparian ecosystems can be restored to a more productive state with relatively little effort and small expenditures.

For more information, write to Dr. Ffolliott at This email address is being protected from spambots. You need JavaScript enabled to view it..

By Peter F. Ffolliott
University of Arizona, Tucson