Trees and shrubs are of great importance to most rural communities in developing countries, and are used for cooking and heating, as roundwood timbers for construction and fencing, as lumber for household uses, as food for people and fodder for animals, as shade from the sun and shelter from wind, and in many instances, for stabilization of soils. Unfortunately, until recently, the potential of forestry in rural communities, particularly those in marginal environments, has often been neglected because of incomplete knowledge of the biology and management practices of many of the arboreal in such areas.
A particular need exists to increase the available information on multipurpose tree species in arid and semi-arid regions of the world, such as those in Mexico and Central and South America, where there are already serious imbalances between the need for wood and the availability of wood resources. The effects of these imbalances, which are becoming more acute with growing population pressures, will eventually be felt in all facets of rural life. Furthermore, depletions of natural vegetation will increase ecological fragility and contribute to a gradual degradation of the total resource base (Palmberg 1981).
To combat these imbalances, it will become necessary to intensify forestry programs to grow multipurpose trees for use by rural communities. To the extent possible, these programs should emphasize the selection of trees with desirable growth rates and form and with other characteristics of value in the locality. Species of the genus Prosopis are particularly useful as multipurpose trees. They are highly adapted for survival under less than ideal conditions in arid and semi-arid regions. Furthermore, they have an unusual capability of recovering from severe injury. Fruits of nearly all Prosopis species make excellent forage, and those of some species are suitable for human consumption. Leaves can provide browse for both livestock and wildlife, and the flowers can supply large quantities of nectar for bees. The wood is strong and durable and is excellent for round wood construction and posts; it has a high calorific value on the order of 1700 joules/kg, therefore, is excellent for fuel. The wood is hard and has a beauty of grain and color that makes it very suitable for furniture, parquet flooring, and small decorative products.
Prosopis is a key niche component in many arid and semi-arid ecosystems, including those of Latin America. It serves an important function in modifying the extreme environmental characteristics of deserts and in allowing a diversity of plants and animals to inhabit what would otherwise be terrain unsuitable to many of man's activities. It is not surprising, therefore, that man long ago developed and maintained a close association with the plants of this genus.
The purpose of this handbook is to provide a guide to the taxonomy of this important genus with specific emphasis on those Latin American species which have been included in the FAO/IBPGR project on Genetic Resources of Arid and Semi-arid Zone Arboreal Species for the Improvement of Rural Living (FAO 1980). The work of Burkart (1976 a, 1976 b) and Simpson (1973) have been liberally used in preparation of the handbook. To complement these and other taxonomic references, a critical review and assessment of taxonomic investigations on Prosopis tree species likely to be encountered in Mexico, Chile and Peru has been undertaken to provide guidance for the practitioner.
