To initiate conservation and planting programs for Prosopis, priority species, provenances, and suggested seed collection areas should first be determined. Preliminary considerations relative to these matters are presented below.
Based on a list of priority species drawn up by the FAO Panel of Experts on Forest Gene Resources (FAO 1977), and after an initial phase consisting of an on-the-ground survey of needs and possibilities of international cooperation in a program on the conservation and better utilization of genetic resources of arid and semi-arid zone arboreal species, a few select species which provide fuelwood and a number of other goods and services for rural communities were shortlisted for inclusion in the present, operational phase of the FAO/IBPGR project (FAO 1980). The list includes a number of species belonging to the genus Prosopis.
Although an in-depth study of the nomenclature of Prosopis was published in 1976 (Burkart 1976a, 1976b), the taxonomy of the genus is still confused. To help clarify the situation, a practial handbook on this subject has been prepared within the framework of the FAO/IBPGR project (Ffolliott and Thames 1983). Some of the information from the handbook on taxonomy is reproduced in Tables 1 and 2.
In the present handbook on Prosopis seed, all the major Prosopis species native to Latin America have been considered, and a review has been made of pertinent literature and current practices for the collection, handling, storage and pre-treatment of seed of all these species. However, documentation of certain species was found to be more complete than that of others. Therefore, the handbook refers mainly to Prosopis tamarugo, P. juliflora (or P. glandulosa), and P. chilensis.
In some instances, where information is lacking for the species included in the FAO/IBPGR project, the literature and practices for other species of the genus Prosopis have been reviewed to develop preliminary guidelines which, as relevant knowledge becomes available, can be verified and refined.
Table 1
Classification of Major Prosopis Species
| FAO (1980) | Most Recent Classification | |
| - Mexico - | ||
| P. juliflora | = | P. juliflora |
| P. torreyana | = | possibly P. glandulosa and/or P. glanulosa var. torreyana |
| P. alba | = | P. alba, not native but may be introduced into Mexico |
| - Chile - | ||
| P. tamarugo | = | P. tamarugo |
| P. chilensis | = | P. chilensis |
| P. siliquastrum | = | P. siliquastrum |
| P. burkartii | = | P. burkartii |
| P. atacamensis | = | P. alba |
| - Peru - | ||
| P. chilensis | = | P. chilensis |
| P. limensis | = | P. pallida |
| P. juliflora | = | P. juliflora |
Source: Ffolliott and Thames 1983.
Table 2
Prosopis Tree Species by Country
| Mexico | Chile | Peru |
| P. juliflora | P. tamarugo | P. chilensis |
| P. pubescens | P. chilensis | P. pallida |
| P. palmeri | P. burkartii | P. juliflora |
| P. articulata | P. alba | P. juliflora var. horrida |
| P. tamaulipana | P. alba var. panta | P. juliflora var. inermis |
| P. laevigata | P. flexuosa | P. strombulifera |
| P. glandulosa | P. reptans | |
| P. glandulosa var. torreyana | P. laevigata | |
| P. velutina | P. alba var. panta |
Source: Ffolliott and Thames 1983.
Many difficulties encountered in plantation programs can be avoided by attention to provenance (geographic origin) of the seed. If information on the best adapted and most desirable provenances is lacking, an effort should be made to obtain seed from trees of native stock growing close to the planting site.
The Report on Phase I of the FAO/IBPGR project (FAO 1980) lists the following collection sites for Prosopis species in Latin America:
Mexico: northern Mexico.
Chile: Salares del Obispo, Pintados, Bellavista, and the vicinity of La Tirana, all in the Tarapaca Region (P. tamarugo); La Tirana and Refresco (P. atacamensis); Coquimbo, Aconcagua, Metropolitan area (other Prosopis species).
Peru: Lambayeque, Piura, and Arequipa.
The above collection sites have been determined by using the principle that collection should initially consist of sampling a relatively large number of seed sources, covering the natural range of the species. In this initial stage, collections comprise range-wide sampling on a fairly coarse grid; in some cases, a second stage, in which sampling is limited to part of the range on a finer network, may be called for after the results of first stage provenance trials are available. In these second stage collections, seed may be kept separate by mother trees to enable the evaluation of genetic variation within, as well as between, provenances.
