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In spite of the fact that a large number of species in the family Meliaceae have a high potential value as sources of wood and timber, only a few of these species are utilized extensively. The two most important genera in this regard in the neotropics are Cedrela and Swietenia. From the last century to the present day, the mahoganies, as they are commonly known, have been the pillars of development in Latin America's forest industry. Species of these two genera cover the neotropical zone from Mexico to Brazil and Argentina, through Central America and the Caribbean islands Mature individual trees are found in a small proportion in tropical forests. The species have a low rate of natural regeneration, which increases their status as rare species.

During recent decades the populations of Swietenia and Cedrela have been affected by a number of factors, particularly deforestation, which decimates populations; and by selective exploitation of the best individual trees, which is likely to have negative affects on the genetic constitution of the populations.

In the case of some species such as S. mahagoni and S. humilis, it is no longer easy to find large, straight trees; it is more common to find small and generally mis-shaped trees. The case of S mahagoni is perhaps one of the most evident examples of genetic erosion in a tropical forest species, and for this reason it is extremely important to biologically understand, manage and conserve the remaining mahogany forests in Latin America. Mahoganies are considered a priority in the establishment of industrial and rural plantations, particularly on good quality sites and in conditions in which the attack of the terminal shoot-borer, Hypsipyla grandella Zeller, which is the most damaging and difficult plague of all to control, can be controlled.

During the Ninth Session of the Panel of FAO Experts on Forest Gene Resources held in 1995, the Panel recommended that FAO adopt measures for promoting action and co-ordinating on-going work in the conservation and sustainable use of species of the neotropical genera of Meliaceae. The activities could subsequently be broadened to include the Asia-Pacific and African mahogany species.

The above recommendation, which was unanimously supported by the Panel, is based on the high value of many species of the Meliaceae, which provide income and support for national economies and local communities in a large number of tropical countries; on the possibility to manage them in natural stands as well as in large-scale and rural plantations and on-farms; and on the fact that many genetically differentiated origins are considered to be threatened with genetic degradation or extinction. It was stressed that many of the Meliaceae species are of great interest, not only in their countries of origin but also in other countries and regions. There are possibilities for increasing their production and, potentially, for producing inter-specific hybrids within breeding programmes. Networking of already existing and emerging national and regional research projects and programmes i.e., on insect resistance, can, furthermore, bring benefits in the form of new contacts and avoidance of overlap of effort.

The present document, based on work carried out under Author's Contracts for FAO's Forestry Department by the four authors of this document, brings together existing information on the genetic resources of species of the two genera considered to have top priority; Swietenia and Cedrela; describes some of the on-going activities in the neotropics; and proposes action to be carried out for complementing knowledge on the two priority species: Swietenia macrophylla and Cedrela odorata. Actions are proposed to be undertaken within the framework of a co-operative network on genetic resources which will facilitate contacts and collaboration between interested individuals and institutions, and will help contribute to the knowledge, management, use, promotion and conservation of the genetic resources of these species.

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