Tropical forests are among the most important depositories of biological diversity and genetic resources on earth, and the disappearance of species and ecosystems, and degradation of the genetic quality of these resources is a cause of greatest concern globally, while occurring at an accelerated rate in some regions and areas. Due to overall lack of understanding of the taxonomy, biology, dynamics, and interactions in tropical forest ecosystems, such losses are causing irreversible damage which can at times only be appreciated after it has already occurred.
It is obvious that efforts to conserve genetic resources have largely been surpassed by the speed with which these resources are being lost, and if this trend were to continue we may not be able to adequately meet future demands. It is obvious that sustainable development has to be based on wise use and conservation of plant and animal genetic resources and these, in turn, must be based on technically and scientifically sound knowledge and information.
Soundly based and dynamic plans and strategies must, without fail, underlie the sustainable management and utilization of available resources. This is especially true for Swietenia and Cedrela in the neotropics.
The term conservation, as used in this document, is the one used in the World Conservation Strategy (IUCN, 1980): “The management of human use of genetic resources so that they may yield the greatest sustainable benefit to present generations, while maintaining their potential to meet the needs and aspirations of future generations”.
For the purpose of conserving and managing the genetic resources of Swietenia and Cedrela, or any other tropical tree species that should be conserved, it is necessary to understand the biological and genetic factors which govern their growth and reproduction, as well as interactions between them and associated species and the environment in which they have developed. For this reason it is very important to greatly increase our knowledge of adaptation, variation and factors related to the reproductive biology of these species.
In situ and ex situ conservation strategies are complementary and by their judicious use the dual objectives of conservation of ecosystems and species of interest, and of the genetic diversity which they contain, can be achieved (Palmberg, 1987).
In 1992 the United States and Costa Rica proposed that species of the genus Swietenia be included in Appendix II of CITES. The Convention participants confirmed the inclusion of S. mahagoni in Appendix II, but the concurrent proposal to include S. macrophylla was modified and later withdrawn. S. macrophylla is presently listed in Appendix III. S. humilis continues to be listed in Appendix II.
The following rules govern the use of species listed in CITES Annexes, in accordance with Article II of the Convention:
Appendix I shall include all species threatened with extinction which are or may be affected by trade. Trade in specimens of these species must be subject to particularly strict regulation in order not to endanger further their survival and must only be authorized in exceptional circumstances.
Appendix II shall include:
other species which must be subject to regulation in order that trade in specimens of certain species referred to in sub-paragraph (a) of this paragraph may be brought under effective control.
Appendix III shall include all species which any Party identifies as being subject to regulation within its jurisdiction for the purpose of preventing or restricting exploitation, and as needing the co-operation of other Parties in the control of trade.
The FAO Panel of Experts on Forest Gene Resources listed both Swietenia and Cedrela species as a high priority for genetic conservation; in priority lists elaborated by the Panel in 1985, 1990, 1994. The in situ conservation of Swietenia macrophylla, S. humilis, S. mahagoni and Cedrela odorata was, in this regard, considered as a high priority, coupled with priority for action aimed at studies on genetic diversity, and conservation ex situ.
Rodan et al (1992) explored the scientific and political arguments for the proposal to include Swietenia species in Appendix II of CITES, analyzing the current status of conservation and genetic knowledge of the species. They suggested recommending control of illegal trade in these species, and action to conserve natural populations. They documented information on the conservation status of relevant species as follows:
“Swietenia humilis Zucc.: the populations in the entire natural range have been reduced and fragmented, primarily due to conversion of forest land to agriculture. The species was included on Appendix II of CITES in 1973, based on a proposal by Mexico.”
“Swietenia mahagoni (L) Jacquin: unmanaged harvesting and clearing of forest land for the past 500 years have considerably reduced the number and quality of trees of this species in the majority of areas in its natural distribution range. Presently, S. mahagoni shows signs of genetic erosion due to the over-exploitation of the best genotypes which were extracted from natural populations in the past (Styles, 1981; Rodan et al, 1992). In 1992 this species was included in Appendix II of CITES.”
“Swietenia macrophylla King: this species constitutes one of the principal timber sources of the neotropics. Available reports vary in their evaluation of the conservation status of this species (Rodan et al, 1992), and it is considered either endangered or abundant, depending on the geographic region and country in question.”
There is some evidence that mahogany genetic resources are rapidly declining. This is especially true in the case of individual trees of large dimension. According to information included in the United States CITES proposal of 1992, the status of Swietenia macrophylla in some Central American countries was as follows: Guatemala, endangered, populations remain in the Petén region only; Honduras, abundant although the species is heavily exploited in accessible zones; Costa Rica, threatened; Panama, undefined, likely extinct in accessible regions.
In Brazil, despite the fact that mahogany has a large area of dispersion over close to 150 million hectares, selective harvesting can negatively affect the integrity of some populations. In this regard it is important to recall that the estimated density is of one individual of commercial dimensions per hectare, with an average volume of 0.4152 m3. It has been estimated that the timber resources in Brazil are close to 60 million m3 (FUNATURA, 1993). On the other hand, Barros (1992), estimating that the annual average exploitation amounted to 500,000 m3 of mahogany timber per year, predicted that mahogany wood in the Brazilian Amazon could only last for another 32 to 42 years, should the current rate of harvesting continue.
Many companies in Brazil, particularly large ones, can harvest mahogany up to a radius of 350 km distance from the sawmill (FUNATURA, 1993); this signifies an area of close to 10 million hectares for each one of the companies of this type. According to Vantomme (1991), there are close to 2,900 sawmill operations in the Brazilian Amazon, of which 160 produce more than 10,000 m3 per year, and 10 of which produce 200,000 m3 annually. Based on this data, FUNATURA (1993) indicated that mahogany timber reserves in Brazil could, in fact, be much smaller than is currently estimated.
Linares (1996b) points out that itinerant forest extractors are predominant in Peru. These make use of the forest without management plans and are permanently on the move in search of valuable timber. Native communities on the other hand, try to conserve and defend their lands from outside interference. In Peru there are more than 1,000 native communities in the Amazon, with title to more than 6 million hectares of tropical forests (INRENA, 1995).
Rodan et al (1992) produced information (Table 6) which reviews data on mahogany imports by the United States for the period 1986–1991. These figures include timber of Swietenia species, as well as Khaya and Entandrophragma species (African mahoganies). The authors indicate that practically all mahogany timber sold in international markets originates in natural forests. They comment that in 1991, 87% of mahogany timber imported into the United States, is known to have come from natural populations.
Table 6. MAHOGANY SAWNWOOD IMPORTED BY THE UNITED STATES (M3) (U.S. CENSUS BUREAU, 1987–1992)
(Source: Rodan et al, 1992).
In the area of distribution of mahogany species in Brazil, there are 160 indigenous communities, landowners, of which 53 (33%) regularly harvest the species. In a study done by FUNATURA (1993), it is indicated that during the 1982–92 period, 23 of these communities harvested two million cubic meters of mahogany wood. The harvesting was made through contracts between the indigenous people and wood industries, with or without the participation of the National Indian Foundation of the Brazilian Government, FUNAI.
In Brazil, the export of mahogany timber was very significant: between 1971 and 1992, the country exported a volume of 3.3 million m3 of S. macrophylla timber only, the United Kingdom and the United States being the principal buyers (FUNATURA, 1993). Bolivia, the second largest mahogany exporter, exported an annual average of 58,000 cubic meters of mahogany timber to international markets during 1990–92; during the same period, Brazil exported a total of 127,000 m3; Guatemala, 9,000 m3; Peru 5,000 m3, and other neotropical countries, 11,000 m3. According to the above, Brazil thus covered 60%; Bolivia, 27.6%, Guatemala, 4.3%; Peru, 2.4% and other countries, 5.2%, of the mahogany timber exported from Latin America. 50% of the timber was exported to the United States, 20% to the United Kingdom and 30% to other countries of the European Economic Community (FUNATURA, 1993).
In the case of Mexico, harvesting of S. macrophylla and C. odorata was carried out primarily by the States in the Yucatan Peninsula (Campeche, Quintana Roo and Yucatan); in recent years the exploitation of tropical timber, including mahoganies, has decreased in terms of volume.
In 1995, IBAMA (Federal Government of Brazil) published a report dealing with Sustainable Forestry Management Planning, providing information from 10 of the largest mahogany export companies in Para, Brazil; the volume of exports of the companies included represented 80% of the State total. The annual area of exploitation of these companies corresponded to 33,000 hectares, and a volume of mahogany timber of about 165,000 m3 (IBAMA, 1995).
Wood extraction in Latin America is generally selective, concentrating on those species which are of proven commercial value and of good form. Species include Swietenia and Cedrela species, and notably S. macrophylla, C. odorata and C. fissilis. In general, harvesting is not carried out within the framework of established forest management plans. This lack of management is likely to cause genetic erosion in mahogany populations, and may lead to irreversible genetic losses.
During the Ninth Meeting of the Conference of Parties to CITES, held in Fort Lauderdale, Florida, USA (1994), the proposal was made to include the neotropical populations of Swietenia macrophylla and the natural hybrids S. mahagoni x S. humilis in Appendix II of CITES. The proposal, subsequently approved, included the following recommendations, for consideration:
"timber and primary wood products traded internationally, including unprocessed wood and lumber, sawnwood, plywood and wood panels, should be included;
"processed wood and secondary wood products (for example, furniture and chipboard) should be excluded;
“derivatives generally excepted should be excluded” (Resolutions 4.24 and 6.18 of the 9th CITES Conference).
As mentioned above, at present (1996), both Swietenia mahagani and S. humilis are listed in Appendix II and S. macrophylla in Appendix III of CITES.
Frankel (1977) identified the primary issues which affect genetic conservation strategies, summarizing them to be: (i) the nature of the material to be conserved; (ii) the objective of conservation; and (iii) the scope of the conservation effort.
Frankel defines the nature of the material by the length of its life cycle, the mode of reproduction, and the ecological status, spatial distribution, abundance and frequency of populations and individuals among others. The objective relates to the level (ecosystem, species, intraspecific variation) and to objectives such as research, breeding etc. The scope refers to the time-scale of concern, as well as to the extent and location considered.
In addition to considering the geographic distribution of the species, which will determine the need for sampling in general, special emphasis must be placed on known or likely ecological and genetic variation of the species. It is important to sample the greatest possible range of diversity and to assure, in this way, that enough variation will be available to meet present-day and future needs.
The first step in planning a conservation programme is to define sampling strategy and size of conservation areas or samples for ex situ conservation: what are the minimum levels, in this regard, to maintain the evolutionary potential of a given species, and to ensure that useful variation is captured and conserved, for each component population and in each target species?
Many authors have dealt with the above issue, although few have done so for species occurring in tropical ecosystems, in which the factors related to diversity and the complexity in number of species and individuals present, interactions between the target species and other components of the ecosystem, and their spatial distribution, while fundamentally important, are little known. Based on experimental work, mainly with animals, it has been suggested that 50 individuals will form an effective minimum population size for short-term adaptation; and that 500 individuals will be needed to sustain long term genetic adaptability to changes over time and space (Frankel, 1982; Frankel and Soulé, 1981; Roche and Dourojeanni, 1984; Palmberg, 1987).
Roche and Dourojeanni (1984) note that when a threatened tree species has been identified, it will be in principle possible to determine the area needed, i.e. an area containing a minimum 500 individuals, based on forest inventory data. Determination of the exact minimum number of individuals to ensure conservation, however, will require knowledge of the genetic variation of the species to be conserved, and will necessitate adjustments also in accordance with patterns of variation, breeding system, and overall “functioning” of the species in question.
The principal strategies of conservation are in situ and ex situ. The two strategies both play an essential part and are complementary; both are an integral part of forest management and sustainable utilization of forest resources (Palmberg, 1987; Patiño, 1987).
According to Frankel (1977), in situ conservation is the continuing maintenance of a population within the community of which it forms part and in the environment to which it is adapted. Protection of the ecosystems to allow for continuity in evolutionary and ecological processes may be needed in this regard. The dynamics of ecosystems in which species to be conserved occur need careful study, with special reference to interactions between plant and animal species present. The same author indicated that this form of conservation is close to nature, as also natural forests house and maintain genetic resources.
Palmberg (1987) notes that in situ conservation areas can be established or demarcated in forests managed for production or protection; and/or in national parks or other protected areas, with the proviso that the objectives and special requirements of in situ reserves are met (adequate sampling; management aimed at the maintenance of intraspecific genetic variation; access to reproductive materials) while stressing the complementarity of in situ and ex situ conservation, the author lists the following main advantages of in situ conservation:
Use of in situ genetic reserves has the following main advantages:
In situ conservation can be considered part of the management objectives of natural renewable resources, compatible with other objectives such as conservation of wildlife, watershed management, erosion control and - with some limitations - production of goods and other services;
In situ reserves can serve several sectors at once, since gene pools of value to different sectors e.g. crop breeding, forestry, forage production) may often overlap, and so can be maintained in the same protected area;
In situ conservation of an economic species within a natural ecosystem at the same time conserves many subsidiary species of no present economic value, which form part of nature's heritage;
In situ conservation allows evolution to continue, a valuable option for conservation of disease- and pest-resistant species which can co-evolve with their parasites, providing breeders with a dynamic source of resistance; and for continued co-evolution between associated species (e.g. woody species/pollinators);
Maintenance of wild gene pools facilitates research on species in their natural habitats;
In situ conservation is an effective way of conserving species with recalcitrant seeds which cannot be dried without rapid loss of viability (and are also short-lived when moist) and hence cannot be maintained in long-term seed storage and cannot be moved safely to any distance for planting in live collections; and the only strategy available to conserve biologically little-known species which cannot be established in viable plantations.
According to Kageyama and Gandara (1993), targeting in situ conservation can be facilitated by identification of keystone species, or alternatively those species in an ecosystem which need relatively large areas for conservation and which are representative of the ecosystem as a whole. The authors consider that species which are “rare” throughout their natural distribution could also be used to determine needs in in situ conservation; the authors, in this regard, use Cedrela fissilis as an example.
In 1986 in Peru, with the financial support of the FAO/UNEP Project on Conservation in situ of Forest Genetic Resources, work was conducted to establish in situ conservation areas of mahogany species within the Alexander von Humboldt National Forest (Linares, 1987). In this connection, Linares (1996a) makes some reflections about in situ conservation:
Weak and unstable forestry institutions do not guarantee the success of in situ efforts outside of Protected Areas, as they are incapable of guaranteeing their integrity;
The most secure way of conservation in situ continues to be conservation within the borders of Protected Areas, which even in critical periods generally can provide better guarantees of integrity;
There is a need to enter into firm agreement with logging contractors and firms to ensure support to ex situ conservation efforts outside natural forests and Protected Areas. In this regard, contractors and firms would undertake to set aside seed production areas for species of major commercial interest, and for species under threat, as an integral part of forest management measures to be followed by them;
Forests under the jurisdiction of local communities seem to offer better chances for conservation than those under the jurisdiction of settlers and forest industries in Peru. These latter two categories seem to view trees only as an economic resource to be exploited in the short term;
In countries such as Peru, with reduced capacity for administrative control in the forestry sector, ex situ conservation is a promising alternative for conservation and it should be applied before valuable genetic resources are lost due to over-exploitation and habitat loss;
In order to assure the effectiveness of ex situ conservation efforts, international support and networking between national and international institutions are indispensable, as it is difficult for a country working on its own to have the resources to meet the costs which an undertaking of this magnitude implies.
In the neotropics there are a number of Protected Areas and Biosphere Reserves which contain a large number of populations of various species of Meliaceae, and which play an important role in their protection in situ. Among these, the following can be mentioned:
In the tropical zone in south-east Mexico several Biosphere Reserves have been established; among the most important of these are (SEDUE, 1989): i) Montes Azules, in Chiapas (331,200 ha); ii) Calakmul, in Campeche (723,185 ha); Sian kan, in Quintana Roo (528,147 ha); and numerous smaller natural reserves in various parts of the tropics.
In Central America, the following Protected Areas are noteworthy: in Guatemala, a natural reserve in the Petén is being maintained, as well as a reserve in the Mayan area. In Honduras, the Rio Plátano reserve. In Belize, there are two natural reserves, 20 forestry reserves, two wildlife sanctuaries, and two National Parks (Weaver and Sabido, 1996). The Belize Protected Areas Programme administers an extensive area in the northeast of the country, in which populations of Swietenia and Cedrela are found.
The work developed by CATIE (Navarro, 1996), related to the sampling of mahogany populations in Central America should be noted. In this programme herbarium specimens and other materials are collected and used i.a. for molecular analyses and for the establishment of field experiments to complement the information provided by molecular level tests on these populations.
In South America, there are a number of Protected Areas and national parks which contain populations of Swietenia, Cedrela and other Meliaceae species. Among these, in Peru, Linares (1996a) mentions the following: National Parks: Manú, Yanachaga-Chemillen, Rio Abiseo and Baguaje-Sonene; the Pacaya-Samiria National Reserve and the Alexander von Humboldt and Biabo-Cordillera Azul National Forests.
With regard to research on aspects underlying genetic conservation, many investigations are being conducted in Brazil focused on S. macrophylla, C. odorata and C. fissilis, aimed at gaining better understanding of the genetic diversity of natural populations with a view to improving conservation efforts F. Gandara and P. Kageyama (University of São Paulo) are studying C. fissilis and C. odorata in the Atlantic Forest; M. Kanashiro (EMBRAPA) studies S. macrophylla and C. odorata in the Amazon; M. Lemes (INPA) studies S. macrophylla in the Amazon; and more recently, M. Loveless (Wooster College-Ohio) has initiated studies of S. macrophylla in the Amazon.
Ex situ conservation implies the protection of genetic materials in locations outside of the area of distribution of the natural populations. This strategy can be carried out using vegetative materials as well as seeds or pollen conserved in seed banks, in living collections, in aboreta in botanical gardens, or in ex situ conservation stands, established following sampling in natural populations.
In this strategy the loss of genetic diversity is minimized through rigorous sampling procedures and paying attention to genotypes and populations (provenances) included in the programme. The ex situ conservation areas have to be carefully selected and appropriate techniques must be developed for the management of the stands. Ex situ conservation is especially useful in certain species or genera in which knowledge exists on the reproductive systems and the biology of the species, in which seed and pollen handling and storage are relatively easy, and in which management in plantations and silvicultural measures are well known. Many forest plantation species are included in this category.