Fernando Patiño Valera
Instituto Nacional de Investigaciones Forestales y Agrìcolas y Pecuarias
Roberto Centeno Erguera
Juana Marín Chávez
INIFAP, CIR Sureste, Mexico
Forest Resources Division
Forest Resources Development Service
Pierre Sigaud
Mahogany (Swietenia macrophylla King) is one of the best-known and more frequently used tree species of forest stands in Latin America. Mahogany and other Meliaceae of Cedrela genus (Cedrela odorata L. and Cedrela fissilis Vell.) are both the backbone of the forestry industry in Latin America and the main sources of income for a large number of people in rural communities.
Due to its biological and commercial characteristics, mahogany has a large potential to become the basis for a sustainable use and management system of the tropical forest, applied in the framework of appropriate silvicultural practices. Nevertheless, former and current traditional use systems tend, in most of the cases, to harvest the best trees, regardless of forest regeneration and future growth.
In the last decades, the quality of Swietenia genetic characteristics has been severely affected and the number of individuals per hectare has decreased, due, among other reasons, to the selective exploitation of the best trees (dysgenic selection); deforestation processes and finally, the interruption of natural evolution, due to stand fragmentation. Selective use of the best mahogany trees, not only directly affects the resilience of the species in tropical ecosystems, it also presents a risk of genetic diversity erosion in natural stands, and a hazard for its natural regeneration, due to the elimination of the best seed producers.
Mahogany natural forest forms stands with low density of commercially exploitable trees per hectare. Mahogany stands are dispersed in groups of a few individuals, and in some regions, estimations show a tree density average of 0.7-2 individuals per hectare (Snook, 1993; Patiño, 1997). The low density of individuals directly affects the natural regeneration of the species, because seed production is not abundant, and the possibility of establishing seedlings, which facilitating the future presence of trees at different growth stages, is less likely to happen. During the rainy season abundant germination of small saplings may be observed close to mature trees, but once the dry season starts, a high percentage of them dies.
Mahogany grows in tropical ecosystems where a large number of tree species grow per hectare and species-level biodiversity is abundant. This high level of biodiversity is a huge challenge for the use and management of tree species with timber potential, mainly because these species grow in the same space and period of time as other species bearing different characteristics, such as wood hardness, colour and also heterogeneous growth rates. This circumstance is coupled by the fact that some species grow few individuals per hectare; besides, such species tend to be those with the highest commercial value, thus making their use and commercialization difficult. While this paper deals with some aspects of mahogany species in the context of its natural distribution range in the neotropical areas, it mainly tackles conditions and characteristics found in Mexico.
Mahogany is mainly found in the tropical rain forest and tropical moist deciduous forest, in Central America, Mexico and South America (FAO, 2002). Rain forest is found in the coastal plains of the Gulf of Mexico region; in the Sierra Madre range in Chiapas, Mexico; and in the Caribbean coast along the Pacific coast in Central America. Tropical moist deciduous forest stretches along the lower region of the central mountain ranges of Central America, located towards the Pacific Ocean; the plains and hills of the Yucatan peninsula and the Gulf of Mexico. The tropical ecological zones in this region cover 134 million hectares (FAO, 2002).
These ecological zones are characterized by an average annual temperature ranging between 20 and 26º C, while rainfall in the tropical rain forest varies between 1500 and 3000 mm, and reaches up to 4000 mm in certain areas, the Tropical moist deciduous forest receives between 1000 and 1 500 mm average annual rainfall. The dry season in these areas lasts up to three months because they are not affected by the tropical depressions occurring between August and November, which produce rainfall during that season (FAO, 2002).
The forest in these areas is high and dense. The crown cover in the tropical rain forest reaches between 30 to 40 m heights, with emerging trees growing over 50 m, while trees in the Tropical moist deciduous forest reach a 30 m height. The lower storey of the crown cover is dense, with trees reaching between 5 and 25 m, strata in the under storey present a large variety of palms, ferns, climbers and grasses. Both ecological zones share many tree species and are characterized by a complex and varied flora, with approximately 5000 vascular plant species and more than 60 different tree species per hectare.
The most common tree species associated to Mahogany in a natural distribution range are Dialium guianense, Pimenta dioica, Brosimum alicastrum Ampelocera hottlei, Pseudolmedia cf spurea, Cordia alliodora, C. dodecandra, C. bicolor, Calophyllum brasiliense, Castilla elastica, Dendropanax arboreus, Tabebuia spp, Manilkara spp, Terminalia spp, Ochroma spp, among others (FAO, 2002).
Swietenia macrophylla covers a wide natural distribution range stretching from 23º N latitude down to 18º S latitude, and covers a vast territory from the southern part of Tamaulipas, Mexico, along the Atlantic coast across Belice, Guatemala, Nicaragua, Costa Rica and Panama, and further down towards the north-eastern part of South America, along the border areas of the Amazon region down to Bolivia and the southern part of the Amazon in Brazil (Patiño, 1997; Bauer and Francis, 1998).
Mahogany is a native species in the following countries: Mexico, Belice, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Venezuela, Colombia, Ecuador, Peru, Bolivia and Brazil (Patiño, 1997; Bauer and Francis, 1998) and it is an introduced species in commercial plantations established in many regions in the world.
In Mexico, mahogany concentrates in the Mayan forest (Yucatan peninsula, Chiapas). In these areas, mahogany is relatively abundant; and presents a normal distribution of diametric classes, thus favouring the exploitation of tropical forest to concentrate in this species.
In Mexico, mahogany stands grow in different soils at intermediate depth, and stretch along the Gulf of Mexico, from the southern part of Tamaulipas to the northern part of Puebla and Veracruz, and to the Yucatan peninsula (Pennington and Sarukhan, 1968; Patiño, 1997). In Yucatan state, mahogany grows in the eastern and southern regions (Pennington and Sarukhán, 1968) and in stands with few individuals in the north-western part and in the Petenes area (Patiño, 1997). In Campeche and Quintana Roo mahogany is found in the central and southern areas, where it becomes the most frequently exploited species in the higher or middle subdeciduous stands of Manilkara zapota and in the north-eastern part of the petenes area, where it forms a continued vegetation joining with the northern stands of Yucatan (Patiño, 1997).
Swietenia macrophylla trees are used along most of its natural distribution range, a trend confirmed by several authors (Rodan et al. 1992; Foster 1990; Lamb 1966; Smith 1965; Foster 1990; Navarro 1996; Patiño, 1997; Linares, 1996; Argüelles, 1999; Navarro, 1999). Detailed forest inventories that include information on this species are few and limited in scope and area, and vary in quality. Most of these inventories have been planned for forest use and concentrate only on high value species and trees with commercial dimensions, while they ignore trees of smaller dimensions that could favour the natural regeneration of the species.
A recent assessment of mahogany stocks in Mesoamerica (Southern Mexico and Central America) (Calvo, 2000) estimates the natural distribution area of the species at 41 million hectares, while estimations show that the region (excluding Panama, due to the low density of trees, and Costa Rica and El Salvador, because commercial stands do not exist) boasts 14 million hectares of broadleaved forest with mahogany trees. Out of these, approximately 1.6 million hectares are located in protected areas, thus implying that there still are about 12.5 million hectares of forests with mahogany trees of some commercial potential. Nevertheless, not all the areas are suitable for forest management on have partially been exploited. According to the national assessments, the commercial volume of mahogany is not more than 5 percent of the total volume of the Mayan forest.
The historical trend of timber use of Swietenia macrophylla stands in the Yucatan peninsula in Mexico, Belice and Guatemala is characterized by the extraction of the best trees and a scarce application of silvicultural practices aimed at favouring natural regeneration of the species.
Mahogany use in the Mesoamerican region after the Maya era started in the 17th century. It initially involved populations located close to watercourses allowing the transportation of logs. It increasingly expanded to the interior, as new ways of access were opened for log extraction by means of animal traction, and later, railroad and trucks (Snook, 1993; Navarro, 1996; Argüelles, 1999; Navarro,1999).
Tropical forests are reported to harbour the largest genetic and biological diversity of all terrestrial populations. The genetic quality of those resources is deteriorating across the world and this trend has grown at an accelerated rate in some regions. Populations and ecosystems are vastly disturbed, while scarce knowledge exists about the organization, dynamics, taxonomy, use and interaction among the components of tree populations within the tropical ecosystems.
Certain tree species growing in the forest stands occur at a very low density of individuals per hectare. On the contrary, other species, very few in general, grow in large numbers of individuals per hectare in those same stands. This is the result of the biodiversity existing in such ecosystems, where more than 60 tree species are often found per hectare.
According to Kageyama, Namkoong and Roberts (1991) a forest inventory carried out in the Atlantic forest of Brazil, showed that 30 percent of the tree species reported had only one tree or less per hectare. Besides, the authors report that three of the most abundant tree species reached 30 percent of all the trees per sampled hectare.
A forest inventory carried out in a 100 ha area of tropical forest (with a sampling intensity of 10 percent, where all trees with 10 cm diametre at DBH and above were measured) in Escárcega, Campeche State, Mexico, reported the existence of 94 tree species. Seven of these species had only one tree on the whole sampled area, while 15 species showed the largest number of individuals, with an average between 4.2 and 2 trees within the tropical ecosystem communities (Patiño, 1997).
The species with very low presence per hectare are designated as rare species according to Janzen (1970). The rarity of the species may be considered an event in the evolution of the tropics, where the interaction between plants and animals created a plant defence system against other organisms, being rarity, one of the strategies to protect the plants against animals and micro-organisms. Many trees considered as species of high commercial value, such as mahogany and cedar, both of which belong to the Meliaceae family, may be classified within the group of rare species.
Forest inventories carried out in the southern communities (Ejidos) of Quintana Roo state in Mexico indicated that mahogany trees per hectare were distributed as shown in the table below (Patiño, 1995). It must be stressed that trees with smaller diametre, or as large as 15 cm diametre, were more numerous, thus it was possible to incorporate more trees to the diametre class of commercial-sized trees and therefore ensure the permanence of the species without decreasing timber availability.
Forest inventories carried out in the central and southern regions of Campeche state in Mexico reported similar numbers, in terms of frequency and abundance of tree species, to those shown by populations in Quintana Roo and generally matched with the findings reported by Patiño, 1987 and Patiño, 1997, at an average of 0.7 trees of commercial dimensions per hectare. Also, according to FAO’s (2001) quoting Snook (1993, 1996) and Patiño (1997) mahogany grows in low densities in forest stands, at an average of one to two trees of commercial dimensions per hectare, mixed with 60 different tree species with lower or no commercial value.
Mahogany (Swietenia macrophylla King)
trees growing in permanent forest areas located in
southern Quintana Roo, 1990
DIAMETER BELOW OR EQUAL TO 15 CM. |
COMMERCIAL SIZED DIAMETER ABOVE 50 CM. | |||||
Location |
Number of trees per ha |
Basal Area m2/ha |
Clean stem Vol. m3/ha |
Number of trees per ha |
Basal area m2/ha |
Clean stem vol. m3/ha |
Caobas |
3.63 |
0.45 |
2.74 |
0.53 |
0.23 |
1.24 |
Plan de la Noria |
5.78 |
0.33 |
2.34 |
0.08 |
0.03 |
0.16 |
Divorciados |
11.11 |
1.13 |
7.95 |
1.07 |
0.38 |
2.28 |
Manuel Ávila Camacho |
4.91 |
0.67 |
3.68 |
0.66 |
0.27 |
1.41 |
Petcacab |
6.68 |
0.84 |
5.36 |
0.92 |
0.36 |
2.00 |
Nohbec |
6.06 |
1.00 |
6.63 |
1.14 |
0.58 |
3.63 |
Tres Garantías |
4.68 |
0.56 |
3.12 |
0.51 |
0.25 |
1.20 |
Botes |
8.29 |
0.78 |
4.72 |
0.70 |
0.24 |
1.21 |
Genetic diversity in the tropical forests, where mahogany grows, is rapidly decreasing due, among other reasons, to deforestation processes and natural populations’ fragmentation. The first phenomenon reduces the population size and natural communities, sometimes eliminating them completely. In the case of forest communities fragmentation, it makes the gene exchange difficult and may isolate continuous populations of a given species until its genetic diversity is lost, as a result of endogamy and genetic erosion. These phenomena highlight the enormous risks that tropical forest resources face, especially some species of commercial value such as mahogany, therefore justifying the urgent need to better understand genetic diversity at its different levels and use such knowledge in the management, improvement and conservation practices of those important genetic forest resources.
Although Swietenia macrophylla is the most important tropical broadleaved species in neotropical regions, little attention has been given to the knowledge related with the genetic variation existing among the populations growing within their natural range of distribution. Newton et al. (1993b) carried out an exhaustive revision of the aspects concerning genetic variation, its capture and use for genetic improvement, and conservation of genetic resources, and found that few studies have been made on these issues. Probably one of the reasons of scarce genetic experimentation on mahogany is due to the difficulty of establishing plantations of this species, given its vulnerability to attacks and damages provoked by Hypsipyla grandella Zeller, a terminal shot borer, which is the main pest affecting the development of Meliaceae.
In Puerto Rico detailed studies have been made on the growth characteristics of Swietenia species, namely, S. macrophylla, S. mahogani and S. humilis and some natural and induced hybrids of these species (Weaver, 1987; Weaver and Bauer, 1986; Newton et al., 1993b), nevertheless, little information describing their different provenance has been published. Geary et al. (1973) report preliminary results of provenance tests of Swietenia species at the age of 4.4 years. In wet areas S. macrophylla was superior in height growth and survival rate, but in dry areas the performance of tree species was very similar (Geary et al., 1973).
In Mexico Patiño (1997) reports provenance and progenies tests of S. macrophylla established in 1988; in this trial he reported an inheritance coefficient for growth in height, for progenies of provenances respectively from Escárcega at h2 = 0.038, Cayal at h2 = 0.265 and Zoh-laguna at h2 =0.164.
Navarro (1999) indicates that both progenies from Costa Rica and those from Central America and Mexico show high added genetic variation levels in terms of yield in height and diametre. As regards resistance to Hypsipyla no variation was found due to the presence or absence of that borer in any of the three tests.
It is important to notice that several tests have been carried out in several Latin American countries, among them those jointly carried out by the Centro Agronómico Tropical de Investigación y Enseñanza (CATIE) with the support of research and academic institutions from Central America and Mexico, such as Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP) on the behaviour and origin of mahogany progenies established in Costa Rica (Navarro, 1999).
Currently, several projects are being carried out by INIFAP in the Yucatan peninsula, in Mexico. The projects are aimed at obtaining information on genetic diversity of populations and at establishing provenance and progeny tests, as well as ex situ germplasm conservation banks for progenies and provenance of mahogany and Cedrela odorata of native populations from Mexico.
Large morphological variability (leaves, fruits, wood properties) of S. macrophylla and other Meliaceae have been pointed out by several authors, suggesting that the species shows a wide genetic variability along its geographic range of distribution and also among many of the single populations, due to natural obstacles or fragmentation of populations caused by anthropogenic or natural causes.
This assumption suggests that each genetic population represents the subdivision of species in adapted biotypes that would correspond to different habitats. Trends seem to point out that tree morphology and resistance to Hypsipyla grandella borer are inherited characters.
This assumption underlines the importance of genetic conservation of populations and individuals with those characteristics, that may be lost if the current trends of fragmentation, population decrease and exploitation of the best phenotypes continue. Selective exploitation acts as a source of dysgenic selection, because the best individuals, in terms of growth and morphology, are being used in forestry activities. This practice leads to populations with decreasing genetic quality with poor phenotype crossings that produce this type of genetic erosion.
The best knowledge of genetic diversity in populations of Swietenia is key to define strategies of genetic improvement, management and genetic resources’ conservation. Besides, the research of genetic resistance to Hypsipyla also requires better knowledge of populations in all the distribution range of species of these genera.
Initiatives are underway in almost all the countries in the region, yet, they only cover one part of the diversity contained in the distribution area. Thus, there is need to promote the development of cooperative studies between the different institutions in Mexico, Central America and the Caribbean, that allow to extend the scope of the research, and also promote the establishment of trials with similar characteristics that allow to analyze the variability in most of the distribution range of the species.
Genetic loss within and between populations, due to the exploitation of the species and the fragmentation and reduction of its populations, is a critical factor to value the conservation state of the populations. Genetic loss is a critical factor to assess the conservation state of Meliaceae populations in their natural distribution range in neotropical regions, including Mexico.
One of the main concerns arising in the forestry scientific community aims at preventing that certain species, such as Swietenia macrophylla, be affected by the genetic erosion suffered by other species like S. mahogani. Due to a series of causes, S. mahogani lost the best individuals in the past and now their descendants are bifurcated, deformed, with many branches and are very different from the original populations.
In spite of in situ and ex situ Swietenia macrophylla conservation projects undergoing in the Central American region and Mexico, there is no doubt that more efforts are needed to better understand what the distribution and dimension of the biological diversity are, in order to correctly plan, manage, use and encourage mahogany conservation.
It is important to gather information, especially on themes like: geographic distribution and size, damage and hazard level, number of individuals per hectare, dispersion and growth behaviour, phenology, reproductive biology, interaction with pollinators, seed characteristics, seeds and sapling damage, natural regeneration.
All these factors together, will allow to adjust the objectives and work goals, as well as to define the location and size of protection areas, and facilitate other necessary tasks for genetic improvement, seed collection, and species’ propagation for plantation and orientation of activities towards the sustainable management of the species.
The use of mahogany within its natural distribution range started many centuries ago, for instance, the Mayans in Central America built large canoes to carry out trading activities in the region (Hammond, 1982). In more recent times, during the Spanish colonization, tropical forests were used to extract timber of different species, among them Haematoxylon campechanum and mahogany Swietenia macrophylla, and export it to Europe for cabinet-making and furniture, mahogany in the region was generally used for ship construction and repair, and for domestic use.
In Mexico, mahogany timber extraction began at large scale in the 20th century in many areas, mainly in the southern region of the country, including Oaxaca, Chiapas and the Yucatan peninsula. During this period, large transnational companies were established and were granted concessions by the government to exploit natural resources. The use of mahogany timber intensified during the Second World War, when the companies expanded extensive exploitation. These activities continued throughout the 70s.
Species of the Meliaceae family differ in terms of silvicultural characteristics. Cedrela odorata is considered a fast growing species, belonging to the more advanced stages of succession and a shade tolerant species.
One of the main problems arising from the management of mahogany populations is the scarce natural regeneration it shows in natural communities where the species grows. Besides the problem related to the decreasing number of mature individuals that could contribute to seed dispersion, an additional difficulty is due to the scarce quality of the remaining trees after the timber has been extracted, as well as the lack of information on the processes that regulate the natural regeneration.
Rodríguez, Chavelas and García (1994) carried out a study to assess the capacity for S. macrophylla seed dispersion and reported their findings regarding the successive establishment of saplings. Seed dispersion occurred from February to April, and a total of 6861 seeds were found, that is to say 84 percent of the potential expected production of a tree. The maximum dispersion distance was 60 m from the mother tree. In August, when the first germination and survival appraisal was made, the authors found a total of 1608 saplings. The conclusion was that 20 percent of the dispersed seeds were able to germinate and establish in the next two months.
Gullison and Hardner (1993) point out that selective use of tropical forests is damaging to the remaining trees in stands with large numbers of tree species with commercial value. The authors of this paper assessed the damage provoked by selective exploitation of S. macrophylla, a species with very low density, located in the Chimanes forest in Bolivia. Damages occurred mainly along the main roads and access tracks for extraction. Minor damage reached 4.4 percent of the total area of extraction assessed.
Nevertheless, the main obstacle to increase use practices through selective harvesting methods in Latin America the lack of international markets for many of the less known species, although in some cases local or national markets exist and could absorb the timber produced.
García, Negreros and Rodríguez (1993) carried out a study in subdeciduous forest in Quintana Roo, Mexico, in order to observe the effects of partial removal of the first storey on natural regeneration of mahogany (Swietenia macrophylla King). Five plots of 0.5 ha were established, where different intensity clearings were carried out, taking the original basal area of the population as a basis and removing respectively 0,8,28,45 and 55 percent of it. The work was assessed four years after the clearings were carried out. The authors observed marked differences in the average number of young mahogany individuals per hectare, varying from 500 in the reference sample (0 percent) to 2100 in the 45 percent intensity clearing, obtaining 700 individuals in the 8 percent intensity clearing, and 1400 in the 28 percent clearing and 900 in the 55 percent one.
The authors point out the outstanding effect on regenerating saplings in relation to the different clearing intensities. Although significant statistical differences were observed when comparing the 45 percent intensity clearing to the 0 percent clearing of reference, in absolute numbers, the former showed up to 4.2 times more individuals than the 0 clearing reference sample, while it was three times more numerous than the 8 percent clearing, 1.5 times more numerous than the 28 percent clearing and 2.3 times more than the 55 percent one. These figures suggest that a direct relation exists between the opening of the first S. macrophylla storey and the quantity of regenerating saplings produced in experimental plot conditions. Nevertheless, in the 55 percent clearing treatment, the number of regenerating saplings decreased, because the species requires shade during the first growth stages.
In terms of maximum height, observations show that the largest average tree dimensions were obtained in the demonstration plot where 45 percent of the existing basal area had been removed. These trees were 2.1 times higher than the reference sample, 2.4 times higher than the sample at 8 percent clearing, 1.9 times more than the sample at 28 percent clearing and 1.4 times more than at 55 percent clearing.
Negreros and Mize (1993) presented the following results: when the trees reached three years of age, their aim was to measure the effect of partial clearings (creation of multiple clearings) in the natural regeneration with special attention to tree species of commercial value, such as mahogany (S. macrophylla). After three years, the population obtained by regeneration was similar in density and composition to the original population before the clearings were made. Regeneration of commercial tree species (with or without tolerance to shade), non-commercial species and those which are not tree species, were compared with the residual basal area and the percentage of basal area removed. The frequency of commercial, shade tolerant species were not affected by residual basal area or by the percentage of basal area removed.
One of the main challenges that forest management programmes face in tropical regions consists in maintaining both timber productivity under long-term management, and conservation of biodiversity in the populations subject to management.
Today, an international trend associates management of forest resources with the sustainable development of communities, while conserving those communities and the genetic diversity within and between plant species’ populations.
Sustainable management may be interpreted in different ways, and it may be considered simply as the management capable of maintaining timber productivity of the species in the management cycle. In a wider interpretation, sustainable management may also be considered as the management that preserves productivity, the forest structure, diversity and the basic ecological process of populations, communities and the ecosystem.
In many tropical regions a wide range of forest management methods may be identified, including those that carry out selective use of the best individuals of some species and those that aim at using the resources in the framework of sustainable management and encourage its natural regeneration.
One of the few examples of sustainable forest management is rubber tree (Hevea brasiliensis) latex extraction in the Brazilian Amazon region, by rubber collectors, who do not damage the trees and conserve the genetic resources of the species under management, while maintaining the diversity and structure of the natural forest (Kageyama, 1991). Another similar example would be latex extraction of “chicle” gum obtained from several species of Manilkara spp. in the neotropical regions, where trees are maintained while carrying out a non-wood forest use, as well as timber use of other species.
Mahogany forests located in south-eastern Mexico are one example of sustainable forest management carried out in the Ejidos of Quintana Roo state, where the use of forests in the past was carried out through concessions that excluded the owners of the resources, a phenomenon, that according to Arguelles (1999), produced a social claim arising from the ejidos and communities to directly manage the forest themselves, as well as the commercialization of its products.
The result was a change in government policy, that granted licenses directly to forest owners, while a project known as the Forest Pilot Project was set up at later stage. These measures filled a gap in forest management left by the forestry concessions in southern Quintana Roo. The greatest success of this project is that 45 ejidos established 500 thousand hectares for permanent forest use, thus stopping uncontrolled clearings that had prevailed during decades.
The success of the Forest Pilot Plan encouraged researchers to replicate it in other regions such as Marqués de Comillas in Chiapas and the Calakmul region in Campeche; Nevertheless, these programmes did not have the expected success, because they were implemented under the influence of political considerations and not according to a productive organization of the users, in order to achieve a rural economic setting based on good management of forest resources.
The importance of a socially oriented initiative in terms of conservation efforts and development of forest populations, stems from the forest lands registration system in Mexico, where 80 percent of the forest land is managed by the communities, 15 percent by private enterprises and only five percent is still under the control of the Federal and State Governments. In terms of participation in productive activities, it is interesting to notice that today 40 percent of timber production is provided by communal forest enterprises. In 1975, only 2-3 percent of timber production was directly managed by the communities. In 1985, this figure had already grown to 17 percent.
The most important risk factor in the establishment of mahogany plantations in neotropical regions is the attack of the terminal shoot borer (Hypsipyla grandella Zeller) (Arreola and Patiño, 1987; Newton et al., 1993). This is an endemic problem in the tropics, especially when these species are planted in monoculture.
Two species of Hypsipyla exist on the American continent (H. grandella and H. ferrealis); the most damaging species for plantations is Hypsipyla grandella. This species is found across the tropical regions of Mexico, Central America and South America, excluding Chile. The species also occurs in the Caribbean islands and in the southern part of Florida, in the United States (Entwistle, 1967). The species’ distribution is closely related to the distribution of Meliaceae, especially Swietenia and Cedrela genera. All the species of these genera are subject to the attack of Hypsipyla. This is an endemic problem in the tropics, especially when the species are planted in homogeneous populations.
The high value of mahogany, its current demand and the rapid decrease of its natural populations require urgent measures to effectively control this pest. Several attempts have been made to control Hypsipyla through biological, chemical and silvicultural methods (Grijpma, 1973a and b, 1974; Whitmore, 1976a and 1976b) but these have not been effective in reducing the damage produced by the borer to acceptable levels of economic loss.
The borer usually attacks the trees during its larvae stadium, when it is easily able to penetrate the soft tissue of the shoot, and sometimes provokes its death. As a result of the death of the terminal shoot, the general growth of the plant is reduced and several new shoots may appear, producing bifurcated and deformed trees. (Rodríguez, 1981; Arreola y Patiño, 1987).
Borer attacks on young trees may start before they leave the nursery to plantation locality. Nevertheless, the most damaging attacks occur during the first four years of the plantation establishment (Grijpma, 1974; Arreola and Patiño, 1987). Young trees are more affected by the shoot borer, because they depend more on the apical meristem growth.
Currently, mahogany plantations in Mexico are being subject to intensive application of solutions containing some of the fungi belonging to Beauveria and Metharricium genera that affect the larvae of Hypsipyla grandella when these encounter the spores, which germinate and penetrate in the larvae’s body reducing its activity and provoking its death. This control method alternated with the application of systemic insecticides during the higher rate of incidence of the pest. The insecticide must be sprayed every month or every 45 days in order to accurately protect the plantation.
The natural forests considered available for wood production, including mahogany, are experiencing heavy pressures for harvesting, which contribute to continuing deforestation and which spill over to “presently unavailable” forests from the production point of view. The expected harvest from the natural forests is expected to decline.
On the other hand, global consumption of timber is projected to increase. Total roundwood consumption was projected as increasing at an annual rate of 1.12 percent between 1994-2010, from 3.21 billion m3 to 3.84 billion m3 (FAO, 1997a). Industrial roundwood was projected to increase 1.20 percent annually, from 1.47 billion m3 to over 1.78 billion m3. This increase of over 300 million m3 by 2010 far exceeds the estimated net current growth from industrial plantations of 84 million m3 (FAO, 2000).
An optimistic estimate of the permanent loss of existing natural forest production through further deforestation and degradation, based on recent deforestation rates, suggests that the annual decline in production from disturbed forests could be 6.2-7.0 million m3 ha-1 yr-1. Removing additional areas of natural forests through the establishment of new protected areas or expanded logging bans would further reduce harvests. Much of this protected area would likely be taken from available undisturbed forests that have higher current growth and productivity (approximately double) than the disturbed forests (FAO, 2000).
Without significant increases in both the available area and productivity of industrial plantations of commercial species the present net growth of 84 million m3 annually would be overtaken by reductions due to deforestation alone within 12-14 years, a shorter period than the growing cycle of most industrial plantations (FAO, 2000).
Forest plantations grown to supply raw material for industry and for other uses, such as fuelwood, also provide additional non-wood forest products and benefits from the trees planted or from other elements of the ecosystem that they help create. They contribute environmental, social, cultural and economic benefits. (Carle et al., 2002).
The potential for forest plantations to partially meet the demand for wood and fiber for industrial uses is increasing. In several countries, a significant portion of the wood supply for industrial uses comes from plantations, rather than natural forest resources.
A large majority of timber production is harvested from currently available natural forest. Globally, an estimated 3354 million m3 was removed from the world’s forests of which 56 percent is fuelwood. Fuelwood is most significant in Asia and Africa while industrial roundwood production is heavily concentrated in North America, Asia and Europe (FAO, 2000).
The global forest plantation estate has increased from 17.8 million hectares in 1980 and 43.6 million hectares in 1990 to 187 million hectares in 2000. Although in 2000, 26 percent of plantations continued to be for unspecified purposes, there was a significant increase in plantations for industrial purposes in the past decade: from 39 percent in 1980 and 36 percent in 1990 to 48 percent in 2000. There has been a corresponding decrease in forest plantations for non-industrial purposes (Carle et al., 2002).
FAO (2001) reports that 326007 hectares of mahogany plantations have been established in 18 countries in the world. The main plantation area occurs in Indonesia (187500 ha), Fiji (42000) Philippines (34000 ha) and Mexico (21400 ha), with 87.4 percent of the total. Sri Lanka, Bangladesh, Solomon Islands, Guadeloupe and Samoa have already been planted with 33300 hectares (10.21 percent of total) and another nine countries have been planted with 7807 hectares (2.4 percent).
Forest plantations make up only 3.5 percent of the global forest area and tropical plantations, including those of Meliaceae species, make up 45 percent of the estimated 187 million hectares of plantations.
The role of planted forests in increasing forest areas, including trees on farms and trees outside the forests, is very important in order to meet the rising demand for wood and non-wood products and ecological services, including carbon sequestration. In countries with low forest cover the planted forests are an option for rehabilitating degraded areas and where possible, the base for re-establishing natural forests.
The planted forests will be established taking in account all the practicable steps to avoid replacing natural communities and ecosystems of high ecological, economical, social and cultural value.
In the case of mahogany, the density of trees in nature is an average of one tree per hectare (Patiño, 1987; Snook, 1993; Snook, 1996; Patiño, 1997) and the final density of mahogany trees in Mexico in a 25 years rotation length, is on average 250 trees per hectare.
In that case, one hectare of plantation corresponds to 250 hectares of natural forests. This shows us the importance of promoting forest plantations in previously deforested lands to produce wood to meet rising demand and help the protection of natural forests.
For several decades FAO has made increasing efforts to link national, regional and international institutions in order to facilitate and promote better knowledge, management and use of mahogany genetic resources. Several years ago, the FAO Panel of Experts on Forest Genetic Resources included mahogany (Swietenia macrophylla King) improvement and genetic conservation as one of its priorities. FAO (1994, 1997, 2001) considers that in situ conservation is a high priority and it has suggested strengthening activities to carry out studies on genetic diversity and promote improvement and ex situ conservation.
In neotropical regions, where mahogany naturally occurs, national and regional institutions, as well as non-governmental organizations work to improve the knowledge, enhance management, use and conservation of mahogany genetic resources. These efforts are carried out in collaboration with international organizations and governmental institutions of all the countries.
Central American countries are working jointly to deal on common issues to strengthen regional integration in environmental matters, with the aim of promoting a regional approach oriented towards economic, social and ecological sustainability. One of these efforts is the Comisión Centroamericana de Ambiente y Desarrollo (CCAD) (Central American Commission for Environment and Development). The organizations acts on a regional basis and aims at harmonizing policies and management systems and promotes like-minded positions in all extra-regional and world fora.
One of the most important projects developed under the umbrella of CCAD are the studies carried out on the biological corridor in Mesoamerica, as well as issues related to species that have a conservation interest, such as mahogany. During its 33rd meeting held in July 2002, the Central American Commission on Environment and Development agreed, at the suggestion of Nicaragua, to request the Convention on International Trade in Endangered Species of Wild Fauna and Flora, (CITES) to include mahogany (Swietenia macrophylla King) in Appendix II of the Convention, during its next Conference of the Parties.
Several non-governmental organizations, both national and international are also present in the region. These organizations have, as part of their most important mandate, to obtain information on the status, management, use and commercialization of wildlife species, and to give more emphasis to those related to the CITES Convention. These organizations are the World Wide Fund for Nature (WWF) and the World Conservation Union (IUCN) which jointly manage the programme TRAFFIC, established to regulate the trade of plants and animals and thus monitor wildlife trade in the world. TRAFFIC works in cooperation with the CITES Secretariat.
Since the 1990s, attempts have been made to include mahogany in the Appendix lists of CITES. These attempts were based on studies carried out by several authors, who have analyzed the deforestation rates within the geographical distribution area in the neotropical regions, as well as the commercialization and general state of the species. In 1994 a proposal was presented to include Swietenia macrophylla King in Annex II of CITES, but it was rejected by CITES parties.
In 1997, the proposal made by Bolivia and the United States to include this species in Appendix II of CITES was rejected by few votes. Nevertheless, the most notorious agreement was reached in 1997 by a exporting countries like Brazil and Bolivia and the largest importer country, the United States, to create a working group in order to examine the state, management and trade of this species along all its geographic distribution areas.
Other countries belonging to the distribution area where mahogany grows, expressed their support for this initiative. Bolivia, Brazil and Mexico also engaged to include their mahogany logging practices in accordance with Appendix III of CITES.
Bolivia has included its mahogany population in Appendix III, as of 19 March 1998. Brazil as well, adopted this decision on 26 July 1998. Mexico included mahogany in Appendix III in November 1997. (Mahogany populations in Costa Rica are included in Appendix III since November 1995.)
The working group on mahogany -integrated by governmental organizations of countries belonging to the geographical area of mahogany distribution and importer countries, as well as non-governmental organizations working in the domain of conservation of natural resources - is currently working to develop text and content to present a renewed proposal to include mahogany in Appendix II of CITES, during its meeting in Chile in 2002.
In Mexico, mahogany (Swietenia macrophylla King) presents a natural distribution range that stretches from the Yucatan peninsula to the coastal plain in the southern Gulf, the warm regions in the states of Chiapas, Oaxaca and Puebla.
Apparently, topography is not a determining factor in the species’ distribution, at least up to a limit of 800 m, below this altitude temperatures of more than +20º C, allow niche areas favourable to the species. Another key element is an annual rainfall intensity ranging from 1000 to 3500 mm.
In addition, soil does not appears to be a limiting factor for the development of this species, as mahogany grows in a large variety of soils, from clay superficial soils to alluvial deep soils. Nevertheless, it does not grow appropriately in terrains subject to floods, or soils with a high proportion of sand with high draining potential.
According to Arguelles (1999) forest systems that harbour mahogany populations, amount to an approximate area of 1500 million hectares in Mexico. Out of these, 500000 ha are located in Quintana Roo; 450000 in Campeche; 300000 in Chiapas; and 220000 between Oaxaca and Veracruz and the rest of them stretch between Yucatan and Tabasco states.
From a historical point of view, mahogany has undergone many stages of depredation. This is due, on one side, to the advantages that the species has with regard to its wood, colour and homogeneous wood grain, and on the other, to its friendly processing properties that allow excellent finishings.
A large part of mahogany genetic resources, with few exceptions, is in danger. It is therefore urgent to make a joint effort to decrease deforestation as much as possible, to include clear guidelines in forest management and use plans that allow concrete conservation of genetic resources.
The knowledge of genetic diversity and the factors linked to the reproduction of the species will allow to take some important measures to achieve its natural regeneration, among which: to conserve the number of individuals necessary to maintain appropriate levels of allogamy and crossing; to identify the most adequate distance between parent trees in order to effectively achieve those results; pollen and seed dispersion patterns and other aspects that allow to maintain genetic diversity and avoid endogamy in fragmented populations.
Both progenies from Costa Rica (Navarro,1999) and progenies from Central American and Mexico show high levels of added genetic variation in terms of height and diametre. As regards resistance to Hypsipyla tests carried out so far do not show any relation to the presence and the number of attacks. The Mayans managed the forest by saving mahogany and other useful species for their community, while they would cut all the remaining trees to cultivate the land, this clearing allowed enough light to penetrate through the forest and space for the forest to successfully regenerate after the land was abandoned, or the people migrated to other locations.
There is no sustainable management of the species in harvesting areas in Mexico and Central America, the reproductive cycle is not taken into consideration and silvicultural treatments do not exist to help in promoting and encouraging regeneration in an efficient way.
The promotion and marketing of unknown species, which still do not have commercial value in the market, necessary. This is particularly important in mahogany forests where this is the only species with acceptable commercial value, thus leading to over-exploitation and a relative decrease in the number of Swietenia macrophylla trees, as compared with the other species growing in the forest.
Fostering the conservation of protected areas located within the distribution range of the species and increasing the knowledge of the genetic diversity they harbour is key. It is also important to study unprotected areas in order to determine if gene pools exist and how they should be maintained, in order to ensure the conservation of those sites.
The role of planted forests in increasing forest areas is very important in order to meet the rising demand for wood and non-wood products and ecological services. The planted forests constitute an excelent option for rehabilitating degraded areas and, where possible, to constitute the base for re-establishing natural forests.
The planted forests will be established taking in account all the practicable steps to avoid replacing natural communities and ecosystems of high ecological, economical, social and cultural value.
Finally, and following Kageyama et al., (1992) it is important to point out that in order to achieve sustainable management of mahogany populations and other species of tropical forests, it is necessary to fill many of the gaps of scientific knowledge that still exist, such as following:
These are controversial questions that are the subject of intense debate and analysis in many countries, by different actors and institutions, while major research efforts are needed to clarify these aspects, especially in tropical ecosystems.
There is no doubt that the answer to these and other questions, that must be considered to achieve the sustainable management of tropical forest resources, lays within the domain of the scientific community, whose efforts focus on better knowing, managing, using and conserving these resources. The task is considerable and an answer may only be given, as soon as possible, by linking the efforts of countries, national and international institutions, as well as professionals who have a genuine interest in achieving the sustainable use of tropical forest resources.
FAO’s mandate as the main United Nations agency working with forestry development, can play a catalytic role in joining efforts aimed at reaching the objectives pursued by all the actors: achieving a sustainable use of forest populations, communities and ecosystems, an effort that implies the use and conservation of genetic diversity of tropical forest resources.
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