Unasylva - No. 118 - Wood for fuel (original) (raw)

Guatemalan conifers

Guatemala is one of the few tropical highland regions in are well represented

Thomas T. Veblen

THOMAS T. VEBLEN, of the Facultad de Ingenieria Forestal, Universidad Austral de Chile, worked extensively in Guatemala.

Vast areas of the world's high altitude tropics have been cleared of their native vegetation and today suffer from accelerated erosion and watershed deterioration. This is especially true in the tropics of Latin America where the densely settled highland regions from central Mexico to the central Andes have long been subject to excessive forest clearing and consequent decline in the productivity of the land (Budowski, 1966, 1968; Crawford et al., 1970; Daugherty, 1973; Ellenberg, 1964; Falla, 1967; Hutchinson, 1967; Smit, 1971). Today, these areas are in critical need of afforestation to provide for watershed stability and to meet rapidly increasing demands for forest products.

MEASURING ONE OF 17 SPECIES OF CONIFERS - a treasure in seeds

Nowhere is the need for conservation of surviving natural forest, as a source of seed for afforestation, more pressing than in highland Guatemala. Guatemala is one of the few tropical highland regions in which conifers are well represented. The conservation and potential of the Guatemalan populations of these coniferous taxa for the afforestation of other tropical highland regions are the subject of this article.

Seven genera of conifers - Abies, Cupressus, Juniperus, Pinus, Podocarpus, Taxodium, and Taxus - which include 17 species are present in highland Guatemala (see table). No other area of equally low latitude - approximately 14 to 16° N - is characterized by as great a variety of coniferous taxa. Except for Podocarpus, which is widely distributed in the tropics, the evolutionary origin of the Guatemalan conifers lies in the mid-latitudes of the Northern Hemisphere. The forests of the western highlands of Guatemala are an extension of the coniferous forests of the Mexican highlands. Although Pinus oocarpa forests occur extensively in central Honduras and the northwestern highlands of Nicaragua (Denevan, 1961) and a few of the other conifers extend into El Salvador and Honduras (Mirov, 1967; Molina, 1964), the number of coniferous taxa rapidly diminishes equatorward from Guatemala.

Mexico and Guatemala possess more species of the genus Pinus than any other region of comparable size (Mirov and Larsen, 1958); nine species are present in the western highlands of Guatemala alone (Aguilar, 1961). Mirov (1967) argues that the highlands of Mexico and Central America are a secondary centre of evolution for the genus Pinus. He cites especially the pronounced interspecific and intraspecific variation characteristic of the pines of this region. In contrast to the pines of other areas, the pines of the American tropics interbreed often and, as a result, new varieties and species are frequently described for Mexico and Central America (Aguilar, 1961; Loock, 1950; Schwerdtfeger, 1953; Mirov, 1958; Martinez, 1948). At least 29 species are now recognized for the highlands of Mexico and Guatemala (Mirov, 1967). The rugged topography and altitudinal variation of highland Guatemala have created an extremely diverse mosaic of physical environments; such habitat diversity favours rapid speciation (Stebbins, 1959). Similarly, the extended tropical growing season favours survival and development of pine seedlings and thus may be beneficial to pine speciation. Furthermore, the long and continuing volcanic history of highland Guatemala has repeatedly created exposed conditions to which the pines are especially well adapted.

In Guatemala the Haplaxylon section of the genus Pinus (i.e. the soft pine group) is represented by two species - P. strobus var. chiapensis and P. ayacahuite (Aguilar, 1961). The former is widely distributed in southern Mexico at altitudes of 500 to 2 000 m, but in Guatemala it is restricted to a few isolated stands in the Cuchumatanes mountains and it is, too rare to be of economic importance. On the other hand, P. ayacahuite is the most highly valued pine in Guatemala because of the relative ease with which its soft wood may be worked with the crude carpentry tools possessed by the Mayan Indian inhabitants of the western highlands. P. ayacahuite is a large tree, normally attaining a height of at least 35 m and occasionally over 45 m; the diameter at breast height of the largest specimens exceeds 2 m. Despite the heavy demands for this species for use in the local construction and furniture industries, P. ayacahuite continues to be abundant at altitudes of 2 500 to 3 200 m in the Cuchumatanes and in the Departments of Totonicapán and San Marcos.

CONIFERS OF HIGHLAND GUATEMALA

Sources: Aguilar (1961), Standley & Steyermark (1958), and Veblen (1975).

Conifer is used to refer to members of the order Coniferales; some authors place Taxaceae and Taxodiaceae in the separate order Taxales. Pinus caribaea Morelet and Podocarpus guatemalensis Standl. are the only other conifers native to Guatemala but do not occur in the highlands (i.e. at altitudes above 1500 m).

The remaining pine species of highland Guatemala belong to the Diploxylon section (i.e., the hard pine group) in which interbreeding of the many morphologically similar species is usually infrequent and is believed to be prevented by genetic barriers. However, the Guatemalan Diploxylon pines - P. montezumae, P. rudis, P. pseudostrobus, P. tenuifolia, P. oocarpa, P. teocote var. guatemalensis, and P. quichensis - interbreed freely, producing fertile offspring, and, thus, constitute an important exception to this generalization (Mirov, 1967). Intermediate forms of P. rudis and P. montezumae and of P. pseudostrobus and P. tenuifolia are common. Although P. oocarpa does not appear to cross with any of the other species, it does produce an easily recognizable variety - P. oocarpa var. tecumumani Schw. (Aguilar, 1961). Together, the pines constitute the most conspicuous element in the native vegetation of western Guatemala between altitudes of approximately 1 600 and 4 000 m.

The most common pines at altitudes of 1 600 to 2 400 m are P. tenuifolia, P. montezumae, and P. oocarpa, all of which exhibit an adaptability to a wide range of climatic conditions. The latter two species possess a remarkable capacity to grow on sites of very thin soil in semi-arid areas such as the east-west trending valleys in the southern part of the Department of Huehuetenango. In Guatemala these three pines constitute an important source of wood for construction and fuel and are heavily exploited for the resinous splinters, known as ocote, which are used for torches and kindling. P. oocarpa ranges from the Sierra Madre of northwestern Mexico to the uplands of northwestern Nicaragua and is, by far, the most important commercial species in Honduras (FAO, 1968). In Guatemala at slightly higher elevations, 2 400 to 2 800 m, P. pseudostrobus predominates and is in much demand as a source of lumber and fuel. P. rudis ranges from 2 300 to 4 000 m, occurring in extensive pure stands at altitudes above 3 200 m; even at these high altitudes, it is frequently cut for lumber and fuel.

Second only to the pines in importance as a source of fuel and lumber in Guatemala is Cupressus lusitanica, the southernmost American cypress. The Guatemalan cypress is probably native at altitudes of 2 200 to 3 000 m but plantings thrive at altitudes near sea level. It grows on a wide range of soil types and often attains a height of over 30 m and a trunk diameter of well over 1 m.

The conifer which is in most imminent danger of disappearing from the forests of Guatemala is Abies guatemalensis, the Guatemalan fir. This magnificent tree, which often reaches a height of 45 m, was one of the most common trees in the western highlands in the nineteenth century (Brigham, 1887; Dollfus and Mont-Serrat, 1868) and was still locally abundant in the 1940s on moist sites at altitudes of 2 700 to 3 500 m (Standley, 1945). Today, it is extremely rare. Excessive cutting of A. guatemalensis saplings, are highly prized as Christmas trees by the residents of Guatemala City, and the destruction of seedlings by sheep and other livestock have nearly eliminated all regeneration of this species. The infrequent production of cones at this southernmost extension of the range of true fir also suggests that A. guatemalensis will soon be eliminated from the forests of Guatemala.

TENDING A SEEDLING NURSERY - reforesting the future

The three coniferous genera of northern affinities which are exploited the least in Guatemala are Taxodium, Taxus, and Juniperus. The Montezuma bald cypress (Taxodium mucronatum) is widely distributed in Mexico but, in Guatemala, is found only in small numbers along streams at elevations of 800 to 2 000 m in the Department of Huehuetenango (Standley and Steyermark, 1958). Although the wood of this large tree is highly appreciated in Mexico for its resistance to decay and insect attacks, in Guatemala the tree is too rare to be of any economic importance. Taxus globosa is the only species of yew found south of the United States. In Guatemala, it is restricted to moist sites at altitudes of 2 200 to 3 000 m in the Cuchumatanes and central Guatemala. T. globosa is also too rare to be of any economic importance although the Indians use its bark as a source of tannin. The two southernmost American species of Juniperus - J. comitana and J. standleyi - occur in Guatemala. Although the former is a very rare tree there, the latter species is one of the most common trees in the Cuchumatanes at altitudes above 3 000 m (Standley and Steyermark, 1958). Locally, J. standleyi is an important source of firewood and lumber, especially for fences and roof shingles, and because of its capacity to grow at altitudes as great as 4 100 m, it has considerable potential as a source of fuel and for watershed control in other high altitude tropical regions.

The practical significance of the presence of this assemblage of coniferous species in highland Guatemala lies in the fact that the development of the modern forest industry has involved primarily coniferous trees which are generally lacking from tropical latitudes. Although the development of forest industries in tropical countries need not necessarily follow the temperate latitude model, the relative lack of conifers adapted to the tropics has been a serious constraint for foresters working in the low latitudes (Dyson, 1965; 1967; Din, 1958). Despite early recognition of the possibilities of Mexican and Guatemalan conifers for use in afforestation of subtropical and tropical highland areas, this potential has been inadequately realized (Mirov and Larsen, 1958; Popenoe, 1941). In afforestation projects in the high altitude tropics, such as in the central Andes, eucalypts and Monterey pine continue to be the overwhelmingly predominant taxa (Budowski, 1968; Cochin, 1962; Dickinson, 1969; Miller, 1974). This is in marked contrast to the importance in plantations in tropical lowland areas of such Guatemalan pines as P. caribaea and P. oocarpa.

One of the few highland Guatemalan conifers to be widely planted outside of its native range is Cupressus lusitanica. In the equatorial highlands of Kenya, extensive forests of the native Juniperus procera Hochst and Podocarpus milanjianus Rendle have been replaced with plantations of C. lusitanica. After 35 years, the plantations of the Guatemalan cypress were yielding 11 times as much wood per hectare as the native species (Dyson, 1965). Similarly, this species has been planted in São Paulo, Brazil, where it has formed excellent stands and is an important source of pulp (Sonntag, 1973). It is also used as a source of pulp in the Venezuelan Andes (Schulz and Rodriguez, 1967) and is one of the most commonly planted species in highland Costa Rica and in the Colombian Andes (Holdridge, 1955; Tschinkel, 1972).

Mexican species

Although the pine populations of highland Guatemala have not been significantly exploited as source material for planting in exotic environments, the Mexican populations of several of the Mexican-Central American pines have been so utilized, especially in Africa. Pinus pseudostrobus, which is fast-growing and one of the world's best timber-producing pines, has done well in northeastern South Africa at altitudes of 850 to 1 250 m (Loock, 1950); it has also been successfully introduced to Malawi (formerly Nyasaland) where its potential for reforestation is very promising (Din, 1958). Although P. pseudostrobus is not listed as one of the principal plantations species for any Central or South American country (FAO, 1968), it has been planted at altitudes of 2 200 to 2 400 m in Venezuela since 1961 (Schulz and Rodriguez, 1967). Experimental plantings of P. pseudostrobus in Venezuela have been discouraging because of the frequency of bifurcated trunks. The seeds used in Venezuela were collected in Mexico rather than in Guatemala where the frequency of bifurcated trunks in populations of P. pseudostrobus is very low; thus, it is likely that seed provenance is a critical consideration in the use of Mexican-Central American pines in afforestation projects. Seeds from populations of P. pseudostrobus growing at middle elevations (1 300 to 2 200 m) have recently been collected and provenance trials are currently under way (Kemp, 1973b).

Seed provenance

The importance of seed provenance is also illustrated by P. oocarpa. In South Africa, seeds from Mexico have yielded trees of poor form while seeds from Honduras, where P. oocarpa is probably represented by different ecotypes, have produced trees of good form and vigour. P. oocarpa has also been successfully established in Kenya (Din, 1958) and Venezuela (Lamprecht and Finol, 1959) and produces good stands in São Paulo (Sonntag, 1973). Due to its capacity to resist drought and fire, as well as its ability to grow on very poor soils, P. oocarpa is of particular interest as a plantation species in seasonally dry tropical areas. Recently, seed has been collected from altitudes of 650 to 1 700 m in Guatemala and provenance testing has been initiated (Kemp, 1973a).

P. montezumae is another widespread species in which its variable success as a cultivated exotic is possibly attributable to genetic variation within its native range. It has been successfully planted in South Africa, Malawi, Kenya, the Rhodesia, Zambia, and northeastern Australia, and is known for its resistance to drought and frost (Loock, 1950; Din, 1958). Despite its great adaptability, P. montezumae is almost unknown in the Americas south of Guatemala (FAO, 1968). Trials with P. ayacahuite in Kenya and South Africa have yielded good results but this species is still not widely planted (Din, 1958). Even though P. ayacahuite lumber is highly esteemed in southern Mexico and Guatemala, this species is known outside of the region primarily as an ornamental (Dallimore and Jackson, 1966). The other Guatemalan pines - P. strobus var_. chiapensis, P. teocote, P. tenuifolia, P. rudis_, and P. quichensis - are almost unknown outside of their native ranges.

The highly successful cultivation in exotic environments of Central American pines, such as P. oocarpa and P. caribaea, has been based on plantings representing only a small fraction of the total genetic variation available. In the case of pines adapted to higher altitudes the provenances have been primarily from Mexico while Guatemalan populations have been largely overlooked. This is lamentable because the Guatemalan pine populations are adapted to lower latitudes than those of Mexico, and, thus, may be especially suitable for planting in the central Andean countries of Ecuador, Peru, and Bolivia where Eucalyptus spp. and Pinus radiata are the most frequently planted species (FAO, 1968). In Ecuador, at altitudes of 2 500 to 3 500 m, P. radiata has done remarkably well (Miller, 1974), and it is likely that the Guatemalan pines would similarly be suitable for planting at both higher and lower altitudes. Even within the altitudinal range at which P. radiata thrives, the planting of Guatemalan species should be considered to avoid basing a country's entire forest plantation industry on one or two species.

Land competition

The most severe threat to the forest gene resources of highland Guatemala is a direct result of the rapid growth of the human population of Guatemala - from 2.8 million in 1950 to 5.2 million in 1973 (Guatemala, 1973a). With over 50 inhabitants per square kilometre, Guatemala ranks second only to El Salvador in density of human occupation in Central America. The need for more land on which to produce the foodstuffs necessary to sustain Guatemala's growing population requires the conversion of vast areas of forest to agricultural land. Attempts to colonize the tropical lowlands of northern Guatemala (the Petén) have not yet been successful on a large scale; and since the fertile soils of the Pacific coast and piedmont are used primarily for the production of export products, it is the highland forests which are being felled most rapidly to make more land available for the production of domestic foodstuffs.

Despite the fact that Guatemala is a net importer of forest products, the domestic demand for lumber and firewood is contributing significantly to the demise of the remaining forests. Pine, especially P. ayacahuite, is heavily exploited for the manufacture of crude, cheap furniture which is used by the lower income groups throughout the country. The pines, along with the Guatemalan cypress, are also in much demand as construction material and firewood. As recently as 1964, firewood was the only cooking fuel in 84 percent of all houses in Guatemala (Guatemala, 1966), and with the currently high prices of petroleum products any abatement in the dependence on forest products for fuel is unlikely.

The highlands

Today, the most extensive forests remaining in the highlands are the cloud-forests, pine-oak forests, and coniferous forests above 2 700 m in the Departments of Totonicapán and San Marcos, in the more isolated areas of the rugged Cuchumatanes, and at the highest elevations of Sierra de las Minas (Department of El Progreso). Frequently, in these high altitude refuges, the regeneration of P. ayacahuite and Abies guatemalensis as well as that of other forest species is seriously inhibited by the destruction of seedlings by sheep and other domestic herbivores. Infestations of bark beetles (Dendroctonus spp.) which first became serious in the 1930s (Johnston, 1942) also have devastated extensive areas of P. rudis at the higher elevations.

Following beetle attacks regeneration is usually vigorous and, thus, the populations are not seriously threatened except where livestock or fire destroy the seedlings.

Cutting

Finally, some of the dysgenic cutting practices of the local population tend to reduce the frequency of some of the more desirable genotypes. For example, a long history of preferential cutting of the best formed trees has allowed the perpetuation of less desirable phenotypes. This is well illustrated by the high frequency of bifurcated trunks in stands of Pinus ayacahuite in the Department of Totonicapán Regardless of the probable diminution of superior genotypes which may have been incurred by the Indians' cutting practices, the persistence of forest land in a region characterized by such a desperate need for more agricultural land is truly remarkable.

Encouraging developments with regard to forest conservation in Guatemala include the growing recognition of the necessity of national parks (Pyle, 1972) and the establishment of reserves for the protection of the Quetzal (Pharomachus mocinno) and other avian fauna (La Bastille, 1973a, 1973b). Similarly, there is substantial interest in land-use planning and resource management policy on a national scale (Guatemala, 1973b) and, given the importance of tourism in Guatemala, forest preservation for aesthetic reasons should be a persuasive economic argument.

Conservation

Undoubtedly, in situ conservation through the establishment of strictly controlled natural reserves would be the ideal way to preserve the forest genetic resources of highland Guatemala. It would permit continued natural genetic evolution and also minimize man-caused genetic erosion. Furthermore, in situ conservation allows preservation of all the constituent species of an ecosystem rather than only those which are judged to be of immediate economic value. However, the social and economic conditions characteristic of many developing countries, such as Guatemala, may render in situ gene conservation a high-risk strategy (Kemp, 1975; FAO, 1974b). For example, in Guatemala the demand for more fuel and for more agricultural land continues to grow at an alarming rate. Until the rate of population growth is greatly reduced the prospects for conserving the remaining forests of highland Guatemala will continue to be bleak

Safer strategies for preserving the valuable genetic resources of the coniferous flora of highland Guatemala include a massive programme of seed collection and the establishment o ex situ conservation stands. Under the auspices of FAO and the Commonwealth Forestry Institute at Oxford, wide-range seed collection of Central American pines was initiated in 1969 for provenance research and the establishment of ex situ conservation stand (Kemp, 1975). Priority was given to the pines of low to middle elevations - primarily P. caribaea and P. oocarpa and secondarily P. pseudostrobus.

Unique diversity

While the concentration of these initial efforts on the lowland pine species of proved economic value is certainly justified, it must be remembered that the seed collections to date represent only a small fraction of the genetic variation of the Central American conifers. The forest gene resources of highland Guatemala which are unique because of the diversity of coniferous taxa growing naturally at a low latitude are today largely unprotected and in imminent danger of serious depletion. The conservation of these forest genetic resources should be a matter of international concern, and the proposal to continue and to expand seed collection and the establishment of ex situ conservation stands of Central American pines deserves international financial support (FAO, 1974a). It is critical that the populations of highland Guatemalan conifers be included in such conservation schemes. This is the most certain means of preserving Guatemalan populations of several tropical conifers which may be especially suitable for planting in the central Andes where the only available source of fuel is frequently animal dung (Cochin, 1962). If the initiation of a programme aimed at the preservation of this gene pool is delayed much longer, the options available to future generations for afforesting much of the world's tropical highlands will be lamentably reduced.

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