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A one-stop location for information on big-leaf mahogany (Swietenia macrophylla, Meliaceae)

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Caribbean mahogany in a school playground, Puerto Rico, where the species is not native.
Caribbean mahogany
Caribbean mahogany in a school playground, Puerto Rico, where the species is not native.

Big-leaf mahogany, Swietenia macrophylla King, is one of three Swietenias which are the American or true mahoganies. The American mahoganies are recognized as different species principally on the basis of their allopatric or non-overlapping distributions, with the Caribbean or Cuban mahogany (Swietenia mahagoni (L.) Jacquin) restricted to the greater Antilles and southern Florida, the Mexican or Pacific mahogany (S. humilis Zuccarini) distributed along the Central American Pacific coast from southern Mexico to Costa Rica, and big-leaf mahogany occurring much more widely from Mexico’s Yucatan Peninsula down the Central American Atlantic coast into South America as far south as Bolivia. First named Cedrelus mahagoni by Linnaeus, big-leaf mahogany was thought to be the same species as Caribbean mahogany until George King decided it was a separate species in 1886, hence the author name ‘King’ (and our website name, ‘swietking’). Environmental conditions across the ranges of the Caribbean and Pacific mahoganies tend to be drier than those faced by big-leaf mahogany, with the former species smaller statured, slower growing, and forming darker, denser wood. Morphological differences aside, the Swietenias challenge traditional concepts of species differentiation, hybridizing freely where planted in proximity or where their natural ranges briefly overlap (for example, S. humilis x S. macrophylla in northwest Costa Rica). In fact, the American mahoganies may just as usefully be thought of as ecotypes of a single species.

The Swietenias belong to a pantropical family of plants called the Meliaceae that accounts for a disproportionate number of the world’s high-value tropical timber species. To mention just a few of the most important genera, this family includes the African mahoganies, Khaya and Entandrophragma, the Asian mahoganies, Toona, Chukrasia, and Xylocarpus, and other economically important neotropical relatives such as Spanish cedar, Cedrela odorata, and Carapa. Timber qualities of these species include rich red to red-orange color, extraordinary dimensional stability, high strength-to-weight ratio, decay resistance, and excellent workability. The Swietenias consistently rate high or highest in all of these qualities.

Cedrela odorata with buttresses at Marajoara.
Cedrela odorata buttresses
Cedrela odorata with buttresses at Marajoara.
Cedrela odorata logs recently harvested in southwest Pará, Brazil.
Cedrela odorata logs
Cedrela odorata logs recently harvested in southwest Pará, Brazil.

Mahogany is a very large-statured canopy emergent tree at maturity, that is, dominant adults often emerge from and spread above the upper layer of closed forest canopy. Stem diameters as large as 3.5 meters have been reported, with buttresses (aboveground supporting roots) rising 5 or more meters up the base of the tree and crowns 70 meters tall and up to 40 meters across. But that’s the exceptional historical tree. We have seen mahogany trees as large as 2.5 meters diameter and 45 meters tall in southwest Amazonia, huge, magnificent trees in their own right. Mature tree crowns tend to be irregular in shape and comprised of a relatively few large primary branches.

Base of 2.5 m diameter mahogany in Acre, Brazil with Seu Baxinho, Frank Pantoja & Antonio Barbosa Lopes.
Large mahogany base
Base of 2.5 m diameter mahogany in Acre, Brazil with Seu Baxinho, Frank Pantoja & Antonio Barbosa Lopes.
Crown of large mahogany tree in Acre, Brazil.
Large mahogany crown
Crown of large mahogany tree in Acre, Brazil.

At maturity stem boles are cloaked in thick, deeply furrowed, nearly black bark that provides excellent fire resistance. Smaller trees have gray bark that may flake off in irregular blocks or vertical strips; a North American species with quite similar bark is the silver maple (Acer saccharinum, Sapindaceae). Most but not all mahogany trees form buttresses, which often appear even before trees reach pole size (~10 cm diameter). Buttresses may be more prominent and to extend further away from the tree when it is growing on low ground prone to brief wet season flooding or waterlogging. Mahogany buttresses tend to be thinner, more numerous, and more sinuous than those formed by other New World Meliaceae like Cedrela and Guarea.

Bark pattern on 50 cm diameter mahogany tree, Marajoara.
Mahogany bark pattern
Bark pattern on 50 cm diameter mahogany tree, Marajoara.
Bark pattern on 1.5 m diameter mahogany tree, Acre.
Mahogany bark pattern
Bark pattern on 1.5 m diameter mahogany tree, Acre.

Leaves on mature mahogany trees are 15–25 cm long, alternate and pinnately compound, with leaflets arranged in 3–4 pairs along a central rachis or leaf stem, and paripinnate, that is, with no terminal leaflet. Interestingly, the first 4 to 6 leaves on recently germinated seedlings are simple; compound leaves appear during the second growth phase if enough light is available for vigorous growth. Saplings – we call mahogany plants taller than about 50 cm and up to about 5 m height ‘saplings’ – can form huge compound leaves nearly a meter long with up to 18 oversized leaflets. But pole-sized trees larger than about 10 cm diameter begin to form adult-sized, smaller leaves. Trees this size and larger are deciduous, that is, they drop all their leaves every year during the dry season and reflush new crowns after one to several weeks. In Mexico and Central America mahogany crowns may turn crimson before dropping but we have not seen this in Brazil.

Mahogany leaves do two interesting things on tree crowns. First, they are quite glossy, with a distinctive sheen that glitters in the sun. Second, the leaflets attach to the leaf stem in such a way that they shimmy and quiver in the slightest breeze, much like the North American quaking aspen (Populus tremuloides). In combination these two qualities make mahogany tree crowns relatively easy to spot from the ground, because the enormous crowns glitter and shimmer in the sun and tropical breeze. This makes life easier for tree spotters (mateiros) working for logging companies in unlogged forests.

Mahogany leaves, flowers, and possible butterfly pollinator.
Mahogany leaves and flowers
Mahogany leaves, flowers, and possible butterfly pollinator.

Mahogany trees flower during the late dry season shortly after flushing new crowns; on sexually mature trees branching flower stalks emerge with new leaves during the late dry season as the rainy season shows signs of returning. Mahogany is monoecious, with axillary panicles of small (< 1 cm across), pale yellow, fragrant flowers that appear perfect but which are functionally either male or female. Small bees and moths commonly pollinate Meliaceous trees, but which species serve mahogany remains unknown. Though more than one flower per inflorescence may be pollinated, only one ripens to maturity over the course of the wet season.

Mahogany fruit held upright on a tree crown in Brazil.
Mahogany fruit on crown
Mahogany fruit held upright on a tree crown in Brazil.

Mahogany fruit are fist-sized woody capsules resembling a pear, held upright above the crown, containing a five-winged receptacle with seeds stacked in two rows within each cell. Fruit mature through the rainy season and dehisce along five suture lines the following dry season, releasing up to 60 large, winged seeds. In plantations mahogany can flower and fruit within 12 years of outplanting, when stem sizes are only 10–15 cm diameter. In natural forests, trees as small as 20 cm diameter may fruit occasionally, but generally trees must be larger than 30 cm diameter to fruit annually. As trees get larger, fruit production rates (fecundity) increase, with a tree 130 cm diameter capable of producing up to 1000 fruit in a given year. Fruit production by both individual trees and by local populations may vary considerably from year to year. Fluctuations in fruiting intensity may be associated with post-disturbance conditions (for example, after large forest disturbances such as hurricanes in Central America or logging) and with atypical seasonality.

Mahogany fruit; cracks show suture lines where outer shell will split apart to disperse seeds.
Mahogany fruit cracks
Mahogany fruit; cracks show suture lines where outer shell will split apart to disperse seeds.
Mahogany seeds exposed after dehiscing outer fruit shell.
Mahogany seeds exposed
Mahogany seeds exposed after dehiscing outer fruit shell.

Mahogany seeds are winged, up to 12 cm long, and wind dispersed. Their geometric stacking within fruit capsules leads to predictable variation in size, with the largest seeds exhibiting the highest germination rates and producing the largest seedlings. They are attached to the capsule receptacle near the apex of the wing, and require some degree of turbulence to dislodge them after the five fruit capsule valves dry and fall off. The actual seed is located at one end of the wing, creating an unbalanced weight that causes the seed to ‘helicopter’ as it flies from crown to forest floor. Seed weights including the wing range from 0.5–0.75 g.

Mahogany seeds ‘unpacked’ from one of 5 fruit capsule chambers, showing geometric arrangement.
Mahogany seeds unpacked
Mahogany seeds ‘unpacked’ from one of 5 fruit capsule chambers, showing geometric arrangement.
The seed with embryo that is found inside the thickened end of the winged seed.
Mahogany seeds embryo
The seed with embryo that is found inside the thickened end of the winged seed.

Seeds disperse by wind while the tree is leafless or almost leafless when exchanging its crown during the dry season. The seed dispersal zone or ‘seed shadow’ forms a parabolic shape on the leeward (downwind) side the fruiting tree. Most seeds land within 30–35 meters of parent trees, though long-distance dispersal up to several hundred meters has been observed. Dispersal distances may be longer where strong winds are common in the late dry season. This means that a given tree’s seed shadow will cover only 1–3 hectares, and within most of that area seed density will be very low. Animal dispersal has not been reported.

Diagram showing pattern of seed dispersal at Marajoara. From Grogan et al. 2006, Biotropica.
Seed dispersal pattern
Diagram showing pattern of seed dispersal at Marajoara. From Grogan et al. 2006, Biotropica.

Seed viability at the time of dispersal is commonly > 90%. Seeds have no long-term dormancy mechanisms, but can survive four to six months in the field under dry conditions and up to 10 months when dried and chilled. Moisture availability associated with the onset of the rainy season triggers germination. Germination generally begins within 10 days of sowing in nurseries under moist conditions, and continues for about three weeks afterwards, with an average time between planting and total germination of 28 days. Differences in germination rates between ‘large’ and ‘small’ seeds and among fruit capsules of different sizes have also been observed.

Mahogany seedling with first simple leaves; about 20 cm tall.
Mahogany seedlings
Mahogany seedling with first simple leaves; about 20 cm tall.
One-year-old mahogany sapling in artificial clearing, with Valdemar Ribeiro la Cerda.
Mahogany sapling
One-year-old mahogany sapling in artificial clearing, with Valdemar Ribeiro la Cerda.

After germination, mahogany seedlings grow to 15–25 cm height, with two to four narrow cotyledons or vestigial leaves spaced alternately along its lower length and then two pairs of nearly opposite, heart-shaped simple leaves on short petioles near the stem apex. From emergence to full-sized first leaves requires 10–14 days. Seedlings will flush new growth within two to four weeks after lignification; when conditions are ideal, especially in high light environments, the first flush may add up to eight simple leaves and 5–10 cm of stem growth, with new leaves much larger and more elongate than first leaves. Vigorous seedlings may begin to form compound leaves during the second flush four to six weeks later, setting bi- or trifoliolate leaves and then, in successive flushes as height extension accelerates, four- to eight-foliolate leaves up to 18-foliolate as saplings rise above 1.5 m tall. New leaves are set in spiraling formation along the expanding apical leader, widely spaced at first and then bunching tightly as apical growth slows, the last (highest) leaves tending to be much smaller than the first. Bunched leaf scars on stems of saplings and poles delineate successive apical flushes which occur three to four times annually.

Certain adult mahogany trees at Marajoara produce albino seedlings at low rates (< 5%) each fruiting year. These are normal sized but pale pink, and cannot photosynthesize in full or partial sunlight, never surviving longer than two to three months.

Seedlings, saplings and poles are strongly heliotropic, capable of growing at steep angles towards the sun in open spaces as overhead canopy gaps close with secondary growth. Fast-growing saplings can add up to one meter’s height in a single flush, setting 20–30 large compound leaves whose combined weight may cause the new crown and even the entire stem to flop groundwards. As saplings grow taller than 2 meters height, apical dominance weakens and lateral sprouting may occur along the upper stem. This tendency is more pronounced on plants growing in open conditions (for example, in plantation settings) compared to plants growing in dense secondary regrowth.

The transition from juvenile to adult growth patterns – from an evergreen habit with multiple annual apical flushes to complete crown loss and reflush once annually during the dry season – occurs during the early pole phase between 5–10 cm diameter. Leaf size and leaflet number also diminish once adult growth patterns are set. Whether this transition is prompted by environmental or genetic factors is unknown.

SELECTED SOURCES

Cornelius J, Wightman K, Grogan J & Ward S (2004) Swietenia (American mahogany). In: Burley J (Ed.), Elsevier Encyclopedia of Forest Sciences, pp. 1720-1726. Elsevier Science Publishers BV, Amsterdam, The Netherlands.

Grogan, JE (2001) Bigleaf mahogany (Swietenia macrophylla King) in southeast Pará, Brazil: a life history study with management guidelines for sustained production from natural forests. PhD dissertation, Yale University School of Forestry & Environmental Studies, New Haven, CT.

Grogan J, Barreto P & Veríssimo A (2002) Mogno na Amazônia Brasileira: Ecologia e Perspectivas de Manejo (Mahogany in the Brazilian Amazon: Ecology and Perspectives on Management). IMAZON, Belém, PA, Brazil. 58 pp.

Gullison RE, Panfil SN, Strouse JJ & Hubbell SP (1996) Ecology and management of mahogany (Swietenia macrophylla King) in the Chimanes Forest, Beni, Bolivia. Botanical Journal of the Linnean Society 122: 9-34.

Lamb FB (1966) Mahogany of Tropical America: Its Ecology and Management. University of Michigan Press, Ann Arbor, MI, USA.

Morris MH, Negreros-Castillo P & Mize C (2000) Sowing date, shade, and irrigation affect big-leaf mahogany (Swietenia macrophylla King). Forest Ecology and Management 132: 173-181.

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