Description
Big-leaf mahogany is a large-statured canopy emergent tree at maturity. Stem diameters as large as 3.5 meters have been reported, with buttresses rising 5 or more meters up the base of the tree and crowns 70 meters tall and up to 40 meters across. Mature tree crowns tend to be irregular in shape and composed of relatively few large primary branches.
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. 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 when a tree is growing on low ground prone to wet season flooding.
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. 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 form huge compound leaves nearly a meter long with up to 18 oversized leaflets but form adult-sized, smaller leaves when the reach pole-size. Trees this size and larger are deciduous and reflush new crowns after one to several weeks.
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 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 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 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.
Read more about this topic: Swietenia Macrophylla
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