|Ochroma pyramidale at the Large tree habit at Tropical Gardens of Maui, Iao Valley Road, Maui|
(Cav. ex Lam.) Urb.
Ochroma pyramidale, commonly known as the balsa tree (also O. lagopus), is a species of flowering plant in the mallow family, Malvaceae. It is a large, fast-growing tree that can grow up to 30 m (100 ft) tall. Balsa wood is a very lightweight material with many uses. Balsa trees are native to southern Brazil and Bolivia north to southern Mexico.
A member of the mallow family, O. pyramidale is native to southern Brazil and northern to southern Mexico, but is now found in many other countries (Papua New Guinea, Indonesia, Thailand, Solomon Islands). It is a pioneer plant, which establishes itself in clearings in forests, either man-made or where trees have fallen, or in abandoned agricultural fields. It grows extremely rapidly, up to 90 ft (30 m) in 10–15 years. The speed of growth accounts for the lightness of the wood; balsa wood has a lower density than cork. Trees generally do not live beyond 30 to 40 years.
Flowers are produced from the third year onwards, typically at the end of the rainy season when few other trees are in flower. The large flowers open in the late afternoon and remain open overnight. Each may contain a pool of nectar up to 1 in (3 cm) deep. Daytime pollinators include capuchin monkeys. However most pollination occurs at night. It was once thought that the main pollinators were bats; however recent evidence suggests that two nocturnal arboreal mammals, the kinkajou and the olingo, may be the primary pollinators.
Ecuador supplies 95 percent or more of commercial balsa. In recent years, about 60 percent of the balsa has been plantation grown in densely packed patches of around 1000 trees per hectare (compared to about two to three per hectare in nature). It is evergreen, or dry-season deciduous if the dry season is long, with large (30–50 cm or 12–20 in) weakly palmately lobed leaves. Trees are classified as hardwood because of the shape of their leaves, so balsa, with its large, broad leaves is classified as hardwood despite being very soft. It is the softest commercial hardwood. The trees are harvested after six to 10 years of growth. The name balsa comes from the Spanish word for "boat".
Balsa lumber is very soft and light, with a coarse, open grain. The density of dry balsa wood ranges from 40–340 kg/m³ (2.5–21 lb/ft³), with a typical density of about 160 kg/m³ (10 lb/ft³). The light weight of the wood derives from the fact that the tree has large cells that contain water. After the water is driven off in an extended drying process (kiln dried for two weeks), the large surface area of the resulting holes gives strength. Unlike dry rotted wood, the surface is made of the usual strong cellulose/lignin mix. As it is low-density but high in strength, balsa is a very popular material to use when making light, stiff structures in model bridge tests, model buildings, and for the construction of model aircraft, as well as full-sized light wooden aeroplanes, most famously the World War II de Havilland Mosquito. Balsa is used to make wooden crankbaits for fishing.
Balsa wood is often used as construction material for radio controlled model aircraft and as a core material in composites; for example, the blades of many wind turbines are made partially of balsa. In table tennis paddles, a balsa layer is typically sandwiched between two pieces of thin plywood. Balsa wood is also used in laminates with glass-reinforced plastic (fiberglass) for making high-quality balsa surfboards and the decks and topsides of many types of boats, especially pleasure craft under 30 m (100 ft) in length. Starting with the 5th generation Chevrolet Corvette, the floor pan of the Corvette was composed of balsa sandwiched between two sheets of carbon fiber reinforced plastic. Norwegian scientist/adventurer Thor Heyerdahl, convinced that early contact between the peoples of South America and Polynesia was possible, built the raft Kon Tiki from balsa logs, and upon it he and his crew sailed the Pacific Ocean from Peru to the Polynesian Tuamotu Archipelago in 1947. Balsa wood is also a popular wood type used in the art of whittling.
Two balsa rafts and a kayak at Lagos de Montebello in Chiapas, Mexico.
Balsa construction in a Paul K. Guillow, Inc. "stick & tissue" model airplane.
See also 
- "Ochroma pyramidale (Cav. ex Lam.) Urb.". Germplasm Resources Information Network. United States Department of Agriculture. 2009-10-26. Retrieved 1997-05-22.
- Angier, N. & Ziegler, C. (2011), "Treetop happy hour", National Geographic 219 (5): 130–143
- "balsa, n.". OED Online. March 2013. Oxford University Press. 9 May 2013 <http://www.oed.com/view/Entry/15041?redirectedFrom=Balsa&>.
- Terry Porter: "Wood Identification and Use", page 160. Guild of Master Craftsman Publications Ltd. 2004
- "Balsa Wood description". Retrieved 2011-01-02.[dead link]
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