Leucaena leucocephala is a small fast-growing mimosoid tree native to southern Mexico and northern Central America (Belize and Guatemala) and is now naturalized throughout the tropics including parts of Asia.
Use by humans
During the 1970s and 1980s, it was promoted as a "miracle tree" for its multiple uses. It has also been described as a "conflict tree" because it is used for forage production but spreads like a weed in some places.
The legume is promoted in several countries of Southeast Asia (at least Burma, Cambodia, Indonesia, Laos, and Thailand), most importantly as a source of quality animal feed, but also for residual use for firewood or charcoal production.
Forage and fodder
In many cases this acid is metabolized by ruminants to goitrogenic DHP [3-hydroxy-4(1H) pyridone] in the rumen, but in some geographical areas, ruminants lack the organisms (such as Synergistes jonesii) that can degrade DHP.
In such cases, toxicity problems from ingestion of Leucaena have sometimes been overcome by infusing susceptible animals with rumen fluid from ruminants that possess such organisms, and more recently by inoculating cattle rumina with such organisms cultured in vitro.
Such measures have facilitated Leucaena use for fodder in Australia and elsewhere.
Green manure and biomass production
Leucaena leucocephala has been considered for biomass production because its reported yield of foliage corresponds to a dried mass of 2,000–20,000 kg/ha/year, and that of wood 30–40 m³/ha/year, with up to twice those amounts in favorable climates. In India it is being promoted for both fodder and energy.
It is also efficient in nitrogen fixation, at more than 500 kg/ha/year.
It has a very fast growth rate: young trees reach a height of more than 20 ft in two to three years.
Food for humans
The young pods are edible and occasionally eaten in Javanese vegetable salad with spicy peanut sauce, and spicy fish wrapped in papaya or taro leaves in Indonesia, and in papaya salad in Laos and Thailand, where they are known as phak krathin (Thai: ผักกระถิน). In Mexico it is eaten in soups and also inside tacos, it is known as guaje. Additionally, the state of Oaxaca in Mexico derives its name from the Nahuatl word huaxyacac, the name for Leucaena leucocephala trees that are found around Oaxaca City.
Pulpwood for paper industry
Recently, the wood part of the Subabul tree is used for making pulp in the pulp and paper industry. In the southern and central states of India, Subabul is the most important pulpwood species for making pulp. It has huge positive socio-economic impact on the livelihood of the small farmers where Subabul is grown as an industrial crop. This provides an alternate crop choice to the farmers of Andhra Pradesh and Telangana states of India where they are also growing cotton and chillies.
It is a highly invasive species in the arid parts of Taiwan, The Bahamas, the Hawaiian Islands, Fiji, Puerto Rico, Hong Kong, South Africa, and northern Australia, as well as in South America and Southern Europe.
It grows quickly and forms dense thickets that crowd out all native vegetation.
In India, this tree was initially promoted for afforestation due to its fast-growing nature. However, it is now considered unsuitable for urban planting because of its tendency to get uprooted in rain and wind. Eight of every ten trees uprooted by wind in Pune are L. leucocephala.
Potential as bioherbicidal agent
Leucaena leucocephala is an allelopathic tree. Phytotoxic allelochemicals, such as mimosine and certain phenolic compounds, including p-hydroxycinnamic acid, protocatechuic acid, and gallic acid, have been identified in the leaves of the species. Bioherbicidal activity of L. leucocephala on terrestrial plants and aquatic weed water hyacinth were reported.
Flowers and immature fruit
Sapling of Leucaena leucocephala. The cotyledons are visible.
Pod and seeds
Subabul growing wild on the outskirts of Mumbai
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