| Calliandra : A Versatile Small Tree for the Humid Tropics |
The genus Calliandra comprises more than 100 Central and South American shrubs or small trees as well as a few herbs. It occurs both in wet and dry tropical regions.
Several Calliandra species (notably Calliandra surinamensis, which produces masses of red flower balls resembling fiery pompons) have been widely planted as ornamentals in tropical countries. Only two species, however, have been planted for forestry purposes: Calliandra calothyrsus and Calliandra tetragona. As noted earlier, both were introduced to Indonesia in 1936 from Guatemala, and since then their use has gradually spread over the island of Java. In the main, Indonesians use Calliandra calothyrsus, which has red flowers. Calliandra tetragona, which has white flowers, has proved to be slower growing and less satisfactory and is not dealt with in this report.
Calliandra calothyrsus is a small tree (or perhaps more correctly, a tall shrub) that usually reaches a height of 4-6 m, but under favorable circumstances it may reach 12 m.
The dark-green compound leaves are feathery (like those of leucaena and other Mimosaceous species) and they fold at night. The crown of individual stems is moderately heavy, but many sprouts occur and the canopy of a stand can become very dense. In humid climates the tree remains evergreen, but in seasonal climates it sheds its leaves during the dry season. Under severe drought conditions young stems and branches may die back, but they usually regrow once rains start.
Calliandra's blackish-brown stems are small, reaching a maximum base diameter of 30 cm in Indonesia. Mostly they are harvested when only 3-5 cm in diameter.
This species has both superficial and deep-growing roots. Sometimes a taproot is formed. Roots on seedlings only 4-5 months old can be 1.5 m deep and spread 2 m out from the stem.
The above-ground parts of the species are short lived, and after 12 years the old stem may get brittle. However, the root stock usually remains vigorous and will sprout readily. This rapid sprouting can be used to manage the trees under a coppice system. In eastern Java trees have been observed still sprouting well after 22 years of annual coppicing.
The flowers are subterminal inflorescences with numerous long, hairlike purple or red stamens, which give the plants a handsome, showy appearance. In Indonesia flowering occurs year-round but is heaviest in the dry season. The flowers begin appearing about 4-6 months after planting. They form more in the open than in shade and are pollinated by insects such as bees.
The fruits consist of pods (8-11 cm long and 12 mm wide) that contain 3-15 seeds. Seeds mature 2 months after pollination and apparently have no dormancy period, so they can be planted immediately.
Calliandra's native range is in Central America roughly from Mexico to Panama (see map, page 19). It does not seem to have been cultivated or studied there. It is a secondary species that grows in thickets, often on steep, open slopes. It can be found as a pioneer species on recently exposed soils such as those resulting from landslides. Under these conditions calliandra often forms low, bushy thickets only 1-3 m high.
As noted, calliandra establishes symbioses with rhizobial microorganisms. It appears not to need specific inoculation: wherever it grows, abundant nodules are dispersed over the root system.
Nodules are elongated and often branched, and they are red inside. Strains of Rhizobium isolated from the nodules are both fast and slow growing. No information is yet available on the amount of nitrogen each can fix.
In nature, calliandra's fine roots and root hairs are also usually infected with a beneficial mycorrhizal fungus, whose network of hyphae helps the plant to obtain phosphorus and other nutrients. This probably enables calliandra to grow in soils deficient in soluble phosphorus and other minerals necessary for quick growth.
These symbioses make calliandra very adaptable. This does not preclude the possibility that growth might be improved by inoculation with selected superior strains of rhizobia and mycorrhizae, however.
In its native Latin American habitat calliandra sometimes grows up to 1,800 m, but normally it is found at mid-elevations below about 1,300 m. On Java it is cultivated at altitudes between 150 and 1,500 m; however, it seems to perform best at elevations between 250 and 800 m.
The plant probably requires rainfall in excess of 1,000 mm per year and does best in areas with 2,000-4,000 mm of annual rainfall. It can withstand drought periods lasting 3-6 months with no loss of leaves. Longer dry spells cause the leaves to fall, and some top dieback may occur.
In Indonesia calliandra is found in such soil types as andosols, vertisols, ultisols, latosols, and regosols, but no data are available on the comparative performances. The tree appears to prefer light soil textures and slightly acid conditions. The plant grows notably well on slightly acid clay soils of volcanic origin. It does not tolerate poorly drained soils, and the trees may die after 2 weeks of oxygen depletion caused by waterlogging. It will, however, grow well where the soil water level is high and if drainage is adequate, such as on stream banks or valley slopes.
On higher slopes or ridges with poorly drained, calcareous clay soils, growth is slow.
Pests and Diseases
In Indonesia calliandra has so far been free of any serious pests and diseases. Several undetermined insects-a scale on branches and stems, a trunk borer, and a looper eating the leaves-have been observed, but the damage they cause appears to be minimal. The only serious attacks have been in nurseries, where snails and rats sometimes destroy the tender, tightly packed seedlings.
The rough coppice harvesting that calliandra receives from villagers can leave the stumps vulnerable to fungus infections. If stems are not cut cleanly, or high enough for vigorous resprouting, then fungi (for example, Xylaria species and Corticium salmonicola) may infect and kill the weakened stumps.