 |
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Tropical Deforestation
Overexploitation, misuse, and poor management have significantly depleted what was once one of earth's most abundant natural resources: its forests. Today forests are being converted to other uses at the rate of nearly 11.3 million hectares a year, with most of the loss-7.5 million hectares-occurring in the humid tropical regions of the Third World.
Many nations in the humid tropics now confront the economic, social, and ecological problems caused by deforestation. A 1982 United Nations survey revealed that the closed tropical forests are declining at annual rates of 4.2 million hectares in Latin America, 1.8 million hectares in Asia, and 1.3 million hectares in Africa.
The decline is uneven. Some tropical forests are only slightly disturbed, but many others face extinction. For example, deforestation in Africa ranges from 0.2 percent a year in Zaire to 10 percent in Nigeria and the Ivory Coast. In Latin America the annual deforestation rate is 0.4 percent in Brazil and Venezuela, but 3.7 percent in Costa Rica. And in Asia the loss of forests each year ranges from 0.5 percent in Indonesia to 4.3 percent in Nepal.
Forests for People
Rapid population growth is a main cause of deforestation. In the less-affluent nations of the tropics, population has increased so much during the last half-century that the land's ability to provide food, shelter, and fuel is being overwhelmed.
New areas of forest are continually opened up for agriculture, particularly for shifting agriculture because population pressures no longer permit the traditional 10-15 years of fallow time required to regenerate a previously farmed area. This shortening of the rotation time destroys the land's capacity to recover its forest and nutrient resources. In Africa, shifting agriculture reportedly accounts for 70 percent of the deforestation; in Asia, 50 percent, and in the Americas, 30 percent. People are destroying the basis of their own livelihood as-out of necessity, and particularly without the fertiliser required to sustain continuous crop production-they exceed the carrying capacities of the available land.
A second major contributor to deforestation is the indiscriminate harvesting of firewood.
More than a third of the world's people depends on wood for cooking, for heating households, and for fueling cottage industries. In fact, more than 80 percent of all the wood consumed in developing countries is used for fuel. Deforestation already affects the supply and price, and many of the poor are so desperate that wood is poached from forest reserves, hedges around homes are cut and stolen at night, and even scaffolding disappears from building sites.
Today there is growing support for the idea of planting trees and managing forests not simply for commercial logging interests but for the diverse goods and services needed by the local community. This concept involves the planned use of trees for the benefit of villagers and for integrating trees into agricultural systems so as to sustain greater productivity of food, fodder, and fuel. The idea has yet to be accepted widely in practice. Nevertheless, there is a new awareness that standing trees can contribute much to the daily welfare of people and that to sustain productive agriculture demands balancing land use among crops, trees, livestock, and, in many cases, wildlife. Unfortunately, most of the conventional forestry species are poorly adapted to the varied and continually changing needs of a rural subsistence society.
Tropical Reforestation Species
Today's tropical reforestation programs concentrate on three traditional plantation trees: pines, eucalypts, and teak. These account for 85 percent of all the area on which reforestation is being attempted, yet they represent a small fraction of the trees that might prove useful in the tropics, especially as trees for village use.
It is now important to consider alternatives, because the three conventional plantation species alone appear incapable of keeping pace with the rapidly increasing deforestation. In part, this is because of the impoverished soils that are relegated to tree growing in the tropics. Characteristically, these lands have infertile, badly eroded, and shallow soils. Some are bare; others are covered by grassy and shrubby weeds that encourage devastating ground fires. Under such conditions, pines and teak, in particular, require careful site preparation and care.
Trees for the enormous task of rehabilitating vast areas of degraded forest and abandoned agricultural lands need not have the high commercial qualities of teak, pine, or eucalypt, but they must fulfill the needs of the local communities. Moreover, they should be fast growing (not only to cover bare ground, but also to compete with aggressive weeds), resist drought and fire, use limited supplies of nutrients efficiently, and be able to thrive on open sites with little or no silvicultural care. They must also produce seeds or other planting materials prolifically, so that large quantities can be available free or at low cost.
Calliandra
Calliandra is a small tree that seems to meet many of these requirements. Since it is a woody shrub rather than a forest tree, however, it is unknown in traditional forestry. Its stems are usually multibranched, crooked, and short, and even at maturity the trees are only 12 m tall and 20 cm in diameter, making the wood too small for most commercial forestry purposes.
Nevertheless, to the villagers on Java, calliandra is a useful plant. Its wood makes good fuel, its foliage is valued for animal feed, and bees use its nectar for producing honey. Over the last 25 years Java's plantings of calliandra have steadily expanded and now cover more than 170,000 hectares. Eighty percent of Indonesians live in rural areas, and on Java most of them now use calliandra as firewood.
On suitable sites this small tree grows with extraordinary speed. Nine months after planting it can be taller than a village house; in just one year it can be harvested for firewood. The remaining stump then resprouts so vigorously that within six months the new stems may rise above the houses again. Because of this rapid regrowth the trees can provide an annual firewood crop.
Calliandra is a good pioneer plant, especially for problem sites. On Java it grows well on steep hillslopes and poor soils. It adapts well to different soils, establishes easily by direct seeding or by planting seedlings, and requires little care. It grows successfully in a range of environments with widely differing altitudes, rainfall, and shade. It is, however, likely to prove useful only in the humid tropics; it is not a crop for arid or temperate regions.
Nitrogen Fixation
Like most other legumes, calliandra forms a mutually beneficial partnership with soil bacteria of the genus Rhizobium. These bacteria penetrate young rootless and multiply to form nodular swellings on the root surface. In the nodules the rhizobia absorb nitrogen gas from air in the soil and biologically transform it into nitrogen-containing organic and inorganic compounds. The plant then uses the nitrogenous products to produce protein, vitamins, and other nitrogen-containing compounds. This process converts an otherwise unusable gas into compounds that stimulate the plant's growth.
Calliandra usually has large, prolific nodules and requires little or no nitrogen fertilizer; the rhizobia provide adequate amounts of nitrogenous compounds for normal growth. This permits calliandra to thrive in soils where nitrogen levels are inadquate to sustain the growth of most other crops.
Nitrogen is one of the principal nutrients that limit the growth of both agronomic and forest crops, accounting for a substantial proportion of crop production. And nitrogen is the single most costly industrial input to agricultural productivity-the energy needed to obtain one kilogram of nitrogenous fertilizer requires 1.8 m3 of natural gas.
Nitrogen fertilizer is becoming increasingly expensive as the cost of natural gas rises. And as a country's foreign exchange becomes more precious, it seems probable that forestry will be allocated a lower priority for nitrogen than agriculture. Thus, although it is important to exploit biological ways to add nitrogen to agronomic crops, it may become critical to do so for forestry crops. Limitations So far, the only extensive experience with calliandra has been on Java.
Therefore, the potential for the tree elsewhere in the tropics is now only speculation: no information has yet been collected about calliandra's growth under different climatic and soil conditions, and comparative trials with other species have only recently been started. Thus the time has not come for widespread commercial planting. Instead, calliandra should be incorporated into trials with tropical multipurpose species such as leucaena and mangium.
From such comparisons will come a better understanding of calliandra's potential. In 10 years it will be known if this is as universally promising as the experience in Java now seems to suggest.
Calliandra has no thorns, it is not known to be toxic to animals, nor does it seem to have other serious drawbacks. But it is a resilient and spreading plant, and the possibility of its becoming a weed should be kept in mind.
Uses and Advantages
A summary of calliandra's main uses and advantages follows. Details are given in chapter 5.
Firewood
Calliandra seems to be an outstanding candidate for meeting village needs for fuel.
Calliandra wood is too small in diameter for lumber, but it is dense, burns well, and is ideally sized for domestic cooking needs. It can also be used for firing brick, tile, and lime kilns and for fueling copra and tobacco dryers.
Soil Improvement
Calliandra is particularly promising for improving the soil and preparing the site for crops.
This is dramatically exemplified in the village of Toyomerto in East Java. There the villagers routinely enrich worn-out agricultural land by growing calliandra on it for several years.
During that period, they make a good living selling calliandra firewood, actually sometimes earning more this way than from their food crops. After the calliandra stumps are removed (for charcoal), sugarcane, corn, and other crops grow vigorously.
Reforestation
Calliandra's ability to thrive on steep slopes, in marginal soils, and in areas with extended dry seasons makes it a prime candidate for restoring tree cover to watersheds, slopes, and grasslands denuded through deforestation and fire. Calliandra can be established on soils dominated by coarse grasses. Its quick growth, thick canopy, and rapid regrowth leave vigorous weeds, such as Imperata grass, little chance to compete.
On denuded watersheds in the tropics calliandra should prove particularly valuable. Its thick canopy and extensive root system may help rainfall to penetrate the soil, thereby retarding runoff and erosion, preventing landslides, improving the perennial flow of springs, and reducing the siltation of dams.
Calliandra is moderately shade tolerant and will grow between young pines, eucalypts, and other tree crops, adding nitrogen to the soil, which benefits the taller trees.
Amenity Planting
In Indonesia calliandra is often cultivated as a border crop along roads, ravines, rivers, and village boundaries. There it may act as a fire barrier or a screen to prevent unwanted grazing-particularly where forests border villages. It also provides shade and beautification.
Forage
Altough not widely tested as a forage source, calliandra foliage contains up to 22 percent protein. It is often produced abundantly and is well liked by cattle and goats. No toxic components have been found so far, although tannin levels are high.
Honey Production
The tree makes good bee forage because its flowers are rich in nectar and it blooms year- round. Calliandra honey is light colored and has a pleasant, bittersweet taste.
 |
 |
