Slash and Burn may Preserve Biodiversity Better than Plantations
New Scientist 15 Nov 97
THE image of the small-time farmer carving his way with fire and axe through the rainforests of Southeast Asia represents, for many people, environmental destruction at its crudest. Known as "shifting cultivators", these roaming farmers have been blamed for large-scale forest destruction, loss of species and uncontrolled burning. In 1990, studies by the World Bank and the UN's Food and Agriculture Organization blamed shifting cultivators for most of Indonesia's forest loss. Along with other small farmers, they were also blamed for the country's devastating fires in 1994. This year's fires have been largely attributed to the reckless behaviour of large-scale plantation companies. But Thomas Tomich, an economist working on the Alternatives to Slash-and-Burn programme at the International Centre for Research in Agroforestry (ICRAF) in Bogor, Indonesia, believes that prejudice against shifting cultivation is still widespread. "The conventional view of most academics and policy makers remains the same as it was in the 1950s," he says. "Shifting cultivators are seen as tradition-bound peasants, trapped by ignorance and unable to manage their resources properly."
However, according to an increasing number of ecologists, this view is profoundly misguided. A growing body of evidence suggests that rotational shifting cultivation can be both a productive and an environmentally sustainable way of using land in lightly populated areas. The problem is that the label "slash-andburn" is associated in the minds of officials and the public with forest clearance by migrants, loggers and plantation companies. Thus governments tend to focus only on the destructive parts ot shifting cultivation and ignore the lengthy period of crop production and forest regeneration. During the colonial period, the Dutch called shifting cultivation a "robber economy". Although the term is no longer used in Indonesia, Tomich says that today's settlement programmes for shifting cultivators are still based on the premise that their farming methods are a major cause of deforestation. In shifting cultivation, a plot of forest is felled and burnt, providing fertile ash in which to grow food crops. After one to three years, as weeds proliferate and fertility declines, the plot is abandoned and left to revert to forest. After a fallow period, ideally of 20 years or more, the cycle is repeated. Olivier Dubois of the International Institute for Environment and Development (IIED), a research group based in London, says that this type of agriculture could be the most efficient way to use land in places where land is plentiful but labour and capital scarce. He points to studies in Kalimantan that demonstrate that dry rice cultivation by shifting cultivators provides far higher returns on labour-up to 276 per cent-than the wet rice cultivation promoted by Indonesian officials. A recent IIED study, conducted in collaboration with local scientists in Thailand, Laos and Vietnam, reveals that shifting cultivation can provide seldom acknowledged environmental benefits. In Thailand, for example, the Karen and Lua people have developed a sophisticated system of community organisation to control forest fires. Elsewhere, shifting cultivation, when it uses long fallow periods, can help to retain high levels of biodiversity. A survey in one Lua village found 223 plant species on land that had been cultivated then left fallow for 10 years. This compares with the 319 speci -s found in virgin forests in the same area. In many parts of the world land scarcity, logging, new markets and aggressive government policies have forced shifting cultivators to shorten the period of fallow, thus turning a sustainable form of land use into an unsustainable one. Do Dinh Sam of the Forest Science Institute in Hanoi estimates that the number of shifting cultivators in Vietnam has fallen to around 1 million. Where the population density is high, fallows have been reduced and food yields have dropped significantly. Replacing the long fallow of shifting cultivation with permanent agriculture inevitably entails further losses of biodiversity. In an effort to counter this, the 80-strong team of scientists working on the ICRAF programme is looking for practices that are not only economi cally attractive to small farmers, but also more environmentally benign than either permanent food crop ping or unsustainable short-fallow slash-and-burn agriculture. The team has concentrated its search on Sumatra, where traditional shifting cultivation has been adapted for rubber cultivation. It "Over the past century, the local people have developed a highly sophisticated form of agroforestry,' explains Tomich "Essentially, they have worked out a way of improv ing the fallow period." A plot of forest is cleared in the usual way and food crops are cultivated for a year or two. Rubber seedlings are planted with the crops, and as the rubber trees mature during a the fallow period they are joined naturally by over 200 wild plant species, many of which supply fruits, timber and fibre. After 10 years, the rubber -a cash crop-can be harvested . After another 15 years or so, th plot is cleared and the rotation begins again. From an environmental point of view, rubber agroforests have much to commend them. Plots of rubber agroforest harbour 50 per cent of the plant species found in similarly sized areas of natural forest, 60 per cent of the birds, and most of the mammals. Compare this with the biologically poor Imperata cylindrica grasslands that now cover 9 million hectares of Southeast Asia. These grasslands are often a direct result of failed permanent agriculture. "On acid, phosphorus-poor tropical soils, it's hard to sustain economic forms of permanent food-crop production," says Tomich just as significantly, rubber agroforestry makes good economic sense for small farmers. Transmigrants to Sumatra are obliged by the government to follow a certain cropping system for 5 years. As soon as this is over, many convert to rubber agroforestry, which they see as more profitable and less labour intensive. The ICRAF programme is keen to promote methods of land use that can help to reduce atmospheric levels of greenhouse gases. its research suggests that agroforestry of the sort practised in Sumatra can help carbon sequestration by converting Imperata grasslands to tree-based systems run by smallholders. Meine van Noordwijk of the ICRAF estimates the maximum amount of carbon held in agroforests at 215 tonnes per hectare, compared with 365 tonnes per hectare for mature forests, 90 tonnes for Imperata grasslands and 63 tonnes for annual food crops.
At a local level, attitudes to so-called slash-and-burn agriculture do seem to be changing, albeit slowly. "Policy makers don't wholly blame shifting cultivators for forest loss now," reflects Sam in Vietnam. Kanok Rerkasem, a coauthor of the IIED study in Thailand, says government officials now realise that shifting cultivation may be the only means some farmers have of maintaining production. There have been positive signs in Indonesia too. Marcus Colchester of the British-based World Rainforest Movement welcomes the fact that the government has blamed plantation and logging companies rather than small farmers for this year's smoke crisis. "This is a very important moment," he suggests. "At last the focus is on big business." The irony is that virtually everyone now accepts that sustainable forestry is about far more than trees and timber production. Biodiversity, local livelihoods and carbon storage are all seen as important functions of forests-and these, as ecologists are now realising, are precisely the sorts of benefits that agroforestry and rotational shifting cultivation can provide. Charlie Pyo-Smith