What might be done to mitigate the effects of continual pressure for agricultural expansion? It is a horrifying fact that the area of badly-degraded former forest land which can no longer be cultivated is equal to that which is currently under cultivation. Something is seriously wrong with our land-use policies if we are willing to throw away millions of square kilometers of formerly extremely productive land for a very short-term gain (if any). It is difficult to feel optimistic about the prospects for either forests or the farms which take their place in the tropics, for reasons given above. Although a lengthy discussion of agriculture is not within the purview of this document, a few changes which could improve the depressing situation are mentioned below.
a. Institute sustainable agriculture: Some scientists feel that sustainable agriculture can be practiced on former forest land, thus obviating the need for further incursions into virgin rainforests for new agricultural land to replace worn-out fields. However, most soils in the tropics are highly weathered and of poor to variable fertility, which makes a great deal of tropical forest land marginal for agriculture. Agriculture on these lands is limited by acidity, nutrient deficiencies, low phosphorus levels, and the poor physical structure and condition of the soils. Because of these factors, the land is farmed for a few years, after which the soil becomes eroded and exhausted, and the farmers move on to fresh forest land. This is a most destructive cycle. Since during cultivation of former forest land essential soil organic matter is rapidly lost by leaching, the key factor in making agriculture sustainable lies in preserving soil fertility. Soil organic matter consists mainly of dead parts of plants and animals, microbes, substances released from plant roots, and fungi. The combination of organic material and microbial mats gives stability and porosity to the soil, and the microbes decompose the organic materials to chemical compounds which can be absorbed by plants. The organic content of soils also enhances its water-maintaining capabilities. Thus the preservation or restoration of all these elements is essential to sustaining agriculture in tropical regions, although maintaining organic matter is more difficult in tropical regions because soils are often easily compacted and easily depleted. Vegetal cover must be maintained, fallows must be sufficiently lengthy, and crops must be carefully managed. Even so, with such a regime, in many of these infertile soils moderate yields can be obtained only with the use of fertilizers. In addition, soil structure must be improved, microbes replaced, and crops suitable to the local environment, mycorrhizae, and soil type chosen. Agriculture must be adapted to take advantage of natural processes rather than relying on great quantities of fertilizers and pesticides.
b. Modern high-tech agriculture: In some places new technology appears to be destructive of forest; elsewhere, protective. As one example, highly mechanized agricultural systems use relatively little labor. In Brazil, much previous rainforest land has been cut for soybean plantations, which are mechanized, and which have displaced small farmers. These farmers are forced to move into the rainforests, where they remove tree cover to make new farms. In the Philippines, in contrast, an irrigation project on Palawan Island was sufficiently labor-intensive to occupy farmers, thus reducing pressure on the forests (Helmuth, 1999). Modern technology can be a mixed blessing, although new irrigation techniques, plant breeding and genetic engineering can raise productivity in some places.
c. A reduction in consumption of meat and animal products: Growing feed for cattle and other domestic meat animals consumes a huge proportion of the world’s agricultural output. It is much more efficient to eat plants directly, rather than to consume them via animal flesh. In this transfer, most of the energy in the plant is lost.
d. Comprehensive land-use planning: This could involve restoring agricultural land to forest or other ecosystems for the ecosystem services which it could provide (watersheds, for example), and by planning agricultural lands so as to minimize fragmentation of ecosystems, to preserve biodiversity, and to preserve wetlands and other types of essential habitat from agricultural conversion.
e. Improvement in agricultural productivity (preferably without resorting to pesticides, herbicides and mineral-laden fertilizers): New equivalents to the “Green Revolution” for rice are needed.
f. Investment in research: This element is essential to design agricultural systems which are more efficient and less destructive to ecosystems and global ecology, to control pathogens and pests and to maintain fertility.
One could sum up the situation as Manners (1978) did some time ago, “The rapid conversion of tropical rain forests into cultivated fields and pastures may appear to offer a solution to immediate problems of a growing population and its demand for space, food and jobs; in the long run, however, present land-use practices risk permanent degradation of the resource base.” And he didn’t know the half of it.