Biodiversity Impacts of Some Agricultural Commodity Production Systems

Despite centuries of urbanization and industrialization, around half of the world’s people still live as subsistence or small-scale farmers. The production of agricultural export commodities represents a major source of foreign income for many developing countries, and commodities such as coffee and cocoa rank second in importance only to oil in legal international trade. Such crops are inevitably produced on land formerly covered with natural habitats, and their production usually involves the loss of some or most of the biodiversity formerly present. Around 15 million ha of the Earth’s primary forest are lost each year, most of it in the tropics. Of this, approximately 60% is lost to slash-and-burn agriculture, the rest to logging, other forms of agriculture, and fire (ICRAF 1995). Because tropical forests may support as much as 70% of the planet’s plant and animal species, deforestation in the tropics represents the greatest single threat to global biodiversity. Deforestation is proceeding most rapidly in those countries holding the planet’s richest biodiversity (Balmford & Long 1994). An estimated 109 ha of land (an area approximately equal to all the planet’s remaining tropical forests; Mayaux et al. 1998) may be cleared for cultivation in the developing world by 2050, mostly in Latin America and subSaharan Africa (Tilman et al. 2001). The external impacts of agriculture, such as water and air pollution, could affect even larger areas. Forest clearance by burning accounts for 25% of total CO2 emissions, making it a major contributor to global climate change (Newmark 1998). Agriculture is an anthropogenic threat to biodiversity that can adversely affect vast areas (e.g., Donald et al. 2001). There are significant conservation implications of agricultural production systems that go beyond their replacement of natural habitats. In many systems, management spans a gradient from low to high intensity. A growing number of consumers in the developed world are prepared to pay a premium to encourage less intensive forms of production in the belief that these have environmental benefits. Quantifying these benefits and identifying the important ecosystem properties of such systems, however, is not easy. The extent to which particular commodity production systems are deemed beneficial or deleterious to the conservation of biodiversity is at least partly subjective. The conversion of natural habitats to commodity production, however sympathetically managed, is likely to result in a loss of biodiversity. On the other hand, environmentally sustainable forms of commodity production are often regarded as valuable habitats in their own right and greatly preferable to other forms of habitat exploitation. Whether habitat conversion to agricultural commodity systems or the subsequent intensification of those systems has the greater environmental impact is unclear, but is likely to differ between crops. Consumers in the developed world are becoming increasingly aware of the environmental advantages of lowintensity production and are prepared to pay a premium on produce from such systems. The next few years are likely to be influential in developing the planet’s long-term agricultural and environmental policies (Crompton & Hardstaff 2001) and in determining the buying patterns of consumers in the developed world of products grown in the developing world for export (Donald et al. 2004), so a review of current knowledge is timely. I reviewed published and unpublished scientific evidence to assess and quantify the environmental implications of several important agricultural commodity production systems. These were chosen to encompass a range of product types (oils, grain, and fruits) grown mainly for export in areas of rich biodiversity where systems of production have changed radically during recent decades. All are regarded as potential threats to biodiversity in at least some parts of their range. A number of other crops, such as tea (Camillia sinensis L.) and rubber (Hevea brasiliensis [Willd.] Muell.Arg.), would have fulfilled these criteria, but too little quantitative information on biodiversity in these crops was available to permit any general conclusions (though see Wu et al. 2001; Schroth et al. 2003). A specific aim of my review is to identify research priorities.