The global human population is rising—today’s 6.9 billion people are predicted to increase to between 9.15 and 9.51 billion by 2050 (Population Reference Bureau 2010). At the same time, per capita consumption is growing at a rapid rate, in part driven by the escalating global demand for meat, biofuels and tropical commodities such as coffee and palm oil (Myers and Kent 2003, Donald 2004). By 2050, overall food demand may have grown threefold, putting immense pressure on the world’s agriculturally-usable lands (Bongaarts 1996, Tilman et al. 2002, Danielsen et al. 2009). Agricultural conversion is most rapid in the developing world—home to much of the world’s, already imperilled, biodiversity. Already agriculture is regarded as the greatest extinction risk to birds, contributing to the declines of 87 % of threatened species (BirdLife International 2008).

In order to reconcile agricultural production and biodiversity conservation, two alternative approaches have been proposed—‘wildlife-friendly farming’ and ‘land sparing’. In wildlife-friendly farming, conservation measures are integrated into farming practices. For example, patches of native vegetation are retained, fewer pesticides are used and mixed cropping regimes are employed in order to create a finely-grained heterogeneous landscape. Such farms clearly sustain more wildlife than their industrial-scale counterparts. Crucially, however, they tend to produce lower yields and are rarely as biologically valuable as intact natural habitat. If the adoption of wildlife-friendly farming methods requires more land to be converted in order to produce the same agricultural output then the conservation value may be limited. Research by Green et al. (2005) and Balmford et al. (2005) suggests that intensifying agriculture on already-converted land could be used as part of a strategy to spare adjacent natural areas from further agricultural encroachment and might ultimately be more beneficial for biodiversity. They argue that maximising per-hectare yield could be critical in meeting rising food demands and securing biodiversity into the coming century. As well as halting agricultural expansion in the developing world, it is suggested that by maximising yields developed countries would be able to ‘rewild’ areas of farmland through large-scale habitat restoration (Sutherland 2004).

There are objections to both sorts of strategies. Both wildlife-friendly and high-yield farming have influences on adjacent habitats, through pollution, edge effects and water abstraction (Matson and Vitousek 2006). These problems are most visible in high-yield farming systems, but they can also be considerable in low-yield systems, especially when they are measured per unit of food produced. Under whatever land-use strategy is adopted, it is important to minimise these negative externalities (Godfray et al. 2010). Wildlife-friendly farming practices can be vulnerable to social or economic changes: this was seen in recent years, for example, when set-aside was abolished in EU member states.

Land sparing is contingent on effective policies to both increase yields and to spare habitats. Increasing yields alone, while necessary to achieve land sparing, is not sufficient. Increasing yields can in fact increase rates of habitat conversion at local or regional scales, but there is some evidence that at the scale of countries, yield increases are associated with a slowing of habitat loss (Matson and Vitousek 2006, Ewers et al. 2009). Conditions that are most likely to facilitate land-sparing include the introduction of labour- and capital-demanding agricultural technologies and technologies that encourage consolidation of production on existing cropland rather than new frontiers (Angelsen and Kaimowitz 2001, Wunder 2004, Ewers et al. 2009). Conditions under which yield increases might work against land sparing include the introduction of innovations that free up capital or labour (e.g., mechanisation), subsidies for overproduction, and situations in which demand is elastic (e.g., for luxury crops or biofuels, or where increased production encourages increased population growth) (Angelsen and Kaimowitz 1998, Angelsen and Kaimowitz 2001, Matson and Vitousek 2006, Ewers et al. 2009).

All of these effects are context-specific, and levels of agricultural intensification are often determined by commercial factors or inherent landscape properties (Fischer et al. 2008). For example, industrial-scale farming tends to occur in flat landscapes, with low-intensity agriculture persisting in more rugged and mountainous areas. Surprisingly, the key information required to assess the merits of different land-use strategies—matched data on species abundances and agricultural yields—have rarely been collated.

Ultimately, neither wildlife-friendly farming nor land sparing represents a universal panacea. Limiting global demand for agricultural products is also necessary if biodiversity is to be safeguarded, for example by minimising food wastage and setting limits on the production of non-food crops. However, at any given level of overall production, evaluating the advantages and disadvantages of wildlife-friendly farming, land sparing, and a range of options in between might often identify opportunities to improve land-use strategies for conservation.