Do increases in agricultural yield spare land for nature?

Authors

  • ROBERT M. EWERS,

    1. Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK,
    2. Conservation Science Group, Department of Zoology, University of Cambridge, Downing St, Cambridge CB2 3EJ, UK,
    Search for more papers by this author
    • 1Present address: Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, UK.

  • JÖRN P. W. SCHARLEMANN,

    1. Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Panama, Republic of Panama, †
    Search for more papers by this author
    • 2Present address: UNEP-World Conservation Monitoring Centre, 219 Huntingdon Road, Cambridge CB3 0DL, UK.

  • ANDREW BALMFORD,

    1. Conservation Science Group, Department of Zoology, University of Cambridge, Downing St, Cambridge CB2 3EJ, UK,
    Search for more papers by this author
  • RHYS E. GREEN

    1. Conservation Science Group, Department of Zoology, University of Cambridge, Downing St, Cambridge CB2 3EJ, UK,
    2. Royal Society for the Protection of Birds, The Lodge, Sandy SG19 2DL, UK
    Search for more papers by this author

Robert M. Ewers, tel. +44 20 759 42231, fax +44 1344 874957, e-mail: r.ewers@imperial.ac.uk

Abstract

Feeding a rapidly expanding human population will require a large increase in the supply of agricultural products during the coming decades. This may lead to the transformation of many landscapes from natural vegetation cover to agricultural land use, unless increases in crop yields reduce the need for new farmland. Here, we assess the evidence that past increases in agricultural yield have spared land for wild nature. We investigated the relationship between the change in the combined energy yield of the 23 most energetically important food crops over the period 1979–1999 and the change in per capita cropland area for 124 countries over the same period. Per capita area of the 23 staple crops tended to decrease in developing countries where large yield increases occurred. However, this was counteracted by a tendency for the area used to grow crops other than staples to increase in the countries where staple crop yields increased. There remained a weak tendency in developing countries for the per capita area of all cropland to decline as staple crop yield increased, a pattern that was most evident in developing countries with the highest per capita food supplies. In developed countries, there was no evidence that higher staple crop yields were associated with decreases in per capita cropland area. This may be because high agricultural subsidies in developed countries override any land-sparing pattern that might otherwise occur. Declines in the area of natural forest were smaller in countries where the yield of staple crops increased most, when the negative effects of human population increases on forest area were controlled for. Our results show that land-sparing is a weak process that occurs under a limited set of circumstances, but that it can have positive outcomes for the conservation of wild nature.

Ancillary