Our share of the planetary pie
- Jonathan A. Foley*,†,
- Chad Monfreda*,
- Navin Ramankutty‡, and
- David Zaks*
- *Center for Sustainability and the Global Environment, University of Wisconsin, 1710 University Avenue, Madison, WI 53726; and
- ‡Department of Geography and Earth System Science Program, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 2K6
The rise of modern agriculture and forestry has been one of the most transformative events in human history. Whether by clearing natural ecosystems or by intensifying practices on existing croplands, pastures, and forests, human land-use activities are consuming an ever-larger share of the planet's biological productivity and dramatically altering the Earth's ecosystems in the process. Although the character of land use varies greatly across the world, ranging from industrialized croplands, grazing on marginal lands, managed timber lots, animal feedlots, or biofuel plantations, the ultimate outcome is the same: the production of forest or agricultural goods for human needs taken at the expense of natural ecosystems. This observation begs the question addressed in this issue of PNAS by Haberl et al. (1): Just how large is the impact of human land use on the terrestrial biosphere?
Simply in terms of acreage, the answer is clear: Croplands and pastures are now among the largest ecosystems on the planet, rivaling forest cover in extent, and together occupy ≈35% of the ice-free land surface (Fig. 1) (2). Logged and managed forests add to this amount.
Global distribution of croplands (Upper) and pastures and rangelands (Lower). Ramankutty et al. (2) provide the most detailed characterization of the world's agricultural land derived by combining statistical data for 15,990 administrative units of the world with satellite-based land cover data at 1-km resolution. Approximately 35% of the world's ice-free land surface was devoted to agriculture in 2000.
However, the geographic extent of managed lands is not the whole story. Although significant land-use expansion has occurred in past decades, the intensification of land-use practices under the aegis of the “Green Revolution” has increased dramatically. Simply put, many of the world's managed lands are being used more intensively as opportunities for expansion are being exhausted. For example, in the last …
†To whom correspondence should be addressed. E-mail: jfoley{at}wisc.edu
