The carrying capacity concept was developed from animal ecology, and applied to rangeland management in order to assess sustainable livestock stocking rates. In it, long-term ecological sustainability was not a well developed criterion. Early applications of carrying capacity concepts to agricultural land-use have been much criticised, but recent developments provide useful insights. The proposed definition of human carrying capacity is 'the maximum level of exploitation of a renewable resource, imposing limits on a specific type of land-use, that can be sustained without causing irreversible land degradation within a given area'. Hence, it is a property of the ecosystem only. The definition is primarily aimed at maintaining ecosystem productivity and resilience, i.e. avoiding irreversible land degradation. The human carrying capacity is based on the sustainable supply of natural resources and on resilience thresholds of the ecosystem. The level of maximum sustained exploitation of natural resources can also be expressed as maximum sustainable agricultural production levels, or sustainable population densities based on such production levels. Such applications require careful definitions of the assumptions and conditions involved. Absolute assessments of human carrying capacity have limited value only, particularly in semi-arid regions. However, comparing human carrying capacity levels with current exploitation rates of natural resources provides a useful framework to consider the ecological aspects of sustainable land-use.
