The Current Conceptualization of Land

Using this land-accounting system based on the single scale conceptualization, we see that approximately one-third of the world's ice-free surface is agriculture, another third is forest, and less than 1% is built-up land. This land-accounting system, however, ignores differences in land quality and land use intensity (Foley et al. 2007). Agriculture is agriculture regardless of yield. The category of urban or built-up land does not differentiate between high density and low density. There are land classification systems that allow for greater detail differentiation (e.g., residential, industrial and commercial) but the assumptions remain that there are simply finer cuts along the same axis. Land-accounting or "mass-balance" approaches have been the principal methods for generating inventories of land, but they fail to provide information that is critical for measuring whether current uses of land are sustainable. The main fallacy of the current land-accounting system is the implication that land is perfectly substitutable. That is, cropland in Asia can be replaced by cropland in Europe. By simply summing up the world's land areas, geographic context is removed. Consequently, it is assumed that place (which is specifi c to geography, location, and context) can be replaced by any space. This assumed interchangeability of space for place disregards differences in biophysical conditions, cultures, economies, policies, and institutions.

One way to move beyond simple, quantitative accounts on the extent of land under use is through estimates on the amount of terrestrial net primary production (NPP) that is used, co-opted, or diverted from its original metabolic pathways by human activity, denoted as human appropriation of NPP (HANPP) (Haberl et al. 2007; Imhoff et al. 2004; Vitousek et al. 1986). NPP is the net amount of primary production of plants after the costs of plant respiration (i.e., the energy needed for the plant's metabolism) are subtracted. NPP equals the amount of biomass produced in an ecosystem in a unit of time and represents the basis of (almost) all heterotrophic life on Earth. NPP is a

Table 5.1a Example of land cover classification system: IGBP land cover legend.

Class Description

Table 5.1a Example of land cover classification system: IGBP land cover legend.

Class Description

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