Human Impact and Appropriation
Extensive human land use results in various levels of impact on actual NPP (NPPact). In some regions, such as the Nile valley, irrigation has resulted in a considerable increase in primary production. However, these regions are exceptions to the rule, and in general there is a NPP reduction due to land changes (ΔNPPLC) of 9.6% across global land-mass. In addition to this, end consumption by people raises the total human appropriation of net primary production (HANPP) to 23.8% of potential vegetation (NPP0). It is estimated that, in 2000, 34% of the Earth's ice-free land area (12% cropland; 22% pasture) was devoted to human agriculture. This disproportionate amount reduces the energy available to other species, having a marked impact on biodiversity, flows of carbon, water and energy, and ecosystem services, and scientists have questioned how large this fraction can be before these services begin to break down.
Read more about this topic: Primary Production
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