Human density is now 1 person to about 2.37 ha (6 ac) of land. When domestic animals are included, the density of one population is equivalent to about 0.65 ha. This is less than 2 ac for every person and person-equivalent domestic animal consumer. If the population doubles during the twenty-first century, and if humans wish to continue to consume and use animals, there will be only about 1 ac (0.4 ha) to supply all the needs (water, oxygen, minerals, fibers, biomass fuels, living space, and food) of each 50 kg consumer; this does not include pets and wildlife which contribute so much to the quality of human life. Most agroecologists believe that too much emphasis has been placed on the monoculture of annuals. It makes ecological and common sense to consider diversifying crops, establishing multiple cropping systems, adopting limited till procedures (less disturbance ofsoil structure), and increasing the use of perennial species.
Each year we use up a certain amount of the Earth's total NPP when we harvest crops for food, cut trees to burn as fuel or use to build houses, deliberately or accidentally burning vegetation, and destroying vegetation to construct buildings and roads. Ecologists have estimated that humans now use, waste, or destroy about 27% of the world's potential NPP (40% for land systems), crowding out or eliminating other species in the process. Many biologists contend that the resulting biodiversity impoverishment is reducing the Earth's capacity to sustain all the species. So likely we may say carrying capacity depends not only on number and biomass, but rather on the lifestyle of individuals and populations. If current estimates of our use of the Earth's annual NPP are reasonably correct, what will happen to us and to other species if the human population doubles over the next 40 years?
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