A growing population, rangelands & the future.

摘要

Conversion of rangeland to other uses during the last 20 years has become an important management concern. This trend is largely driven by rapid human population increase and a demographic shift from the eastern to western USA. The consequences could be disadvantageous for rangelands until they are valued for the ecosystem services they provide. In 2000 the world's human population reached 6.1 billion which is twice as many as in 1960. Presently the world human population is growing at a rate of 80million/year. Although fertility rates have declined faster than expected, the world population growth rate is 1.3%/year compared to 1.5% in 1990. By 2050 it is expected that 10 billion people will inhabit the planet. Over the past 300 years, world population growth rates per year increased from 0.3% in 1700 to 0.6% in 1900 to the current rate of 1.3%. This rate of increase has actually exceeded the growth rate calculated by Thomas Malthus who predicted the world human population would exceed food supplies sometime between 1850-1900. Although birth rates have fallen substantially from 6 children in 1900 to 2.2 children per female in 2000, human longevity has increased from 40 years to 60-80 years depending on country. Improved health care, rapid increases in food production, and other technological advances explain how the world today can support nearly 4 times more people than in 1900 at a much higher standard of living. Although various scenarios are possible, most experts believe the world's humanpopulation will be between 10 and 12 billion by 2100. This will lead to unprecedented demands on the earth's natural resources.