Introduction: The Growth of Cities and Urban Forestry
In the last 100 years, there have been two very dramatic changes in human society. First, our global population quadrupled to its present 6.3 billion, and second, we have become an urban species (United Nations Department of Economic and Social Affairs/Population Division, 2004). In 1900, 86% of humanity lived in the rural countryside, interacting directly with the natural world on a daily basis. However, as of 2006 over 50% of us now live at densities greater than 625 people per square kilometer in cities containing more than 100,000 individuals. United Nations predictions hold that by 2050 nearly two thirds of the estimated world population of 9 billion people will live in cities. This demographic shift has occurred at an uneven pace throughout the world, with Western industrialized nations having experienced it earlier, accounting for the fact that today about 75% to 80% of Europeans and North Americans are already city dwellers. Therefore, the lion’s share (90%) of the increase in urbanized humanity over the next few decades will occur in the developing nations, particularly those in Asia. Moreover, the number of large cities throughout the world is increasing rapidly. In 1900, there were only 19 cities with a million or more inhabitants. Today, there are over 400, with 564 projected by 2015 (United Nations Department of Economic and Social Affairs/Population Division, 2004). There now are 19 megacities, with 10 million or more people each, whereas just 20 years ago there were only eight.
Many of these cities are struggling to provide basic services such as drinking water, waste removal, sanitation, and shelter for their people. Other cities are not experiencing such crises as acutely, but nevertheless suffer chronically from vastly unequal allocation of resources and services to their citizens, hotter mesoclimates (urban heat-island effect), flooding, poor air and water quality, and intermittent water shortages that portend more serious scarcity in the future (Hinrichsen, 2002; Shao et al., 2006; Yang and Pang, 2006; Zhao et al., 2006). Cities, and therefore the majority of humanity, are becoming increasingly stressed by environmental and social factors that negatively impact our physical and psychological well-being. As the economist, John Kenneth Galbraith, stated: “The test of the quality of life in an advanced economic society is now largely in the quality of urban life. Romance may still belong to the countryside—but the present reality of life abides in the city” (quoted in Miller, 2002).
KeywordsGeographic Information System Green Space Urban Forest Urban Green Space Urban Tree
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