Spheres of influence. Where do we stand? Global ecosystem assessments ask the big question.

H ow healthy are the earth's ecosystems? Will they continue to provide the food, water, shelter, and other necessities on which all life depends? These pressing questions have been receiving attention from two international collaborations: The Pilot Analysis of Global Ecosystems (PAGE) was completed in late 2000 and detailed in World Resources 2000–2001, the biennial report of the World Resources Institute (WRI), and the upcoming Millennium Ecosystem Assessment (MEA) is due for completion in 2005. The degradation of ecosystems is literally ancient history. Desertification—an enduring ecosystem degradation—gets much of the blame for the decline of ancient civilizations in the Middle East. More recently, the severe soil erosion of the Dust Bowl in the U.S. Great Plains during the 1930s started with unsustainable farming practices and was exacerbated by drought. In total, according to a 2000 report by the United Nations Environment Programme (UNEP) titled An Assessment of Risks and Threats to Human Health Associated with the Degradation of Ecosystems, desertification is now damaging 30% of irrigated areas, 47% of rainfed land, and 73% of rangelands. Other examples of broad ecosystem degradation include the hypoxic " dead zones " in the Gulf of Mexico and other waters around the world, the disastrous decline of Black Sea fisheries due to the introduction of exotic species, and intensified flooding in Bangladesh and Central America caused partly by deforestation. These and other such alterations reflect global-scale changes caused by human activities, particularly climate change and stratospheric ozone depletion. Ecosystem assessments stand traditional environmental monitoring on its head by examining an entire ecosystem, such as a watershed, mountain range, or coastline, rather than, say, a tract of land or an industrial sector. No longer, says David Rapport, a professor in the School of Rural Planning and Development at the