BOX 1.
NATURE'S SERVICES:
WHAT ECOSYSTEMS PROVIDE TO PEOPLE, WHAT IS AT RISK AND WHY NEW INTERDISCIPLINARY KNOWLEDGE IS REQUIRED

Individual organisms or species provide familiar services—trees provide shade or windbreaks, marigolds discourage garden pests. Ecosystems, too, provide a multitude of services, though they are generally less appreciated. Recent widespread conversion of many ecosystems from former forest or grassland to agricultural, industrial, or urban use has brought to light the concomitant alteration or loss of the services formerly provided by those ecosystems. In some cases, the altered system may be preferred, but a complete assessment of the tradeoffs, including services lost or gained, will enhance informed decisions.

A recent example highlights the potential threats to vital services, the economic consequences of disruption, and the potential for restoration efforts to conserve essential services (Chichilnisky and Heal 1998). Historically, the watershed of the Catskill Mountains provided a plethora of ecosystem services including air purification, flood control, pest control, nutrient recycling, carbon sequestration, the provision of places for recreation and education, as well as a particularly high-profile service—water filtration and purification. As recently as 1948, New York City had what was billed as the purest water in the world. Over time, this watershed ecosystem became overwhelmed by incremental development and the accompanying land conversion and generation of sewage, industrial waste, and agricultural runoff. As a consequence, the water quality in the city fell below Environmental Protection Agency drinking water standards. An economic analysis provided comparative costs of two alternatives for restoring water quality. The cost of purchasing and restoring the watershed so that it could continue to provide the service of purification and filtration was calculated at approximately $1 billion. The cost of building and maintaining a water purification and filtration plant was $6 to $8 billion in capital costs, plus annual operating expenses of $300 million. The city has opted to buy and restore the watershed, i.e., to let nature work for people. An additional benefit of this choice is that the watershed also provides multiple other services not included in the analysis. As this example illustrates, ecosystem services provide fertile ground for new collaborations between economists and ecologists (PCAST 1998; Dasgupta, Levin, and Lubchenco 2000).