Although it seems obvious today that humans depend on ecosystems for survival, explicit recognition of the services they provide and their value is rather recent. Environmental writers introduced the idea of “natural capital” in the 1940s; it was in 1970 that ecosystems were first said to provide people with a variety of “goods and services.” Here we consider more recent efforts to understand the importance of ecosystems to humans.
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Ecosystems provide four types of benefits to humans: provisioning, regulating, supporting, and cultural services.
Alteration of ecosystems for human benefits involves trade-
To develop more sustainable use of ecosystems, the value of ecosystem services must be measured.
Ecosystems services are the benefits people obtain from ecosystems. Ecologists recognize four different categories of services depending on their role in the ecosystem:
Provisioning services provide products such as food, clean water, timber, and fiber.
Regulating services regulate events such as hurricanes, floods, disease outbreaks, and water and air quality.
Supporting services function in such processes as soil formation, carbon sequestration via net primary production, and nutrient cycling.
Cultural services provide nonmaterial benefits such as recreational activities and aesthetic and spiritual enrichment.
Most of these benefits are either irreplaceable, or the technology necessary to replace them is prohibitively expensive. For example, fresh drinking water can be provided by desalinating seawater, but only at great cost. The aesthetic, spiritual, and recreational benefits of ecosystems are less tangible, but no less important, and no more easily replaced.
Although humans have been altering ecosystems for millennia, the pace and scope of human alterations to ecosystem services have increased considerably in the past century. For example, the 2005 Millennium Ecosystem Assessment estimated that approximately 60 percent of the ecosystem services identified in its study are being degraded or used unsustainably, including fresh water, wild-
Human alteration of ecosystems has had many positive effects on human health and prosperity, but it necessarily involves trade-
Similarly, the loss of wetlands and other natural buffers has reduced the ability of ecosystems to regulate flooding and other natural hazards. The damage from the tsunami that hit Indonesia and other Southeast Asian countries in December 2004 was greater in many places than it would have been had the mangrove forests that protect the coast not been cut down and converted to shrimp aquaculture farms. Hurricane Katrina, which struck the U.S. Gulf Coast less than a year later, would not have caused as much flooding in New Orleans had the wetlands surrounding the city been intact. Katrina’s devastating effects were due in part to a situation that had been developing for decades.
New Orleans is located on the Mississippi River delta. Much of the city lies below sea level, buffered by dams and levees constructed by the Army Corps of Engineers. The upstream dams that protect New Orleans from flooding also prevent the river from depositing the sediments that have sustained the surrounding delta wetlands for centuries. Oil and natural gas producers have cut thousands of small canals through those wetlands in order to lay pipelines and install drilling rigs, and the extraction of oil and gas from beneath the land has caused it to sink. Increased dredging of shipping lanes and rising sea levels have contributed to a rise in salinity, killing off many of the great cypress tree swamps. These extensive alterations resulted in the loss of more than 80 percent (1.2 million acres) of the delta wetlands between 1930 and 2005. By the time Katrina made landfall, those wetlands could no longer protect New Orleans from flooding. Storm surges raced along the paths carved by canals and shipping lanes to breach the levees, inundating much of the city.