The Services that Biodiversity Provides

Assessments of the economic benefits of biological diversity have been based primarily on our ability to generate revenue from biodiversity, through activities that produce measurable results in current markets, such as pharmaceuticals or tourism. But there are additional benefits from biodiversity that are not so easily included in commercial market analyses, and that come under the name of ecosystem services. These are the end results of natural biological processes that either improve the overall quality of the environment, or provide some benefit to the human users of the landscape--such as improvement of water quality and reduction of flooding. The concept of ecosystem services is unabashedly tilted toward human uses.

The study of ecosystem services is relatively new, but what is known points consistently in one direction: maintaining diversity on a variety of levels of ecological and biological organization--within forests, or among the trees that are there, or even within the genes of a single variety---is critical if services are to be maintained on a sustainable basis.

Ecosystem services can be provided in a variety of forms. One example is the purification of water that generally occurs by flowing through forested ecosystems and wetlands, which is an extremely important function from the standpoint of human populations that live downstream. The presence of living vegetation provides an efficient sink for many atmospheric pollutants as well. The regulation of stream flow by vegetation in the upper reaches of watersheds has long been recognized as an important ecosystem service, and watershed managers manipulate both the amount and type of vegetation in watersheds to help control sedimentation, floods, and sometimes stream flow.

The services that ecosystems provide often depend on the underlying physical structure of the habitat, such as the conditions for feeding and breeding that may be needed for the continued survival of an important animal species. What is often required is a diversity of habitats over an entire landscape. Ecosystem services may also depend on the presence of a particular species, as is the case in highly co-evolved plant-pollinator systems, or in highly managed agroecosystems that rely on specific pollinators, such as honeybees.

Biodiversity also plays an important role in maintaining ecosystem services over long periods of time, through the ups and downs of natural variations. Ecosystems that have lost either genetic or species diversity are less resistant to the effects of environmental perturbations, such as droughts, and are slower to recover when disturbed. Diversity is a form of ecosystem health insurance: those ecosystems that include several species that serve the same or similar functions tend to be more resistant to environmental stress and recover faster from perturbations.