Ecosystem functions – the
physical, chemical, and biological processes or attributes that contribute to the self-maintenance
of the ecosystem; in other words, what the ecosystem does. Some examples of
ecosystem functions are wildlife habitat, carbon cycling, or trapping nutrients.
Ecosystem services – the
beneficial outcomes, for the natural environment, or for people, that result from ecosystem
functions. Some examples of ecosystem services are support of the food chain, harvesting
of animals or plants, clean water, or scenic views. In order for
an ecosystem to provide services to humans, some interaction with, or at least some appreciation by,
humans is required.
Equivalent variation - the amount of money that leaves a
person as well off as they would be
after a change. Thus, it measures the amount of money
required to maintain a personÕs satisfaction,
or economic welfare, at the level it would be at after a change.
Existence value – the value
that people place on simply knowing that something exists, even if they will never see it or
use it.
Externalities - uncompensated side effects of human
actions. For example, if a stream is polluted by runoff from
agricultural land, the people downstream experience a negative externality.