systems—tools that were applied in ecology from the
beginning of the 1970s. Ecological, and later ecological-
economic, systems are seen as hierarchies
(such as food-webs), where small fast-moving systems
are embedded in and constrained by large slowmoving
ones, and where the dynamics at one level
emerge from phenomena occurring at lower levels of
the overall system. The systems are linked in time and
space, and their development is path dependent, so
changes might be irreversible. As the systems are
characterized by non-linear feedbacks, small disturbances
can become magnified and lead to qualitatively
new and unexpected behaviours at more
macroscopic levels. In general, ecological–economic
systems have multiple locally stable states (or multiple
equilibria) with different properties, and a system can
flip from one state to another when a threshold is
crossed. The development of a system can thus be
discontinuous and characterized by punctuated equilibria.
There are numerous examples of discontinuous
ecological change as a result of a gradual build-up of
economic pressure, for instance, grazing pressure
beyond a critical threshold can lead to desertification.
Sometimes the connections are very indirect, for
instance, when Canadian boreal forests are threatened
by budworm outbreaks because of the destruction of
habitats of certain bird species in Central America
(Perrings, 1997 p. 237 on the findings of Holling and
cooperators)