Ecological Resilience

Holling drew a distinction that reshaped ecological thinking. Engineering resilience is the rubber ball bouncing back to its original shape—the speed at which a system returns to equilibrium after a disturbance. Ecological resilience is something different and more important: the magnitude of disturbance a system can absorb before it crosses a threshold and reorganizes into a qualitatively different state. A forest can survive fire, drought, insect infestation—each disturbance damaging but not destroying the web of relationships that permits recovery. But if disturbances come too fast, or too many keystone relationships are severed simultaneously, the system crosses a threshold and reorganizes into a new configuration from which the original state is unreachable. Grassland where forest was. Desert where grassland was. The transition is a phase shift, often irreversible on human timescales.