Threshold (in an ecosystem)

The level of magnitude of a system process at which sudden or rapid change occurs.

Source: PhysicalGeography.net Glossary of terms 

A point or level at which new properties emerge in an ecological, economic, or other system, invalidating predictions based on mathematical relationships that apply at lower levels.

For example, species diversity of a landscape may decline steadily with increasing habitat degradation to a certain point, then fall sharply after a critical threshold of degradation is reached.

Human behavior, especially at group levels, sometimes exhibits threshold effects. Thresholds at which irreversible changes occur are especially of concern to decision-makers.

Source: MA  Glossary

Non-linearity

GreenFacts Summary on Ecosystem Change:

• 7.2 When do non-linear or abrupt changes occur in ecosystems?

Español: Umbral (en un ecosistema)
Français: Seuil (dans un écosystème)

Arctic Climate Change

Desertification

Ecosystem Change

Climate Change

Particulate Matter