Ecosystem tipping points and stressors

Simply defined, a tipping point is the point when a number of changes or incidents become significant enough to cause a large change in the way the system functions. The tipping point concept is used across many disciplines – medicine, economics, sociology and the sciences – and each will have its own set of factors that define and lead to rapid change in a system.

Imagine stacking blocks to make a tower. As it gets taller, the tower becomes less stable and may wobble. At some point, adding a single small block (in itself not a big change) will cause the tower to topple. In nature, identifying a tipping point is not so straightforward. For a start, ecological changes are non-linear and they often come from a variety of sources, so it can be difficult to identify the one particular stressor or combination of stressors that leads to an abrupt change. Ecosystems can also be enormously complex, so the challenge to identify the tipping points before they occur can be equally complex.

Ecosystems – interdependent and dynamic states

An ecosystem is an intricate community of living things – animals, plants, bacteria and viruses – as well as the physical and chemical environment they live in. They are dynamic by nature – they continually recycle chemical nutrients and energy flows through food webs. Populations fluctuate and change due to seasonal variations, migration and other natural events.

Although ecosystems are dynamic, they are also reasonably stable – sometimes for tens of thousands of years. Ecosystems have the capacity to withstand and overcome disturbances. This concept is called ecosystem resilience. For example, the 2016 Kaikōura earthquake caused huge geological changes to the deep offshore Kaikōura Canyon. Scientists surveying the area a year on found that the deep-sea ecosystem was making a quick recovery due to favourable physical and biological factors, but it still has a long way to go.

Ecosystem functions and ecosystem services

Ecosystem functions are the components that make up an ecosystem and its interactions. These functions are valuable for maintaining both the ecosystems and biodiversity. The functions are also valuable for the ecosystem services they provide. These are services that contribute to ecosystem and human wellbeing such as shellfish filtering and cleaning seawater or sand dunes protecting coasts from erosion and flooding. We rely on these free and beneficial services – but the ecosystems have to be functioning properly to provide them.

Stressors within ecosystems

Stressors can be natural – drought, fire or seismic events – or they can be the result of human activity – like pollution, overharvesting or invasive pests. Ecosystems often have multiple or cumulative stressors. Although ecosystems are resilient, they can be pushed to a point at which resilience can no longer protect them from major ecological alterations – they reach a tipping point.

The complex nature of ecosystems means that it can be difficult to gather evidence of tipping points until after the fact. Hindsight helps us to understand why a systematic change occurred, but by then it is too late.

Tipping points in New Zealand ecosystems

New Zealand has a unique natural environment due to its isolated location. It can be quite a balancing act to protect our valued ecosystems while meeting the needs of our citizens and advancing economic growth. The New Zealand National Science Challenges are a government initiative to bring scientists, stakeholders and Māori together to tackle big ecological issues and sustainability.

Three of the Challenges – Biological Heritage, Our Land and Water and Sustainable Seas are investigating terrestrial and aquatic ecosystem tipping points. Each Challenge has its own focus, but as New Zealand’s land and freshwater and coastal ecosystems are intricately linked, research from each Challenge will help inform the others.

Learn more about the work of Sustainable Seas in the article Investigating marine and coastal tipping points.