Spatial resilience: The role of local positive feedbacks for large-scale collapse and recovery

Background/Question/Methods

The concept of alternative stable states has become an influential paradigm in ecology. Implications of alternative states are profound from a restoration perspective, but also when it comes to understanding the potential response of ecosystems to change in conditions such as the climate. A problem in extrapolating our current insights to such problems is that so-far most work on alternative stable states comes from relatively small and spatially isolated systems such as lakes and ponds, from controlled, isolated experiments, or from small enclosures in large-scale systems. In reality we often face spatially extended heterogeneous ecosystems rather than well isolated homogeneous ecosystems. The question how stability changes in spatial settings is still underexplored. We used classical bi-stable models in a spatial context to systematically explore how local positive feedback that lead to local alternative stable states, could affect large-scale collapse and recovery.

Results/Conclusions

We show that resilience of the dominant state in a spatially extensive system does not change gradually as environmental conditions change, in contrast to a well-mixed system. Instead, resilience remains large, until it drops sharply around a critical level of the environmental factor (a ‘stationary front bifurcation’) where it becomes fragile in the sense that even a rather small local perturbation can cause a domino effect leading to a systemic shift to the more resilient state. Our results hint at conditions under which restoration efforts can succeed or fail locally, or even cascade through a landscape. Importantly, they also hint at factors that may determine the character of major biome shifts projected to happen as a result of climatic change.