|Contributing Authors:||Matteo Jucker Riva, Gudrun Schwilch, Hanspeter Liniger|
|Source document:||Jucker Riva, M., Schwilch,G., Liniger, H. 2016. A method for resilience assessment. CASCADE Project Deliverable 7.2, 61 pp
1. Resilience and regime shifts
A regime shift is defined as an abrupt change of the way an ecosystem functions and of its internal structure (Andersen, Carstensen, Hernández-García, & Duarte, 2009). Regime shifts are a concern because they are difficult to predict (Guttal & Jayaprakash, 2008): even if a system has remained stable for a long period, a regime shift can occur abruptly and with very limited warning signals (Brock & Carpenter, 2012). Moreover, It can cause a profound change in the provision of ecosystem services and can, e.g. in drylands, lead to desertification (Crépin, Biggs, Polasky, Troell, & de Zeeuw, 2012). Recovery from a regime shift is usually difficult if not impossible: once the system has shifted to a new configuration (called "degraded stable state"), it tends to display hysteresis (Groffman et al., 2006). Thus, it is not sufficient to reduce the pressure on the system for the ecosystem to return to the previous situation.
From a conceptual point of view, a system can undergo a regime shift for two reasons:
- The external pressure grows beyond a threshold point (Walker & Meyers, 2004). This is normally caused by a change in processes at bigger scale (e.g. climate change causes an increase in fire frequency and intensity), but can be intensified through feedback mechanisms (e.g. the drought degrades the soil, reducing its water holding capacity, which in turn increases the impacts of the drought).
- The internal capacity of the system to withstand pressure is eroded (Folke, Carpenter, & Walker, 2010). This is normally due to internal changes of the ecosystem (e.g. a deforested slope is much less stable, and will not be able to withstand an intense rainfall event, even if the precipitation regime isn't changed).
In real world ecosystems the two are often mixed, so that an erratic disturbance regime, together with a gradual depletion of the resilience mechanisms (Jucker Riva, Liniger, & Schwilch, 2016) causes a regime shift.
Effectively acting on the disturbance regime is difficult, as it requires acting at large scale on many different processes. While in some cases it is possible to prevent disturbances acting at the local level (e.g. by excluding fire from an area using fuel breaks), this also represents a major change for the ecosystem, and can produce negative consequences and ultimately bring the ecosystem towards another regime shift (e.g. exclusion of fires will increase the risk of pests and diseases, and will also decrease the amount of fire-prone species. This can result in a regime shift when fire eventually returns to the area). Thus, both mathematical modeling (Gunderson 2000) and empirical observations (Reinhardt et al. 2008) suggest that it is much more valuable to increase the ability of the system to withstand pressure, or in other words, to increase the resilience of the ecosystem. This has a beneficial impact on the ecosystem, regardless of the changes that may occur in the disturbance regime or in other external factors.
2. The concept of resilience
The concept of resilience, developed in the seventies (Holling, 1973), has since long been used in the ecology field to explain the dynamic of ecosystems. Theoretical elaboration and ecosystem observation have led to the definition of "Ecological resilience" as the capacity of a system to maintain its structure and function in the face of a disturbance (Gunderson, 2000). Integrating an increase in resilience into land management objectives, the so called “resilience thinking”, is important to avoid regime shifts and to design cost-effective management strategies (Rist & Moen, 2013). However, there is still a wide gap between ecological knowledge, theoretical elaboration on resilience, and land management practice (Folke et al., 2013).
Recent elaboration on resilience concepts distinguishes two approaches:
- Resilience as an internal property of the system, and
- Resilience as a reaction of the system to a specific disturbance (S. Carpenter, Walker, Anderies, & Abel, 2014).
Studies that follow the first approach focus on the structure of the system and on the features that have a general positive effect on the resilience of the system, such as the capacity of self-organization, the functional response diversity, the exchanges between different parts of the system and others (Cabell & Oelofse 2012). This approach is virtually more applicable, as it does not relate the property of the system to specific disturbances or to the context in which it is found (Brand & Jax, 2007). However, it doesn't help to identify specific actions that could help the system to recover in the short term. For example, allowing the administrators of a municipality in a forested area to establish their own land use planning (increasing the self-organization capacity of that socio-ecological system), while probably beneficial in the long term, does not guarantee that the forest will recover after fire.
The second approach, often used by natural scientists, implies a closer study of the perturbation and of the specific context in which the system is: “To assess a system’s resilience, one must specify which system configuration and which disturbances are of interest” (S. Carpenter et al., 2014). It implies studying the reaction of the system (in a specific configuration) to a certain disturbance: e.g., what measures can be taken to increase the probability of the forest stand to recover after fire, given the knowledge and resources available for land management at the moment?
This approach allows identifying specific actions to increase the resilience of the system, and thus was selected for this section of CASCADE.
Note: For full references to papers quoted in this article see