What is the difference between resilience and vulnerability, and why is it key in the forestry sector?

Imagine you are a policymaker working to manage the impacts of global change on forest ecosystems—drought, pests, or fire risk. In your discussions with colleagues and perhaps with researchers, two critical concepts often emerge: resilience, understood as a forest’s ability to recover its normal functioning after a disturbance, and vulnerability, which refers to the degree of susceptibility a forest has to a given risk.

How different are these concepts, and how should they be applied? Understanding them is essential to developing effective strategies that help manage and adapt forest systems to the future they face.

This analysis of resilience and vulnerability stems from a rigorous debate among researchers at the Technical University of Munich, CREAF, and the Autonomous University of Barcelona. We realized the need to closely examine these two concepts, as their misuse could lead to confusion when conveying large-scale messages to policymakers—for example, in recommendations provided by the IPCC or IPBES. This discussion led to the publication of the article “Resilience and vulnerability: distinct concepts to address global change in forests” in Trends in Ecology and Evolution, which we summarize below.

Resilience generally refers to a forest’s ability to absorb or withstand disturbances, including those exacerbated by global change, such as extreme climate events. It focuses on how a forest ecosystem responds over time and how it recovers after a fire or storm while maintaining its functions and services. For example, if a windstorm knocks down trees in a temperate forest, that forest may lose some of its climate regulation capacity because it can no longer absorb as much CO₂. Over time, the ecosystem regenerates as new plants grow, restoring its ability to sequester carbon.

Vulnerability, on the other hand, focuses on a forest’s susceptibility to adverse impacts and its ability to adapt. It takes a more analytical approach and is often used to identify which forests are most vulnerable, typically through mapping.

Both concepts provide valuable perspectives, but they have different origins and applications. Resilience studies originate in ecological theory, emphasizing recovery and resistance over time. In contrast, vulnerability assessments stem from disaster risk management, focusing on susceptibility and identifying areas of highest risk. This difference in perspective leads to distinct approaches to forest assessment and management.

• Resilience: Originates from ecological studies and is less commonly used in policymaking. It often involves identifying thresholds and tipping points. For example, if fire frequency increases to the point that forests lose their ability to regenerate, they will have crossed a threshold and could transform into a different ecosystem.
• Vulnerability: Developed within the field of disaster risk reduction, it has been more widely used in policymaking (e.g., in IPCC reports).

• Resilience: Focuses on post-disturbance trajectories, including resistance and long-term recovery. It examines mechanisms such as seed bank dynamics or soil characteristics that promote regeneration.
• Vulnerability: Focuses on pre-disturbance conditions, analyzing susceptibility and adaptive capacity, generally through spatial assessments.

• Resilience: Useful for understanding how to enhance forests' ability to cope with global change. For example, some pine species have serotinous cones that remain closed until the intense heat of a fire triggers seed release, allowing forest regeneration. This concept helps identify critical processes that ensure long-term ecosystem stability.
• Vulnerability: Provides practical tools to identify high-risk areas and prioritize interventions based on spatial and adaptive assessments. Since it has been more widely used in policy contexts (such as IPCC reports), it also facilitates stakeholder engagement and integrates socioeconomic factors.

Resilience and vulnerability are complementary concepts when understanding how forests respond to climate disturbances. While both are important, their use depends on the objective of the analysis. For example, if the goal is to create maps or assess susceptibility, vulnerability may be more appropriate. In contrast, if the focus is on tracking changes in forests over time—such as determining whether they have crossed a threshold and are transitioning into shrublands due to frequent fires—resilience is the more relevant concept.

Applying these concepts rigorously can improve policymaking and forest management practices. A solid understanding of these terms will enable more effective strategies in a constantly changing world.
 

Reference article: Lecina-Diaz J, Martínez-Vilalta J, Lloret F, Seidl R (2024). Resilience and vulnerability: distinct concepts to address global-change in forests. Trends in Ecology and Evolution. Volume 39, Issue 8, 706–715. DOI: https://doi.org/10.1016/j.tree.2024.03.003

Acknowledgments: J.L-D. was funded by the Alexander von Humboldt Foundation. J.M-V. received support from an ICREA Academia award. F.L. acknowledges funding from the Spanish Ministry of Science and Innovation (PID2020-115264RB-I00). R.S. was funded by the European Research Council under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 101001905, FORWARD). F.L., J.M-V., and R.S. also received support from the H2020RUR-2020-2 RESONATE project (Grant No. 101000574).