Assessing global change impacts on fire regimes in Mediterranean Ecosystems

Andrea Duane Bernedo

Lluís Brotons Alabau

Fire regimes are changing or are expected to change under the influence of global change, with potentially adverse impacts on ecosystems and society. The main objective of this thesis is to increase our knowledge of the processes that influence fire dynamics on a large scale, integrate them into modeling tools that help predict the impacts of global change, and ultimately help in the implementation and design of strategic management plans that reduce the negative effects of fire. The approach that has been followed is based on deciphering the mechanisms that govern different typologies of fire spread patterns and evaluating the dynamism in fire activity. Once identified, all these factors are integrated into a landscape modeling tool that allows estimating the impacts of future climate change and different management strategies on the fire regime. All these questions are assessed in Catalonia, a densely populated Mediterranean region (~32,000 km2) facing a period of great uncertainty in the face of global change. The results of this thesis provide new evidence of the underlying processes that govern fire dynamics in Catalonia. Using fire spread patterns, a classification widely used in the operational world of extinction, I have promoted a paradigm shift in how environmental processes are integrated into landscape assessments, since fire spread patterns allow us to explain the mechanisms of the fire regime operating at the landscape scale. I have found that their occurrence and propagation depend on different environmental factors, and that future changes will impact different fires in an idiosyncratic way. The increase in fuel accumulation due to rural abandonment and higher temperatures have promoted the emergence of new 'convective' fires, characterized by extreme behavior, in the 1990s. However, firefighters have been able to control fires associated with hot and dry situations in the last decade, but not those associated with windy situations, a fact that should serve as a basis for future management plans. Furthermore, in this thesis I also demonstrate that the role of meteorology in fire activity is dynamic: past fires can create periods of time where the main limiting factor for the occurrence of fires is the lack of fuel. If fires are reduced by extinguishing, what is really being done is to rely increasingly on highly uncertain meteorological phenomena. By analyzing future climate conditions in Catalonia, I have also found new climate conditions that may induce extreme fires. Finally, I demonstrate that the application of prescribed burning plans with reasonable amounts (15,000 ha/year) can counteract the negative impacts of fire associated with climate change and maintain pre-defined ecological states. Fire management, therefore, must shift from the era of extinction to the era of regime management. This thesis provides quantitative evidence for implementing effective fire management policies, which can lead us towards a sustainable coexistence with fire.

This thesis allows us to contribute to the development of public policies that ensure the reduction of fire risk in Catalonia under forest and territorial planning. Therefore, the degree of applicability and transfer is potential in two main areas: 1. On the one hand, the application of public policies of forest planning and fire prevention through effective and sustainable prescribed burning plans. By sustainable, it is considered that prescribed burning is applied below thresholds that ensure that the forest mass is not excessively affected (~15000 ha / year for all of Catalonia). By effective, it is understood that this amount is sufficient to affect the fire regime. Until now, the few prescribed burns applied in Catalonia were based on experts' intuition about their suitability. Now, legislation and regulations (for example the General Forest Policy Plan) should contemplate the possibility of applying these prevention plans in the long term and on a large regional scale. 2. On the other hand, the construction of mathematical landscape models also allows, not only to influence strategic planning, but also tactical. It would allow to specifically evaluate the location, intensity and frequency of application of technical plans of prescribed burns. This thesis can serve to help managers and landscape planners to choose priority areas of management and go to a more local and adjusted level of decision-making (Ordinance plans, technical plans, management plans, etc.).

Fire Regimes; Global Change; Adverse Impacts; Ecosystems; Society; Fire Dynamics; Modeling Tools; Predict Impacts; Strategic Management Plans; Negative Effects of Fire; Fire Spread Patterns; Fire Activity Dynamism; Landscape Modeling Tool; Future Climate Change; Management Strategies; Densely Populated Mediterranean Region; Catalonia; Environmental Processes; Landscape Assessments; Convective Fires; Extreme Behavior; Fuel Accumulation; Rural Abandonment; Higher Temperatures; Firefighters; Hot and Dry Situations; Windy Situations; Meteorology; Limiting Factor; Fuel Lack; Prescribed Burning Plans; Ecological States; Fire Management; Era of Extinction; Regime Management; Quantitative Evidence; Effective Fire Management Policies; Sustainable Coexistence with Fire.