Fire Severity as a Determinant of the Socioeconomic Impact of Wildfires

Abstract

Fire has played a crucial role in shaping Earth's landscapes for millions of years and has been used as a cultural tool for human development for millennia. However, changing fire regimes driven by global change drivers and human influences are reshaping landscapes and leading to more severe wildfires, with significant socioeconomic and environmental consequences. These wildfires have substantial direct impacts on human lives, properties, and mental health, as well as indirect impacts on ecosystem services, negatively affecting provisioning, regulating, and cultural services. In general, severe wildfires disrupt the functioning of ecosystems and the subsequent recovery of the ecosystems services. Remote sensing techniques represent efficient tools for monitoring post-fire ecosystem service recovery. On the other hand, the impact of large fires is perceived differently by society influenced by socioeconomic factors, previous experiences, and community dynamics. Understanding these perceptions is essential for developing effective wildfire management and mitigation strategies at the local level. To address the challenges posed by changing fire regimes, a Fire Smart Territory (FST) approach could be considered, emphasizing integrated fire management that considers prevention, effective response, and post-fire restoration. This approach presented in this book chapter also promotes the involvement of local communities in fire prevention and management. So, the conservation of ecosystem services in fire-prone areas requires a holistic and adaptive approach that incorporates ecological knowledge, societal needs, and sustainable land management practices. By adopting an FST framework and considering the complex interactions between fire, ecosystems, and human communities, it is possible to mitigate the impacts of wildfires and promote resilience in these vulnerable landscapes.

1 Introduction

Fire is a key environmental disturbance that has shaped biomes since 400–350 million years ago across most of Earth’s land surface (He et al., 2015). Specifically, for more than 9000 years, fire has been used as a management cultural tool targeted to the opening and maintenance of pastures and croplands, thus largely contributing to human development (Carracedo et al., 2018). Nevertheless, during the last decades, historical fire regimes are shifting due to multiple interactions among global change drivers (mainly climate and land use change) and due to direct human influences, such as ignition and suppression (Rogers et al., 2020). Complex socioeconomic changes (i.e., rural depopulation, land abandonment, or proliferation of rapid-growing forest plantations) have imposed shifts in fuel amount and connectedness (due to massive woodland and shrubland increases in the European countries of the Mediterranean Basin) across traditional landscape mosaics (Delgado-Artés et al., 2022). This landscape homogenization, occurring in a context of climate change (i.e., warmer and drier conditions), is driving a significant change in wildfire typology from small, fuel-limited fires to drought-driven fires (Chergui et al., 2018).

In global terms, it has been noticed an increase in the number of mega-fires and extreme wildfire events that are strongly severe, such as those that occurred in 2017 in Portugal (Turco et al., 2019), in 2020 in California (Higuera & Abatzoglou, 2021) and, recently, in 2022 in Spain. Indeed, the frequency of heat-induced fire weather is projected to increase by 14–30% by the end of the century (2071–2100) depending on the climate change scenario, being suggested that the frequency and extent of large wildfires will increase even more throughout the Mediterranean (Ruffault et al., 2020) and the Boreal region (Drobyshev et al., 2021). The higher the warming level is, the larger the expected increase of burned area, ranging from 40 to 100% across the IPCC scenarios, with significant benefits if warming is limited below 2 °C (Turco et al., 2018).

These new patterns of fire regime are generating multiple (economic, social, and environmental) impacts on society that are driving extraordinary damages (Thomas et al., 2017), increasing direct risks on human lives, and also on good provision and poverty (Paudel et al., 2021), particularly at the wildland–urban interface (Radeloff et al., 2018; Rosenthal et al., 2021). The main impacts of these severe wildfires on society are direct such as human losses, damage to homes and other infrastructures and physical and mental health (Rosenthal et al., 2021). In addition to direct impacts on people and economic losses, severe wildfires also have other substantial effects on society through indirect impact as the alterations of the ecosystem services, defined in the Millennium Ecosystem Assessment (MEA, 2005) as “conditions and processes through which natural ecosystems sustain and fulfil human life”.

Wildfires are highlighted as one of the major disturbances that negatively trigger ecosystem services. In this context, some studies (Taboada et al., 2021) have demonstrated these negative effects on the provisioning services in a fire-prone landscape dominated by pine forests, because they interrupted the capacity of providing timber, mushroom, firewood, and animal hunting, all of them very relevant for the local rural economy of the surrounding areas. Furthermore, wildfires affect negatively most of the regulating services due to the effects on soil erosion, runoff, water quality, and soil fertility, among others (Roces-Díaz et al., 2022). Finally, cultural services, such as cultural heritage and recreation are also negatively affected (Roselló et al., 2020). However, the negative effects on ecosystem services will depend on the type of vegetation affected and their adaptations to recover easily after a fire since in areas dominated by species with fast regeneration some services may be favored, but always depending on the fire severity. Mola & Williams (2018) reported a positive influence of a low severe fire affecting shrublands and grasslands by the creation of open landscapes with an increase in the floral density that represents a more favorable environment for pollinators’ net. Therefore, fire severity is one of the main constraints of the effects of forest fires on the provision of ecosystem services to society.

2 Impacts of Fire Severity of Large Wildfires on Ecosystem Services

Comprehensive analysis of the socioeconomic impacts of large wildfires is often addressed through the ecosystem services approach. These wildfire impacts have been studied across the globe (Roces-Díaz et al., 2021), revealing both positive and negative effects depending on the type of service assessed (provisioning, regulating, and cultural), and the type of ecosystems and society in terms of development (Pausas & Keeley, 2019; Pereira et al., 2021; Roces-Díaz et al., 2021). However, the impacts of fire severity on ecosystem services are less known. The fire severity impacts are the result of immediate impacts on ecosystems and biogeochemical cycles, and of indirect influences on post-fire recovery (Huerta et al., 2022). Concerning the immediate impacts, fire severity is inherently linked to a different degree of vegetation consumption and mortality (Keeley, 2009), to a different magnitude of change in litter and soil properties (Fernández-García et al., 2019), and affections to fauna (Jager et al., 2021). This unavoidably extends to the inter-relationships of all these elements, as well as to ecosystem structure and processes. Focusing on ecosystem responses, fire severity shapes vegetation recovery, as plants have differential responses depending on their functional traits, ones being favored by severe fires (i.e., some herbaceous, and many shrub species with adaptative traits) while others temporarily decline (usually arboreal vegetation) (Fernández-García et al., 2020). Similarly, fire severity influences the post-fire trajectories of soil properties in different ways (Fernández-García et al., 2019). Pioneer work in heterogeneous mountainous landscapes (Huerta et al., 2022) has shown how several ecosystem services and related functions change in function of fire severity one year after the fire (Fig. 1). The analysis revealed decreases in the supporting service proportional to fire severity, a consequence of the loss of photosynthetic activity, nutrient cycling capacity, and soil quality. An increase in the provisioning service was found after low-severity burning and a decrease in severely burned areas, in response to analogous shifts in grass production for livestock and wood production. The regulating service decreased proportionally to fire severity, as it caused significant decreases in carbon stocks and erosion protection. The cultural service, studied through the woody species diversity and aesthetic value (diversity of floral colors of woody species), decayed mainly at moderate severities. Among the studied functions, only soil fertility increased proportionally to fire severity. These results are in line with those reported in previous studies comparing prescribed fires (usually less severe) and wildfires (usually more severe) (Fig. 1) (Pereira et al., 2021; Roces-Díaz et al., 2021), suggesting similar underlying mechanisms. Despite the foregoing, further work is necessary to achieve a better understanding of the complexity of fire severity's influence on ecosystem services, as multiple environmental site-dependent factors might intervene (Fernández-Anez et al., 2021).

Fig. 1

Based on Pereira et al. (2021), Roces-Díaz et al. (2021), Huerta et al. (2022)

Influence of burn severity on four ecosystem functions or services, each one included in a different major group of ecosystem services is shown in the upper part, with balloon sizes proportional to the service provision. The influence of prescribed burning and wildfires on these services is shown in the lower part.

3 Ecosystem Services Recovery After Large Wildfires: A New Methodological Approach

Current and predicted fire regime shifts in the Mediterranean Basin may harm the high resilience to fire that fire-prone Mediterranean ecosystems have exhibited under historical fire disturbance regimes. In this context, the natural recovery of ecosystem functions and services provided by these ecosystems could be endangered by unprecedented fire impacts on the soil and vegetation, as well as by transitions to alternate stable ecosystem states (Johnstone et al., 2016). Therefore, the assessment of how the functional indicators of ecosystem functions and services recover to a pre-disturbance state is essential for supporting adaptive management strategies to safeguard the ecosystem services’ flow for human well-being worldwide, especially in the most vulnerable regions.

Field-based inventories have been traditionally used to measure soil and vegetation functional indicators as proxies of the recovery of ecosystem functions and services with high reliability. However, in the context of global change, with increasingly large burned areas encompassing several plant communities, this approach is no longer versatile. Field inventories may not capture the total ground spatial heterogeneity in large, heterogeneous burned areas and do not allow wall-to-wall (i.e., spatially explicit) estimates. In this sense, the synoptic nature of active and passive remote sensing earth observations, in combination with precise field measurements, offers nowadays an efficient way to achieve this goal.

Conventionally, open data from multispectral passive optical sensors have been used to estimate supporting services’ recovery, mainly ecosystem productivity. For instance, McMichael et al. (2004) applied a normalized difference vegetation index (NDVI)–leaf area index (LAI) model using multi-temporal Landsat data to estimate LAI in a chronosequence approach as a proxy of ecosystem productivity recovery in chaparral shrublands in central California. The temporal dynamics of ecosystem productivity in burned sagebrush communities of the western United States were examined through a dynamic global vegetation model and the gross primary production product from MODIS (Pandit et al., 2021). Fernández-Guisuraga et al. (2022a) proposed the use of physical-based approaches (radiative transfer and pixel unmixing models) for retrieving fractional vegetation cover from a pre- and post-fire time series of Sentinel-2 data as a vegetation productivity resilience metric in several forest and shrubland communities in the western Mediterranean Basin.

Passive optical reflectance data is related to the general trends in the recovery of ecosystem services related to the top-of-canopy vegetation traits in multilayered plant communities (Fig. 2) such as ecosystem productivity. The recovery assessment of other ecosystem services closely related to the vertical profile of the vegetation structure (e.g., aboveground carbon stocks and wildlife habitat), or to the soil properties, requires the implementation of active remote sensing techniques (Fig. 2), or fusion approaches with passive data.

Fig. 2

Appropriate remote sensing products for the assessment of several ecological variables

The sensitivity to the quantity and distribution of vegetation scatterers throughout the canopy of light detection and ranging (LiDAR) and synthetic aperture radar (SAR) sensors has been exploited to evaluate the ecosystem services of the recovery of aboveground carbon stocks (Fernández-Guisuraga et al., 2022b) and structural complexity for wildlife habitat (Fernández-Guisuraga et al., 2022c) in Mediterranean fire-prone plant communities worldwide. Regarding the ecosystem services supported by the soil, Fernández-Guisuraga et al. (2022d) leveraged the increased interaction of SAR backscatter data in the L-bandwidth with soil surface properties for retrieving soil organic carbon and nutrients content as proxies for post-fire recovery of belowground carbon stocks and nutrient cycling services. Although LiDAR and SAR data have the potential to monitor other types of ecosystem services such as timber production (Yoga et al., 2018) or edible fungi production (Peura et al., 2016), to date these methods have not been applied to the assessment of ecosystem services recovery after fire.

The remote sensing-based research presented above has provided a sound methodological basis and reliable results on the recovery trends of specific ecosystem services after different scenarios of fire severity, which also allowed the estimation of their driving factors regarding the fire regime, the dominant vegetation life-history traits, and the environmental conditions in Mediterranean landscapes. These studies evidenced that plant communities dominated by resprouting species exhibit an enhanced recovery of ecosystem services such as ecosystem primary production, habitat structural diversity, and aboveground carbon stocks in the short term after a fire, as compared to communities dominated by obligate seeders. Likewise, fire severity undermines ecosystem services recovery by affecting both resprouting and seeding capability of the dominant species in the communities, but the magnitude of this effect seems to be modulated by environmental resource availability. Enhancing the resilience of ecosystem services provided through the promotion of resprouter species and the implementation of adaptive management strategies to prevent high fire severity burnings should be a priority in Mediterranean fire-prone landscapes.

4 Social Perception of the Impact of Large Wildfires

In the last few decades, the greater occurrence of large and destructive wildfires leads to an increase in the impact on social systems. Although in most studies this impact is measured in terms of economic losses (e.g., home loss or suppression costs), significant research has been developed on the human dimensions of wildland fire since 2000 (McCaffrey et al., 2013), by addressing topics such as social dynamic change after a wildfire, public response during fires, or attitudes toward implementation of forest fire mitigation measures (McCaffrey et al., 2013; Paveglio et al., 2015). These studies were carried out through surveys of the population, workers and volunteers in medical facilities, social services agencies, and non-profit organizations located in communities affected by wildfires (Rosenthal et al., 2021).

Social perception of wildfires can be shaped by their previous experiences, people’s standard of life, their interaction with land and forests, and their worldviews. For instance, Yulania et al. (2021) found that the inhabitants of rural areas of Indonesia had a perception that usual practices of burning forest and land will be detrimental to their society, so their participation and supervision of forest and land use would be fundamental to manage the environment properly. Other populations in the northwest of Spain have a similar perception of the damage of wildfires both for the ecosystem and for the people living in these areas. In this case, they attribute the responsibility to mitigate the fire damage to the local and regional authorities but did not perceive a social co-responsibility in this problem (García-Mira et al., 2008), because they consider that wildfires are caused by criminal behavior. A different perception was found in a study following the largest wildfire that occurred in Sweden in 2014 (Lidkogs et al., 2019). The population did not blame forestry companies or fire departments, rather they considered this disaster as a learning opportunity to improve the prevention of future events and to create a nature reserve with positive consequences (higher biodiversity). However, people’s perceptions change when, in addition to living in areas affected by frequent fires, they live under poverty conditions, and overcrowded and structural issues, such as what happens in some areas of Chile. In such a context, people perceived that authorities were not concerned about the risk, and so, they felt very vulnerable to the occurrence of a disaster caused by wildfires. Sapiains et al. (2020) recommended that in these situations local communities should have responsibilities to improve the negative perception of themselves and should create more social interactions. After destructive fires in California, Rosenthal et al. (2021) found that wildfire survivors perceived (i) accessing safe and secure shelter mainly for those whose homes were lost; (ii) the economic instability which increases anxiety or depression; and, (iii) mental and emotional well-being and access to health resources as the main social problems. Participants in this survey pointed out the deficiency of private and public recovery resources used to restabilize following the fire, and therefore, the administrations should implement structural changes to cover the needs of wildfire survivors.

The studies mentioned above showed the variability in the social perception of the impacts of large forest fires, which implies that the solutions to mitigate this problem are complex. Further study and new methodologies for its assessment are needed to understand the social consequences at the local level (Paveglio et al., 2015). Future research could help to strengthen the role of the community in designing and implementing preventive measures together with governmental agencies.

5 Management and Conservation of Ecosystem Services in Fire-Prone Areas

Despite the intense efforts dedicated to forest fire suppression in western countries, the challenge of reducing the impact on ecosystem services is far from being solved. Current forest fire policies in these countries have not solved the problem, and probably they will not be effective in the future, as all initiatives focus on fire suppression and minimize the traditional use of fire based on the ecological knowledge of former European communities. This traditional use of fire as a tool for land management has been manipulated and almost criminalized by an urban-centric perspective and an anti-fire bias (Tedim et al., 2016).

From an anthropogenic, technological, and ecological approach, the most “holistic” concept is the so-called “Fire Smart Territory” (FST), which puts at the center of the problem the “territory” understood in a broad sense, not only as landscape but as the social and psychological interpretation of the landscape. The fundamental assumptions of FST are that fire is a dual and ambiguous process, and that it is not simply a biophysical process with social connotations but a social process. It is a complex issue that can be understood only in coupled human and natural systems. The local understanding of the wildfire problem prepares strategically each territory to make it less prone to wildfire and its inhabitants less vulnerable and more resilient, in the scope of economic valorization, sustainable development, and security of the territory's resources.

We have designed a new model, based on a triad or group of three factors especially linked to each other, to carry out an integral and coherent management of forest fires within the framework of ecosystem services conservation (Fig. 3). This figure depicts the triangle that serves to define an FST and expresses the interaction among risk management in mosaic landscapes (prevention), the effective response when a fire occurs, and the post-fire restoration supported by proven ecological knowledge.

Fig. 3

Triangle defining management strategies and conservation of ecosystem services in fire-prone areas in Fire Smart Territories (FST)

In this sense, strategic thinking and planning that FST posits must recognize and accept fire as a natural process necessary for the maintenance of many ecosystems and strive to reduce conflicts between fire-prone landscapes and people. Thus, Integrated Fire Management implies a greater integration of the different components of fire management (prevention, detection, suppression, and use).

The first question to be asked when the goal is to create an FST is: how to design fire prevention in fire-prone agroforestry landscapes? As indicated above, the socioeconomic change in land uses has created a continuity of wooded forest stands together with high fuel accumulation that could favor the occurrence of large wildfires, with crown fires and massive secondary outbreaks. In this sense, fire prevention and suppression approaches that have relied exclusively on silvicultural measures and containment infrastructures are increasingly ineffective in stopping the spread of wildfires. Given that agroforestry landscape mosaics composed of a mix of different land cover and land use types are considered less prone to fire than forests, approaches that support the involvement of rural people in agricultural and forestry activities should be proposed (Bertomeu et al., 2022).

This preventive management model aims to defend the vulnerability of ecosystem services, i.e., the physical, social, economic, and environmental factors that increase the susceptibility of individuals, communities, settlements/buildings, ecosystems or systems to damage, and loss from wildfires. This model contributes to increasing the effectiveness of resistance (reducing fire severity to give trees a chance to survive) and promotes resilience (post-fire rehabilitation and landscape diversification to give vegetation a chance to regenerate in case of future fires). Marino et al. (2014) carried out a quantitative Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis applied to Spain to analyze fuel management for forest fire prevention. The study highlighted how solutions to forest fires should be based on rural development that includes sustainable forest management and an integrated defense against fires. The impulse of the public administration with active policies that allow taking advantage of these opportunities is proposed as a priority if the challenge of reducing the severity of forest fires in the context of climate and socioeconomic change is to be faced with guarantees.

As a complement to risk management in mosaic landscapes, Madrigal et al. (2019) proposed the creation of Strategic Management Zones, areas of the territory defined and prioritized according to a specific methodology that, taking into account the fire risk, the fire behavior in the study area and the vulnerability of its natural, rural, or urban values to be protected, allows to establish and optimize space-temporal planning of fuels and infrastructures that limits the fire potential, detecting extinction opportunities, and anticipating an effective and safe defense strategy for large forest fires type for which it has been designed.

The second key question related to the creation of an FST is: what should be the fire suppression approach to avoid the wildfire paradox? To answer this question we have followed the approach taken by projects such as “Fire Paradox” (Silva et al., 2010) which is based on the paradox that fire can be “a bad master but a good servant”, so it is necessary to take into account the negative impacts of current wildfire regimes (understanding initiation and spread) and the beneficial impacts of controlled fires in vegetation management and as a planned mitigation practice (prescribed burning along with some traditional fire uses) and for fighting wildfires (suppression fire).

Faced with the challenge of climate change, this second FST strategy proposes to take an unbiased view on the value of both the use of fire to mitigate risks—through prescribed, indigenous, and controlled burning—and to allow some wildfires considered to be low risk to run their natural course. This path also requires identifying the most at-risk ecosystems from large and severe wildfires and prioritizing mitigation measures to balance their impacts.

Finally, the third and last question is: how to deal with post-fire restoration when the first two strategies have not worked? According to the Spanish National Ecosystem Assessment (SNEA), in Spain, 45% of the ecosystem services assessed have been degraded or are being used unsustainably, with regulating services being the most affected. One of the main drivers of degradation has been large, high-severe wildfires.

6 Conclusions and Final Remarks

Post-fire restoration aims to mitigate or reverse the negative ecological and socioeconomic impacts of fire. These impacts are related to the fire regime and its interactions with ecosystem resilience to fire. In the case of severe fire regimes, the main environmental impacts affect nutrient balance, soil erosion risk, and biodiversity reduction. Post-fire restoration planning requires the identification of specific fire-triggered degradation processes, including their temporal and spatial dimensions, and vulnerable ecosystems. Restoration should address the identified vulnerable areas and mitigate the risk of soil erosion and runoff in the short term, as well as the recovery of nutrient cycling and key plant species in the long term (Vallejo & Alloza, 2015).

An important decision in post-burn forest management, when restoration of the old forest type is the primary objective, is whether to use natural regeneration (indirect restoration), if present or expected to occur, or active restoration (plantings and seeding). Depending on the objectives, this may involve thinning, shoot selection, and control of unwanted vegetation. The costs associated with assisted natural regeneration can be much lower compared to active restoration, meaning that a much larger area can be effectively treated with a similar amount of available funds. Of course, the decision of active versus natural restoration will be conditioned by vegetation type, ecosystem response, burned area objectives (Mola et al., 2018), and the societal needs of these burned landscapes.