Research articleClearing shrubland and extensive livestock farming: Active prevention to control wildfires in the Mediterranean mountains
Introduction
Wildfires are very common in the Mediterranean European countries: every year, they cause significant economic and environmental losses, and even human lives (Shakesby, 2011). The climate of the Mediterranean environments makes them highly prone to fires, as summer is dry and hot with frequent lightning storms (Pereira et al., 2005; Amraoui et al., 2015). Indeed, fire has been an essential part of the ecosystems and landscapes in the Mediterranean area since at least the Miocene era, with humans intervening in the fire regime over the last 10,000 years (Daniau et al., 2010).
Fire has been used since Pre-history as a management tool to remove trees and shrubs to create agricultural land and pastures (Rius et al., 2009; Bal et al., 2011; Seijo and Gray, 2012; Pausas and Keeley, 2014), giving rise to highly heterogeneous cultural landscapes with a great deal of biodiversity (Antrop, 1993; Farina, 2000; Lasanta et al., 2005; Varga et al., 2018). However, throughout the 20th century, especially after 1960, fire regimes changed, with an increase in frequency and magnitude (Pausas and Keeley, 2009), causing serious damage to ecosystems and human infrastructures (Westerling et al., 2006; Rodrigues et al., 2013). Approximately 65,000 fires occur each year in Europe, and about 85% of the total burned area is in the Mediterranean European countries (San-Miguel-Ayanz et al., 2013). Several reasons have been put forward for the increase in fires: i) climate change and rising temperatures with a prolonged hot season (Pausas and Fernández-Muñoz, 2012); ii) policies prohibiting the use of fire for agricultural purposes, leading to a larger amount of combustible material (Minnich, 1983; Piñol et al., 2007; Curt and Frejaville, 2018); and iii) rural abandonment followed by revegetation that increases the combustible biomass (Moreira et al., 2011; Seijo and Gray, 2012; Pausas and Fernández-Muñoz, 2012).
More than 95% of fires in Europe are due to human causes, through accident or intent (San-Miguel-Ayanz et al., 2013). In Spain, for example, lightning strikes account for just 4% of the fires (de la Riva and Pérez-Cabello, 2005). In the Mediterranean mountains, the main causes of wildfires are depopulation of the countryside, farm abandonment, the loss of the forest's function, mass reforestation with pines, and reduction of pasture areas since the mid-20th century, leading to a rise in shrubland and forest, landscape homogenization and, in short, an accumulation of combustible biomass (Scarascia-Mugnozza et al., 2000; Chauchard et al., 2007; Serra et al., 2008; Pausas and Keeley, 2009).
Among the proposals for modelling fire risk appearing in scientific literature, the one developed by Chuvieco et al. (2012) integrates the concepts of vulnerability and fire danger at the same level (Fig. 1). While the former relates to the potential effects of fire and assessment of the resources affected at an ecological and socio-economic level, fire danger includes factors affecting ignition and propagation of fire (Chuvieco et al., 2012). Among these, the fuel type sums up the properties of the vegetation that plays a crucial role in the propagation of fire and the amount of energy released and, thus, on the magnitude of the consequences for the ecosystems involved. In theory, more fuel could justify greater intensity (temperature and exposure time to flames) and therefore, much more destruction of key elements in the process of post-fire recovery (alteration of the seed banks, changes in physical and chemical soil properties, dieback of vegetation, etc.).
Regardless of competition from other types of factors, assessment of the vegetation in terms of combustibility is a complex task. In this context, the fuel models enable characteristics of the vegetation affecting the behaviour of fire to be simplified (size, compacting, density, chemical substances, etc.). One of the best-known classifications is the one proposed by Rothermel (1983), and adapted in the 1980s to the plant formations in Spain (MAPA, 1989). This author proposes 13 models of vegetation structure, depending on its combustibility. These models are identified by a quantity of fuel available (T/ha) and are arranged in 4 groups, based on combustibility and the propagation mode: pasture, shrub, litter below trees and felling residues.
Land managers try to control wildfires by prevention policies. Some of them seek to reduce the fuel by clearing shrubland. With this in mind, prescribed burning or prescribed fires are used, meaning planned fire to burn the accumulated fuel in a controlled manner (Fernandes et al., 2013). Many regional and national governments in Mediterranean areas of Europe finance prescribed burning (Ascoli et al., 2013), in some way similar to the burn-off traditionally done by shepherds to remove shrubland and promote pasture regeneration (Meitalié, 2006). Prescribed fires started in the United States and reached the Mediterranean European countries in the 1960s (Liacos, 1986). In the 1980s, they were carried out fairly frequently in Portugal, Spain, France and, to a lesser extent, in Italy (Montiel and Kraus, 2010). At present, approximately 10,000 ha/year are managed via prescribed burning in the European Mediterranean region (Fernandes et al., 2013). However, prescribed burning is not effective as the sole instrument to control the invasion of shrub into pasture (Briggs et al., 2005; Heisler et al., 2004; Nadal-Romero et al., 2018; Badía et al., 2017). The combination of controlled burning and guided grazing has been suggested as a good method to restore the ecosystems in areas with a long history of fires and grazing (Fuhlendorf et al., 2009; Ascoli et al., 2009; Komac et al., 2013), although the low number of livestock currently observed in many mountain areas leads to the failure of the fire-pasture balance (Ruiz-Mirazo et al., 2012).
Livestock grazing is another method used to try to control an accumulation of fuel. The European Union has strongly supported extensive livestock farming since 1992 with its Common Agricultural Policy (CAP), through the payment of subsidies, and extensification policies. In subsequent reforms of the CAP, measures promoting extensive livestock farming have been amplified, due to its socio-economic contribution, the preservation of the environment in depressed areas, and the provision of ecosystem services (Bernués et al., 2014). Against this backdrop, extensive livestock farming has been used as a tool to prevent shrubland expansion and densification by subsidising grazing in particular places, such as the fire-breaks and strategic areas to prevent fires or control their propagation (Lasanta et al., 2014). However, various studies have evidenced that grazing alone, with the present numbers of livestock in the Mediterranean mountains, is insufficient to prevent the advance of shrub (Bartolomé et al., 2000; Casasús et al., 2007; Ruiz-Mirazo et al., 2011; Álvarez-Martínez et al., 2016), which increases the likelihood of dangerous pasture fires, a difficult and sensitive issue in the Mediterranean countries of Europe (Ruiz-Mirazo et al., 2012).
In La Rioja (Spain), the Regional Government started an action plan in 1986 (henceforth called the Plan for Shrub Clearing, PSC) which combines shrubs clearing with livestock grazing. The PSC aims to control fire and boost the sustainability of mountain areas through managing extensive livestock farming (Lasanta et al., 2009). In a recent paper, Lasanta et al. (2019) concluded that the results for the development of extensive livestock farming are very positive: pasture land increased threefold and the number of livestock rose fourfold after the PSC.
Our hypothesis suggests that shrub clearings and livestock expansion are key factors in preventing wildfires. This paper studies the influence of shrubs clearings on controlling forest fires. It includes a brief outline of the shrub clearings plan, an analysis of livestock and farm evolution, and an analysis of the evolution in the number of wildfires and the burned surface area in La Rioja, compared with Spain from 1968 to 2017. In addition, maps on land use and land cover are the basis for an assessment of the reduction in fire danger in three mountain municipalities, based on the levels of structural combustibility of the vegetation following the introduction of the PSC.
Section snippets
Study area
This study was carried out in La Rioja (Spain), a region in the north-western area of the Iberian Peninsula (Fig. 2). The area (5045 km2 and 317,055 inhabitants in 2015) encompasses two very different units. The northern half belongs to the Ebro Valley, a Tertiary sedimentary basin featuring sloping lowlands used intensively for agriculture. The majority of the population, industry and services are located there. The southern half is a mountain area (north-western Iberian System), worked
Shrub clearings in La Rioja (1986–2017)
Between 1986 and 2017, 33,900 ha were cleared in the mountain areas of La Rioja, representing 25.9% of shrubland, or 13.2% of the total surface area. Most of the clearings took place on former crop fields that had been abandoned after 1960 and were now in a process of plant succession. Fig. 4 shows the annual and accumulated evolution of the cleared area, highlighting a strong inter annual fluctuation, with years with more than 2000 ha cleared (2002–2006) and others where clearing did not take
Discussion
Wildfires are one of the most important factors in transforming ecosystems and landscapes, with global impacts, such as the emission of greenhouse gases. In the Mediterranean European countries, wildfires have been one of the main causes of environmental problems for the last 40 years (San Emeterio et al., 2016). Historically, fire has been used as a management tool, so that many ecosystems have adapted to fire regimes. Nevertheless, recent climate and social changes have transformed the
Conclusions
Land Managers in Mediterranean European countries have attempted, not always successfully, to reduce wildfires and strike a balance between conservation and exploitation of natural resources. However, the policies adopted until now have usually been based on fire-fighting, often not achieving satisfactory results.
The most popular preventive policies (prescribed burning, livestock grazing and a combination of both) have also proved incapable on their own of controlling the accumulation of
Acknowledgements
This research was supported by the ESPAS project (CGL2015-65569-R, funded by the MINECO-FEDER) and ECOHIPRO (1560/2015), funded by the Natural Parks-Ministry of Agriculture and Environment. The “Geoenvironmental Processes and Global Change” (E02_17E) and the “Procesos GEOambientales en espacios FORESTales” (GEOFOREST, S51_17R) research groups were financed by the Aragón Government and the European Social Fund (ESF-FSE). Estela Nadal-Romero was the recipient of a “Ramón y Cajal” postdoctoral
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2022, AnimalCitation Excerpt :This is however costly, does not create the same degree of structural heterogeneity as grazing, and over time leads to nutrient depletion. A build-up of dead, undergrazed vegetation also poses an increasing fire risk (Lasanta et al., 2018; Gonzalez-Hernandez et al., 2020). The biodiversity benefits of mixed low-intensity grazing systems in such situations have been well documented (Critchley et al., 2008; Fraser et al., 2014b; Evans et al., 2015; Lopez et al., 2017) (Fig. 4), but as indicated previously, hill and upland areas tend to be managed predominately as sheep-only systems.