ACTIVE MANAGEMENT AGAINST SHRUBLAND EXPANSION: SEEKING A BALANCE BETWEEN CONSERVATION AND EXPLOITATION IN THE MOUNTAINS

. The mountains of Europe, especially in the Mediterranean, have undergone a significant process of revegetation since the mid-20 th century with the spread of shrublands and forests in succession stages. This leads to negative effects (degradation of pasture, accumulation of biomass with the subsequent increase in fire risk, loss or trivialized of cultural landscapes, etc.) and other positive ones (greater rewilding of landscapes, recovery of forest life, more CO 2 fixation, less soil erosion, etc.). Thus, two alternatives must be put forward: either allow the rewilding process to continue, or intervene in the region to reduce the negative effects of revegetation. In this paper, the literature forms the base for a discussion on the main interventions in the territory: extensive livestock grazing, combined with prescribed fires and shrub clearing. Prescribed fires are found to be insufficient to control the spread of shrublands, and in some cases promotes its regrowth ( Echinospartum horridum ), as well as degrading the pasture land and increasing soil erosion. On the other hand, clearing shrubland has positive effects: a reduction in wildfires, increased livestock numbers, and improved indicators of heterogeneity and fragmentation of the landscape. En este trabajo se discute, a partir de la literatura, sobre las principales inter-venciones en el territorio: ganadería extensiva en combinación con quemas prescritas y desbroce de matorrales. Se señala que las quemas prescritas resultan insuficientes para controlar la expansión de matorrales, favoreciendo en algunos casos ( Echinospartum horridum ) su rejuvenecimiento, además de degradar la co-munidad de pastos e incrementar la erosión del suelo. El desbroce de matorrales, por el contrario, muestra efectos positivos: disminución de incendios, aumento de los censos ganaderos e incremento en los índices de heterogeneidad y fragmen-tación del paisaje.


Environmental effects from rewilding after land abandonment
Changes in land management, transforming both land cover and use (LCLU), have significant implications for sustainability and are included among the main causes of global climate change, since they impact biological diversity, contribute to local climate change, are the principal factors in soil degradation, and alter the ecosystems that support the needs of humans (Lambin et al., 2001;Foley et al., 2005).
Among the LCLU, there is a noticeable spread of vegetation, a common process in the mountain areas of developed countries (Riebsame et al., 1994). For some authors, higher temperatures are the main cause of the positive growth in plant biomass (Kawabata et al., 2001;Lucht et al., 2002). Without diminishing the role of warming, it seems to be more justifiable to attribute the main responsibility for land management and land use changes, in particular, depopulation, farmland abandonment, less pressure from livestock in the territory, and scant use of forest products (wood, firewood, etc.), all caused by an intense rewilding process (Ramankutty and Foley, 1999;MacDonald et al., 2000;Kozak, 2003;Lasanta and Vicente-Serrano, 2007;García-Ruiz and Lana-Renault, 2011). In mountain areas, especially in the Mediterranean, cropland abandonment and sparse pasture land are the main reasons for enormous land cover and landscape changes, as shown by the dominance of forests, shrublands and secondary shrubs where, before, there had been crop fields and pastures (Molinillo et al., 1997;Poyatos et al., 2003;Metailié and Paegelow, 2004;Vicente-Serrano et al., 2005;Motta et al., 2006;Gellrich et al., 2007;Sluiter and de Jong, 2007;Sitzia et al., 2010;Komac et al., 2011;Gatzia et al., 2014;Sanjuán et al., 2018).
The unbridled spread of vegetation, shrub succession and forest possibly constitutes a positive process on a global scale, as far it helps to compensate for the loss of large areas of forest, especially in the tropics (FAO, 2006;Austin et al., 2017). In fact, Song et al. (2018) calculate that tree cover worldwide increased by 2.24 million km 2 (+7.1%), while bare soils decreased by 1.16 million km 2 (-31%) between 1982 and 2016. However, in developed countries, rewilding can have several negative effects, among which are: i) loss of cultural landscape and the knowledge required to manage its preservation (Strijker, 2005;Arnáez et al., 2011;Lasanta et al., 2017a;García-Ruiz and Lasanta, 2018); ii) a reduction in bio-and eco-diversity in the medium-and long-term (Suárez-Seoane et al., 2002;Laiolo et al., 2004;Nikodemus et al., 2005;Cohen et al., 2011); iii) homogenization of the landscape (Meeus et al., 1990;Vicente-Serrano et al., 2000;Wood and Handley, 2001;Jongman, 2002;Van Eetvelde and Antrop, 2003;Varga et al., 2018); iv) loss of agricultural land and pasture resources, essential for sustainable development of mountain communities (García-Ruiz and Lasanta-Martínez, 1993;Laguna and Lasanta, 2003;García-Martínez et al., 2008); v) water flow reduction in the rivers and decrease of water in river basins, due to interference and consumption by vegetation, which is especially important in Mediterranean areas where water is in short supply ; vi) fewer environmental and leisure services (Benjamin et al., 2007;Rescia et al., 2008;Sayadi et al., 2009;Bernués et al., 2014); and vii) an increase in natural risks, such as increased pests and diseases, but more particularly, forest fires (Westerling et al., 2006;Chauchard et al., 2007;Pausas et al., 2008;Varga et al., 2018).
The marginalization of farm production and revegetation therefore cause environmental, economic and social impacts that not only affect the mountains, but also the rest of society. It must not be forgotten that mountains, even today, provide resources and essential services: water, high levels of biodiversity, wood and meat, attractive countryside for recreation and leisure, carbon sequestration, prevention of natural hazards, etc. (Schmitz et al., 2003;Viviroli et al., 2007;Petanidou et al., 2008). Price (2004) states that, in this respect, the mountains supply goods and services to over half the world's population.

Two different trends: rewilding or intervention in the territory
Given that revegetation has positive and negative effects on the environment, two alternatives have been suggested for abandoned land: allow the process to continue and with it the rewilding of the landscape, or intervene in the territory in order to control the negative effects of revegetation. The issue has gained a certain importance and is under discussion between scientists and land managers (Conti and Fagarazzi, 2005;Gellrich et al., 2007;Navarro and Pereira, 2012;Lasanta et al., 2015;Nogués-Bravo et al., 2016, Fernández et al., 2017. The rewilding alternative first appeared in 1998 (Soulé and Noss, 1998) and is the passive management of ecological succession in order to restore the natural ecosystem and reduce human control over landscapes . Rewilding is based on an irrefutable fact: the widespread land abandonment in Europe throughout the 20 th century (MacDonald et al., 2000;Keenleyside and Tucker, 2010;Lasanta et al., 2017b), which could be an opportunity to renaturalise and recover wildlife on a large scale (Navarro and Pereira, 2012).
In defence of renaturalising ecosystems, its supporters claim that rewilding creates a more natural landscape and greater biodiversity, by promoting the reintroduction or return of wildlife (Ceausu et al., 2015). In this context, more wild ungulates are proposed to fulfil the traditional role of extensive livestock grazing in maintaining a diverse and stable landscape (San Miguel-Ayanz et al., 2010). Navarro and Pereira (2012) point out that the Mediterranean landscape is more sustainable if the land is more renaturalised, since the erosion risk is reduced. They emphasise that forest regeneration could provide certain ecosystem services, such as carbon sequestration, and serve as a recreational element for numerous city dwellers. Lastly, they suggest that those wishing to maintain traditional uses, especially agriculture, underestimate the huge amount of human work needed to sustain them. Merckx (2015) states that intensive farming killed the moths and butterflies in Europe, while farmland abandoned has helped to halt their decline and contributed to improve biodiversity. In addition, he found that forests had a higher diversity of species than areas with shrublands or pastures.
The rewilding concept has been gradually extended, with a wide range of differing views on how to understand it, from allowing ecosystems to evolve with no human control (Schnitzler, 2014), to supporting the need for sustained intervention to minimise conflicts between humans and wildlife (Hobbs et al., 2015;Boitani and Linnell, 2015). The only thing these varying perspectives have in common is the wish to improve the naturalness of the landscape and wildlife, but with very different ideas on how the ecological processes and communities of species should be restored (Hobbs et al., 2015;Boitani and Linnell, 2015). For Deary and Warren (2017), the many-sided nature of the concept is one of the reasons why rewilding is attractive and widely accepted; because it is imprecise, the concept can be appropriated and moulded to each person's vision and particular values, while users benefit from the fact that it is widely accepted. Jørgensen (2015) points out that it has become a "plastic word" which embraces so many issues that it lacks a specific content, a claim that is refuted by Prior and Ward (2016) and by Cloyd (2016). The truth is that rewilding is being promoted internationally by NGOs, environmental activists and owners of large farm holdings. The Rewilding Europe project aims to restore 1 million hectares of abandoned fields as a natural space. It has 5 areas of application, where the Rewilding Europe Foundation has joined up with NGOs to implement revegetation and increase biodiversity (Helmer et al., 2015). In addition, over the last few years, scientific publications have proliferated, and the concept habitually appears in journalism and professional activities relating to nature Corlett, 2016;Svenning et al., 2016). Nogués-Bravo et al. (2016: 87) put it, that 'the drumbeat for rewilding is getting faster and louder', although they caution that it might be 'the new Pandora's box in conservation'.
On the other hand, some authors state that the advantages of rewilding are more apparent than real (Conti and Fagarazzi, 2005). They emphasise that the landscape in Europe, especially the Mediterranean, is one that has been humanised (Grobe and Rackham, 2001;Agnoletti, 2014). Gill (2006) says that the concept of "forest" in Europe refers to places with trees and herbivores, which is more like a park or savannah than a closed space of trees. Similarly, it is argued that the most common landscape in Mediterranean regions is cultural, due to agriculture on the slopes and extensive livestock grazing (Farina, 2007;San Miguel-Ayanz et al., 2010;García-Ruiz and Lasanta, 2018).
Several scientists and managers advocated intervening on the land, in order to reduce the negative effects of farmland abandonment and massive revegetation. This is in a bid to break off with an over-naturalised landscape and, in some way, maintain the traits of a cultural landscape, because of its high ecological (Moreira et al., 2006), productive (Quetier et al., 2005;Kizos and Koulouri, 2006) and aesthetic (Vanslembrouck et al., 2005;Sayadi et al., 2009) value. In addition, some authors agree that, to be sustainable, landscapes must be multifunctional: they need to produce food, contribute to social structuring and maintain environmental values. Only in this way, they help in the sustainable development of the population and ensure the resources and values of the territory (Kinzing et al., 2006;Kizos and Koulouri, 2006;Pelorosso et al., 2011).
The wide area occupied by abandoned land is an opportunity to manage it by introducing new uses (Cogliastro et al., 2003;Benjamin et al., 2008). Land managers have mainly supported two strategies: reforestation and extensive livestock grazing.
Reforestation, especially with conifers, is a very common strategy in Mediterranean areas. In Spain, approximately 5 million hectares were reforested between 1940 and 2006 (S.C.F.C., 2011). Forests are replanted for economic and environmental reasons: to generate jobs, avoid depopulation, produce wood and paper pulp, reduce soil erosion and control flooding (Ortigosa Izquierdo, 1990;Pausas et al., 2004). However, the economic objectives are not very successful, as hardly any jobs are created except at planting time, it does not retain the rural population, and production of wood and paper pulp is small and only in the long-term (García-Ruiz, 1976;Chauvelier, 1990). Ortigosa et al. (1990) point out that reforesting had a highly negative impact in the local development of the central Spanish Pyrenees: it reduced the pasture area and livestock census, which accelerated emigration of the local population. Moreover, the environmental results are very heterogeneous, depending on the location of the perimeter and technique used in reforesting. Thus, soil erosion and growth of pine trees is lower in plantations on terraces built with bulldozers than when made by digging holes or furrows manually (Ortigosa Izquierdo, 1991). Furthermore, Nadal-Romero et al. (2016) found that, in abandoned fields in the Pyrenees, forest plantations did not speed up recovery of soil properties (fertility and quality) in comparison with secondary succession (natural revegetation). In addition, it must be remembered that large plantations of pines create a highly uniform, fire-prone landscape (Pausas et al., 2008;Martínez-Fernández et al., 2013).
Over the last few decades, land managers have tried to control the expansion of shrublands, and conserve cultural landscapes by supporting extensive livestock grazing, especially with economical aids to maintain it. This has been the case in the European Union since 1992 through its Common Agricultural Policy (Mottet et al., 2006;García-Martínez et al., 2008). It must be remembered that extensive grazing provides certain advantages that are supported by public policies, as it combines production (meat, milk, wool, etc.), social (maintenance of cultural landscapes, fixing the rural population) and environmental (increasing landscape diversity, reduction in wildfires) purposes (Mouillot et al., 2003;Calvo-Iglesias et al., 2006;Rescia et al., 2008). Gibón (2005) states that, with extensive grazing, a landscape consisting basically of shrubland can be transformed into another, characteristic of European mountains, with a mosaic of land uses, such as forests, pasture, shrub and some fields as meadows. A landscape containing huge production (pasture, wood, firewood, by-products, etc.), ecological (pollination, biochemical cycles, etc.), cultural (aesthetic, educational, recreational, etc.), for regulation (land conservation, hydrological control, water quality, flood control, etc.) value, and which also supports very varied habitats, the basis for maintaining biodiversity.
However, in the control of revegetation, various studies (Bartolomé et al., 2000;Casasús et al., 2007;Komac et al., 2013;Álvarez-Martínez et al., 2016) highlight the fact that, with the small number of livestock currently in mountain areas, livestock grazing will only slow down the encroachment of shrub, but not deter it from expanding. Similarly, Muñoz-Barcia et al. (2019) deem it crucial to establish the grazing pressure needed to keep the habitats in optimum condition so as to ensure their preservation.

Combining extensive livestock grazing with prescribed fires and shrubland clearing
The limited role of extensive grazing, on its own, to control the expansion of shrubland has resulted in combining grazing with other actions on the territory, especially prescribed fires and shrubland clearing.
Prescribed fires, or controlled fires, are a tool to reduce the accumulation of fuel and the risk of fire. In addition, they promote the regeneration of pastures for livestock grazing, and conserve biodiversity and cultural landscapes (Fernandes et al., 2013;San Emeterio et al., 2016). Canals (2019) justifies the environmental interest in the combination of prescribed fires-guided grazing (pyro herbivory) as a tool for handling mountain ecosystems, for which it is essential to combine traditional knowledge of shepherds with the technical and scientific knowledge. Alcasena et al. (2019) try to identify areas in the landscape on which to intervene to reduce wildfires spreading to particularly sensitive areas, due to their environmental value. They start from the idea that, to lessen fire risk, fire-resistant landscapes must be created by managing fuels, with extensive grazing and prescribed burning suitable strategies for eliminating fuel and making open spaces acting as fire breaks.
Prescribed fires began experimentally in Mediterranean areas of Europe in the 1960s, although it was not definitely implemented until the 1980s (Fernandes et al., 2013). At present, it is used on 10,000 ha yr -1 , which is approximately only 3% of the burned surface in Portugal, Spain and France (Ascoli and Bovio, 2013). In Spain, prescribed burning for grazing started in 1998, when the Environment Ministry introduced forest fire prevention teams (EPRIF), to reduce farmers' uncontrolled use of fire to remove shrub and regenerate pastures (Lasanta et al., 2014).
However, prescribed fires proved to be insufficient in controlling the spread of shrubland. Komac et al. (2011), in a study carried out in sub-alpine pastures in the central Spanish Pyrenees, highlight the fact that Echinospartum horridum grows back two or three years following fires, and is fully revitalised and widespread after four or five years. Badía et al. (2017) concluded that burning E. horridum rejuvenates the community which, far from being eliminated, undergoes self-succession in time. Nuche et al. (2018) also found that burning E. horridum increases its germination and helps to sow seeds that were not previously present in the rich sub-alpine pastures of the Pyrenees. Ruiz Mirazo et al. (2011) state that the current low numbers of livestock in many mountain areas result in the failure of the fire-grazing balance. Gómez-García et al. (2011) analysed the effect of controlled fire and clearance combined with livestock grazing in the north-western Spanish Pyrenees. Their results show that the ideal situation is grazing and shrub clearings on gentle slopes with abundant vegetation cover, while fire-grazing is a more effective combination in areas with medium or steep slopes and sparse vegetation. In a more recent article, Gómez et al. (2019) recommend frequent clearance (every 1-2 years) and heavy grazing after clearing, in order to prevent the spread of unsuitable grasses for pasture, which are precursors of shrub recolonization. In turn, Alados et al. (2019) studied the effects of prescribed burning and shrub clearance in sub-alpine pastures in the central Pyrenees on the recovery of E. horridum and on Bromion erecti pasture, finding that clearing was better at controlling colonisation of E. horridum than burning, as well as degrading the soil loss. They concluded by saying that clearing is a better strategy than burning to restore sub-alpine pasture land after invasion by shrubs.
Prescribed fires also affect the land to a certain extent. San Emeterio et al. (2016) point out the reduction in microbial biomass in the soil for at least the first two years following fire. Fonseca et al. (2017) observed chemical changes in the soil. Thirty-six months after fire, values of organic material, pH and electrical conductivity had recovered, while those of potassium, assimilable phosphorus and exchangeable bases differed from those observed before fire. Moreover, notable increases in runoff coefficients and soil loss were found. In addition, prescribed fires comes up against certain factors that restrict its consolidation and expansion in the Mediterranean countries of Europe, such as concerns on fire risk, the scarcity of experts and organisations with experience, the public's view of fire as a nuisance, and regulations prohibiting or limiting the use of fire (Fernandes et al., 2013;Mierauskas and Pereira, 2013).
Another action on the territory is to combine shrubland clearing and extensive grazing. In selected areas, especially abandoned fields, shrub has been removed by mechanical techniques to encourage grass to grow. The purpose is to promote livestock farming, control wildfires, maintain the cultural landscape and high rates of biodiversity. Although shrubland clearing occurs occasionally in various parts of Spain (Lasanta et al., , 2014, La Rioja is where the strategy has been widely implemented. 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 clearing took place on former crop fields that had been abandoned after 1960 and were now in a process of plant succession . After more than 30 years of taking action on the territory by shrub clearing, it can be seen that the results are very positive in controlling fires, increasing the numbers of livestock, and the structure of the landscape. Lasanta et al. (2018) found that the number of fires and burned area has been greatly reduced in comparison with Spain. In La Rioja, fires account for about 20% of incidents, while in Spain this rises to 30%. Similarly, in La Rioja from 2008-2017, only 7.5% of the area burned in the decade of 1978-1987 was burned, while in Spain it was 42.2%. Shrubland clearing has several positive effects in decreasing the burned area: i) it removes combustible material, which reduces the risk of fire; ii) it creates a mosaic and fragmented landscape with small patches where pasture land is interspersed with shrub and thickets of trees, which helps to control and extinguish any fires; iii) livestock farmers no longer need to burn to regenerate grazing land. It is well-known that the livestock sector is closely linked to forest fires, as a large part of these start with the use of fire as a tool in regenerating pastures. Also, Lasanta et al. (2019) found that, in the Leza Valley (north-western Iberian System), shrubland clearing led to an increase in livestock numbers, rising from 1,833.9 LU in 1972 to 7,207.8 LU in 2017, with the size of farms also expanding (27.6 LU in 1972to 115.2 LU in 2017. In addition, new livestock farms are being started by people from outside the study area (41.7% in 2017), which is a clear factor in socio-economic and environmental sustainability. Lastly, Lasanta et al. (2016) studied the effects of clearing on the heterogeneity of the landscape and found that, in the study area, the number of patches doubled (from 26 to 52), while the average size of each patch was smaller (from 61.6 ha to 30.8 ha). This action has created a more fragmented landscape, a mosaic of land uses comprising trees, shrub and pasture, highly valued by the public and with great potential for developing tourism (Sayadi et al., 2009). Furthermore, rates of heterogeneity show an increase in diversity and a reduction in dominance following shrubland clearing , confirming that clearing creates a more complex landscape with greater ecological value (Bignal and McCracken, 2000).
This volume discusses the combined use of extensive livestock grazing with prescribed fires or shrubland clearing, strategies used over the last few decades to prevent the spread of shrubland, control fire risk and preserve pasture ecosystems, cultural landscapes and their biodiversity. The volume consists of several articles highlighting the importance of extensive grazing for cultural landscapes if a balance is to be reached between the use of resources and preserving ecological and cultural values.