Conclusion: Land degradation and complex socioecological systems

Ecosystems can be considered as complex systems where different elements (productive, institutional and contextual) act synergistically on environmental conditions and land degradation processes. Soil degradation, drought, poverty, cultural and technological backwardness are the main causes of degradation of both natural and social environments. Such issues usually affect marginal areas, and this happens both in economically-developed countries and in developing regions. In these areas, sustainable land management is recognized as the element on which to act to improve people's living conditions and safeguard the environment (Salvati and Zitti, 2008b; Salvati and Carlucci, 2011, 2014; Salvati et al., 2013a; Zitti et al., 2015; Biasi et al., 2017; Pili et al., 2017). Desertification is the most emblematic case of land degradation, the effects of which were first recognized at the beginning of the 20th century (Kosmas et al., 1999, 2003, 2013; Salvati et al., 2009; Kairis et al., 2013a, 2013b). In 1930, most of the Great Plains of the United States of America suffered a prolonged drought which, together with inappropriate agronomic practices, led to soil degradation, which has gone down in history with the term "dust bowls". Specifically, adverse weather and climate conditions appeared that affected the Central United States and Canada between 1931 and 1939 which, leading to soil deterioration, gave rise to sandstorms. This ecological disaster caused an exodus of more than half a million Americans who left their farms in Texas, Kansas and Oklahoma. Only the adoption of more appropriate cultivation methods and the sustainable management of water resources prevented catastrophic consequences in the event of similar droughts. Unfortunately, this has not remained an isolated episode because adverse climatic conditions and poor land management have led to cases of land degradation in almost all areas worldwide (Moonen et al., 2002; Montanarella, 2007; Salvati et al., 2012a; Colantoni et al., 2015a). Nowadays, global warming, together with the intensification of economic development and population growth, have led to soil degradation, that now affects nearly 40% of the Earth's surface, including some areas of southern Europe (National Committee for the Fight against Desertification, 1998). After experiencing droughts with a general increase in climatic aridity, the Mediterranean basin has in fact been considered one of the most important hotspots for the observation of soil degradation and desertification processes (Kosmas et al., 1999, 2003, 2013; Salvati and Zitti, 2005; Salvati et al., 2009, 2012b; Kairis et al., 2013a, 2013b; Karamesouti et al., 2015; Zambon et al., 2018). It has been widely demonstrated that, in this region, the increasing level of environmental vulnerability is associated with long-term ecological dynamics (e.g., climate aridity, soil deterioration, erosion, salinity and land-use changes) together with socioeconomic, cultural and institutional dynamics that contribute to anthropogenic pressure leading to major landscape transformations (Moonen et al., 2002; Montanarella, 2007; Salvati and Zitti, 2008a; Salvati et al., 2012a; Colantoni et al., 2015a; Di Feliciantonio and Salvati, 2015; Zambon et al., 2017, 2018). All these conditions can be exacerbated by unsustainable land management, especially in fragile areas (Moonen et al., 2002).