El abandono de campos de cultivo en la Región de Murciacausas y consecuencias medioambientales y socioeconómicas

Laburpena

The abandonment of crop fields is a territorial phenomenon that has recently taken on great importance in the agricultural system, where intensive farming and industrial market dynamics now predominate. However, not all agricultural holdings have been able to withstand these changes. The main objective of this dissertation is to demonstrate this situation in the Region of Murcia, identifying it, evaluating it and proceeding to attempt to determine its causes and effects. The identification of abandoned land has resulted in a cartography design, according to which 4% of what is farm land today has been abandoned (24,522 ha). The most affected areas are the Fortuna-Abanilla Basin and the Jumilla-Yecla Plateau. The most commonly abandoned crops are grapevines, arable land and carob trees. Abandoned land can be found with practically any altitude, slope or orientation; it is spread out over the most common lithologies and soils, and primarily in areas with the greatest risk of erosion. One fifth is within a Red Natura 2000 protected area. This pioneering cartographic design constitutes a methodological proposal to identify abandoned land in the current agricultural system through the photo interpretation of orthoimagery, digitalization and processing in a GIS. The threshold according to the traditional agricultural system was established in 1981, based on photogrammetric and historical criteria. The result was the creation of a valuable georeferenced database that could constitute the basis for any subsequent study. The causes for abandoning the land are situated in a specific agricultural context, the components of which can be perceived as indicators of the phenomenon, according to the agricultural holdings that have adapted better or worse to the changing circumstances. Through a study of a strongly econometric nature, it has been demonstrated that these reasons are primarily due to a scarce rural population, highly mechanized agriculture that requires well-trained workers, the intensification of irrigation and production, business concentration, crop diversification, over exploited soils, etc. This regional context determines the local causes, which are of an environmental and/or socioeconomic nature. Among the first causes, quantified through a mathematical model (random forest and logistic regression) that has generated an abandonment risk map, we can highlight weather conditions, slope, distance to natural areas, rainfed systems and land less devoted to agricultural use. The most commonly mentioned socioeconomic causes, in turn, quantified by means of social survey, are: the idea of an excessive increase in production costs, speculation in terms of land sales or lease, small plot sizes, out-of-date production methods, retirement without professional succession and rural depopulation. The effects of abandonment, which are interrelated, have been studied from an environmental perspective; on the one hand, through soil condition analysis, geomorphic evaluations, rainfall simulations and ecological sampling; and on the other hand, from a socioeconomic point of view, through a study of the landscape configuration of the territorial abandonment units, the quantification of future expectations according to social surveys and the latest preliminary soil occupancy data and the political analysis of abandonment management, based on the Common Agricultural Policy (CAP). It has been established that the environmental effects depend primarily on lithology. In general, soil quality improves when it is abandoned, more so in plots over metamorphic rocks than in marls and alluvial/colluvial deposits, where precisely the greatest evidence of erosion has been registered, including extreme forms such as piping, which generates very large soil losses. Water erosion, which depends locally on the slope and ground coverage (both plant and rocky), is more intense in marls, due to the weaker infiltration capacity and greater runoff, which transports a greater sediment load. The greatest overall floral richness has been registered in metamorphic plots of Mesomediterranean ground, which are key to the colonization of the surrounding natural areas and the internal elements of the plots. The most effective endozoochoric species are Pistacia lentiscus and Rhamnus lycioides (in metamorphic and limestone plots, where inhibitory species predominate), and Asparagus horridus, in the case of marl plots (more facilitator species). The most common abandonment landscape is dominated by the agricultural environment, where ten types of landscape units can be distinguished. The owners are generally unwilling to resume cultivation, allowing things to continue as they are or selling/ leasing the land. In fact, in 2013, 90% of the abandoned surface registered in 2011 was maintained; the same trend was repeated in 2016, which goes to show the marked structural nature of the phenomenon. Agricultural management usually halts abandonment, since it seeks to provide incentives for active farming. Only the agri-environmental improvement in abandonments in protected spaces seems to have been successful in environmental terms, although it has had barely any territorial or social effects. In limestone and metamorphic lands, abandonment can be encouraged to create ecological corridors, expand forest areas or to build firebreaks and create a more heterogeneous landscape, while in more loamy plots, actions should be taken to promote soil conservation and fixing species. The conclusion is that abandonment is a phenomenon of immense significance, due to both its scope and the range of causes and effects associated with it. Plots whose use has not been modernized or has not been implemented in a sustainable manner have ended up being abandoned, and this triggers a large number of effects of all types, which may be either environmentally positive or negative, mostly depending on the lithology. Knowledge of this is essential for proper land management, and even more so if we consider the current context of climate change among its socioeconomic effects and the fact that it is a very stable phenomenon, which has also generated important changes in the landscape. However, there is a profound deficit in the public management of abandonment, which could be resolved based on the applied scientific knowledge provided by this dissertation.