By Julia Martínez and Miguel Ángel Esteve
Desertification is a process of degradation of soil, water, vegetation and other resources that in Spain is due, above all, to water erosion, which in turn is largely due to the centuries-old destruction of vegetation. The only definitive remedy is the reconstruction of the protective vegetation cover.
Erosion and desertification are two magic words because they connect with deep collective feelings, such as abandonment, desolation and death, and are an example of environmental problems about which there seems to be no great disagreement, neither between citizens nor between different public institutions. , researchers and environmental voices. This apparent consensus is favored by a series of topics, that is, ideas easily accepted from the beginning for their explanatory power, practically unquestioned and with a large dose of inertia in the face of their possible replacement.
The following reflection is based on the analysis of the most generalized discourse around desertification, whose approach could be the following: “Desertification is a process of degradation of soil, water, vegetation and other resources that in Spain is due, above all , to water erosion, which in turn is largely due to the age-old destruction of vegetation. The only definitive remedy is the reconstruction of the protective vegetation cover ”. This connection of ideas offers an avenue for their orderly discussion.
Desertification, soil degradation and erosion
In 1991, UNEP defined desertification as "The degradation of land in arid, semi-arid and sub-humid areas due to negative human impact". This concept is very vague and broad, since in principle it must consider any type of land degradation including processes as varied as salinization, landscape quality, the trivialization of ecosystems, the impacts generated by extractive activities, soil contamination , etc. However, at least in Spain, in practice it is usually only associated with a few specific processes such as salinization and especially soil erosion, without necessarily implying that such processes are the main or most relevant degradation processes existing in a given territory.
The use of the term desertification as an expression of the different degradation processes also has various counterproductive effects. First of all, it is a definition that does not add anything new or is useful, since it can refer to processes that are too different. It is at least confusing to refer with the same term to the diversity of degradation processes and problems existing in each place. The usefulness of the concept of desertification has also been questioned in other territorial contexts (1, 2, 3, 4), due to its broad and vague definition.
Second, by assimilating desertification with degradation, the negative connotations that are unjustifiably received by another close term: desert, negative connotations deeply rooted in public opinion and in much of the technical field are strengthened. Thus, desert areas and arid areas, which are defined in strictly climatic terms, are considered as degraded areas, which is why they are receptors of all types of infrastructures, industrial estates, spills and accumulations of waste without generating a special concern. . These areas are therefore suffering an alarming loss of landscape and environmental quality, especially in the salt marshes and steppe areas.
Soil erosion in Spain
Erosion is generally defined as the removal, transport and sedimentation of materials, although in non-scientific settings erosion tends to be associated only with removal of materials and not with sedimentation processes. In Spain desertification has been associated mainly with erosion, especially with erosion in the natural environment. This identification, still active in many areas, cannot continue to be sustained either from a scientific point of view or from the point of view of the socio-economic implications that are usually associated with desertification processes. A growing number of research works show that most of the erosion rates that had been estimated in natural and semi-natural environments in Spain, and still in use, are considerably overestimated for various methodological reasons:
1 First, in Spain the USLE equation has been used in a generalized way, with some modifications, to estimate erosion rates on a large spatial scale. This is inappropriate because said equation was designed for small agricultural plots (with a length of tens of meters) and outside this context (small scale, agricultural use), it gives rise to significant overestimates (5, 2). In a review on erosion rates in Murcia, which is usually considered a territory especially vulnerable to erosion and desertification, and after analyzing 316 research works (6), it has been shown that the USLE and similar methods give rise to rates erosion between 10 and 60 times greater than those obtained with measurements.
This has played an essential role in the technical justification of the past Spanish forest policy, which considered that scrubland, especially in areas such as the Iberian Southeast, suffered high rates of erosion that had to be tackled through hydrological corrections and reforestation. The erosion rates estimated with the USLE and similar methods still constitute the basis of the thematic mapping and of the technical instruments applied in Spain by the administrations (such as the Valencian Community Forest Plan and the National Action Plan to Combat Desertification) .
2 The USLE underestimates the role of scrub and vegetation with little coverage, typical of arid zones, in controlling erosion processes. Measurements in experimental plots in Murcia on open bushes and arid zone vegetation show erosion rates between 0.1 and 1 tons per hectare and year, with a maximum of 3 tons per hectare and year found on marl (6, 7, 8 ).
3 Due to complex control factors and material sedimentation and redistribution processes, erosion rates are closely dependent on the spatial scale (9, 10, 11), in such a way that they decrease dramatically when going beyond a scale of square meters to square kilometers or entire watersheds.
4 The high rates of erosion in non-agricultural environments in Spain are restricted to very limited areas, such as badlands, generated by active geomorphological processes (12) and which constitute special landscapes with high scientific and ecological value and which maintain habitats of great interest , all of which has begun to be recognized with the declaration of some of them as a protected space. This is the case of the Tabernas Desert Natural Park (Almería), proposed as a National Park, and the Barrancos de Gebas Protected Landscape (Murcia).
In Spain, the main soil erosion problems are located in marginal agricultural areas on loose materials and high slopes, areas where CAP subsidies have promoted the expansion of olive and almond trees. The other source of erosion problems in agrarian systems derives from the proliferation of greenhouses in the coastal mountain ranges and areas of high slope in Murcia and Almería. The construction of these greenhouses, which sometimes occupy very large areas on the slopes of the coastal mountain ranges, requires large earthworks, sometimes similar to those required by quarries. Despite this, these processes are not considered in the national plans to combat erosion, such as the National Action Plan to Combat Desertification and the National Plan of Priority Actions for Hydrological-Forest Restoration and Erosion Control.
However, and at least in Spain, the process that is really causing the greatest irreparable loss of fertile soil, as a non-renewable natural resource, is not erosion but rather the urbanization and occupation of river valleys with traditional irrigation and other high-value soils. agricultural with buildings, roads and other infrastructures. Already in 1992, the most affected European country was Spain, which was both the country with the lowest proportion of soils of high agricultural value and the country in which the annual loss due to urbanization of this type of high-quality soils was greater (13 ). We are currently witnessing a serious acceleration of this worrying process, in the heat of widespread urban speculation. The apparent concern about erosion in areas of poor agricultural quality, such as marl areas, is a paradox when the truly fertile soils of agricultural valleys are irreversibly disappearing under urbanization and occupation by different infrastructures, without causing a special concern.
Myths about vegetation and human action in arid areas
Associating arid areas with age-old destruction of vegetation cover is based on simplistic and often wrong ideas. In arid areas such as the Iberian Southeast, the dynamic climate-vegetation balance prevents the existence of an arboreal layer. In fact, a good part of the plant communities in these areas, although small in size, present a much higher degree of conservation and maturity than that found in other areas with higher rainfall and tree strata. And the fact is that the acute scarcity of water resources has kept these areas, until recently, very far from production processes and intense human intervention and exploitation.
Such simplistic ideas reinforce the erroneous belief - and profoundly negative for the conservation of the biodiversity of arid zones - that the secular action of man has deforested the land devoid of forest and that in this territory erosion acts without control. This simplistic and false image has contributed to a low valuation in technical circles of the vegetation of arid zones (14), which has been creating difficulties for an effective conservation of these ecosystems. These topics have justified a disastrous forest policy, which has constituted a clear factor in the degradation of the biodiversity of arid zones, by supposing the elimination or a serious impact on communities of great ecological and naturalistic value, whose exceptional importance has been shown with the inventory of habitats of community interest and priority for the European Union and with the SCI proposals for the Natura-2000 network (15, 16). Despite this, hydrological-forestry actions are still included in the National Forest Strategy as an important instrument to combat desertification.
Desertification in Spain: an unsustainable water management problem
The uncontrolled growth of irrigation in the Iberian Southeast, which has recently been joined by urban proliferation, is generating an unprecedented intensive exploitation of aquifers. Irrigation in the Segura basin was already consuming 225% of renewable resources in 1995 (17), which represents the greatest pressure on the natural systems of all the European Mediterranean countries (18). This consumption well above the available resources is sustained by a generalized overexploitation of aquifers.
The overexploitation of the entire basin between 1983 and 1995 has grown at an exponential rate, with a growth rate of 15.3% per year, which implies that the volume of overexploitation of the aquifers doubled every 4.5 years. The environmental and social consequences of this overexploitation include the decrease in piezometric levels, the progressive salinization of many aquifers, the disappearance of numerous sources and springs, the degradation of various wetlands, including upwelling within the river itself, the depletion of water from reserve and landscape degradation and loss of scenic value of springs and wetlands. In coastal areas of the basin such as Mazarrón and Águilas, the overexploitation of aquifers has caused the loss of 85% of the existing spring flows in 1916.
This process of depletion of aquifers, destruction of wetlands and unsustainable water management is the process that in Spain best fits the desertification syndrome, as an irreversible loss of the natural productivity of the systems, and which the plans should address national fight against desertification.
* Julia Martínez and Miguel Ángel Esteve, teachers at the University of Murcia and members of Ecologists in Action Murcia Region
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