{xtypo_alert}Editor's note 30 Apr 2012: Text source D111, section 3.1.{/xtypo_alert}

Although LEDD issues are primarily environmental problems, they generate associated socio-economic consequences. The LEDD issues in cropland that are examined in this deliverable are presented in Table 1 below. The table distinguishes between the environmental and the socio-economic aspects of these issues which are manifested at all spatial levels (global, national, regional, local).

Table 1. LEDD issues in cropland

Source: LEDDRA Study Site Application Plan 2011

Cropland worldwide is facing various LEDD issues related to the demands for: (a) increasing food and biomass production for a growing world population; (b) adaptations to climate change; (c) expansion of urban areas; and (d) over-exploitation of land resources. These issues lead to various degradation processes such as soil erosion, soil compaction, soil salinisation, soil contamination, organic matter decline, and soil sealing (Albaladejo 1990).

Agricultural production per unit area has increased substantially over the last few decades due to irrigation, fertilization, mechanisation and modern varieties of crops with higher yields and stronger resistance to pests and diseases. Intensive agricultural production, however, affects land degradation by causing heavy metal contamination, soil organic matter decline, soil erosion and soil salinisation amongst other issues. Land degradation and desertification are reducing the available land area for agricultural production (Bullock and Houerou 1996).  At present, soil erosion has resulted in a loss of croplands at about 0.06 to 0.07 x106 km2 per year, and soil salinisation has already affected up to 8 percent (0.2x106 km2) of the 2.53x106 km2 of currently irrigated croplands (World Resource Institute 1992). In the last decades, intensification of agriculture coupled with mismanagement has led to soil erosion rates which are faster than the rate of soil formation. Once this threshold is crossed, the inherent fertility and water storage capacity of the land begins to fall, adversely affecting crop production. Furthermore, the expansion and mismanagement of cropland has resulted in the advance of deserts in Africa both north and south of the Sahara and throughout the Middle East, the Central Asian republics, and western and northern China (Brown 2005), further reducing the available cropland area.

Soil erosion

Soil erosion remains the world's biggest environmental problem, threatening both developed and developing countries (Figure 1 below). It is a widespread problem throughout Europe, Asia, Africa, and America.  Soil erosion on cropland ranges from about 13 tons per hectare per year (tonnes/ha/year) in the US to 40 tonnes/ha/year in China (Pimentel and Wen 2004). Worldwide, topsoil erosion averages 30 to 40 tonnes/ha/year, or 30 to 40 times faster than the replacement rate of topsoil (Pimentel 2006).  Between 1945 and 1990, an estimated 20 million km2 of agricultural land (almost 18 percent of the earth's vegetated land) has been degraded as a result of human activity. Of these, an estimated 12 million km2 (almost 11 percent of the earth's vegetated land) has been moderately or strongly degraded. Soil erosion has caused abandonment of 4.3 million km2 of arable land during the last four decades (World Watch Institute 1990; World Resources Institute 1990).

Soil erosion occurs naturally due to the interaction of the atmosphere and the water cycle with land surfaces. Although the future distribution and intensity of natural erosion processes may be affected by climate change, leading to land degradation, accelerated erosion due to unsuitable land uses and land management practices is the main LEDD issue in sloping areas. Factors mainly responsible for accelerated soil erosion are clearance of forests for expansion of agriculture, changes in plant cover due to intensive cultivation, over-grazing, controlled burning or wildfires, levelling of the land surface, ploughing of soil mainly in directions perpendicular to the contour lines, poor maintenance of terracing land and cultivation of steep slopes.

Figure 1. Global water erosion vulnerability. Source: (United States Department of Agriculture, Natural Resources Service 1999).

Land degradation and desertification due to soil erosion is a serious threat to soil quality and productivity.  The effects of soil erosion on productivity depend largely on the thickness and quality of the topsoil and on the nature of the subsoil (Acton and Padbury 1993). Productivity of deep soils with thick topsoil and excellent subsoil properties may be virtually unaffected by erosion. However, most hilly soils are shallow or have some undesirable properties in the subsoil such as cemented horizons, or bedrock that adversely affects yields. In either case, productivity decreases as the topsoil gets thinner and undesirable subsoil is mixed into the Ap-horizon by tillage, or as water-storage capacity and effective rooting depth decrease. Several authors (Frymire 1980; Hipple 1981; Kosmas et al. 1993) have found a significant positive correlation between topsoil depth and wheat production, noting that this relationship was largely influenced by slope position on the landscape.

Many studies have shown that soil erosion in sloping areas is attributed to vegetation cover and land use management changes (Patton and Schumm 1975; Bryan and Campbell 1986). Many authors have demonstrated that in a wide range of environments both runoff and sediment loss decrease exponentially as the percentage of vegetation cover increases (Elwell and Stocking 1976; Lee and Skogerboe 1985; Francis and Thornes 1990). Vegetation and land use are clearly important factors controlling the intensity and frequency of overland flow and surface wash erosion (Bryan and Campbell 1986; Mitchell 1990). Extensive Mediterranean areas cultivated with rain-fed crops such as cereals, vines and almonds mainly expand into hilly areas with relatively deep or shallow soils, and which are very sensitive to erosion. Kosmas et al (1997) has graded the different types of land use under Mediterranean conditions in order of decreasing effect on soil erosion as follows: vines, eucalyptus, winter wheat, shrubland and olives under semi-natural conditions (Figure 2 below).

Figure 2. Average annual soil erosion rates measured in various land uses along the Mediterranean Europe. Source: (Kosmas et al. 1997)

Rain-fed cereals, and particularly wheat and barley, which cover the largest parts of the Mediterranean uplands, present serious threats of soil erosion from late October to early January when soils are only partially covered by growing plants. Repeated cultivation of soils, associated with continuously burning plant residues, has favoured soil crusting and overland water flow.  Measurements conducted during the implementation of the MEDALUS projects in areas cultivated with cereals have shown that in areas with total precipitation of less than 280mm, sediment loss was not a threat. Sediment loss increased with increasing rainfall and may fluctuate generally between 15 and 90tkm-² per year, in the range of 280mm to 700mm rain per year (Kosmas et al. 1997). Inbar (1992) reported values of 20t km-² yr-¹ for the Catalunya (Spain) area with annual precipitation of 600-700mm which lack behind the values measured in wheat fields in wet years.

Vineyards under existing land management practices remain almost bare during the winter period, creating favourable conditions for overland water flow and sediment loss. Repeated cultivation of vineyards, associated with other management practices (application of herbicides and pesticides) resulted in decreased organic matter content and aggregate stability favouring soil crusting, overland flow and erosion. Soil compaction is also another form of soil degradation resulting from heavy machinery used in vine-cropping. Measurements on soil erosion conducted in vineyards along the Mediterranean have shown that sediment loss ranged from 67t km-² yr-¹ to 460t km-² yr-¹. These values greatly exceed those measured in fields cultivated with wheat (Kosmas et al. 1997). Therefore, vines in hilly areas in the Mediterranean region promote high erosion rates and desertification risk is high.   

Olives are another type of land use widely expanded in hilly areas of the Mediterranean region. Olives are particularly adapted to Mediterranean climatic conditions. Contrary to perennial crops lacking under storey vegetation, the lowest rates of runoff and sediment loss should be expected under olive groves grown under semi-natural conditions. Under this land use, annual vegetation and plant residues have a high soil surface cover (Figure 2), occasionally up to 90 percent, so preventing surface sealing and minimising the velocity of the runoff water. Sediment losses measured in Greece were lower than 5.3t km-² yr-¹. The presence of annual vegetation and plant residues on the soil surface are responsible for the drastic reduction of soil loss, even to nil values. Therefore, olives can greatly protect Mediterranean uplands from further degradation and desertification.

Soil erosion generated by surface water runoff is one form of soil loss affecting land degradation, another is soil erosion caused by tillage implements and this has greatly contributed to land degradation. Tillage erosion has contributed to a progressive down slope translocation of soil exposing light-coloured subsoil materials on the soil surface in the upper parts of a hillslope, dispersing rock fragments over larger areas, reducing soil water holding capacity, and plant productivity (Poesen and Lavee 1994; Govers et al. 1994; Poesen 1995; Lobb 1997; Thapa et al. 1999). The availability of heavy, powerful machinery in previous decades has favoured deep soil ploughing with high speeds in directions usually perpendicular to the contour lines. This has resulted in the displacement of large amounts of soil materials from the upper convex parts (summit, shoulder, backslope) of a hillslope to the concave parts (footslope, toeslope) and decreased significantly the production of various crops on the convex positions, especially on soils with subsurface limiting layers.  Lindstrom et al. (1992) have estimated an annual soil loss of approximately 30tha-¹, after simulating moldboard ploughing for a period of 8 years. Soil erosion data measured in areas cultivated with cereals in Greece has clearly shown that water erosion was responsible for the loss of a few millimetres (1-3) of soil per year or even less (Kosmas et al. 1997), while the estimated total annual loss of soil due to tillage in the same areas ranged from 4-16mm per year (Tsara et al. 2001).

Soil salinisation

According to the FAO (Land and Plant Nutrition Management Service), over six percent of the world's land is affected by salts. Salt-affected soils cover over 400 million hectares. Much of the world’s land is not cultivated, but a significant proportion of cultivated land is salt-affected (Table 2 below). Of the current 230 million ha of irrigated land, 45 million ha are salt-affected (19.5 percent) and of the 1,500 million ha under dryland agriculture, 32 million are salt-affected to varying degrees (2.1 percent). Salinity is a major problem in semi-arid and arid zones (Bot et al. 2000). Salinity is a problem in irrigated areas with poor drainage. It is estimated that at least 20 percent of all irrigated lands are salt-affected. Salinity costs global agriculture an estimated 12 billion dollars a year – a figure that is increasing.

Table 2. Regional distribution of salt-affected soils, in million hectares

Source: (FAO Land and Plant Nutrition Management Service 2007)

In the last four decades, favourable soil and climatic conditions and the availability of ground or surface water has resulted in intensive farming of the lowlands of the Mediterranean. Furthermore, the development of fast and cheap transportation has encouraged the expansion of domestic and international mass tourism especially in the Mediterranean region.  Tourism development has affected the physical environment, land-use patterns and the allocation of water resources. The high demands of water for human consumption have caused water allocation problems, over-exploitation of aquifers and increases in the price of water, forcing the use of water of low quality for irrigation. Soil salinisation and the related threat of sodification have mainly affected areas with semi-arid, arid and dry sub-humid climatic conditions. The accumulation of salts in the soils occurs naturally when there is a net upward movement of water to the soil surface due to high evapotranspiration rates, as well as when irrigation is poorly managed and/or depends on poor quality water.

The three main processes which have caused soil salinisation are: (1) Rising ground water table close to the soil surface; (2) excessive use of water for irrigation in dry climates with clayey soils, and (3) intrusion of saltwater into aquifers when water enrichment of aquifers is lower than water use. In areas with Mediterranean climatic conditions, where evaporation exceeds rainfall, there is a potential for the accumulation of soluble salts. According to expert assessments about 25 percent of Mediterranean irrigated lands face severe problems of salinity/alkalinity and each day many thousands of hectares would be affected by salts due to poor-quality irrigation water, improper irrigation practices and climate change (Bellino and Varallay 2004; EEA 2003).  

Generally, plant productivity is not affected by low salt concentration, but above a certain concentration, depending on the plant species, productivity is drastically reduced.  High concentrations of salts such as sodium chloride, magnesium and calcium sulphates, and bicarbonates affect plant growth both directly, for their toxicity, and indirectly, by increasing osmotic potential and lowering root water uptake. Under dry climatic conditions, continuous salt accumulation has led to land desertification, especially in low lands with poorly drained soils. Furthermore, land management practices, such as extensive use of heavy amounts of fertilizers or the use of heavy cultivation machinery, which reduce the quality of soil drainage, have contributed to increasing salt concentrations adversely affecting plant growth.

Soil contamination

Anthropogenic contamination of soils includes a wide range of contaminants, from atmospheric deposition, industrial activities and vehicle traffic to waste spreading, application of fertilizers and pesticides. Higher levels of some heavy metals have been shown to affect soil biota and therefore potentially soil system functioning. In general, soil contamination presents a problem that can affect water resources, food production, above-ground biodiversity, and human health.

Since World War II, there has been a rapid increase in the use of synthetic organic chemicals for the control of weeds, insects, and other pests, contributing significantly towards the increase in global food production. It has also been recognised that the use of chemicals for pest control is a cost as well as being an effective measure. Agricultural systems and agronomic practices in Europe have been the subject of major changes, particularly in the last 30-40 years, leading to even greater dependence on chemical inputs. Land degradation problems such as soil erosion (Kosmas et al. 1997), soil organic matter decline and surface water eutrophication are posing serious threats to the sustainability of modern agricultural systems (Francis and Thornes 1990). Tillage operations present a serious threat to soil erosion in sloping areas (Tsara et al. 2001). The use of herbicides facilitates the practice of minimum-tillage or no-till, which, together with crop rotations, probably contributes to environmental protection through reduction of soil erosion and runoff losses of nutrients and other contaminants (Kookana et al. 2006).

Organic matter decline

In terrestrial ecosystems the amount of carbon in soil is usually greater than the amount in living vegetation (Post and Kwon 2000). Various land-uses result in very rapid declines in soil organic matter (Davidson and Ackerman 1993; Post and Mann 1990). Much of this loss in soil organic carbon can be attributed to reduced inputs of organic matter, increased decomposability of crop residues, and tillage effects that decrease the amount of physical protection to decomposition.  Recent trends in land use and climate change have resulted in soil organic carbon loss at a rate equivalent to 10 percent of the total fossil fuel emissions for Europe as a whole. In general, soils with low organic carbon content can be found in warm, dry climates and soils with a higher organic carbon content can be found in colder, wetter climates. Almost half of European soils have low organic matter content, principally in southern Europe but also in areas of France, the United Kingdom and Germany.

Soil organic matter plays important role in maintaining key soil functions. It affects physical properties such as soil aggregate stability, water absorption, soil erodibility, as well as chemical properties related to plant nutrient availability and accumulation of contaminants (Reeves 1997). Decline of organic matter content constitutes a component in land degradation. The equilibrium of organic matter content in the soil is strongly influenced by climate, soil water regime as well as texture and land management practices such as tillage. The amount of organic matter content of soil reflects a dynamic equilibrium between input rates of plant residues and rate of organic matter decomposition by the soil biota. The strategic role of soil organic carbon in reducing atmospheric CO2 concentrations was recognised in Article 3.4 of the Kyoto Protocol of the United Nations Framework Convention on Climate Change.

Apart from climatic factors (mainly temperature), the main processes responsible for loss of soil carbon are soil erosion and mineralisation of organic matter. Leaching of dissolved organic and inorganic carbon is another important mechanism of loss of carbon from the soil in cropland. Exact evaluation of this C pool is difficult because of heterogeneity in time and space. The global loss by erosion could be in the range of 150 to 1500 million tonnes per year, which is rather less than it was estimated at the continental level (Lal 1995). Methods used in the past for erosion control, such as land terracing, contour farming and increases in plant cover have also contributed to carbon sequestration.

Tillage operations have been conducted to increase aeration of the soil promoting mineralization of organic matter by soil micro-organisms. Tillage practices have caused a general decrease in organic matter in intensively cultivated soils, especially in Europe, and the important CO2 emissions linked to agriculture in the past.  Carbon sequestration in cropland and a reduction in losses to the atmosphere are ways to meet emission reduction targets. Average global carbon sequestration rates, when changing land use from agriculture to forest or grassland, are estimated to be 33.8 and 33.2 gCm-² per year, respectively (Post and Kwon 2000).

The main land management practices proposed in the past to increase soil organic matter were conservation agriculture, involving minimum or zero tillage, continuous protective cover of living or dead vegetal material on the soil surface, application of biosolids (manure, crop residues, compost), cover and deep-rooting crops, land use change to  grassland or woodland, fertilization and irrigation (Lal 2004). Furthermore, farmers used to burn plant residues instead to incorporate them into the soil, reducing drastically organic matter content and aggregate stability.  Residue-burning had negative consequences on carbon sequestration, aggregate stability, and soil erosion rates.

Soil sealing

Soil sealing is characterised as the cover of soil by inert material, such as cover by infrastructure, roads and urban and industrial development. The term is also used to describe a change in the physical properties of the soil leading to impermeability to air and water (e.g. compaction by agricultural machinery). This degradation process leads to interruption of the interface between soil, the biosphere and the atmosphere, affecting water and gas cycles, energy flows between the pedosphere and atmosphere, and the geochemical cycle of nutrients (Burghardt et al. 2004). The most significant impact of soil sealing is the increase of surface water runoff, often leading to catastrophic flooding (Burghardt et al. 2004). The consequence of soil sealing is the formation of an artificial environment largely devoid of biological activity and associated ecosystems. The extent and intensity of soil sealing in areas of Europe is significant, particularly in urban coastal zones such as those in the Mediterranean, where there has been significant in-migration into urban coastal areas over the last few decades for work and as a result of tourism development (LACOAST ATLAS 2000).  

Spatial planning strategies determine, to a great extent, the progression of soil sealing. Unfortunately, neither the economic, ecological or social impacts of soil loss due to soli sealing have been considered adequately to date. In the meantime, as the EU has recognised, there is a clear need to include environmental concerns and objectives in spatial planning, in order to reduce the effects of uncontrolled urban expansion. Rational land-use planning is therefore critical; to enable the sustainable management of soil resources, and to limit the impact of soil sealing (Blum 1998).

Soil compaction

Compaction is a major problem in areas with high livestock population density and/or areas where cultivation is done using heavy machinery. Compaction due to livestock pressure is a severe problem in the Sahelian region, the Horn of Africa, Central Asia, north-eastern Australia, Pakistan, and Afghanistan (Nachtergaele et al. 2010). Compaction due to the use of heavy machinery is severe in the United States, Europe, South America, India and China (Nkonya et al. 2010).

Soil compaction is a process of land degradation and desertification  in which the biological activity and the productivity of agro-ecosystems is reduced due to decreased air and water conductivity into the soil causing higher risk of soil erosion. Soil deforms in response to external forces arising from surface loadings and tillage. Higher forces may cause compaction when the pore structure is compressed and the functioning of the soil system to water and gas flow, as well as root extension, is impeded. Soil compaction has been enhanced in the last few decades due to the introduction of heavy machinery for cultivation with high speeds and ploughing the soil to depths greater than 30 cm (Figure 3). The pressure exerted on the soil is diffused across the whole volume causing reduction of soil porosity or increase in bulk density and disintegration of soil aggregates (Hillel 1980; Soane and Ouenwerkerk  1994). The pressure applied to the soil is positively related to the weight of the machinery, and negatively related to the area of contact of the soil with the tractor wheel, and the speed movement.  

Figure 3. Change in soil porosity in sub-surface horizons due to soil compaction from cultivation machinery. Source: (Author, C. Kosmas)

Soil compaction is a particular issue when machinery is used in wet conditions (Lawrance 1978). Changes in the physical properties of soils as a result of compaction affect plant growth, crop production, and movement of biota. Plant root length is restricted in compacted soils due to high resistance to penetration, therefore, nutrient and soil water absorption is reduced by the growing plants. Furthermore, increased soil compaction is associated with low rates of soil hydraulic conductivity, causing water ponding in flat areas of land or high surface water runoff in sloping lands.

Land desertification

The United Nations Convention to Combat Desertification (UNCCD) in 1994 defined desertification as “land degradation in arid, semi-arid and dry sub humid areas, resulting from various factors including climatic variations and human activities”. Although this definition does not clearly distinguish between desertification and land degradation, though it explicitly includes climatic conditions as a causative element, it is now widely regarded to be the authoritative definition of desertification.  Desertification occurs in drylands, which cover a third of the earth’s land surface - over 110 countries (GEF-IFAD 2002). The estimates vary between four percent and 74 percent of drylands being affected (Safriel   2007). The USDA-Natural Resources Conservation Service (USDA-NRCS) has developed maps of ‘Global Desertification Tension Zones’ which depict areas vulnerable to desertification (Eswaran et al. 2001).  Figure 4 highlights the growing problem of desertification worldwide.   Desertification reduces the land’s resilience to natural variations in climate. It disrupts the natural cycle of water and nutrients. It intensifies strong winds and wildfires.

The principal desertification processes are degradation of the vegetative cover, accelerated water and wind erosion, salinisation and water-logging (Nkonya, et al. 2010). These processes affect major land uses in arid regions including irrigated agriculture, and rain-fed cropping. Rain-fed cropland desertification is commonly expressed as increased water and wind erosion. Salinisation and water-logging are the principal degradation processes on irrigated land.

Figure 4.  Global land desertification vulnerability. Source: (USDA- Natural Resources Service 1998)

The effects of dust storms and the sedimentation of water bodies can be felt thousands of kilometres away from where the problems originated. Desertification is a threat to biodiversity. It can lead to prolonged episodes of famine in countries that are already impoverished and cannot sustain large agricultural losses. Poor rural people who depend on the land for survival are often forced to migrate or face starvation. Desertification affects the life of over 500,000 people; the so-called environmental refugees, who include many of the world’s poorest and most marginalised populations. Each year 12 million hectares of land are lost to deserts. This is the area of land to grow 20 million tonnes of grain. Land degradation, in turn, threatens the livelihoods of a billion of the earth’s inhabitants. Degradation caused by over-cultivation, overgrazing, deforestation and inefficient irrigation affects an estimated 20 percent of the world’s drylands, an area as large as China.

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Greece has undergone important transformations since the middle of the nineteenth century, when intensification of agriculture really began. Land mismanagement stimulated by demographic dynamics resulted in shifting of the agricultural population (and activities) to marginal areas unsuitable for agriculture. Human impact on the landscape was increasingly negative through conventional large-scale extensive agriculture, negatively affecting soil properties and enhancing erosion processes. The extension of cultivated areas at the expense of forest land has resulted in high ecological alterations due to deforestation and the break-up of the original equilibrium between cultivation, grazing and forestry (Yassoglou 1989).

Crop production in Greece changed significantly after accession to the European Union in 1981. After that, agricultural development focused on maximisation of fodder and cash crop production, which resulted in intensive arable cropping on all fertile, irrigable lands. Further mechanisation and expansion of the irrigated area to 1 million hectares were realized soon after the country became a full member of the European Union (Boyatzoglou 1983). National production targets for major crops (maize, cotton, sugar-beet, etc.) were achieved as early as 1985. Furthermore, the development of fast transportation means and the availability of cheap holidays have encouraged the expansion of domestic and international tourism over the last 50 years. The rapid expansion of tourism in coastal areas has resulted, in recent decades, in the intensification of agriculture on low lands, abandonment of agricultural terraced land on slopes, and an increase in the number and frequency of fires. Demands for water consumption have increased and have affected water availability and quality. Irrigation using water with high salt concentrations has increased the salinity of the soil, rendering land unproductive, abandoned and desertified, particularly in the plains located along the coast.

The concentration of tourism in narrow strips along the coast or around major cities has resulted in the loss of fertile agriculture soils, over-exploitation of natural resources, soil and water pollution and the loss of valuable coastal habitats.  Increasing tourism exerts a significant impact on the environment and results in changes in land-use patterns and resource availability. The most immediate changes in land-use are: (a) Shifts in crop production to meet tourist requirements; (b) a change from traditional to modern crops; and (c) abandonment of low quality land. The need for intensification of agriculture to meet the increasing costs of production, poor quality irrigation water (sea water intrusion) and the lack of proper drainage systems are in many cases responsible for soil degradation resulting from water-logging, salinisation, alkalinisation, and soil erosion.

One of the main effects of land degradation in Greece is the reduction in the area of productive cropland. As good quality soils become scarce, agriculture becomes concentrated in areas with rich soils. This process aggravates the problem of land degradation by increasing inputs in these richer areas, over-loading the land system and creating further problems of land degradation and loss of cropland. The main LEDD issues in cropland in Greece are therefore soil erosion, soil salinisation, and land desertification.  

Soil erosion

Soil erosion in Greece has proceeded at a rapid rate over the past 50 years, following the intensification and mechanisation of cultivation. One of the most spectacular examples of severe soil erosion is the complete removal of the thick dark surface soil horizon that occurred in the hilly Tertiary landscapes of central Greece at rates exceeding 1 cm yr-¹ (Danalatos 1993).  Erosion processes mainly responsible for land degradation in Greece are related to water, tillage, and wind erosion.

As can be seen in Figure 1 below, extensive areas of Greece are at high risk of erosion (Kosmas et al. 2006a). Water erosion is attributed to climatic conditions, vegetation cover and land use management practices. The large scale deforestation of hilly areas which has occurred in recent decades, accompanied by intensive cultivation and overgrazing has resulted in accelerated erosion and the formation of badlands with very shallow soils. Extensively eroded areas are confined to rock formations primarily of Mesozoic limestone and secondarily of acid igneous and metamorphic rocks (Kosmas et al. 2006a).

Figure 1. Areas of high potential erosion risk in Greece. Source: (Kosmas et al. 2006a)

Erosion rates measured on different types of land use, such as cereals, vines, olives, bare land and shrubby vegetation show wide variation depending on the type of vegetation.  Rain-fed cereals cover a large part of the country’s uplands. The most crucial period for soil erosion under rain-fed cereals is from early October to late February, when the soils are almost bare or partially covered by the growing crop. Erosion rates measured in hilly areas located in Thiva (central Greece) and Petralona (northern Greece) ranged from 0 to 52t km-²yr-¹ (Kosmas et al. 1996). Today, production of rain-fed cereals in the hilly areas has declined due to degradation of the soil and cultivation has become more concentrated in the lowlands.

Perennial crops such as almonds and vines occupy extensive hilly areas, although the area under vines has declined during the last decades. These areas require frequent removal of annual vegetation using pesticides (weed control) or ploughing the soil. Such soils remain almost bare during the whole year and the frequent use of heavy machinery negatively affects aggregate stability and organic matter content, creating favourable conditions for overland flow and soil erosion. Soil erosion rates measured in vineyards in the Attica area ranged from 15 to 252t km-²yr-¹ (Kosmas et al. 1996).

The lowest rates of runoff and sediment loss usually occur in olive groves under semi-natural conditions, i.e. maintaining understory vegetation of annual plants, which in combination with the dense leaf canopy of the trees efficiently protects the soil surface from raindrop impact. Under such conditions, water runoff and sediment loss is highly restricted. Soil erosion rates measured in the Attica area and Zakynthos island show that erosion may range from nil to 5.63t km-²yr-¹. Of course higher erosion rates are expected if the soil is cultivated and the annual vegetation is removed.

Tillage erosion is considered one of the most important processes of land degradation in hilly cultivated areas in Greece. It is estimated that 8 percent of the hilly agricultural land in Greece has been abandoned in the last decades due to diminished productivity caused by soil erosion (Kosmas 1999). Tillage erosion exposes subsoil, which may be highly erodible by wind or water, and fills in ephemeral flow areas, acting as a delivery mechanism for water erosion.  Studies conducted over long periods in areas cultivated with cereals, such as in Thessaly (Tsara 2001) have clearly demonstrated that tillage - rather than water erosion - is the most important factor controlling land degradation in hilly cultivated areas. Water erosion in areas cultivated with cereals, vines or olives is responsible for a loss of a few millimetres (1-3) of soil per year or even less (Kosmas et al. 1996). The estimated total annual soil loss in the same areas cultivated mainly with cereals reaches 4-14 mm per year (Kosmas et al. 2000). Soil studies in the Thessaly plain show that soil depth has been reduced by 24-30cm in a period of only 63 years.

Wind erosion is another erosive process, particularly in the semiarid areas of Greece. However, information on the extent of wind erosion in Greece is rather limited. Areas more vulnerable to wind erosion are the islands of the Aegean Sea (Figure 1) and the north-eastern part of the mainland. Strong north or north-easterly winds prevail during the dry period in Greece, creating favourable conditions for wind erosion. The main factors controlling wind erosion are vegetation cover, slope exposure, soil water deficit, grazing, and fires. Mainly steep slopes with shallow soils and semi-arid climatic conditions characterize the Aegean islands and Crete.  The vegetation cover may range from bare to fully covered depending on slope gradient, slope exposure, soil depth, parent material and grazing intensity. Land usually remains bare when soil depth is less than 20 cm. Under dry climatic conditions, perennial vegetation cannot grow, and only annual vegetation is present during the wet period. If the land is grazed, soils remain virtually bare during the summer period, favouring conditions for wind erosion. Fires destroy the existing vegetative cover and contribute to wind erosion by exposing the soil surface to wind action (Kosmas et al. 2006a).

One of the study sites investigating LEDD issues in cropland is located in Crete (the Messara Valley), the largest island of Greece located in the south part of the country.  Soil erosion in Crete is a major land degradation issue. Areas vulnerable to erosion are located in the upper hilly and mountainous areas.  Such areas are characterised by (Kosmas et al. 2006a):

• Steep slopes,
• Relatively shallow soils
• High soil erodibility especially in soils formed on shale parent materials
• Low infiltration rates in soils formed on marl and conglomerate deposits
• Moderate to poor  plant cover
• Removal of understory annual vegetation in olive groves
• Burning and overgrazing of natural vegetation
• Clearing of natural vegetation and planting olives without actions to prevent soil erosion
• Heavy rainstorms occurring frequently in the area

The effects of soil erosion caused by surface water runoff, tillage or wind are either on- or off-site.  On-site effects can be either long-term, such as the progressive degradation of soil or short- to medium term such as the effect on crop production. The main on-site effects in Greece are the removal of fertile topsoil, removal of organic matter, leaching of plant nutrients, exposure of large amounts of rock fragments or bedrock on the surface, reduction of crop production, desertification and land abandonment.  Off-site effects can be either short- or medium- to long term such as damage to crops and infrastructure from uncontrolled runoff and flooding, siltation of channels and reservoirs, environmental alterations of wetlands, lakes and estuaries, decline of the economy of local communities, and migration of local people (Kosmas et al. 2000; Tsara et al. 2001; Kosmas et al. 2006a).

Soil salinisation

Salinisation is an important process of land degradation and desertification in Greece, especially in irrigated lowlands with poor drainage conditions. The basic conditions that promote salt concentration in soils are: irrigation with low quality water, poor drainage, and dry climatic conditions favouring a negative water balance. Due to warmer and drier conditions in the last few decades, aridity and drought hazards for growing plants have increased (Sala et al. 1998). Therefore, irrigation has been extended over large areas for efficient agricultural production to meet increasing market demands. According to expert assessments, about 15 percent of the present irrigated lands face salinity/alkalinity problems. Problems of salinisation in Greece are expected to become more severe in the future if: (a) the area of irrigated land expands, (b) new more productive and water consuming plant varieties are introduced into cultivation, and (c) the climate becomes warmer and drier (Yassoglou 1989).

Typical management regimes for protecting areas from salinisation are surface drainage and irrigation of soils with good quality water. Surface drainage is mainly achieved by the construction of surface ditches. In the semi-arid regions of Greece under irrigation, drainage ditches are necessary for removing excess water, and required for leaching of undesirable salts from the soil and disposing of excess rainfall. Ground water recharge is another management practice to improve ground water quality and to avoid soil salinisation. For example, on the Argolis plain, which is facing severe problems of intrusion of brackish water and soil salinisation, recharge of the aquifers is achieved by supplying good quality spring water through wells during the winter period (Yassoglou 1989).

Soil salinisation risk in Crete is mainly confined in the lower plain areas along the coastal line, such as the Messara valley, Kissamos and Kolimbari plain areas and the Ierapetra plain.  The soils of these areas are mainly characterized as poorly to very poorly drained with ground water tables fluctuating between 30 to 150cm during the year. Other areas are sensitive to salinisation only if poor quality water is used for irrigation. Studies carried out in previous EU research projects, such as DESERTLINKS (contract No: EVK2-CT-2001-00109) and DESIRE (contract No: 037046) have shown that important indicators related to salinisation risk and which are affected by land management characteristics are; frequency of flooding, land use type, and efficacy of reclamation. As the frequency of flooding increases, salinisation risk also increases. Salinisation risk decreases as land use type changes from pasture, wetland, recreation area, and agriculture (DIS4ME, 2005). Reclamation of salt-affected areas was mainly related to the presence of a drainage network. As the efficacy of reclamation increased due to lowering of ground water, desertification risk decreased. Other important indicators related to salinisation risk are; distance from seashore, elevation, water quality, ground water depth, drainage and rainfall.

Land desertification

Desertification of land in Greece is a phenomenon that has been taking place for three millennia and is causing loss of land productivity and available water reserves. Such extreme degradation of these two important resources occurs in hilly areas cultivated with olive trees, vines and cereals.  Areas threatened by desertification cover approximately 34 percent of the total area of Greece (Figure 2); 49 percent is moderately affected; whilst 17 percent is at low risk. Areas particularly vulnerable to desertification are the eastern Peloponnese, Sterea Hellas and Thessaly; central and southern areas of Macedonia; central and eastern Crete; and the Cyclades islands in the Aegean. In spite of the adverse physical conditions observed in Greece, desertification proceeds only if land is not managed appropriately.

Figure 2. Potential desertification risk map of Greece. Source: (Greek National Committee for Combating Desertification 2001)

Processes of desertification in Greece are either physical or chemical. The dominant physical process is soil erosion, which is initiated by the destruction of the vegetative cover and affects marginal sloping lands. Soil salinisation and sodification is the dominant chemical process. It is localized but affects valuable low lands and is the result of poor irrigation practices. Unsustainable human actions can easily trigger desertification in the semi-arid and in the dry sub-humid zones of Greece, because several land parameters are unfavourable and/or sensitive to such actions (Yassoglou and Kosmas 2000):

• Climate and bioclimate is characterized by large moisture deficits, temporal variability and frequent extreme events.
• Landscapes are rugged, with steep slopes, large elevation differences and are highly dissected by torrential steams.
• Surface geology favours formation of soils which are sensitive to drought and erosion.
• Hydrology is characterised by the scarcity of surface and ground waters, and by the need to bring water from elsewhere to satisfy demand.
• Soil formation rates are much slower than soil loss, resulting in inadequate rootable depth and water storage capacity on sloping land.
• Out of phase rainfall and vegetative periods.
• Four millenniums of human land use and frequent abuses of land.

The natural resources of Crete have been overexploited for many years. Large scale deforestation of sloping lands accompanied by intensive cultivation and overgrazing have resulted in accelerated erosion and the formation of badlands with very shallow soils through the progressive inability of the vegetation and soils to regenerate themselves. Based on the land desertification risk map of Greece (Greek National Committee for Combating Desertification 2001), more than 50 percent of the island of Crete is characterized by high desertification risk.  The high erosion rates occurring in the island are attributed to the climatic conditions, to topographic characteristics and to the generally poor vegetation cover. Semi-arid landscapes by definition are water-limited and therefore are potentially sensitive to environmental change, with associated effects on biomass production. These areas become vulnerable to erosion because of the reduced protection of the ground surface by vegetation from heavy rains with high intensity.

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Soil degradation is a major and widespread environmental problem in Italy which is related to the history of both agricultural and non-agricultural land use. It is estimated that in recent decades, with the modernization of production systems, erosion has exceeded 30 times the tolerable rate of erosion (Pagliai 2004; Pimentel 1993).

About 70 percent of all land is subject to risk of accelerated soil erosion (over 5 t/ha/year) and about 12 percent is prone to high risk (over 10 t/ha/year) (Grimm et al. 2003). While soil erosion risks are exacerbated by a combination of climate and steep topography, erosion has also been aggravated by: poor adoption of soil conservation practices, notably limited soil cover over the whole year, and less than 10 percent of arable land under conservation tillage (European Environment Agency 2005); monoculture cropping systems; and uncultivated land, notably conversion of cultivated mountain terraces to other uses.

Soil compaction risks have grown, mainly in the plains, due to greater use of heavy farm machinery in wet conditions. Three quarters of Italy’s territory was reported to be at a medium risk of susceptibility to soil compaction in the National Agency of Environmental Protection Environmental Data Yearbook of 2009 (ISPRA 2009). Broadly speaking, the areas which are most susceptible to compaction are those characterised by clayey soil and shallow water tables.     

In the South and in the major islands, approximately five percent of land is affected by desertification, including soil salinisation, associated with expansion of intensive agriculture on fragile land; excessive use of groundwater for irrigation, with the consequent intrusion of saline waters; and poor grove tillage practices (APAT 2000; Beaufoy 2001).

Linked to these soil degradation problems, there has been a loss of soil organic matter (SOM). Data from the Environmental Data Yearbook (ISPRA 2009) reveals that organic carbon levels in Italian soil are worryingly low.  Organic matter content, relative to the top 30cm of soil, has been divided into 4 categories (very low:  < 1 percent, low: 1-2 percent, medium:  2-6 percent and high: >6 percent).  Around 80 percent of Italian soil has an organic matter content of less than two percent whilst no single region in the national territory showed “high” levels, more than six percent, at least not on the scale used.  The spatial distribution of organic matter levels follows climatic distribution with an increase in “medium” levels in the North of Italy and along the principal mountain ridges of the country.      

Another process which limits ecological soil functions is soil sealing.  According to the Environmental Data Yearbook (ISPRA 2009), over six percent of the national territory was sealed in 2006 compared with 5.5 percent in 2000. Northern Italy shows the highest percentages of soil sealing whilst values are slightly lower in the south and on the islands.  Indicators show that soil sealing has progressively increased throughout the country over the last 50 years and, as a consequence, soil consumption has also risen.  In recent years soil sealing trends have varied notably between northern and southern Italy.  Northern regions experienced a relatively steady increase in soil sealing between 1994 and 2006.   Central and Southern regions, however, saw a period of relative stability, from 1994 to 2000, followed by a marked increase, though not enough to match levels found in northern Italy.  The highest soil sealing values are reported in the North-West where over seven percent of land surface is sealed.  North-eastern and central regions have figures of between 6-7 percent, whilst in the South and on the islands the figures are largely above five percent.  Sealed areas are concentrated in urbanised areas and along main roads.  This phenomenon becomes particularly concerning in coastal areas and on large plains where the problem of soil sealing by urbanisation is compounded by soil damage caused by intensive farming. The negative effects of land impermeability are already very significant and concern climate changes resulting from annual average temperature rises, the destruction and fragmentation of the habitats of internationally important species (in central Italy, for example, the bear, the wolf and the lynx), the alteration of surface and ground water, the reduced capability to absorb civil and industrial emissions, the irreversibility of the use of land, once transformed by urbanisation and, in short, overall reduced ecological resilience to disturbances and perturbations affecting ecosystem (ISPRA 2009).

Water pollution is still a problem, although it is decreasing. In fact rivers in the Po Valley are still polluted by different activities including agriculture, especially from livestock farms, while in the South eutrophication of reservoirs for drinking water has resulted from excessive fertiliser use. Groundwater is the source of nearly 85 percent of drinking water, but about 25 percent of groundwater supply requires treatment before it is fit for drinking. The reduction in agricultural nutrient surpluses has lowered water pollution. But absolute loadings of nutrients into water bodies remain high, contributing two-thirds of nitrates and one-third of phosphates delivered into rivers, and a major, but decreasing, share of pollution of groundwater, while efficiency of nutrient use is low (ISPRA 2009).

In Italy overall agricultural land use changes since 1960 have been detrimental for biodiversity, with a reduction in semi-natural farmed habitats, including the conversion of permanent pastures and meadows to commercial forestry and crop production (ISPRA 2009). Flooding and landslides are also a problem. The increasing occurrence and severity of droughts, floods and associated landslides are imposing a considerable human and economic cost (Guzzetti 2003). Although some hilly and mountainous land was ploughed in the 1970s and 80s, during the 1990s certain areas reverted to shrub and low forest, which has helped increase water holding capacity. However, the 16 percent decline in farm dams and ponds over the period 1985-2000, has reduced the water retention capacity of agricultural land (ISPRA 2009).

Alento study site

Soil erosion is by far the most important land issue in the Alento study area, mainly due to its on- and off-site effects. In fact it causes severe damage to both agricultural productivity and to infrastructure (mainly dams).  In the Alento, soil erosion is largely caused by the collapse of terrace systems, mainly due to the lack of maintenance and abandonment of agriculture.

The plains and coastline of the study area pose new problems though are still closely linked to those described for hilly areas. The biggest challenge facing plains and coastlines is soil sealing. Soil sealing, especially in the plain areas, is related to three interconnected processes.  The first is a flux in population moving from inland areas to areas with greater socio-economic opportunities, better infrastructure, and more services.  The second is the intensification of agriculture through building of greenhouses and the third is the expansion of the tourist industry.

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In the last 15 years, land use in the source region of the Yangtze River has changed noticeably. This has resulted in a number of negative effects on the environment (Pan 2005), discussed below.

Soil and water loss

Soil loss area in the source region of the Yangtze River is 10.63×104km², which is 31.17 percent of the soil loss area in Qihai province. Within this figure, the anthropogenic soil and water loss area reaches 930 km². Serous soil loss causes the sediment loading to increase in the upper reaches of the Yangtze River. The mean sediment discharge per year in Qinghai reaches up to 1232×104 t. The average soil erosion loss is 650 t/km² per annum.

Land desertification

The area of land desertification in the source region of the Yangtze River is 3328.03 km², which is 84.58 percent of all land desertification in the upper reaches of the Yangtze River. The yearly rate of increase in desertification is more than 0.9 percent.

Degradation of wetlands

The middle dry plateau vegetation is a succession from swampy, wet meadow vegetation. The peat bog land has become dry and exposed. As a result, the function of maintaining the watershed has been reduced. In addition, due to the degeneration of wetland areas, the natural environment on which many living organisms depend is being lost and thus, poses a threat to biodiversity. Because wetlands are regarded as the land use type with the highest ecosystem services value, the loss of wetlands in the source region of the Yangtze River is a serious issue.

Loss of vegetation cover

The forage yield and vegetation cover of grassland has been reduced and as a result, the carrying capacity in terms of livestock has also been reduced. Following this, there is often an infestation of mice, which accelerates the process of grassland degeneration. As a result, degeneration of grassland significantly affects livestock production and this has an associated impact in restricting local economic development.

Decline in the availability of cropland

The land in the Yangtze River delta has experienced long-term development and utilisation by humans   (Peng and Gao 2004). The form and structure of land use has been continuously evolving. With recent rapid economic development, the degree of intensification of land use is increasing. Currently, land use in the Yangtze River delta faces the following issues:

• The area of available cultivated land has been reduced.
• The quality of the cultivated land has also been reduced.

The main reasons for this reduction are: (a) because the economy is developing so quickly in the delta, more construction land is needed; (b) local farmers change their land use in response to the need for income growth; (c) Some cultivated lands are used for eco-tourism and afforestation; (d) population increases but the area of cultivated land decreases. For example, the density of the population was 20 people/ha in 1985, but has risen to 26 people/ha in 2000. Three waste products (waste gas, waste water and industrial residue) have also increased significantly and have resulted in the pollution of cultivated lands. In addition, large amounts of chemical fertilizers and pesticides have been used so that soil quality is declining. For example, in 1982 around the Taihu Lake, nitrogen application rates per year amounted to 395kg/ha for cultivated land but rose to 520kg/ha in the 1990s. Other issues are low utilization efficiency of land for construction and irrational land use structures including the increase in cropland and the loss of forest and grassland.

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Modern agriculture is based on the use of chemicals, which are highly dependent on a non-renewable resource: oil. The sustainability of current agricultural practices is low and will result in a reduction in soil fertility once oil prices increase significantly or become exhausted. The main difficulties with oil dependent agriculture are: i) farmers lose their knowledge of traditional agriculture and it will be difficult to return to traditional agriculture as a result of that discontinuity of knowledge; and ii) soils are being depleted of organic matter and are becoming more dependent on mineral fertilizers, which only contribute to a short-term increase in soil fertility. This can be the beginning of the collapse of production, as once chemical fertilizers are no longer available, there will be neither knowledge nor natural fertility in the soils to maintain food production in the area.

Soil erosion

Soil erosion rates are high in Spain and the Júcar River watershed due to the lack of vegetation cover. Farmers use herbicides and ploughing to reduce and eliminate weeds and this reduces soil organic matter, increase soil sealing and soil erosion due to splash and sheet erosion. These LEDD conditions are mainly found on new and intensively managed farms such as orange and olive plantations and are also widespread in land used for cereal production, fruit orchards, olive groves and vineyards.

Soil organic matter decline

Forest soils at the Canyoles river basin show three to 15 percent organic matter content. Agricultural soils have 0.6 to three percent organic matter content with average values of one percent. These soils have a weak structure and low infiltration rates due to their lack of organic matter.

Soil compaction

The intensive use of machinery and the application of agricultural chemicals results in an increase in soil compaction. The bulk density is on average greater than 1 kg cm-3. The use of heavy machinery also results in disturbance of the soil.

Soil sealing

The use of concrete contributes significantly to the increase in soil sealing. Asphalt and concrete are widely used in road building to avoid erosion but this strategy results in increased runoff and soil and water losses. Farmers are increasing soil sealing by using asphalt and concrete to improve the surface of farm tracks, which facilitates easier access into their fields. Easy access to land is especially important during harvest when fruit needs to be picked and transported quickly.

Soil and water pollution

The extensive use of chemicals in agriculture is triggering an increase of nutrients and pesticides in watercourses and rivers. This is mainly an issue in groundwater where nitrates are widely found, and is resulting in water supply shortages in coastal areas where aquifers have become polluted. Some researchers have found a relationship with stomach cancer. The pollution of aquifers results in an increase in water exploitation from mountainous areas where water is unaffected by pollution, as there is little intensive agriculture in the mountains because the population migrated to the lowlands over 50 years ago.

Loss of biodiversity

Chemical-based farming and drip irrigation are contributing to a reduction in plant and animal biodiversity. As a result of a lack of ponds and irrigation ditches, amphibians have almost disappeared. This new type of intensive agriculture which uses chemical fertilizers and drip irrigation means that there is no vegetation to cover the soil between the rows of fruit trees

Aquifer depletion and the loss of traditional water management

Traditional irrigation in the Canyoles River basin was based on springs which emerge from karst aquifers. This is the basic water resource system in Mediterranean agriculture, as summers are hot and dry. The over exploitation of aquifers by the new citrus and olive plantations has resulted in the loss of these traditional springs.

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Aquifer depletion

Huelva province has the highest concentration of strawberry production in the world. Spain is the biggest producer of strawberries in Europe and of the total production of strawberries in Spain, 95 percent come from Huelva province (AE MARM 2010). A significant issue related to the commercial production of strawberries in the region is the overexploitation of aquifers. In areas near the Doñana natural park this has lead to a fifty percent reduction in water levels in aquifers and natural watercourses (WWF/Adena 2008). Amongst other impacts, the depletion of water resources affects biodiversity in the park and in the region as a whole.

Soil erosion

Orange plantations are particularly susceptible to erosive processes (Cerda et al. 2009). Trees stand on bare soil on undulating slopes, with very little or no undergrowth. During the wet season, runoff of sediment into local drainage systems is a particular issue. Evidence of rill erosion is common and at longer established plantations, gullies can be seen in the depressions in between the planted mounts. Little use is made of natural patterns of relief in the landscape in new plantations. Often, the mount-depression-mount pattern is created parallel to the angle of the slope. With no undergrowth present, runoff and soil movement processes find no resistance and soil is lost through existing and newly created or eroded waterways.

Cerdá et al (2009) have also found that soil erodibility in recent, newly converted and intensive citrus orchards is higher than in any other land use in the western Mediterranean basin.  The Western Andévalo is one of the fastest expanding areas of this type of commercial citrus operation in Spain. High erosion rates and the off-site impacts of sediments are having, and will continue to have, a significant impact on the biophysical and human systems across the region..

Contamination of soil and water

The inappropriate use of fertilizers, herbicides and pesticides can lead to pollution both on and off site (Curfs 2009). Agri-chemicals are frequently used in large scale commercial citrus production in Huleva. The use of nitrogen to improve crop yield is a common practice in citrus production.  However, as a result of a lack of knowledge of the physiological and biochemical basis of the nutrition process, the application of nitrogen fertiliser is indiscriminate and results in nitrate leaching and loss into watercourses (Talon 2004).

The off-site impacts in relation to soil and water contamination are also important considerations. The orange plantations are part of the Guadiana drainage basin. In wet periods, eroded soil (and associated agri-chemicals) enters the Guadiana River. This may contribute to contamination of river sediments and beaches at the mouth of the estuary, where the tourism industry is currently expanding.

Land desertification

The process of converting the landscape into orange plantations in broad terms can be described as follows: Heavy earth moving machinery is used to scrape the soil bare in order to collect boulders, which are put in mounds for collection by lorries. Mechanical diggers are then used to create the parallel mound-depression-mound pattern. The boulders are then used to cover the mounds on which the trees are planted. The LEDD issues that are associated with this process include:

• Loss of biodiversity - citrus orchards are a monoculture and existing vegetation is cleared and removed;
• increased soil erosion by wind and water because of
• compaction by heavy machinery
• the removal of vegetation
• the long periods in which the area is left bare before planting starts