LEDD issues in grazing land: Crete and Asterousia

Editor's note 14Jun2012: Text source D211, section 3.1.2

Grazing land covers extensive areas of Greece. Animal husbandry contributes significantly to the economy of the country. In addition, grazing land is faced with many problems of land degradation and land productivity decline. Irrational and uncontrolled land clearing, forest fires and overgrazing are the main causes of land degradation and desertification of grazing land (Greek Action Plan for Combating Desertification 2001). Removal of natural vegetation, especially in degraded land, favours accelerated soil erosion leading to land desertification. The most important issues related to LEDD in grazing land in Greece and in Crete are the following: (a) low land productivity, (b) soil erosion, and (c) land desertification.   

Low land productivity

In Greece, long periods of grazing combined with adverse climatic, soil and topographic conditions, in association with or without wildfires, have led to soil degradation and negative effects on land productivity and conservation of natural ecosystems. This has resulted in decisive measures to exclude livestock from some areas, particularly those characterized by specific environmental characteristics. However, it has to be noted that no-grazing or under-grazing may also cause adverse effects, such as the disappearance of grazing-prone species, or the accumulation of flammable biomass, which is one cause of recurring wildfires (Seligman and Perevolotsky 1992).

The long history of livestock husbandry in Greece has resulted in the adaptation of the flora to grazing pressure (Rackham and Moody 1996), and there is growing evidence of plant community response to grazing that suggests that grazing at moderate or even high intensities can in certain areas be a necessary component of a conservation strategy (Papanastasis 2008). It may locally be considered as a solution for the protection of abandoned rural areas and for a reduction of livestock production costs in a highly competitive European and international market (Papanastasis and Peter 1998). Low land productivity has a significant impact on farm income and grazing land management. When land productivity is low, farmers need large areas of additional land to produce animal feed or must buy feed from other areas, increasing the cost of production. Furthermore, under low land productivity conditions, rangeland is usually overgrazed leading to accelerated soil erosion rates, land degradation and desertification.

Soil erosion

Pastures in Greece have been significantly affected by soil erosion processes for many years. Greece is a rugged, mountainous country with high variation in altitude. Due to its predominantly steep terrain and adverse climatic and bio-climatic conditions, the country is facing considerable soil erosion problems. Natural environmental factors, adverse as they are, would not have caused the current extent of land degradation without the addition of human pressures. Deforestation has taken place to provide fuel, timber for house building, ship construction, and other purposes over many centuries. Shepherds used fire to eradicate woody vegetation and encourage the growth of grass, which has subsequently been overgrazed.

Extensively eroded areas in grazing land are confined to rock formations primarily of Mesozoic limestone and secondarily of acid igneous and metamorphic rocks. Soils formed on limestone usually have moderately fine to fine texture. Drier microclimatic conditions prevail in these areas, reducing the potential for plant growth, and the soils remain bare for long periods, favouring overland flow and erosion. The soils on these areas are very shallow or the parent rock is exposed at the surface (Yassoglou and Kosmas 2000).

Soil erosion experiments conducted in Mediterranean shrublands which are used mainly for grazing have shown that soil erosion rates depend on annual rainfall (Kosmas et al. 1996), vegetation cover and livestock density. Vegetative cover is highly dependent on annual rainfall and the time of year. Areas located in the western part of the country have higher annual precipitation (650-1150 mm) and usually higher vegetation cover if the soil is relatively deep. In contrast, the eastern and southern parts of the country receive lower precipitation (380-650 mm) and usually have a poorer vegetation cover. Erosion rates measured on Zakynthos range from 0.2 to 1.6 t km-² yr-¹, while higher erosion rates are expected in the eastern part of the country (Kosmas et al. 1996).  Soil depth and type of parent material affect vegetation cover and erosion rates. Long-term studies conducted in various shrublands or abandoned lands of Greece have shown that the following two classes of soil depth may be distinguished for land protection (Kosmas et al. 2000):

• A critical soil depth (25-30 cm), below which the recovery of the natural vegetation is very low, and the erosion processes may be very active resulting in accelerated soil erosion rates;
• A crucial soil depth (4-10 cm) under which perennial vegetation cannot be sustained, the soil is rapidly removed by wind or water erosion, so that degradation of the land is an irreversible process.

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 (Lee and Skogerboe 1985; Francis and Thornes 1990). Vegetation cover of 45-50 percent greatly reduces surface water runoff (Kosmas et al. 1996). Therefore, land management of pastures for reducing soil erosion in highly degraded soils is crucial for combating land degradation and desertification.

Soil erosion in grazing land in Crete is the most important LEDD issue. The application of the PESERA model in grazing land in western Crete has shown various rates of soil erosion depending on soil, vegetation, topographic and vegetation characteristics (DESIRE contract No: 037046). The following soil erosion classes: 10-20 t ha-¹ yr-¹, 20-50 t ha-¹ yr-¹ have been estimated under very steep slopes (slope gradient >35 percent), shallow soil depths (less than 30 cm), and plant cover less than 55 percent. Of course, there are areas highly degraded with extensive rock outcrops, mainly limestone, in which soil erosion is hardly active any more.

Land desertification

Desertification, as defined by the UNCCD, has affected large areas of pastureland in Greece. The vulnerability of the land to severe degradation, and as a consequence to desertification is attributed to unsustainable land management practices combined with unfavourable physical environmental characteristics.

The following main factors are considered as the most important affecting land degradation and desertification of pastures in Greece:  

• Large moisture deficits, temporal variability, and frequent rainfall extreme events due to Mediterranean climatic conditions.
• Rugged landscapes with steep slopes, large elevation differences and areas highly dissected by torrential steams.
• Surface geology favouring the formation of soils very sensitive to drought and erosion.
• Lower rates of soil formation than soil loss, resulting in inadequate depth for roots to grow and low water storage capacity.
• Four millennia of human actions including overgrazing and forest fires.

Studies conducted in the context of the EU research project DESERTLINKS have shown that land degradation and desertification risk in pastures is affected by socio-economic factors and land management characteristics such as land ownership, farm size, period of land use, erosion control measures and controlled grazing (Figure 1). If the land in question is rented, the main concern of the land user is overexploitation of the natural vegetation without applying any erosion control measures. In recent decades, degraded agricultural land in Greece has been abandoned and converted to pasture. In such cases, the land presents a lower desertification risk because soils are relatively deeper with lower slope gradient than the surrounding grazing land. The period of existing land use type has decreased desertification risk. Controlled grazing is a major management issue for reducing desertification risk in pastures. In some cases, land is fenced and animals are moved from one place to another to avoid overgrazing.

Figure 1. Important characteristics affecting desertification risk in pastures. Source: (Kosmas 2004)

Desertification in pastures is either reversible or irreversible depending on the characteristics of the land. In cases where soil moisture has been depleted beyond the tolerance level of the economically and environmentally valuable plants, but rootable soil depth has not been decreased below critical thresholds, desertification is reversible. Irreversible desertification has occurred in areas in which accelerated soil erosion has permanently reduced rootable space and the water storage capacity of the soil is below the levels needed for growing plants. Such cases are mainly found in areas with soils formed on limestone.

Desertification in grazing land in Crete is a very important issue. Based on the Greek National Action Plan for Combating Desertification (Greek National Committee for Combating Desertification 2001), grazing land in eastern Crete is under high desertification risk. Furthermore, grazing land located in the Asteroussia and Psilorites Mountains is mainly characterized as critical or sensitive to desertification. The evolution of the natural vegetation of Crete followed the turbulent history of the island (Bambakopoulou 1985), starting with the first episode of degradation during the Minoan civilization. Cretans, moved into the mountainous areas, clearing forests for cultivation and animal breeding. Later, in the period 327-287 B.C., in his book "About the history of plants", Theophrastus, the father of Botanical science, refers to the great spreading of cypress forest in Crete.

During the invasion of Venetians in the 13th century, colonization of the uplands and mountains took place again. During this occupation, many forests were cleared to produce timber for exports, especially timber from cypress for ship-building. The Venetian occupation was followed by the Turkish invasion in the 17th century. During this period, forest fires were used to sabotage the economy. After the revolution against Turkish occupation (ca. 1900 A.D.), shepherds, who until that time remained on the high mountains, started moving to the lowland for the winter. In the meantime, forest fires continued in the densely vegetated areas to create new pasture-lands. The number of sheep and goats continued to increase, resulting in overgrazing of the area and reduced regeneration of the natural vegetation.

Until 1920, the slopes of the Asteroussia Mountains (south of the Messara Valley) were cultivated with cereals. As mechanisation could not be applied in these areas, they have been abandoned and natural vegetation consisting mainly of phrygana has returned. Although the natural vegetation in the Asterousia area shows a capacity for succession to higher forms, reducing desertification risk, this is not the case since the area is used for grazing during the winter months mainly by the inhabitants of the Psilorites mountainous areas. Overgrazing of the regenerated young plants during this period ceases their growth further degrading the natural vegetation.

• < Prev
• Next >